Atlas of Flood Maps

Q4397 

Prepared for: 

RWS - RIKZ 

Atlas of Flood Maps 

Examples from 19 European countries, USA and Japan 

September, 2007

Prepared for: 

RWS - RIKZ 

Atlas of Flood Maps 

Examples from 19 European countries, USA and Japan 

September, 2007

EU Flood Risk Maps Q4397 September, 2007 

Examples from EU countries 

WL | Delft Hydraulics 

Contents 

1 Introduction................................................................................................1—1 

2 Flood mapping............................................................................................2—1 

3 Cartographic aspects of flood risk mapping .............................................3—1 

3.1 Layout issues and GIS approaches.................................................................3—1 

3.1.1 Basic and explanatory information .......................................................3—1 

3.1.2 Meta-data.............................................................................................3—2 

3.1.3 Background mapping or imagery..........................................................3—2 

3.1.4 Location and navigation .......................................................................3—2 

3.1.5 Colour palettes and symbols.................................................................3—3 

3.1.6 Numerical flood data............................................................................3—5 

3.1.7 Additional considerations.....................................................................3—5 

3.2 Map Content...................................................................................................3—6 

3.2.1 Flood extent.........................................................................................3—6 

3.2.2 Flood probability, depth, progress.........................................................3—6 

3.2.3 Potential damage and casualties............................................................3—6 

3.2.4 Flood risk.............................................................................................3—7 

3.2.5 Flood Hazard .......................................................................................3—7 

3.2.6 Evacuation maps..................................................................................3—7 

3.3 Conclusions.....................................................................................................3—8 

4 Examples of flood risk maps ......................................................................4—1 

4.1 Austria ............................................................................................................4—1 

4.2 Belgium ...........................................................................................................4—5 

4.2.1 Flanders ...............................................................................................4—5 

4.2.2 Wallonia............................................................................................. 4—11 

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4.3 Croatia .......................................................................................................... 4—15 

4.4 Denmark ....................................................................................................... 4—20 

4.5 Great Britain.................................................................................................4—23 

4.5.1 England & Wales ............................................................................... 4—23 

4.5.2 Scotland............................................................................................. 4—32 

4.6 Finland.......................................................................................................... 4—34 

4.7 France ........................................................................................................... 4—38 

4.8 Germany ....................................................................................................... 4—46 

4.8.1 Baden-Württemberg........................................................................... 4—46 

4.8.2 Bayern (Bavaria)................................................................................ 4—49 

4.8.3 Nieder-Sachsen / Bremen ................................................................... 4—51 

4.8.4 Nordrhein-Westfalen .......................................................................... 4—52 

4.8.5 Rheinland-Pfalz ................................................................................. 4—55 

4.8.6 Saarland............................................................................................. 4—58 

4.8.7 Sachsen.............................................................................................. 4—59 

4.8.8 Sachsen-Anhalt .................................................................................. 4—62 

4.9 Hungary ........................................................................................................ 4—64 

4.10 Ireland........................................................................................................... 4—69 

4.11 Italy ............................................................................................................... 4—72 

4.12 Latvia ............................................................................................................ 4—75 

4.13 Luxembourg ................................................................................................. 4—78 

4.14 Netherlands................................................................................................... 4—80 

4.15 Norway.......................................................................................................... 4—87 

4.16 Poland ........................................................................................................... 4—89 

4.17 Spain ............................................................................................................. 4—95 

4.18 Sweden ........................................................................................................ 4—100 

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4.19 Switzerland ................................................................................................. 4—105 

5 Transboundary flood hazard mapping.................................................. 5—113 

5.1 European Flood Risk Mapping .................................................................. 5—113 

5.2 Comrisk and Safecoast ............................................................................... 5—116 

5.3 ELLA .......................................................................................................... 5—117 

5.4 FLAPP ........................................................................................................ 5—121 

5.5 IKRS ........................................................................................................... 5—122 

5.6 SAFER ........................................................................................................ 5—125 

5.7 TIMIS ......................................................................................................... 5—126 

6 Insurance maps.......................................................................................6—130 

6.1 CatNet......................................................................................................... 6—130 

6.2 Austria ........................................................................................................ 6—133 

6.3 Czech Republic ........................................................................................... 6—137 

6.4 France ......................................................................................................... 6—140 

6.5 Germany ..................................................................................................... 6—141 

6.6 Italy ............................................................................................................. 6—143 

6.7 USA............................................................................................................. 6—143 

7 Evacuation maps ....................................................................................7—147 

7.1 Germany – Hamburg ................................................................................. 7—147 

7.2 Japan........................................................................................................... 7—148 

7.3 Netherlands................................................................................................. 7—152 

7.4 USA............................................................................................................. 7—153 

7.4.1 Mississippi....................................................................................... 7—153 

7.4.2 Florida ............................................................................................. 7—154 

7.4.3 Louisiana – New Orleans ................................................................. 7—155 

7.4.4 California – Sacramento................................................................... 7—158 

8 Final Remarks ........................................................................................8—162 

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1 Introduction 

Aware of the growing need for flood mapping development in the future in Europe, early 

2006 the European Water Directors decided to establish a European exchange circle on 

flood mapping (EXCIMAP). 

Today EXCIMAP is an informal circle consisting of nearly 40 representatives from 24 

European countries or organizations. It has been set up for encouraging and facilitating 

exchanges between European experts in view of developing flood mapping. The main 

objective of EXCIMAP is to produce a Guide presenting the good practices (available in 

Europe) to mobilize when executing flood mapping. 

In the mean time, the European Union is currently developing a European Directive on the 

Assessment and Management of Flood Risks. The proposed Directive sets out the 

requirement for the Member States to develop three kinds of products: 

� a preliminary flood risk assessment: the aim of this step is to evaluate the level of flood 

risk in all regions and to select those regions on which to undertake flood mapping and 

flood risk management plans (see below) 

� flood mapping, with a distinction between flood hazard maps and flood risk maps: 

� the flood hazard maps should cover the geographical areas which could be flooded 

according to different scenarios. These maps are also indicated by flood extension 

maps; 

� the flood risk maps shall show the potential adverse consequences associated with 

floods under those scenarios. 

� flood risk management plans: on the basis of the previous maps, the flood risk 

management plans shall indicate the objectives of the flood risk management in the 

concerned areas, and the measures that aim to achieve these objectives. Examples are 

evacuation maps. 

The focus in this Atlas is on river flooding, but some examples of coastal flooding are also 

included. 

According to this directive Member states shall produce flood mapping according to some 

minimum recommendations. To be consistent with this proposed European document, 

EXCIMAP has decided to focus its work on the minimum requirements of the Directive 

concerning flood mapping. 

As part of the work to be done for this Guide an inventory was made of examples of maps 

and mapping programmes in the participating countries. The result of this inventory is this 

“Atlas of Flood Maps”. It contains examples from 19 European countries, not counting the 

subdivisions that are made in some instances (Belgium, Great Britain and Germany) and 

from the USA and Japan. In addition special chapters are dedicated to transboundary flood 

mapping, flood maps for insurance purpose and evacuation maps. 

In each chapter the authors of this Atlas have made remarks on content and layout of the 

maps, based on general cartographic principles. 

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The Atlas is compiled by the Netherlands Ministry of Transport, Public Works and Water 

Management. The material is submitted by the EXCIMAP members. WL|Delft Hydraulics 

assisted to collect and organize the material and has made both the descriptions and the 

analysis of the maps. After the publication of a draft edition, the material was reviewed by 

representatives of the various countries and for some countries new material was received 

(Croatia, Denmark, Ireland, Switzerland and Wallonia (Belgium)) that was incorporated in 

this edition. 

We hope that this valuable collection of examples will stimulate flood mapping efforts in 

countries that have to start with it, and discussion to improve these practices in countries 

that have experiences with it already. 

The editors: 

Jos van Alphen, Ron Passchier and Victor Jetten 

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2 Flood mapping 

For the purpose of consistency, this Atlas is based on the same definitions as the EXCIMAP 

Guide on Good Practices on Flood Mapping: 

� Flood: is a temporary covering by water of land normally not covered by water. This 

shall include floods from rivers, mountain torrents, Mediterranean ephemeral water 

courses, and floods from the sea in coastal areas, and may exclude floods from sewerage 

systems 

� Flood risk: is the combination of the probability of a flood event and of the potential 

adverse consequences to human health, the environment and economic activity 

associated with a flood event 

� Flood plain maps indicate the geographical areas which could be covered by a flood 

(from all sources except sewerage systems – see above definition of flood) according to 

one or several probabilities: floods with a very low probability or extreme events 

scenarios; floods with a medium probability (likely return period >=100y); floods with a 

high probability, where appropriate 

� Flood hazard maps are detailed flood plain maps complemented with: type of flood, the 

flood extent; water depths or water level where appropriate; where appropriate, flow 

velocity or the relevant water flow direction 

� Flood risk maps indicate potential adverse consequences associated with floods under 

several probabilities (ref. flood plain maps / flood hazard maps), expressed in terms of: 

the indicative number of inhabitants potentially affected; type of economic activity of 

the area potentially affected; installation which might cause accidental pollution in case 

of flooding […] potentially affected ; other information which the Member State 

considers useful 

� Damage is the negative effect of an event or process 

In this Atlas, also flood risk management maps in a special chapter dedicated to evacuation 

maps. 

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3 Cartographic aspects of flood risk mapping 

This Chapter aims to describe the basic content and cartographic good practices of flood risk 

mapping. It is meant to form the background information for the description of the 

compilation of various examples of flood maps from countries that are part of EXCIMAP . 

The text in the first paragraph on map layout and the use of GIS is identical to the text on 

cartographic aspects in the ‘Guide of Good Practice for Flood Mapping in Europe’ produced 

as part of EXCIMAP. In the second paragraph, map content is discussed. 

3.1 Layout issues and GIS approaches 

Cartographic aspects are important issues in flood mapping. They need to be adequate to the 

intended user to help ensure that the content of the maps is correctly understood and that the 

maps might convey the relevant information to their users, thus achieving the objectives for 

which they have been developed. This Section discusses some of the key issues related to 

the presentation of flood maps. 

3.1.1 Basic and explanatory information 

Information that is important for use and that explain the content of the map includes: 

� Title: brief description of the map, including its content and / or purpose (for flood maps 

particularly important are the considered probabilities or recurrence intervals 

� Responsible authority (organisation responsible for the development and publishing of 

the maps, with contact details) 

� Date of preparation / publication 

� Legend (textual description of symbols, colours, line features, etc.) 

� Purpose of development and intended use 

� Method of development 

� Limitations of map and / or assessment of uncertainty (if available) 

� Disclaimer (to enforce explanatory information and limitations, and provide legal 

protection to the responsible authority against adverse consequences of misuse) 

� North and scale: preferably using scale bar as this allows for changes in page size 

The scope and detail of the explanatory information should be appropriate to the intended 

audience. 

� Maps intended for public use should be simple and self-explanatory and include a clear 

legend, such that as little supporting or explanatory information as possible is required 

for correct interpretation. 

� Maps intended for organisational users (governments, local authorities, etc.) will 

generally be used by professionals to inform decision makers that may potentially have 

significant impacts, and will often contain more information than public maps. They are 

therefore likely to require more detailed explanatory information to help the user to fully 

understand the development and limitations of the maps, particularly in relation to 

methods of development, limitations and uncertainty. 

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3.1.2 Meta-data 

Appropriate meta-data should be provided where maps are issued / downloadable in GIS 

format. Such data should include standard meta-data (dates, responsible organisation, etc.) 

as well as information necessary for use of the GIS data, including the map projection and 

any datum levels used. Consideration should also be given to any relevant meta-data 

protocols or requirements. 

3.1.3 Background mapping or imagery 

Background mapping (i.e., maps showing topography, towns / buildings, roads, rivers and 

waterbodies, land use, etc.) or imagery (often ortho-rectified aerial photographs) are almost 

universally provided to a flood map to provide geographical reference for the flood 

information. 

Clear, and appropriately scaled, background mapping facilitates location directly from the 

principal map (although it might be noted that at very detailed scales this can be difficult to 

achieve). Care should be taken to ensure that background mapping colours will not be 

readily confusable with those used in the flood mapping (or vice versa), and background 

mapping is sometimes provided in black-and-white or grey-scale to improve clarity of the 

overlying flood map information. 

Imagery may be more readily interpreted than mapping as a background layer, although 

users may find it more difficult to geographically locate the relevant area, particularly if they 

are not closely familiar with the specific area. Imagery can also be expensive to procure if 

not already available, although Google Earth has recently become a powerful tool to provide 

affordable imagery (see Polish examples, Figure 4.88 and Figure 4.89). 

3.1.4 Location and navigation 

A location plan is often provided alongside the principal flood map to help users identify the 

geographical location that the flood map represents. This plan, which may be an 

appropriately scaled map or schematic plan (with appropriate key locations, such as towns, 

roads, rivers, etc.), shows the coverage and the location of the map within a wider 

geographical area (e.g., the nation, region or river basin). 

Navigation tools will be required for internet-based maps to enable users find an area of 

interest. Tools often include zooming (in and out) and panning and can include relocation 

from a location plan (as described above) or a return to default view (e.g., regional or 

national scale view). 

An indication of orientation (direction of North bearing) and map scale are also required for 

correct interpretation. Scale information may be provided by: 

� A written scale (e.g., 1:10 000) in the title box or legend 

� A scale bar provided on the map; this allows easy change in paper size 

� Grid squares provided on the map (with the grid square size defined in legend) 

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3.1.5 Colour palettes and symbols 

Simple flood maps may show only a single flood parameter (such as the flood extent for one 

flood frequency or return period) using a single coloured layer over a background map. The 

use of different colours (or shades of a single colour) may be used to present multiple 

parameters (such as flood extents for multiple flood frequencies, flood depths within a given 

flood extent, or classes of flood hazard or risk) in a clear and comprehensible format on a 

single map. 

The choice of colour coding may be guided by a number of factors: 

� Social conditioning: People are conditioned to interpret information based on colour, 

e.g., blue may be taken to represent flood extents, and red, orange and green are taken to 

represent danger, caution and safety respectively. Care should be taken with respect to 

possible interpretations of colour, and particularly misunderstandings. 

� Graduations of colour: Graduations of colour (or within similar colours, such as red, 

orange and yellow or purple, blue and green) may be used to represent different degrees 

of a single parameter (e.g., deeper shades to represent more severe flooding or higher 

risk). The graduation may be discrete or continuous, whereby: 

� Discrete graduation is used to represent a set number of ranges or classes of degree 

(e.g., flood extents for a small number of flood event frequencies, or specified 

ranges of flood depth). The choice of range or class of degree may be based on 

equal divisions, or perhaps more appropriately, on classifications related to 

consequence (e.g., depth categories related to safety and the ability of people to 

evacuate, or to depth-damage data for economic damage calculation) 

� Continuous graduation is used to represent a continuum of degree. This provides 

more detail but may not be as easy to interpret as discretely graduated maps. An 

example of discrete and continuous graduation is shown in the next two figures. 

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� Black and White Reproduction: The possible reproduction of a colour map in black-andwhite 

might be considered in choosing a colour scheme, noting that different colours 

may appear as the same shade of grey once copied. An example of a colour palette that 

does not translate well into grey scales (both the blue and red translate into dark grey, 

but the blue is low and red is high) as can be seen in the next two figures. 

� Accessibility: The accessibility of maps for the partially-sighted or colour-blind should 

be considered in choosing colour-schemes, particularly within the context of any 

national, regional or organisational regulations, policies or guidelines. 

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� Clarity: Strong colours may be used to provide clarity over a coloured background map, 

although it might be noted that an excessive number of strong colours can make a map 

difficult to interpret 

Hatching may be used as an alternative to different shades or colours in representing 

different parameters or, as is more often the case, parameter variants. Examples might 

include hatching of flood extent areas that are defended by protection measures or form 

flood storage areas / washlands, to differentiate these types of area from those that are 

undefended or naturally flooded respectively. 

The use of different line types that bound a polygon or flood extent provides another 

opportunity for differentiation. This approach is generally more suitable to visualise variants 

of a parameter or meta-data associated with the primary mapped parameters, such as 

differentiation between observed historic and predictive flood extents, or an indication of 

uncertainty associated with a flood extent. 

Line types variations that might be used include ranges of line: 

� Thickness 

� Colour 

� Continuity (e.g., solid, chain, dashed, dotted) 

� Definition (e.g., clearly defined line of set thickness as opposed to fuzzy boundary) 

3.1.6 Numerical flood data 

Flood maps represent information graphically. This visualisation can be supplemented with 

numerical data, such as values of water level or flow, either directly as text on the map or in 

a table on the legend. Such data can also be provided as attributes or tables associated with 

the flood maps where the maps are issued or downloadable in digital GIS format. 

3.1.7 Additional considerations 

In preparing flood maps, other considerations may be relevant to the presentation. 

The location, type, standard and condition of flood defence assets, and other flood-related 

information such as evacuation routes, shelter areas, flow direction, properties, etc., can also 

be shown on flood maps. The scope of the information provided might be more or less 

detailed dependent on the intended purpose and audience (i.e., public or organisational). 

This information may be associated with the flood maps, and possibly with particular flood 

cells, where the maps are provided in digital GIS format. 

The presentation of flood maps in trans-national or trans-regional river basins should, as far 

as reasonably possible within the requirements and constraints prevalent in each jurisdiction, 

be co-ordinated and consistent in presentation. 

Consistency should also exist between different types of flood maps for a given area. For 

example, the outer extents of flood risk zones should be spatially consistent with flood 

extent maps for a given flood event frequency, and a given colour should preferably not be 

used to represent more than one parameter within a related set of maps. 

Most EU countries now have a multi-cultural, and hence multi-lingual, society. Minority 

language versions of maps may therefore be deemed appropriate where significant 

minorities exist. 

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3.2 Map Content 

3.2.1 Flood extent 

The extent of potential flooding has to be presented as surface covering the topography for a 

specified flood level /frequency. For reference roads, railways, houses, property boundaries 

and the permanent waterbodies from which the floods may originate may be included. 

Recently Google Earth has become a powerful tool to use as background layer for this kind 

of information. A drawback of the use of Google Earth is the fact that the interactive site 

depends on third-party software which, although it is rather new on the internet, might easily 

be discontinued and there is always the risk that the server producing the images goes offline 

for whatever reason. Other problems may occur when the layout c.q. technical aspects 

of Google Earth are changed. 

Flood extent should be presented for a specified frequency, e.g. 1/10, 1/100 or 1/1000. In 

addition the protecting effect of defence works may be shown. 

3.2.2 Flood probability, depth, progress 

A very useful, but more advanced tool, for flood inundation mapping is the use of 2-D 

hydrodynamic models for the presentation of the actual process of inundation in a 

simulation movie. Evidently it is not possible to capture this type of information on a (hardcopy) 

map, although successive stages of the inundation process can be shown. Nevertheless 

this type of information is extremely valuable, especially for the assessment of most reliable 

escape c.q. evacuation routes. It is very important for the presentation of this information to 

describe precisely the specifications that form the boundary conditions of the simulation. 

There are an infinite number of possibilities, in terms of location of a dyke breach, initial 

size and development of the breach, form of the flood hydrograph that produces the flood 

(in case of river floods), local roughness conditions in the flooded area, etc. 

When many computations from different locations are available (scenario simulations), the 

resulting information can be combined into probability of flooding of a gridcell and 

maximum inundation depth per gridcell. However, since this requires many computations, 

these maps are relatively scarce. These probability maps can also be produces as flood 

likelihood maps for reassurance purposes. 

Potential (maximum) inundation depth maps exist on national, regional and local scales 

(1:2.500.000 – 1:10.000). In the legend it is possible to present the important relationship 

between inundation depth and “what to do”, with an illustration in a diagram: 50 cm, 1 m, 2 

m, 5 m and > 5m, see above in Chapter Error! Reference source not found.). Other related 

information may be evacuation routes, shelter areas. 

3.2.3 Potential damage and casualties 

Maps about flood damage may use indicators of potential damage like: 

� land use (rural, urban, infrastructure, water, etc.) 

� real estate value /ha (shown per dike-ring, or municipality) 

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� population density /ha (shown per dike-ring or municipality); 

When more sophisticated models and information is available potential damage can be 

computed per gridcell as a result of different flooding scenarios and damage functions that 

relate water depth to damage to structures and land use as well as to numbers of casualties. 

Since this is very sensitive information the data, models and assumptions have to be 

explained in detail in accompanying reports. 

Relevant information related to this theme has to do with the objects/services that may 

increase flood damage substantially: storage of chemicals, vital networks and services 

(highways, railways, airport, lifeline services like electricity, sewerage and drinking water, 

hospitals, etc). This information is expressed as line or point symbols, and may be combined 

with inundation-class maps. 

3.2.4 Flood risk 

Risk is often defined as probability x adverse effects. Consequently, a flood risk map may 

express flood risk as expected annual flood damage or casualties per gridcell, given the level 

of protection. When different flood scenarios are available, the resulting flood level 

frequency curve per gridcell, population density and casualty function may be combined 

into personal risk of decease per gridcell. However, the availability of these types of maps is 

very limited, and not public. They are also difficult to interpret and it might lead to 

confusing information when presented e.g. on the Internet. 

3.2.5 Flood Hazard 

Flood hazard maps present information on the typical dangerous aspects of floods that are 

important for e.g. evacuation and rescue operations: current velocity, sometimes in 

combination with inundation depth and/or debris content. This type of information may be 

relevant for very specific locations, e.g. near breaches in the embankment or narrow 

passages in river valleys, where current velocities become relevant. Therefore this 

information is presented on detailed maps (1:2.500). 

Current velocity may be presented as (magnitude) classes or vector (magnitude and 

direction). However, it should be kept in mind that current velocity depends very much on 

local topography and may be of limited accuracy. Vector maps may be difficult to read when 

flow direction and vector locations coincide. 

3.2.6 Evacuation maps 

Evacuation maps present public information on “what to do”. USA has a large tradition with 

evacuation routes in coastal areas related to hurricane and storm surge threats, but other 

countries start to produce these types of maps as well. Evacuation maps relate the magnitude 

of the threat (hurricane category) to areas (zipcodes!) that are evacuated or should consider 

it. In addition recommended evacuation routes may be shown, with detailed road maps 

about traffic contra flow direction on junctions. 

Complementary information may be added about things to carry with you to survive the trip 

(food, water, batteries, emergency telephone numbers, etc.). 

In general for river flooding there are too many options for evacuation maps, as the best 

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evacuation route depends on the flood characteristics e.g. It is therefore suggested that such 

information is used as background data for decision makers instead of published information 

to the general public for taking decisions on evacuation routes themselves. 

3.3 Conclusions 

Establishing guidelines to the cartographic aspects of flood risk maps should be given 

priority, not only to avoid problems of the public not understanding flood risk maps, but also 

to assure for instance that specialists dealing with floods actually use the same basis for 

information, in particular where river systems are concerned that cross national boundaries. 

Maps and GIS products should be tested on the public to see if they are as effective as 

scientists like to believe. However, it is unlikely that flood maps in the EU countries will 

become completely comparable as not only the underlying methodology is different, but 

also the data collection and method of measurement are different. It is possible, though, to 

arrive at a more generalized layout of the maps. This is particularly interesting now that 

most countries are in the process of producing interactive Internet sites where any user can 

access the map layers. 

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4 Examples of flood risk maps 

4.1 Austria 

General information 

The flood maps of Austria are produced by the Federal Ministry for Agriculture, Forestry, 

Environment and Water Management. Two types of maps are being produced: 

� Flood plain maps 

� Flood hazard maps 

Flood plain maps are provided for about 5000 km of river stretches on a scale between 

1:5.000 and 1:10.000. A second group of flood plain maps are called Hochwasser 

Risikozonierung Austria (HORA). These maps are an example of insurance maps and as 

such are further discussed in Chapter6.2. 

Flood hazard maps are produced for limited areas on scales between 1:1.000 and 1:5.000 

with an accompanying text. They show expected flood extension for a return period of 1/100 

years. For both types of maps, information is provided on methodology, accuracy, etc. 

Hazard is expressed in two classes: yellow and red, which is determined by a combination 

of flood depth and flow velocity (Figure 4.1). 

Figure 4.1 Criteria that determine medium and high risk using depth and velocity 

There are yet no flood risk or flood damage maps available. 

A further distinction is made between flood control for major rives and torrents (flash 

floods). Flood hazard maps for the latter are produced for ‘catastrophic events’ with a return 

period of 1/150 years. Hazard zones are in fact given for torrents, avalanches and erosion 

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events. Maps normally cover only a certain village or community. 

More detailed information can be found on the internet 1 . 

Comments on the maps 

Four maps are shown as examples of flood maps in Austria for the same region (fictitious 

region ‘Muster’, Figure 4.2 - Figure 4.5). As a general comment the maps are very clear and 

especially the cadastre background of the urbanization and infrastructure make them easy to 

read. It may be useful for anyone not familiar to the region to have a small map added that 

shows the location within Austria. Another comment is that the North indication on the map 

is rather small and may obtain a more prominent position, especially in this case where 

North is not at the top of the map. 

In Figure 4.2 both flood extension and expected water depth are given. In fact both water 

depth and water level (absolute value) are given. The latter might give an indication of the 

flow direction, although a flood extension map is normally a representation of a static 

situation, not of the inundation process. For the flood extension, three standard return 

periods of 1/30, 1/100 and 1/300 yr are used that are the norm in Austria, but the water 

depth is given for the 1/100 yr flood event. The differences between the extensions 

corresponding to the three return periods are shown by symbols on lines instead of a system 

of coloured surfaces. As an alternative use can be made of an indication of altitude similar 

to topographic maps, either with colours and/or putting the actual value (30 – 100 – 300) 

within the lines. 

The water depths are given in an interval of 0.25 m, which is probably in line with the 

accuracy of the information, but the combination of colours is less common. The smallest 

depth (0 - 0.25 m) is shown in light blue and darker hues of blue are used for larger depths 

up to 1.25 m, but then a shift is made to green with increasing depth indicated by lighter 

hues (up to 3.00 m). Green is normally used as an indication of safety and as was explained 

in Chapter 3.1. Water depth is preferably indicated by hues of blue. In case there are many 

intervals the differences between the various shades of blue may become obliterate and it 

might be an option to change to a larger interval (e.g. 0.5 m) instead of using a combination 

of colours. 

Although it can be deduced from the legend that the flood extension and water depth in 

numbers refer to the event with a return period of 1/100 yr, this is not indicated in the 

subtitle of the map. 

In Figure 4.3 flood hazard zones are indicated using four levels of hazard (blue, orange, 

yellow and red). Although red is normally the highest hazard, it is not immediately clear 

from the map what the order of the hazards is. The colour blue is already being used for 

inundation depth and may be left out of the colour palette here. It is very useful in this map 

that the hazard zones are combined with land-use information, although the overall use of 

the same colour for this purpose (green) does not allow for an easy distinction between 

various types of landuse. There is however also another map available showing these hazard 

zones on top of an aerial photograph. 

1 http://www.wassernet.at/ 

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In the map showing flow velocities (Figure 4.4) both expected flood extension and flow 

velocities are shown. The flow velocities are shown as light blue lines with the value of the 

velocity indicated by the length of the vector. There is no indication to which return period 

the velocity field belongs and the user might assume that the velocity field is independent of 

the return period, which is probably not the case. Based on the extension of the velocity 

field it can be deduced that it belongs to inundation with the highest (1/300 yr) return 

period. As a general remark it should be mentioned that the use of vectors for flow 

velocities, although in general very clear, might lead to problems in case of parallel flow 

lines, because the length of the vectors becomes obliterate. 

An interesting and very rare type of map is shown in Figure 4.5 which gives the shear stress 

/ drag force of the flowing water (in N/m 2 ). There is no indication to which return period the 

information belongs. In general the information provided can be used to assess e.g. the 

probable locations of highest force on buildings and/or where major erosion can be 

expected. These locations are also the most dangerous and should evidently be avoided in 

case of evacuation. 

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Figure 4.2 Flood extension and water depth map in Austria 

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Figure 4.3 Flood hazard map and indication of danger regions in Austria 

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Figure 4.4 Map showing flow velocities and flood extension for three return periods 

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Figure 4.5 Flood map showing drag force (shear stress - Schleppspannung) as a result of flow velocity 

4—4




4.2 Belgium 

4.2.1 Flanders 

For the Province of Flanders in Belgium, three types of flood plain maps are developed: 

� The NOG-maps (Naturally flooded area map) contain the areas that are known as being 

flooded through soil-mapping. These maps show the river sediments (alluvium) and 

slope (gravity-caused) sediments (colluvium) zones in the soilmap that has been 

constructed on a scale 1:20.000 

� The ROG-maps (Recently flooded area map) show the recently flooded areas in the 

period 1988-2006 based upon manual cartography, local terrain knowledge, 

photographs, (areal) movies, water authorities, Provinces, municipalities, consultants 

and others on topographical maps with scale 1:10.000. An automatic correction of the 

ROG-map has been performed using the DTM-Flanders (5*5 m) and GIS-techniques. 

This side-product is called the ROG-DHM map 

� The MOG-maps (Modelled flooded area maps) shows the flooded areas for about 2000 

km of rivers that have been modelled hydrological and hydrodynamical. The maps show 

flood extent, flood depth, flood time, flood frequency (2, 5, 10, 15, 20, 25, 30, 40, 50, 

75, 100, 150, 200, 250, 300, 500 and 1000 years). The MOG-map can be used till a 

scale of 1:2500. 

The flood extension maps are available from an interactive internet site 2 called the “Geoloket 

Overstromingskaarten” and “Geo-loket Watertoets”; the same site is also used for 

other map purposes, e.g. soil maps, colour orthophotos, satellite images, water quality, etc. 

The dark blue in the “Overstromingskaarten” can be chosen for the ROG or NOG maps or 

for a combination of the surveyed ROG together with the MOG with a return period of 25 

years. In the “watertoets” the dark blue zones are the combination of the ROG and a MOG 

with a return period of 100 years. The light blue zones are the NOG without the built-up 

areas. Explanation on the interactive information, and how the flood extensions have been 

calculated, are given in an accompanying digital document (“Risicozones overstroming – 

Begeleidende Nota”). Examples of a map produced with this internet site are shown in 

Figure 4.8 and Figure 4.9. There is a legend to the maps, but this is written in Dutch. 

Comment on the maps 

On the maps, colours are used to indicate areas that are floodable: 

� from any water course (pink) 

� from the sea (dark green) 

� recently flooded (ROG – dark blue) 

� floodable by excessive rainfall (brown) 

� floodable by either excessive rainfall or from a water course (orange) 

Especially the two last items are rare on flood maps. 

2 http://geo-vlaanderen.gisvlaanderen.be/geo-vlaanderen/overstromingskaarten/ 

4—5




An example of a ROG maps is shown in Figure 4.6 (overview) and Figure 4.7 (example of 

detailed map). 

Figure 4.6 Overview of ROG areas in Flanders 

Figure 4.7 Detailed ROG map in Flanders 

4—6




In general the possibilities to find information on the interactive site are very good and it is 

easy to use also for non-experts. A drawback is that once a certain area is selected and the 

user has zoomed into a detail of the map, there is no overview anymore where in Flanders 

the location is, e.g. there is no accompanying window that gives the overall view of the 

province as is often shown on other internet sites. The amount of information is limited, but 

this is evidently also the reason why the maps are easy to interpret. The colour light blue for 

inundated area is well-chosen, especially given the low return period. However, both the 

floodable areas from any water course and ‘risk zones, version 2006’ are shown in light blue 

and it is not immediately clear what is the difference between the two. Neither is there any 

indication in the legend on the meaning of the two different hues of blue in the map. A 

similar problem occurs in Figure 4.9 where there is no indication what is meant with the 

thick pink lines. 

Figure 4.8 First example of a flood extension map from the Geo-loket of Flanders (Belgium) 

4—7




Figure 4.9 Second example of flood extension map from Geo-Loket of Flanders (Belgium) 

Also available – not on the internet – are modelled flood maps, damage maps (as a 

combination of hazard and vulnerability for different return periods) and risk maps as a 

mathematical combination of several damage maps. Some of the most important inputs are a 

detailed Elevation Model for the water depths and land use maps to delimit potential 

damage zones. 

Every hydraulic scenario for the navigable waterways leads to a risk calculation with 

detailed maps of the present situation and the alternatives and a generalized overview map 

has to be made 2-3 times a decade. 

Examples of flood risk maps are shown in Figure 4.10, Figure 4.11 and Figure 4.12. 

4—8




Figure 4.10 Original flood risk map (Actual situation) 

Figure 4.11 Flood risk map with alternative discharge assessment 

4—9




Figure 4.12 Difference between the two foregoing maps 

4—10




4.2.2 Wallonia 

In view of the repeated floods in recent years and the extent of the damage they produce, the 

Walloon Government decided on 9 January 2003 to implement an overall plan for 

preventing and fighting against floods and their effects on victims, called the « Plan 

PLUIES 3 ». 

One of the objectives of the “Plan PLUIES” is to determine the flooding areas for the whole 

territory of the Walloon Region, taking advantage of the preparatory work already done 

(topographic measurements of minor and major beds of rivers, inventory (survey) of areas 

flooded by overflowing rivers in the past, soil numerical map,…). Concretely speaking, it 

consists of establishing two types of maps: 

� the flood hazard map, showing the territories that are likely to be flooded by 

overflow of rivers, which is the main subject of this memo; 

� the flood risk map, showing potential damage to vulnerable, flood-sensitive 

elements located in zones where there is a flood hazard. 

The principles of the methodology developed by the GTI (Groupe Transversal Inondations – 

Cross-sector Flood Group of the Walloon Region) were inspired by the « floodability » 

method developed by Cemagref, the French Institute for agricultural and environmental 

engineering research, duly adapted to the specificity of the Walloon topography and 

territory. While taking account of basic data available or being collected, it provides a 

coherent set of various tried-and-true scientific methods and can be applied to the entire 

Walloon territory. 

This methodology was approved by the Walloon Government on 21 November 2002. 

Flood hazard maps 

A flood hazard by overflow of rivers exists in areas where flooding can take place, with 

variable frequency and severity, as a result of a "natural" overflow of a river. The map 

shows the areas and their characteristic level of hazard. The hazard level can have three 

values: low, medium and high. 

In practice, the degree of flood hazard is based on a combination of two factors: recurrence 

of flooding (return period or occurrence) and its extent (depth of submersion). 

� Recurrence 

Recurrence of a flood is linked to the return period of high water regimes, which implies 

statistical computing of a historical series of flow data or of a synthetic series drawn from 

precipitation measurements using a hydrological integrated model. When the data required 

for statistical computing are not available, recurrence can be determined through evaluation 

of the occurrence of flooding, on the basis of observations and surveys in the field. 

3 Plan PLUIES : plan de Prévention et de LUtte contre les Inondations et leurs Effets sur les Sinistrés 

(plan for preventing and combating floods and their effects on the victims) 

4—11




� Submersion 

The submersion of a flood is characterised mainly by its extent and depth. Hydraulic (2D or 

1D) models that digitally reproduce minor and major beds of rivers are needed to determine 

this. When data needed to use hydraulic methods are not available, submersion is 

characterised by its extent, by applying the "hydropedological" method, based on 

information taken from digital topographic map and pedological maps, among others. 

� Hazard of flooding 

The flood hazard (low, medium, high) is computed from combining the values of recurrence 

and submersion (see Figure 4.13). In the event of frequent flooding with a high submersion, 

the flood hazard will be high and, conversely, rare flooding with a low submersion will 

result in a low flood hazard. Note that corrective factors can be inserted for specific 

conditions of the speed of the current or the duration of submersion, or when protective 

works are present. 

Cliquet - 

Yes 

Users: 

� Urban planning services 

� Notaries and real estate agencies, … 

� Landlords 

T = 25 years 

T = 50 years 

T = ou > 100 years 

Return period of flow Q T 

Recurrence 

Depth of 

submersion 

Extent of 

submersion 

Speed of 

current 

Duration of 

submersion 

Flood Hazard 

Protection facility : Dike, embankment, levee, … 

Figure 4.13 Determination of flood hazard in Wallonia 

H 

M 

L 

M H H 

M M M 

yes 

M 

H M L 

0 � H < 0,3 � H < 1,3 � H (m) 

High 

Medium 

Submersion 

Cliquet + 

V > 1m/s 

D > 3 days 

Prohibition 

Prohibition except for compliance 

with major constraints 

Prohibition except for compliance 

with minor constraints 

Frequent 

( >2x/10 years) 

Medium 

Rare 

(




Figure 4.14 Integration of the methods for determining recurrence and submersion 

Examples maps 

The flood hazard maps for Wallonia are produced as the outcome of the combination of 

maps showing field surveys (occurrence of historical floods), extension of the floodplain 

and the results of a hydraulic modelling. An example of the resulting flood hazard map is 

shown in Figure 4.15. 

4—13




Figure 4.15 Example of a flood hazard map from Wallonia (sub-basin Dendre) 

Comments on the map 

The general layout of the map forms an attractive combination based on transparent colours 

overlaying a topographic background map in grey scale. The choice of the colours on the 

example flood hazard map for Wallonia are logic and intuitive, but it would be interesting to 

mention both a qualitative (‘low / medium / high’) and quantitative value (’25 / 50 / > 100 

years’) for the hazard in the legend. The information provided on the map is also rather 

limited compared to other example maps in this Atlas. 

4—14




4.3 Croatia 

In Croatia a pilot project has been carried out for the preparation of flood risk maps for river 

basin management purposes in 2004. The maps are produced on a scale of 1:100.000. In the 

Figure 4.16 to Figure 4.21 the results are shown for the river Krapina subbasin. 

Figure 4.16 Overview of the river Krapina basin 

4—15




Figure 4.17 Extent of expected flooding for events with a return period of 5 years Figure 4.18 Extent of expected flooding for events with a return period of 1000 years 

4—16




Figure 4.19 Landcover flooded for events with a return period of 1000 years Figure 4.20 Damage map for events with a return period of 1000 years 

Naselja = settlements 

4—17




Figure 4.21 Overview of expected extent of flooded area for various return periods 


Although the overview map of the Krapina basin (Figure 4.16) is very nice from a 

cartographic point of view, it lacks a legend and as such it is not very informative. Similarly 

the two maps of the expected flood extension for return periods of 5 and 1000 years (resp. 

Figure 4.17 and Figure 4.18) do evidently show the difference flooded area, but lack 

background information, e.g. a subset of the information provided on the overview map. On 

the other hand the map showing the expected flooded area for various return periods (5, 10, 

25, 50, 100 and 1000 years) does have a reasonable background, although in fact it only 

shows the basin limits and the drainage pattern. The information provided is difficult to 

judge as there is no clear measuring rod to read the actual difference between the flooded 

areas for the various return periods. It does show very neatly the difference in flooded area 

between the upper basin (very large) and lower basin (relatively small), but this is simply a 

function of the size of those subbasins. It would be interesting to show the relative inundated 

area, i.e. as percentage of the total basin area. 

4—18




Croatia is one of the few countries that provides flood damage maps and in Figure 4.19 and 

Figure 4.20 a land cover map and flood damage map are shown for the same river basin. In 

general the areas that are expected to witness damage during an event with a return period of 

1/1000 years correspond with the flood extension map in Figure 4.18. In addition to that, 

although the flood damage map lacks a legend, it is evident that the darker red colours 

correspond to higher expected damage as these areas coincide with the settlements (Naselja 

in Croatian) on the landcover map. 

4—19




4.4 Denmark 

In Denmark the Danish Coastal Authority has only published a few flood maps for specific 

study areas, such as the areas along the Danish West coast and the Ribe polder area (Wadden 

Sea region). Flood maps on the internet are not available yet. Two examples of flood maps 

in Denmark are shown in Figure 4.22 and Figure 4.23. 

Figure 4.22 A very extreme flood disaster event with a return period of 1/4000 yr in the Ribe polder area 

4—20




Figure 4.23 A flood event of 1/100 yr for a dune area at the Danish West coast 


In Figure 4.22 both the expected inundated area and the infrastructure of the same region are 

shown. In the legend, a distinction has been made between roads with a height of 3-6 m and 

those above 6 m, but it is not clear which of those roads might become inundated for the 

particular event (probably both, given that the situation refers to a 1/4000 year flood). Such 

information might form the basis for an evacuation map. They roads are also difficult to 

distinguish on the map and the line for roads over 6 m might easily be confused with the 

‘dike line’, although the latter is much more pronounced. 

The map in Figure 4.23 is difficult to interpret for an outsider as it is not immediately clear 

on which side the sea is located. The fact that the buildings on the right side of the map are 

inundated suggests that this is the land side and the left side the coastal area which also 

4—21




becomes partly flooded during the event. This map would benefit from more background 

information on the map and in the legend and both maps lack a North indication and a scale 

rod. 

4—22




4.5 Great Britain 

4.5.1 England & Wales 


In England & Wales the Environment Agency has developed several mapping products to 

raise awareness of flood risk and support decision making. Examples of these are shown as 

Figure 4.24 to Figure 4.28. All are available for public or professional use; some data is 

published on the Environment Agency’s internet site 4 . 

The Flood Map is currently the Environment Agency’s main map to raise awareness of flood 

risk with the public and our partner organisations, such as land use/spatial planning 

authorities, emergency planners, emergency services, developers and drainage authorities. 

It has been available on the internet since 2004, although an earlier version was first 

published on the Internet in 2000. The Flood Map shows: 

� Flooding from rivers or the sea without defences – the natural flood plain area that could 

be affected in the event of flooding from rivers and the sea. 

Two shaded areas are presented, which are aligned with the Flood Zones as defined by 

land use planning policy for England: 

� Areas that could be flooded either from rivers with an annual probability of flooding 

greater than 1% (1 in 100) OR areas that could be flooded from the sea with an 

annual probability of flooding greater than 0.5% (1 in 200) 

� Areas other than covered by the above that would be flooded by an extreme flood 

with an annual probability of 0.1% (1 in 1000) from rivers and the sea 

� The location of flood defences – such as embankments and walls, and flood storage 

areas 

� Areas benefiting from these flood defences in a 1% fluvial flood or 0.5% coastal flood – 

where possible the areas that benefit from the flood defences are shown. However, not 

all areas that benefit from flood defences are currently shown (Figure 4.24 is an 

example of this). Figure 4.25 shows how areas benefiting from defences are shown 

where the information is available. There is ongoing work to increase the coverage of 

this information. 

On the internet the Flood Map is presented as a single layer in map form. Users search for 

their location of interest through a standard search tool by entering either a post code or a 

location name. The mapped output shown on the internet site (default scale 1:20,000) is very 

similar to Figure 4.24, which has been shown at a scale of about 1:45,000. 

The online Flood Map also has the facility to allow users to gain further information by 

opting to ‘learn more’ by pointing at a specific location within the map. This leads to data 

from the National Flood Risk Assessment, a mapped data set which provides further 

qualitative information on the probability of flooding taking into account the location, type 

4 http://www.environment-agency.gov.uk/ 

4—23




and condition of flood defences. This information on the actual (residual) probability of 

flooding is presented in three categories used by the insurance industry in the UK, as noted 

below: 

� Significant: the chance of flooding in any year is greater than 1.3% (1 in 75) 

� Moderate: the chance of flooding in any year is 1.3% (1 in 75) or less, but greater than 

0.5% (1 in 200) 

� Low: the chance of flooding in any year is 0.5% (1 in 200) or less 


A number of examples of mapped flood data are provided for England & Wales. Most relate 

to the city of Carlisle in Cumbria to allow direct comparison of outputs, but a further 

example from Burton upon Trent (Figure 4.25) is shown to illustrate information not 

available on the Carlisle maps. 

Figure 4.24 and Figure 4.25 both show extracts from the Flood Map. Flood extents ignoring 

the presence of defences, as described above, are shown. These extents are shaded in hues of 

blue, with the area of greater probability in the darker colour. The map also shows flood 

defences. Although these do not stand out well at the scale shown in the Atlas, they are 

clear on the internet version of the map shown at a scale of 1:20,000. Data on areas 

benefiting from defences is not available at all locations, but exists for all defences built 

since 1998. Further data is added to the Flood Map, as it becomes available, when modelling 

is updated. The Carlisle maps do not show the areas that benefit from defences, although 

this is available for Burton upon Trent. The map layout is clear, with the topography shown 

on the background without too much detail. The internet site also provides an overview 

map, to orientate the location within the national scale, although this is not shown on the 

example here. No ‘North’ indication is deemed necessary – it is customary that ‘North’ is at 

the top of the map in the UK. The grid with its coordinate references provides confirmation 

of this. 

Figure 4.26 is a presentation of the assessment of flood probability bands for Carlisle as 

produced by the National Flood Risk Assessment. It maps the ‘Low’, ‘Moderate’ and 

‘Significant’ flood probability bands as defined above and takes into account the reduction 

in probability as a result of flood defences. The underlying information used to generate the 

map (the flood probabilities and depths) is also a step in the subsequent assessment of risk 

when combined with depth/damage information. This banding is tailored more for 

commercial concerns as the insurance industry in the UK has a particular interest in the 

1.3% limit. Whilst this data is not available in mapped format on the internet, the 

information is available on the internet through the ‘Learn more’ option on the Flood Map. 

There may be discrepancies between this map and the areas benefiting from defences on the 

Flood Map. This is because the assessment used to develop the Flood Map does not take 

into account the presence or condition of flood defences, and so ignores the possibility of 

breach under different loading conditions. The areas benefiting from defences on the Flood 

Map may therefore show a greater area of ‘benefit’ when compared with the National Flood 

Risk Assessment results. 

Figure 4.27 shows flood hazard rating data, with 7 bands of assessed hazard rating from 0 

– 30 on a non-linear scale. The hazard rating (HR) is calculated as a function of velocity (v), 

4—24




depth (d) and a debris factor DF such that HR = d x (v + 0.5) + DF. The hazard rating 

provides an assessment of the direct risk to life arising from the combination of water depth 

and its velocity of flow, based on experiments, and includes a debris factor which recognises 

that debris-filled flowing water increases the danger to people. The map shown in this figure 

gives the absolute values of this calculation. As this is a more specialized type of 

information, this map will be more useful to the expert in flood risk than to the general 

public. 

The formula on which this map is based is taken from the “Flood Risks to People – Phase 

II” report 5 . A simplified presentation of the information for general use has been proposed in 

the report, as in the table below: 

d x (v + 0.5) Degree of Flood 

Hazard 

Description 

2.5 Extreme Dangerous for all 

“Extreme danger: flood zone with deep fast flowing 

water” 

Figure 4.27 could have been produced using this banding rather than the banding shown. 

However, there are several uses for such maps and the needs of the user must be understood 

before deciding on the bandings. For example, the bandings in the table may be most useful 

for planning emergency response (evacuation routes, for example) whereas the more 

detailed banding may be better for deciding where buildings and other infrastructure should 

be located. This data has not been developed for the whole of England and Wales but will be 

produced where needed (using a risk based approach). The data is not available on the 

internet. 

Figure 4.28 shows Social Flood Vulnerability. This map is very easy to read for the nonexpert 

and gives a quick insight into the vulnerability of either a person or property at 

different locations within extreme flood outline. The number of people at risk from flooding, 

and their social status, is measured by “social vulnerability”. The Flood Hazard Research 

Centre at Middlesex University developed a Social Flood Vulnerability Index (SFVI), based 

on three social groups (long-term sick, single parents, the elderly) and four indicators of 

financial deprivation (unemployment, overcrowding, non-car ownership, non-home 

ownership). The SFVI can take a range of values, and these are divided into bands from 1 

(very low vulnerability) to 5 (very high vulnerability). Each Output Area of the UK National 

Census has a SFVI band calculated, and the number of districts with each score in a flood 

5 http://sciencesearch.defra.gov.uk/Document.aspx?DocumentID=3646 

4—25




risk area such as Carlisle is used to calculate the overall social vulnerability of that area. On 

the map provided for Carlisle, the ‘very low’ class is not present. This data is not available 

on the internet. 

4—26




Figure 4.24 Flood extension map for the region of Carlisle 

4—27




Figure 4.25 Example of flood map with indication of area benefiting from defence works 

4—28




Figure 4.26 Flood hazard map of the region of Carlisle 

4—29




Figure 4.27 Flood hazard rating map of the region of Carlisle 

4—30




Figure 4.28 Social Flood Vulnerability map of the region of Carlisle 

4—31




4.5.2 Scotland 

In Scotland the organization SEPA looks after all aspects of flood control. Recently an 

interactive internet site has been activated 6 where for the whole of Scotland the expected 

flood extension is shown for a return period of 1/200 years. Both flooding from rivers and 

the sea are incorporated. The information provided is very similar to what is available for 

England & Wales, although they use a return period of 1/100 yr for river flooding and 1/200 

yr for flooding from the sea. An example is shown on Figure 4.29 for the city of Edinburgh. 

Figure 4.29 Flood extension map for the city of Edinburgh from interactive internet site 


The maps that can be produced with the interactive internet site have a very clear outline 

and are easy to read, partly because only a limited amount of information is presented 

(topography and expected flood extension by flooding from rivers and the sea). On the 

6 http://www.multimap.com/clients/places.cgi?client=sepa 

4—32




example shown in Figure 4.29 both types of flood origin are included. There is an option to 

show the flood defence works instead of the flood extension, but not both types of 

information at the same time. 

4—33




4.6 Finland 

In Finland many types of flood maps are produced which are summarized in the following 

table with an example of the layout of each of them. 

Some flood map types used in Finland. 

There are also many historical flood maps, i.e. maps showing the extent of historical floods. 

They can be used in combination with flood extension maps, but their use may be limited 

when referring to floods that occurred many years ago, especially in urban areas, as major 

changes may have occurred in the geometry of the river bed. 

4—34




Figure 4.30 Flood hazard map for the city centre of Lapua for 1/1000 yr flood event 

4—35




Figure 4.31 Flood hazard map of the city of Pori (water depths for 1/250 yr event) 

4—36





The flood maps from Finland are among the most complete and clearest examples that can 

be found. The maps are available for various return periods. In Figure 4.30 an example is 

given for the city of Lapua in Western Finland for a flood event with a return period of 

1/1000 yr. The layout of this map is very clear and easy to read also for a non-expert. It is 

also interesting that it not only gives the extent of the expected flooding, but also the 

maximum extent of the area that was incorporated in the flood modelling (with a green line), 

i.e. no information is available outside these boundaries. Isolated areas within the flooded 

areas are shown by hatching, but this is more difficult to distinguish on the map. The 

combination with type of urbanization makes the map useful as basis for flood damage 

assessment. There is an inserted window to show the location of the detailed map and both 

scale and orientation of the map are very clearly indicated. All information on the 

background data of the map, including the basis for the delineation of the flood extension, is 

summarized in a table on the same map page. 

For the flood hazard map that is shown in Figure 4.31 for the city of Pori the expected water 

depths are given for an event with a return period of 250 year. The map shows both the 

flooding of unprotected areas and, with shading, the areas that will be flooded in case of 

failure of dikes. It is assumed that all dikes will fail, i.e. it is a worse-case scenario. Also 

here the maximum extent of the modelled area is indicated by a green line. 

As with the flood extension map, at the bottom of the map, additional information is given, 

among which the basis for the calculation of the corresponding discharge: frequency 

analysis with the Gumbel distribution. The corresponding water levels are calculated with a 

1-D hydrodynamic model. Such information is rarely given with flood maps and it is often 

even difficult to find this type of technical background information in accompanying 

documents. 

It is also interesting that this map shows in a very prominent position a disclaimer in red: 

“The purpose of the map is to give a general view of the extent and depth of a 250-year 

flood. It is not reasonable to use the map for a building-specific analysing. More 

information: http://www.ymparisto.fi/.”. This is a very clear statement and it can be assumed 

that this message will not easily be overlooked as might happen with disclaimers in separate 

internet pages and/or accompanying documents. On the specified internet site, more detailed 

information is indeed provided (albeit evidently in Finnish) and more examples of flood 

maps can be downloaded. 

4—37




4.7 France 

France has interactive flood maps for various regions on the internet. A few examples are 

given below. 


In the following figures first examples are given of four interactive internet sites that are 

available in France to obtain flood extension maps for different regions. 

In Example 1 a nationwide system is shown that allows the user to access flood-related risk 

information for a number of regions in France. 

The other three examples are administered by different agencies and as such the layout of 

these sites is completely different. The three examples are produced by different methods: 

� Example 2 – Carte Rhône river – region of Avignon: based on hydrogeomorphology; 

� Example 3 – Nord Pas-de-Calais: based on modelisation 

� Example 4 – Ile-de-France region: based on historical flood maps. 

A fifth example of flood maps from France is produced by the insurance sector and 

therefore discussed separately in the corresponding Chapter 6.4. 

Example 1 – Ministere de l’ecologie et du developpement durable 

An interesting source of information on the risk of natural disasters can be found on a 

central internet site of the Ministère de l’écologie et du développement durable 7 . On this 

site, called ‘Cartoristique’ the risk of natural disasters has been centralized from various 

local sources. One of the main reasons for making this information available to the public is 

the “Plan de Prévention des Risques naturels (PPR)”, which was created by the law of 2 

February 1995, and which includes evidently flood risk. The use of the risk information in 

the insurance against floods is further discussed in Chapter 6.4. 

7 http://cartorisque.prim.net/index.html 

4—38




Figure 4.32 Overview page of the nationwide risk internet site 

On Figure 4.32 an overview is given of the regions in France for which risk maps are 

available (shown in dark blue, light blue means “not yet available”). Risks refer to a number 

of natural risks, including avalanches, etc., but for this purpose flooding is only relevant. 

After choosing a certain region, a new map becomes available within which by zooming the 

flood hazard along a river can be shown (e.g. Thionville along the Mosel river in Figure 

4.33). Depending on the choice of the region, the extent of a number of historical floods can 

be shown. By clicking anywhere within a flood-prone region, additional information 

becomes available which shows that the flood extent refers to a flood with a return period of 

1/100 years and it also makes a background document available on the chosen location with 

an overview of historical natural disasters (in this case floods). 


The main advantage of this system is evidently that it uses a common layout for all the 

departments in France, despite the fact that different sources of information may be at the 

basis. The layout is straightforward and easy to understand, with both the detailed map with 

the actual required information and the overview map in the same window. There is, 

however, no indication on the maps themselves to which return period the flood risk map 

refers. The use of different historical floods makes it impossible to compare adjoining maps, 

but this is not a major drawback. The use of the various map layers is well organized, with 

an indication that certain background layers, such as a scanned topographical map and 

orthographic (aerial) photos, can only be shown after the user has zoomed in sufficiently 

(Figure 4.34). 

4—39




Figure 4.33 Example of a flood extension map for Thionville on the Mosel river 

4—40




Figure 4.34 Effect of different levels of zooming in on the availability of background layers in the Cartorisque system (Abbeville on the Somme river) 

4—41




Example 2 - Rhône river – region of Avignon 8 

Figure 4.35 Example of flood extension internet site of the Rhone river region 

Figure 4.36 Flood inundation maps for city of Avignon with both historical floods (1856 and 2003) and 

expected inundation areas 

8 http://www.geomapguide.com/diren/Risques/Dynamap_risques.htm 

4—42





The layout of the interactive internet site for the Rhône river, and more in detail shown for 

the region of Avignon in Figure 4.36, is very attractive and easy to work with also for a nonexpert. 

It shows a combination of historical floods (in this case 1856 and 2003) and 

expected flood extension. For the latter, though, there is no information to which return 

period the indicated area belongs. The map was build on the basis of a topographic map with 

a scale of 1:25.000. There is a clear indication of the location of the detailed map within the 

overall region. There is no North indication, but in this case all maps are automatically 

orientated with North at the top of the map. 

Although it is interesting to show historical floods with the flood extension information, it 

should be remarked that the extension of floods in the 19 th century, as in this case for 1856, 

may be of limited value given the fact that many changes may have occurred since that time 

in the geometry of the river cross-sections. 

Example 3 - Nord Pas-de-Calais 9 

Figure 4.37 Example of the river Yser in Nord Pas-de-Calais 


The layout of the internet site for the Nord Pas-de-Calais (Figure 4.37) is clear and easy to 

interpret. In this case also a combination is shown of historical floods (here a flood of 2001) 

and the expected flood extension for evens with a return period of 1/10 yr (‘décennale’) and 

1/100 yr (‘centennale’). There are also indications possible of the preferential flow path and 

storage areas. The former may be used as indication where higher flow velocities can be 

expected, although no flow velocity map is provided. Information on flood depth and 

duration of the flooding is given for isolated points (depth with green, duration with black) 

9 http://carto.ecologie.gouv.fr/HTML_PUBLIC/Site de consultation/site.php?map = 

azi_yser.map&service_idx=24W htm 

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and this type of data is shown whenever such a point is highlighted with the mouse. Depth is 

given with 0.1 m precision for the historic flood and the two return periods. The duration is 

given as an order of magnitude (e.g. 1 – 2 days), but there is no information on the map to 

which return period this information refers. 

Example 4 - Ile-de-France region 10 

Figure 4.38 User-interface of the flood map site of the Ile-de-France 

10 

http://carto.ecologie.gouv.fr/HTML_PUBLIC/Site%20de%20consultation/site.php?map=essai_PHE 

C.map&service_idx=18W 

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Figure 4.39 Detail of the flood inundation map for the Ile-de-France 


For the Ile-de-France region only historical flood extensions are given and it is only 

included here as an example of a flood map of a very densely populated urban area (region 

Paris). Different historical floods can be chosen from the internet site. 

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4.8 Germany 

For Germany there are many different maps as each of the “Länder” makes its own maps, 

but recently (2006) recommendations have been published on national level for the 

production of flood maps 11 . Examples in this document include maps from Baden- 

Württemberg, Bayern, Nieder-Sachsen (including Bremen), Nordrhein-Westfalen, 

Rheinland-Pfalz, Saarland, Sachsen and Sachsen-Anhalt. 

4.8.1 Baden-Württemberg 

For Baden-Württemberg there are interactive maps available for both flood extension and 

flood depth on the internet 12 . However, there is still very limited information available (only 

the Neckar river between Mosbach and Heidelberg, see Figure 4.41). There is a clear 

corresponding document available in PDF-format directly from the map page in which the 

procedure is explained of the production of the flood maps. Information is given for return 

periods of 1/10, 1/50, 1/100 and an ‘extreme’ situation. The latter is explained in the text as 

a ‘statistically very rare event. It can be defined as a historical event, which may be different 

for different locations, e.g. due to obstruction by bridges’. It is not possible to give any 

return period to such an event. 

In Figure 4.40 the various concepts are shown that are used for the elaboration of the flood 

maps of Baden-Württemberg. Important are the possibilities to indicate whether a certain 

area is located behind a flood defence and the return period for which this flood defence is 

still effective. 

In Figure 4.41 the (restricted) river stretch is shown for which flood maps are made publicly 

available (Neckar river). Examples of flood maps for this region are shown in Figure 4.42 

and Figure 4.43. They can be accessed from the internet 13 . As stated on the internet site of 

Baden-Württemberg all the maps are produced as part of the EU-funded SAFER project (see 

Chapter 5.6). Baden-Württemberg has also produced an English-language guidebook ‘Flood 

Risk Maps in Baden-Württemberg’, as part of the SAFER EU project, which forms the basis 

for the production of the flood hazard maps. The map in Figure 4.43 is an example of a map 

that is produced following these (SAFER) guidelines. 

11 Deutsche Vereinigung für Wasserwirtschaft, Abwasser und Abfall (DWA), Arbeitsgruppe 

Hochwassermanagement: “Empfehlungen der Bund-/ Länderarbeitsgemeinschaft Wasser (LAWA) 

zur Aufstellung von Hochwasser-Gefahrenkarten” 

12 http://rips-dienste.lubw.baden-wuerttemberg.de/rips/hwgk/ 

13 http://www.hochwasser.baden-wuerttemberg.de/ 

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Figure 4.40 Examples of the definition of flood inundation areas (Baden-Württemberg) 

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Figure 4.41 Location for which flood maps are available in Baden-Württemberg (Neckar river) 

Figure 4.42 Example of a flood extension map from Baden-Württemberg (Neckar) 

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Figure 4.43 Example of flood depth map (Neckar river) 


The flood extension map (Figure 4.42) is rather detailed and easy to read. The inundated 

area for each return period is shown as the increment compared to the lower return period, 

the results on the map being in line with the intuitive interpretation that higher return 

periods result in larger (=darker hue of blue) water depths. 

For the flood depth map (Figure 4.43) the information is only provided for the ‘extreme’ 

flood, which has no clear return period, although in the case of the maps shown above it 

corresponds with the extension of the 1/100 year flood (possibly because no major historical 

flood information is available). The use of colours is unusual as normally flood depth is only 

shown in shades of blue. The present succession from yellow to red is normally used in 

flood risk maps to indicate increased level of danger. Step size of 0.5 m is logic and 

probably consistent with the level of precision of the underlying data. 

4.8.2 Bayern (Bavaria) 

With the “Information Service on Flood Hazard Areas” detailed flood plain maps for Bayern 

are shown on the internet 14 , open to the public. The service was published by the Bavarian 

Environment Agency in March 2004. It contains: 

� Flood plains (German: Überschwemmungsgebiete). Usually these areas are calculated 

for a 100 year flood by means of hydraulic modelling and based on high-precision 

14 http://www.bayern.de/lfw/iug/ 

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digital elevation models. Up to the end of 2008 flood plain maps will be produced for all 

big and medium rivers in Bavaria (~ 9.000 river kilometres) in a scale of 1:2.500 to 

1:5.000. Furthermore the extension of the programme on small rivers is planned. 

� Flood prone areas (German: Wassersensible Bereiche): Derived in a scale of 1:25.000 

they represent an estimation of potentially hazardous areas by interpreting soil maps 

(natural flood plains). Water sensible areas are only developed for online presentation. 

As they are available almost all over Bavaria, they are provided as very simple and 

basic information for the public, to assess the risk of flooding or high ground water 

level. 

The integration of flood hazard maps into the web mapping service is planned. First pilot 

studies are already started. 

The internet site with an example for the region of Regensburg is shown in Figure 4.44. 

Figure 4.44 Interactive internet site for flood maps in Bayern 

Comment on the map 

Compared to many other interactive flood map sites, the site for Bayern shows limited 

information and as such is of course also easy to interpret. The outstanding feature of the 

mapping service is the possibility to get very detailed information on the extension of 

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floods. With changing background map zooming in is possible up to a scale that shows 

every house and parcel (Figure 4.45). Thus utilization restrictions due to water legislation 

are comprehensible for everyone. In the information provided on the map, it is indicated that 

the flood inundation area normally corresponds with an event with a return period of 1/100 

yr, but in some cases either 1/30 yr or 1/300 yr. In a few cases it represents the extent of a 

historical flood and further inquiry may be necessary to clarify what the flood extent for a 

certain location means. 

Figure 4.45 Detail of the interactive internet site precisely showing the affection of houses and parcels. 

4.8.3 Nieder-Sachsen / Bremen 

For Nieder-Sachsen and the city of Bremen flood hazard maps are available on the internet 

as downloadable map sheets in PDF format 15 . An example is given in Figure 4.46. The 

legend to the maps is only available in German, but the expected flood extension for a return 

period of 100 years is shown in light-blue. Diagonal hatching indicates regions for which 

the maps are still being produced, while dark-blue is used for flood water retention areas. 

The city of Bremen is covered by two map sheets (nrs. 4 and 9). According to the 

accompanying text (in German) the inundation areas are calculated by 1-D hydraulic models 

and, for more complex situations, with 2-D hydraulic models. The approach is based on a 

steady-state situation, i.e. no calculations are made of the actual inundation process and 

15 http://www.mu1.niedersachsen.de/master/C7774004_N11348_L20_D0_I598 

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therefore no information is available on the duration of the inundation. Maps are given on a 

scale of 1:200.000. New detailed maps for some areas on a scale of 1:25.000 are also 

available on the same internet site and it is the aim to finalize the inundation mapping for 

the whole of Nieder-Sachsen in 2008. 

Figure 4.46 Example of flood map for Nieder-Sachsen with part of the city of Bremen 


The flood hazard maps of Nieder-Sachsen are easy to read due to the combination of clear 

colours for the inundated areas and a topographical background. The information provided 

is limited, with only the expected extension of the inundation without any indication of the 

expected depth. The legend is only provided on the overall map with the location of the map 

sheets, no legend is available on the map sheets themselves. Such a legend is available, 

though, on the newly produced more detailed maps. 

4.8.4 Nordrhein-Westfalen 

For Nordrhein-Westfalen use is made of maps, which can be downloaded from the 

corresponding internet site 16 . Information on flood extension is given for the Rhine river for 

a return period of 1/500 yr and the smaller streams for 1/100 yr. The maps are available as 

16 http://www.lua.nrw.de/wasser/hwberkarten.htm 

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PDF files and are very detailed. Interestingly the maps also show regions that may be used 

as emergency inundation areas. In Figure 4.47 this is shown with the normal flood extension 

in dark-blue and the emergency inundation areas in yellow and pink. The yellow areas are 

flooded in for floods with a return period of 100 years in case no action is taken, while the 

pink areas are restricted region for inundation and only used in special cases. 

Figure 4.47 Flood extension maps in Nordrhein-Westfalen including emergency inundation area 

In Figure 4.48 an example is given of the Rhine river in the region of Köln that shows the 

expected inundation area for an event with a return period of 1/500 yr for the Rhine, with a 

distinction between inundated area along the main river channel (light blue) and behind 

dikes (hatched yellow). For the tributary of the Sieg in the right upper part of the map, both 

the expected inundated area for a return period of 1/100 yr is given as well as the emergency 

inundation area (in yellow and pink). 

The legend is rather small and not easy to read, even when printed on A3 format as in this 

case. This illustrates the problem of reproducing scanned original topographic maps as 

background to flood maps. 

The access link to an interactive map is already shown on the internet site where the maps of 

Nordrhein-Westfalen are available, but has not yet been activated. 

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Figure 4.48 Example of a flood extension map with indication of emergency inundation areas along the Rhine 

4—54




4.8.5 Rheinland-Pfalz 

Rheinland-Pfalz has a very complete interactive map internet site 17 for the Mosel basin with 

many possibilities for adjusting the map and searching for e.g. rivers, locations, etc. It is 

based on a high-precision elevation model. The use of river kilometres (in steps of 500 m) to 

focus on river stretches is particularly helpful. The map is used to show information on 

expected flood extension (for return periods of 1/50, 1/100, 1/200 and ‘extreme’ events) and 

also for a second class of information (‘Danger classes’, with a distinction in four classes). It 

is possible to show the four types of extension as well as the danger (or hazard) classes in 

one map, but evidently the information will overlap and may be partly lost. Deriving the 

hazard stages is based on a method in which the degree of hazard is expressed by the 

intensity (water depth and flow velocity) of a flood event in combination with the 

probability of its occurrence. Using a hazard matrix - an intensity-probability diagram - 

these two parameters are summarised to be expressed as hazard stages (see below). 

The hazard stages show the degree of danger to persons, animals and property and are 

differentiated into three degrees of hazard, distinguishable by the colours red (substantial 

hazard), orange (moderate hazard) and yellow (minor hazard). In order to be able to 

calculate the residual hazard, the hazard situation for very rare events (extreme floodwater 

run-off) was examined. These areas are shown as yellow-white hatched. 

A similar approach with a hazard matrix is adopted in Switzerland and Belgium (Wallonia). 

17 http://www.gefahrenatlas-mosel.de 

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Figure 4.49 Example of flood extension map for the Saar river 

Figure 4.50 Danger class map of the lower part of the Kyll river 

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Figure 4.51 Flood extension map of the lower part of the Kyll river 

The danger or hazard classes do not correspond with the flood extension classes and return 

periods. They are defined based on the initiative of the international TIMIS-project (see 

Chapter 5.7) through which hazard maps for more rivers in Rhineland-Palatinate are 

elaborated. The maps will be available in the internet in 2008 and will provide a lot more 

information for the user. The four danger classes that are used on those maps are further 

discussed in Chapter 5.7 on the TIMIS project. Figure 4.52 shows an example of an 

improved hazard map for Rheinland-Pfalz. 

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Figure 4.52 Example of a hazard map for Rheinland-Pfalz 


The internet application for the Mosel river in Germany is among the most complete that is 

presently available. The layout is very clear and the information provided also very 

complete. The three examples of the internet site itself (Figure 4.49, Figure 4.50 and Figure 

4.51) show expected flood extension and flood risk according to the classification explained 

above. It is possible to show both the flood extension and the risk level in one map, although 

sometimes the information will be obliterated. Return periods can be chosen (1/50, 1/00, 

1/200 and ‘extreme flood’) and the user can interactively change the details of the 

background information, including vegetation, names of towns, etc. Colours are well-chosen 

and make it immediately clear to the user which areas have the highest risk. There are very 

easy to use search options, e.g. for a certain town and it is also possible to jump directly to a 

certain location along a river using river kilometre indications. This internet flood map site 

might form an interesting example for other agencies that want to provide their information 

interactively. 

4.8.6 Saarland 

Also the maps for the Saarland region are based on an interactive map site 18 . An example is 

shown in Figure 4.53. 

18 http://www.gis.saarland.de/website/usg1/viewer.htm?Title=%DCberschwemmungsgebiete 

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Figure 4.53 Example of a flood extension map for the Saarland region (1/200 yr event) 


Although the map is rather clear, especially the topographical information, the large number 

of parallel dark-blue lines, indicating the limits of the expected flood extension for a 1/200 

year event, may be more difficult to distinguish than the method based on coloured surfaces. 

4.8.7 Sachsen 

For Sachsen there is an interactive internet site 19 where a choice is given between flood 

inundation maps (Uberschwemmungskarte) and flood damage maps (Schadenpotentialkarte). 

In Sachsen some major cities are located, such as Leipzig, Dresden and Chemnitz. 

Dresden is particularly interesting as it has witnessed major flood events in the recent past 

due to high water levels on the Elbe river (especially August 2002, for which a historical 

flood extension map is also available). It should be remarked that the maps have been 

produced as part of the transboundary ELLA project (see Chapter 5.3). 

Flood extension maps 

On the flood extension maps it is possible to show expected flood extensions for three return 

periods: 1/20, 1/100 and ‘extreme’, which according to the description is higher than any 

historical flood extent and at least more than 1/300 years. For the three return periods it is 

possible to show the corresponding expected flood extent, but only for the ‘extreme’ 

situation it is also possible to show the expected flood depth. Use is made of an intelligent 

map program that avoids ‘overlapping’ information, e.g. trying to show both extension and 

water depth, the latter showing evidently automatically already the extension. It is 

interesting that it is possible also to show vulnerable locations such as hospitals, energy 

installations, water production and industrial areas. The examples are shown for Leipzig and 

19 http://www.umwelt.sachsen.de/de/wu/umwelt/lfug/lfug-internet/interaktive_karten_10950.html 

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Dresden (Figure 4.54 and Figure 4.55). 

Figure 4.54 Flood extension map of the region of Leipzig 

Figure 4.55 Flood extension map of the region of Dresden 


In general the use of the colour green for flood extension (and in this case use is made of 

hues of green to show the flood extension corresponding to the three return periods) is 

unusual, but most likely has been chosen to allow for the combination of both flood 

extension and expected water depth in the same figure. It should be remarked, though, that 

green is normally used to indicate safety, which is not the case in this map. This shows the 

conflict in colouring that will occur when several themes are shown in the same map. 

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Flood damage maps 

The layout of the flood damage maps is similar to the flood extension maps. Examples for 

Leipzig and Dresden are shown again (Figure 4.56 and Figure 4.57), but with a higher level 

of detail as in this case map layers with details on the expected damage become visible. 

Figure 4.56 Flood damage map of the region of Leipzig 

Figure 4.57 Flood damage map of the region of Dresden 


These maps give very detailed information on the potential damage during ‘extreme’ floods, 

with a distinction between industry and urban damage. Colours are well-chosen and 

evidently the user can change interactively both the region and the scale that is wanted. 

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4.8.8 Sachsen-Anhalt 

For Sachsen-Anhalt a number of very detailed maps are available on the internet 20 in PDF 

format. In Figure 4.58 an example is shown for the river Elbe at the city of Magdeburg for 

an event with a return period of 1/100 yr. 


This is an example of a very clear map, partly due to the limited type of information that is 

provided. They have a detailed topographical background. Flood depths are given in a nonlinear 

scale (0.5, 1, 2 and 4 m), which may lead to confusion. Although the maps are freely 

available from the internet, they can not be copied or printed. 

20 http://www.ella-interreg.org/gefahrenkarten0.html 

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Figure 4.58 Flood extension map for the river Elbe at Magdeburg 

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4.9 Hungary 

In Hungary flood maps have been produced for the major rivers, but most of the maps are 

rather old and have not been updated since 1977. Only flood extension has been presented. 

Figure 4.59 Flood map of the Tisza river basin 

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Figure 4.60 Flood map at Madocsa on the River Danube in Southern Hungary 


In Figure 4.59 example of a flood extension map is given for the Tisza river. The example is 

the version in scale 1:500,000, but the maps are originally made in 1:50,000 and 1:100,000. 

Although it is originally called flood hazard map, it shows the expected flood extension for 

return periods of 1/100 and 1/1000 yr. The map is an example of a flood extension map 

without any special additions and as such is very easy to interpret. 

A map of a Danube flood area in 1:50,000 is shown in Figure 4.60. The same return periods 

are used at this example and also the flood embankments are shown. Flood embankments 

are very important in Hungary: about 97% of the floodplains are protected by dikes. 

Recently new flood maps are being prepared and will become available for the whole 

country in the near future based on statistical analysis. In many cases hydraulic modelling is 

used to determine the flood extent, flood depth and the propagation time of inundation. The 

processing of new flood maps for Hungary is still in progress. In the future many other types 

of flood maps will be available, among which flood risk and flood damage maps. 

Examples of new flood maps for Hungary are shown in Figure 4.61 (extension of 

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inundation), Figure 4.62 (flood depth) and Figure 4.63 (propagation of inundation). 

Figure 4.61 Bereg flood area, River Tisza right bank, highest elevations of inundation (masl Baltic) 

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Figure 4.62 Bereg flood area, River Tisza right bank, flood depth (m) 

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Figure 4.63 Bereg flood area, River Tisza right bank, propagation of inundation (hours) 

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4.10 Ireland 

In the past flood mapping in Ireland has focused on mapping of flood extents for various 

event probabilities (return periods) only in high-risk areas. This practice has recently been 

expanded to include the mapping of flood velocities and depths (See Figure 4.64) based on 

2-Dimensional hydraulic modelling and high-resolution digital terrain models. 

Figure 4.64 Flood depth map – 1% Annual probability event 

A national flood mapping programme has been initiated to provide greater spatial coverage 

of flood maps, principally for planning and development management and flood risk 

management planning. Phase I of this programme has recently been completed, with the 

development of a web-based information management system, and its population with 

collated and verified historic flood data (www.floodmaps.ie, see Figure 4.65). Before the 

user can enter the internet site, a disclaimer has to be acknowledged: 

Introduction 

The Office of Public Works (OPW) is the leading state agency in relation to flood-related matters in 

the Republic of Ireland. The information in relation to past flood events that is displayed on this Web 

site is collected by OPW from Local Authorities, other state bodies and members of the general 

public. The information is then put through a rigorous verification process in order to provide the 

maximum degree of confidence in its accuracy. However, due to the type and character of the 

information involved there are a number of issues and considerations that users should take 

account of in relation to the Content and the Use of the Web site. 

The user can search on the name of a location or zoom in on the map and interactively 

choose a location. For each location for which specific information is available a clickable 

indication in the form of yellow triangle is shown on the map. As is shown in Figure 4.65 

for each location the available information on historic floods is given, which can be 

accessed directly on-line, also reports on the event. There is also a complete glossary on the 

technical words and an extendable legend. 

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Figure 4.65 Website view, indicating historic flood extents and reported flood incidents 

In addition to historic flood extent and incident locations, the website also makes available 

to the user information such as photographs (see Figure 4.66), reports, hydrometric data and 

other supporting information. 

Figure 4.66 Website view, available photographs of historic flood events 

Predictive flood maps currently under development through the flood mapping programme 

will also be made available via the website. The foreseen format of the flood extent maps is 

provided in Figure 4.67. It might be noted that the line type varies for different reaches of 

each of the flood envelopes to indicate a high, medium or low level of confidence (indicator 

of uncertainty) associated with the flood extent. A table of flood levels (above datum) is also 

provided for nodes along the river channel. 

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Figure 4.67 Predictive flood extent mapping format, with indicator of uncertainty and table of flood levels 

(Note: Map is provided only as example of map format) 


At present Ireland has one of the most sophisticated interactive internet sites to access 

information and maps on historic flood events. The combination of both documents, photos 

and maps makes it very easy for the user to get a complete picture of the situation. 

For flood extent maps at present only maps for high-risk areas are available, which though 

are easy to read with a well-chosen range of colours for the various levels of risks. For the 

whole of Ireland, the work on flood mapping is still in progress, but the example provided 

shows that these maps are also easy to read and the use of colours intuitive. 

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4.11 Italy 

For Italy a number of flood-related maps have been made available. However, no 

information has been provided on the mapping programme, mapping authorities or any 

other background information. 

Figure 4.68 Flood extension and risk map in Italy (location Rieti) 

On the flood extension map (Figure 4.68) both the flood extension is shown (for 3 return 

periods: 1/50, 1/200 and 1/500 yr) and three levels of risk (R2, R3 and R4). This risk factor 

R is defined on the basis of two parameters: sensitivity and probability. One of these two 

factors (probability) is already shown on the same map (inverse of the return period) and the 

risk factor is obtained by overlying this information with land use and urban planning. The 

latter is remarkable, because it implies that future urban layout is taken into account. In total 

there are four levels of risk (R1 – R4). Risk area R1 is characterized by a low sensitivity, 

because its specific use implies a low probability of human loss or because it falls within 

areas characterized by high return periods. The level of risk increases from R4 to R2: 

� R4: Return period of 1/50 yr and high level of sensitivity 

� R3: Return period of 1/50 – 1/200 yr and high level of sensitivity 

� R2: Return period of 1/200 – 1/500 yr and high level of sensitivity 

The process of derivation of risk areas is shown in Figure 4.69 - Figure 4.71 for the river 

Tevere with a total population of about 4.3 million persons. The Tevere river passes through 

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the city of Rome towards the Mediterranean Sea and as such is a very relevant example of 

flood mapping in an urban area. 

On Figure 4.69 the vulnerability / sensitivity is indicated of exposed assets (i.e. types of 

buildings, sport facilities, waste dumping areas, power plants, etc.). In the vulnerability 

maps, red indicates the most vulnerable locations, which is logical. However, green 

indicating the least vulnerable locations might suggest that these areas are safe, which is 

misleading. 

On Figure 4.70 the flood extension for the three return periods is shown. Use is made of 

colours that are normally associated with a danger level, e.g. red is used for the flood with 

the highest probability (1/50 years) that can be expected to have the highest water depths 

and flow velocities. 

On Figure 4.71 the combination of the two former maps into a flood hazard map is shown. 

Use is made of the colour red again for the highest flood hazard. 

Figure 4.69 Vulnerability of exposed assets in the river valley of the Tevere 

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Figure 4.70 Flood extension map for 3 return periods (1/50, 1/200 and 1/ 500 years) 

Figure 4.71 Hazard map (combination of vulnerability and flood extension maps) for 3 return periods 

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The maps for Italy give one of the scarce examples of flood risk maps (probability versus 

consequences). The method is easy to understand, but the use of the same colour (e.g. red) 

for high vulnerability and high probability might cause some confusion. 

In addition, the use of green for areas of low probability c.q. vulnerability may lead to the 

misleading conclusion that those areas are safe, while this is not the case. 

4.12 Latvia 

Latvia doesn’t yet have a well established flood mapping system, partly because there was 

no urgent need for such mapping for the whole of Latvia or separate river basins. For 

historical events maps are available as hard copies. Many maps are produced on special 

request e.g. for a municipality. 

In Latvia there is no great flooding as in most of other European countries where larger 

rivers are present. However, some flood mapping efforts are made - mostly if there are 

requests from municipalities. Calculations are made for some territories for 1/100 yr (1% 

probability) and sometimes other frequencies (5%, 10%, 20% or 50% probability etc.), 

depending on request. 

For the examples of flood maps in Latvia two maps are available. The map in Figure 4.72 

shows the expected flood extent for an event with a return period of 1/100 yr for the city of 

Jekabpils, which lies along the Daugava river, which is the most important river in Latvia. 

Most floods in the city of Jekabpils occur in spring due to ice-jams. 

The map in Figure 4.73 shows the flood extension for the city of Lubana on the Aiviekste 

river, a tributary of the Daugava river, also for a return period of 100 years. This is an 

example of a map that was especially produced for a municipality, who requested also to 

have land use on the same map. 

Both maps where made in Latvian Environment, Geology and Meteorology Agency 

(LEGMA) in year 2006. It should be remarked that the layout of both maps map is rather 

clear and easy to read. 

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Figure 4.72 Flood extension map for the city of Jekabpils in Latvia on the Daugava river 

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Figure 4.73 Flooded area (diagonal blue lines) for the city of Lubana for a return period of 100 years 

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4.13 Luxembourg 

The flood maps for Luxembourg are in fact part of the total map availability for the Mosel 

basin and as such restricted to this basin (TIMIS project, see Chapter 5.7). The interactive 

map allows for the use of various types of backgrounds: topographic map, satellite image, 

shaded relief and a combination of these types. Of these types the combinations topographic 

map/satellite map and topographic map/shaded relief give the best results. Flood related 

information that can be provided include: expected flood extension, water depth and flow 

velocity for return periods of 1/50, 1/100, 1/200 and ‘extreme’ floods. In Figure 4.74 an 

example is shown of the expected flood extension and depth for a return period of 1/100 yr, 

while the corresponding velocity field is shown in Figure 4.75. 

Figure 4.74 Flood depth map for the Mosel river in Luxembourg for return period of 1/100 yr 

Figure 4.75 Same location as former figure, with flow velocity indication 

4—78




Another set of maps is available for the Mosel basin, but these are produced as part of an 

EU-funded project (TIMIS) that is further described in Chapter 5.7. 


The map is rather basic compared to other interactive internet sites and although hues of 

colours are used, the use of a ramp of colours instead of class intervals makes it more 

difficult to interpret the information. Here the comments made on fuzziness of the colour 

palette (see Chapter 3.1) are relevant: it is not easy to read the actual water depth or flow 

velocity from the map without going into very large detail (zooming in), which does lead to 

a loss of orientation by the user (see figure below, which is a detail of Figure 4.74). 

The use of pink for the flood extension is unusual, although this is probably chosen because 

the more likely blue colour is used for expected water depth. The same applies for the use of 

green for flood velocity, instead of e.g. red, because flood velocity is very intimately linked 

to danger. There is no overview map for orientation and no North indication is given, 

although it can be assumed that North is always at the top of the map. 

4—79




4.14 Netherlands 

The Netherlands is flood prone for about 60% of its surface. 95 so-called dike-rings protect 

the polders from being flooded from the North Sea, rivers or lakes. The protection level has 

a legal status, expressed in the following exceedance frequencies per year: 1/10.000 along 

the central section of the North Sea coast, 1/1250 along the main rivers, 1/2000 and 1/4000 

in the intermediate estuaries, lake IJssel and Wadden Sea. Flooding of these dike rings may 

occur as a result of the failure (or overtopping) of embankments or other defence works 

(sluices, storm surge barriers). Under these conditions a relatively large area may be flooded 

in a couple of days. The extent, progress and final flooding depth (and hence potential 

damage and affected inhabitants) depend on the location and process of the failure, 

hydraulic boundary conditions and terrain characteristics. This can be simulated by 2-D 

model computations. Only relatively small, unprotected areas outside these dike-rings 

experience the natural dynamics of rising waters due to the tide, storm-surges or river 

floods. Along the river Meuse isolated villages have minor embankments with a protection 

level of 1/250. 

Official flood (extent) maps in the Netherlands are available for public and official use on 

Internet (www.risicokaart.nl, access on provincial level). These maps show flood prone 

areas, as defined by more than 1 meter flooding depth with a frequency larger than 1/4000 

per year. Figure 4.76 shows an example for the province of Gelderland. Many types of 

disasters are shown on this site, including accidents in tunnels, traffic, forest fires, 

earthquakes etc. To show maps related to floods (the light blue horizontal hatching), the 

other options can simply be turned off. 

In addition to these official maps many types of flood maps exist for study and disaster 

management purposes. As a result of these studies a new generation of flood maps will 

become available on the provincial Internet-sites the coming years. Anticipating the EU 

Flood Risk Management Directive these maps will distinguish between flood extent, depth 

and probability, flood progress (and rate of rise), dangerous current velocities, potential 

damage and affected inhabitants, flood risk (probability x adverse effects) and finally 

information for evacuation. 

4—80




Figure 4.76 Interactive flood risk map of a part of the province of Gelderland in the Netherlands 

Figure 4.77 shows, for the Netherlands as a whole, the maximum depth of flooding for any 

location that may occur due to embankment overtopping without any reference to return 

period. As such it does not represent a real situation, but the worst case for every location. 

Figure 4.78 and Figure 4.79 show examples of depth and potential damage for a specific 

event: a flood caused by failure of the coastal dunes between The Hague and Rotterdam by a 

specified North Sea storm surge. Increasing flood depth (and damage) is visualized by 

increasing intensities of blue (and red). Maximum flood depth and damage not necessarily 

coincide. Of course damage only occurs where flooding occurs, but the amount of damage is 

much more determined by socio-economic value of a specific location than the expected 

depth of inundation. 

Figure 4.80 shows the travel time of the flooding process. This is important information for 

the preparation of evacuation plans by disaster management organizations. 

Figure 4.81 is an interesting example, as it shows flood depth classes related to the height of 

a human body (dark blue: ankle-deep, light blue: knee-deep, light rose: hip-deep, orange: 

head-deep, red: submerged). 

Another example of the information that can be obtained from series of simulations of the 

inundation process is shown for the region of ‘Land of Maas en Waal’ in the Netherlands in 

Figure 4.82 (time of arrival of front of inundation with a depth of 50 cm) and the rate of rise 

of the water (Figure 4.83). The rate of rise has a major impact on the number of casualties, 

especially for inundation depths between 0 – 1.5 m. The highest values of the rate of rise 

occur evidently close to the locations of dike failure (red spots). A combination of such a 

map with a map of population density and expected inundation depth can be used to derive 

an image of the potential number of casualties in an area vulnerable to floods. 

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Figure 4.77 Flood depth after inundation in the Netherlands at any location 

4—82




Figure 4.78 Example of maximum flood inundation depth caused by sea flooding in the Netherlands 

4—83




Figure 4.79 Potential flood damage resulting from flood depth and land use 

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Figure 4.80 Map showing the progress of an inundation front from dike failure at the coast of the Netherlands 

4—85




Figure 4.81 Flood hazard map with indication of expected water depth with ‘human’ terminology 

Figure 4.82 Inundation front arrival time for depth of 50 cm 

Figure 4.83 Example of a map showing rate of rise of the water (m/hour) 

4—86




4.15 Norway 

The map shown in Figure 4.84 is part of a program that was started after Norway suffered 

from a major flood event in 1995 which caused extensive damage (approx. 225 million 

Euro). An extensive flood zone mapping project was governmentally launched after this 

event. After a pre-study a total number of 134 sites were selected for detailed flood zone 

mapping. These are the most flood prone and most densely populated areas of Norway. The 

program ends in 2007, and then all the 134 flood zone maps will be finalized. The maps are 

published on the internet and paper copies are also available together with the report. These 

are handed over to the local authorities. The maps are important premises to local land use 

planning. The local land use planners are bound by the maps from a legal point of view. The 

project has awakened the local authorities and new sites will be mapped in the years to come 

in a following up project. More information on the flood mapping procedures in Norway is 

given in a document on the internet (“Procedures And Guidelines For Flood Inundation 

Maps In Norway” 21 ). 


The example of the flood zone map for Norway is an interesting combination of a map sheet 

with additional information. In the subtitle to the map it is clearly stated to which return 

period the map refers (here 1/100 yr) and the legend is very clear. On the map sheet there is 

not only information on the flood extension, but also on the vulnerability of the buildings in 

the region, e.g. “Buildings with potential damage to basement”. Detailed information is 

provided on technical details of the map, date of the flood calculations, name of the 

corresponding report, etc. In separate windows extra information is given on expected water 

levels at a cross section for other return periods (1/20 – 1/500 yr) and the water profiles 

along the length of the river axis. There is a very clear indication of the location of the 

detailed map and the North of the map is also indicated. Although much of the information 

is provided on this map, most of it is probably only useful to a flood expert. In general, 

though, it is probably one of the clearest flood map layouts at present available. 

21 http://wwf.pl/powodz/publikacje/hoydalflood.pdf 

4—87




Figure 4.84 Flood zone map from Norway 

4—88




4.16 Poland 

For Poland both ‘traditional’ flood maps are available as well as interactively produced 

maps using Google Earth as background. 

“Traditional” flood maps 

Figure 4.85 Flood extension map in Poland 

Explanation of the legend: 

Strefa zalewów o prawdopodobie�stwie przewy�szenia p = 1% - flood zone with the exceedence 

probability p=1% 

Istniejace wa�y powodziowe – existing levees 

4—89




Figure 4.86 Flood extension and depth map at Wroclaw for Motorway A1 Study 


The flood extension map in Figure 4.85 is easy to read and as it provides only the expected 

flood extension for one event the information is straightforward. In Figure 4.86 both flood 

extension and depth are given, without compromising the readability of the map. 

The flood extension map shown in Figure 4.87 is very detailed, but the aim to show 

expected flood extension for seven return periods in the same map leads to an image in 

which it is not easy to distinguish the various lines that show the borders of the flood 

extension for each return period. It may be interesting to use coloured surfaces instead of 

lines, showing the increment in inundated area for each subsequent return period. 

4—90




Figure 4.87 Flood extension map for various return periods 

Explanation of legend: 

Granice zalewów o prawdopodobie�stwie przewy�szenia p = 

0,2% …50% - flood zone boundaries with the exceedence 

probability p=0,2% … 50% 

Obszary bezodp�ywowe – non - runoff areas 

Obszary osuwiskowe – landslide areas 

Erozja brzegowa – bank erosion 

Powiaty – counties 

Gminy – communities 

Rzeki – rivers 

Wa�y przeciwpowodziowe – levees 

Budo wle pi�trz�ce (jazy, zapory)– hydrotechnical structures 

(weirs, dams) 

Przekroje poprzeczne – cross-sections 

Zlewnia 1 .. Iv rz�du – 1 st . .. 4 th grade catchment 

Kilometra� rzeki – river mileage 

Sterunki wodowskazowye– gauging stations 

Posterunki meteorologiczne – meteorological stations 

Mosty – bridges 

�luzy wa�owe – embankments sluices 

Zbiorniki retencyjne, poldery – reservoirs, polders 

4—91




Google Earth based flood maps 

Figure 4.88 Flood extension map using Google Earth 

4—92




Figure 4.89 Detail of flood extension map with Google Earth 

4—93





The use of Google Earth as a basis for mapping purposes is becoming more usual, e.g. in 

showing weather radar and many other spatial phenomena. An excellent example is now 

available from Poland. On Figure 4.88 and Figure 4.89 flood maps are placed on top of the 

photo-images of Google Earth. The procedure to transfer GIS-based flood maps to Google 

Earth is rather straightforward and the resulting ‘*.kmz’ files can be read immediately by 

Google Earth, who places the flood map information exactly upon the right location. In 

general this way of presentation is very good to provide information to the non-specialist, 

because it is easy to operate and a lot of extra information can be made available by using 

links to other internet sites. In the document accompanying the Google Earth images the 

following advantages and disadvantages are mentioned: 

Advantages: 

� Attractive image 

� Easy to operate, similar to net browsing 

� Large amount of information possible, especially when using www sites links 

� Easy and fast to convert data from existing ArcGIS geodatabase 

Disadvantages: 

� A fast computer with Windows XP is required 

� A fast internet connection is required 

� Data presented in *.kmz file is given free of charge to the user, who can download the 

kmz.* file to the local hard disk, so it not possible to use it for restricted data 

� It is possible to edit *.kmz data, but there is no connection with the geodatabase and the 

changes will not appear in it 

� If many *.kmz files are placed in the ‘favourites locations’ map, Google Earth will 

operate slowly. 

In addition it should be mentioned that there exists the risk that people will zoom in towards 

their own house / property and consider the flood information provided at this level as 

reliable, which may not be the case (see Chapter 3.2). 

There is another possible disadvantage that might be less evident with Google Earth recently 

released and still in development is the continuity of this service. This has been explained 

already in Chapter 3 on the cartographic aspects of flood mapping. 

4—94




4.17 Spain 

In Spain, inundation studies are responsibilities of the respective Hydrographic Confederations 

of each river basin (River Basin Authorities). The actual status of inundation studies 

varies from basin to basin with significant differences in the level of achievement. 

Figure 4.90 Flood extension maps for the Besós river basin (N of Barcelona) for 3 return periods 

A good example of inundation studies is the one corresponding to river basins in Catalonia, 

where the Government of Catalonia (Generalitat de Catalunya) through the Catalan water 

Agency has elaborated a inundation management plan, Inuncat 22 , where all the inundation 

areas corresponding to rivers in Catalonia have already been produced. In what follows, 

some examples of these maps are presented. 

22 http://mediambient.gencat.net/aca/ca//planificacio/inundabilitat/inici.jsp 

4—95





The Catalonian Water Agency (Government of Catalonia) has evaluated for the river basins 

of Catalonia inundation maps for the main river courses (Delimitació de zones inundables a 

les conques internes de Catalunya) as well as for the Ebro river (Delimitació de zones 

inundables a les conques de l'Ebro) which has a basin shared with other regions. These 

studies define the inundation areas for return periods of 1/50, 1/100 and 1/500 yr 23 (Figure 

4.90) and, also delineate potential flood areas from the geomorphological standpoint (Figure 

4.91). In addition to this, the study also includes a database with critical points, which are 

defined as locations where the experience acquired during many years of river management 

has shown that they present repeating problems 24 . 

The inundation maps for return periods of 1/50, 1/100 and 1/500 yr (Figure 4.90) are 

interactively available in PDF format. In the example shown here, corresponding to the 

Besós river (the Northern natural border of the city of Barcelona) only a part of the total 

map is shown and the legend has been placed on top in order to show only the most relevant 

information. 

The layout of these maps is very clear and it is also relatively easy to distinguish between 

the three return periods. From the map it is clear though that emphasis is placed on the 

presentation of the flood extension for a return period of 1/50 yr, which is shown both with a 

bordering line as well as with a hatched surface. The use of red for the lowest return period 

(1/50 yr) is chosen not to indicate the highest danger, but the highest risk of occurrence (i.e. 

the highest probability). 

23 http://mediambient.gencat.net/aca/ca/planificacio/inundabilitat/delimitacio/pl_periode.jsp 

24 

http://mediambient.gencat.net/aca/documents/ca/planificacio/inuncat/conquesinternes/punts_critics.p 

df 

4—96




Figure 4.91 Flood hazard map for Besós river basin (N of Barcelona) for 3 return periods 


In Figure 4.91 an example is shown a flood hazard map for the Besós river basin at the 

northern part of the city of Barcelona, with a part of the legend shown above. These maps 

are also available as PDF files directly from the internet 25 . Also in this case this is only a 

part of the total map; the original full sheet includes information on the map and a clear 

indication of the location of the map area within the total province of Catalonia. In this case, 

there is no indication of the return period that is represented in the map, because they 

delineate potential flood areas from the geomorphological standpoint using historical 

information (areas already subjected to floods) or geologic evidences. Use is made of signs 

in green, orange and red to indicate level of low, medium and high risk (see legend). In 

25 http://mediambient.gencat.net/aca/ca/planificacio/inundabilitat/delimitacio/pl_potencial.jsp 

4—97




Figure 4.92 a full flood risk map is shown of a part of the Spanish coast in order to show the 

general outline of such a map, which when printed on a larger scale result very clear and 

easy to read. 

4—98




Figure 4.92 Full image of a flood hazard map in Catalonia 

4—99 

English translation of legends 

Type/level of hazard Level of affectation 

Low effects on an area 

Medium effects on a stretch 

High Critical point / hot spot (e.g. bridge) 

Description code 

AA: river or creek 

BB: municipality 

NN: number of order of hazard 

From top to down: 

Legend Geomorphology Symbols 

Flood hazard area 

Embankment area 

Limit of historical flood area 

Mark of recent movements 

Active cone of dejection = floodable 

Possible flow direction or water flow 

effects on large areas 

Flow deviation due to existing anthropogenic actions 

Flood retaining wall 

Mark of alluvial erosion / old meanders 

Former lagoon/ dried deltaic lagoon or wetland




4.18 Sweden 

Swedish risk management programs are lead at local level. Sweden has chosen the “bottom 

up” approach to make sure that all risks are addressed on the basis of the resources that are 

available. Risk assessment has to be dealt with locally due to the fact that accident and 

hazards occur locally - every accident/hazard has a geographic position but the effects of the 

accident/hazard may be of local, regional, national or international character. Therefore, the 

subsidiary principle is the key factor in Sweden’s risk management policies. The Swedish 

Civil Protection Act supports this view. 

The Swedish Rescue Services Agency (SRSA) is the government authority tasked to 

improve safety against accidents within society. Among other things, the agency works with 

risk assessment and risk management in several different sectors, for example, natural 

disasters. 

SRSA mainly supports rescue services and municipalities with knowledge and subsidises 

preventive measures in the built up environments that may be at risk of flooding and 

landslides. The SRSA also has the responsibility, on commission from the government, for 

providing the municipalities and county administrative boards with general planning 

information such as general stability maps and general flood inundation maps. Flood risk 

assessment is a municipal responsibility. 

The Swedish Rescue Services Agency (SRSA) is conducting a general mapping of parts of 

Sweden’s waterways. The mapping began in 1998 and the goal is to achieve maps of 

approximately 10,000 km (approx.10%) of Sweden’s waterways. In January 2007 almost 

8 000 km are mapped and 56 of the rivers are covered with Flood Inundation Maps. 5 new 

rivers are going to be mapped in 2007. 

The general maps are intended for the overall planning of fire & rescue service work and as 

information for land-use planning. The flood mapping covers natural floods in both 

governed and ungoverned waterways, but not floods that occur, for example, as a result of a 

dam break or an ice-dam. 

The priority is made by a preliminary risk assessment based on risk identification and 

urbanized areas along the rivers together with records of occurred flood events in the past. 

In Figure 4.93 an overview is given of the rivers for which interactive maps are available 

now. The maps can be accessed through a map browser on the internet 26 , showing the same 

map as in this figure, by clicking on a region. This loads the corresponding PDF document. 

Both the internet site as well as all the texts accompanying the maps are only available in 

Swedish. 

26 http://www.raddningsverket.se/templates/SRV_ExternalPage____2257.aspx 

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Figure 4.93 Flood Inundation Mapping in Sweden 

Flood Inundation Maps highlight the areas that are at risk from flooding during two known 

high water discharges. Two types of flood are used: 

� the 100-year flood 

� the highest estimated flood. 

The latter is calculated in accordance with the Swedish Flood Committee’s guidelines for 

the dimensioning of dams (dams in risk class I). The calculation is made on a systematic 

combination of all the critical factors (rain, melting of snow, levels of ground moisture, and 

the filling of basins in governed waterways) that contribute to a flood. The calculated return 

period is approximately 10 000 years. 

Map production 

Three elements are involved in the production of flood maps: 

� Calculation of the two floods. The 100-year flood is calculated by the statistical analysis 

of observed water flow measurements. The highest estimated flood is calculated in 

accordance with the Flood Committee’s guidelines. In the latter case a hydrological run- 

4—101




off model is programmed with maximum adverse conditions as regards precipitation, 

melting of snow and ground moisture conditions, while at the same time giving 

consideration to possible waterway governing and dam basin activities. 

� Calculation of the water level along waterways during the two floods. This is achieved 

using a hydraulic model. The description of the waterway and stretch of river is 

achieved with the help of dam and bridge diagrams, and looking at the qualities of the 

waterway and the topography of the surrounding land. The model is calibrated against 

previous measurements taken of the water level and flow. After which the water level 

across sections of the waterway is calculated. 

� Mapping out of flooded areas along stretches of waterway. This mapping out is achieved 

with the help of a geographical information system (GIS). The water level along the 

whole waterway is interpolated and with the aid of a topographical database and Digital 

Elevation Model (DEM) the area that will be flooded can be calculated. 

An example of a flood inundation map from Sweden is shown in Figure 4.94. 

Figure 4.94 Example of a Swedish flood inundation map 

Fields of applications 

Legend: 

Highest estimated 

flood according to the 

Swedish Flood 

Committee 

100 year flood 

Urban area 

The mapping out work is presented partly in a report with printed maps and partly as GISlayers 

for further work by users in the municipalities, county administrative boards etc. The 

idea is that the overlays shall be connected to a suitable map (e.g. 1:50,000) that shows 

where floods can occur and suggests likely problems with roads, railway lines, bridges and 

buildings. The map overlays can also be connected to various co-ordinate registers, such as, 

4—102




for areas sensitive to landslides, property registers detailing numbers of inhabitants, wells, 

sewage treatment works, industries, environmentally hazardous operations, warehouses etc. 

Examples of the combined use of flood hazard and land use information are shown in Figure 

4.95 27 and Figure 4.96 28 . The former shows the flood-affected roads, while the latter shows 

the occurrence of quick-clay areas at risk of flooding. These two maps are examples of 

dedicated maps that combine flood inundation information with other types of information 

and therefore the colour setting of the maps are also completely different. 

681 

681 

256 

Figure 4.95 180 km of roads at risk of flooding 

27 Source: Swedish Rescue Services Agency and County Administrative Board of Västmanland 

28 Source: Swedish Rescue Services Agency 

767 

256 

4—103




Figure 4.96 An overlay analysis of the General Stability Map and the General Flood Risk Map 


In the flood map on Figure 4.94 the expected flood extension is shown for two situations 

(pink area = area at risk of 1/100 yr flood, hatched area = area at risk of 1/10,000 yr flood, 

grey area = area of municipality). The use of the latter return period is unusual and as 

expected the corresponding flood extensions are large. The colour pink is not common for 

flood extension, but it does stand out very clear in both maps. 

In the map of the flood-affected roads (Figure 4.95), it is not clear what is meant with the 

red lines (flood extension ?) and the dark-blue double lines, although the latter probably 

represent those road sections. 

4—104




4.19 Switzerland 

In Switzerland several types of flood maps are produced. They include flooding (dynamic 

and static), debris flow activity and bank erosion/scouring. Flood indication maps (flood 

extension maps) are produced on a scale of 1:25,000 for the bigger cantons as shown in 

Figure 4.97. The maps represent an extreme event (generally set equal to a return period of 

1/1,000 y) to get a quick insight in the most critical areas (by overlaying the vulnerable 

elements on the flood areas). 

Figure 4.97 Example of a food indication map for an extreme event 

Flood hazard maps are produced in a scale of 1:5,000 for return period similar to those used 

in Austria (1/30, 1/100, 1/300, extreme event; the latter is not available in Austria). By 

combining the probability and the intensity (magnitude), the latter expressed as flow 

velocity or depth, the flood hazard class is obtained as indicated in Figure 4.98. The criteria 

used for the definition of flood hazard are given in detail in the following table. 

Process low intensity medium intensity high intensity 

Debris flow -- D < 1 m 

and 

v < 1 m/s 

D > 1 m 

and 

v > 1 m/s 

Static flooding h < 0.5 m 0.5 < h < 2 m h > 2 m 

Dynamic flooding q < 0.5 m 2 /s 0.5 < q < 2 m 2 /s q > 2 m 2 /s 

Bank erosion t < 0.5 m 0.5 < t < 2 m t > 2 m 

D = thickness of debris front; v = flow velocity (flood or debris flow); h = flow depth; q = 

specific discharge (m 3 /s/m) = h x v; t = extent of lateral erosion 

Table Criteria for intensity of different hazards 

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Intensity: 

high 

medium 

low 

Probability: 

30 100 300 

high medium low very low 

Figure 4.98 Assessment of flood hazard in Switzerland 

Hazard: 

high 

medium 

low 

very low 

In Figure 4.99 an example is shown of a flood hazard map in Switzerland. Note that the 

processes represented in this map are debris flows and related phenomena. The meaning of 

the three colours (including the hatching) is explained in the text following the figure. 

4—106




Figure 4.99 Flood hazard map in Switzerland based on the hazard levels 

RED: high hazard 

The red zone mainly designates a prohibition domain (area where development is 

prohibited). 

BLUE: moderate hazard 

The blue zone is mainly a regulation domain, in which severe damage can be reduced by 

means of appropriate protective measures (area with restrictive regulations). 

YELLOW: low hazard 

The yellow zone is mainly an alerting domain (area where people are notified at possible 

hazard). 

YELLOW-WHITE HATCHING: residual hazard 

Low probability of high intensity event occurrence can be designated by yellow-white 

hatching. The yellow-white hatched zone is mainly an alerting domain, highlighting a 

residual danger. 

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Figure 4.100 Flood depth map for a return period of 1/300 yr. 

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Figure 4.101 Map showing the flood hazard zones for the same region as in Figure 4.100 

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The direct interpretation of the hazard classes (red, blue, yellow, yellow-white) constitutes 

an excellent (legal) mechanism to directly implement the hazard maps into spatial planning 

and building regulations. In the red zone, all new urban development is prohibited, where as 

in the blue zone restrictive regulations are enforced. In the yellow zone there are principally 

no restrictions (except for highly sensitive infrastructure) but the residents are made aware 

of the flood hazards. 

The basis for the production of hazard maps is the so-called “intensity map”. The intensity 

(or magnitude) of a particular process is delineated for each return period. In Figure 4.100 

an example of a flood depth map is shown for an event with a return period of 1/300 y with 

the flood depth indicated in steps of 0.25 m. Use is made of a colour ramp from light pale 

green (0 to 25 cm) slowly intensifying through orange to red for the greatest depth. 

In Figure 4.101 the flood hazards using the definition explained above is shown for the same 

region in Switzerland. 

There are very detailed documents available on the explanation of flood hazards and the use 

of the hazard zones. An interesting example is given in Figure 4.102 where the effect is 

shown of the implementation of flood mitigation measures (e.g. lowering of river bed, 

raising of dikes etc.) on the flood hazards. 

In Switzerland the flood risk maps are not yet widely distributed. However, a qualitative risk 

can be depicted by overlaying the hazard zones with the various land use classes (damage 

potential). In a first attempt this is done by just using the topographic information 

(settlements, housing or industrial estates, transport infrastructure etc.). An important 

instrument is the so-called “Map of Safety Deficits” relating flood risks with protection 

objectives as shown in Figure 4.103. 

4—110




Figure 4.102 Change in hazard level before and after implementation of flood mitigation measures 

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Figure 4.103 Map of safety deficit showing the degree of the lack of protection 


Switzerland has one of the most complete systems for the delineation of flood hazard and 

flood risk with and excellent set of documents in German, French, Italian and English. 

Concepts, guidelines, and recommendations are available on the internet (environmentswitzerland.ch 

/ Documentation) 

4—112




5 Transboundary flood hazard mapping 

Especially the EU-funded projects are excellent examples of transboundary flood-related 

projects. In Figure 5.1 an overview is given of the flood-related EU-funded projects that 

were either on-going or had been recently finalized by the time of the compilation of this 

Atlas. In this chapter a number of these projects will be discussed as far as they contribute to 

transboundary flood mapping, but no attempt has been made to give a complete overview of 

all transboundary flood mapping activities in the EU. 

Figure 5.1 Overview of EU-funded transboundary flood-related projects 29 

Another example of a transboundary approach to flood mapping is the CatNET, which aims 

at providing flood information for insurance purpose. For this reason it is further discussed, 

with examples, in Chapter 6.1. 

5.1 European Flood Risk Mapping 

European flood risk mapping is one of the components of the work carried out in the 

WDNH (weather-driven natural hazards ) action by the JRC (Joint Research Centre) of the 

EU. Three components of flood risk have been addressed, i.e. flood hazard, flood 

vulnerability and flood exposure. The assessment is based on a database of map layers with 

information on GDP, population density, land use, flood hazard, etc. The flood hazard is 

29 http://www.iu-info.de/fileadmin/user_upload/news_Inhalte/Flapp_report.pdf 

5—113




derived using a 1 km digital elevation model and the 1 km grid European flow network 

developed by JRC. The outcomes from this work are: 

� Flood risk assessment for the EU + Romania and Bulgaria; 

� Flood risk layer: Standardised index map for flood risk (spatial resolution 1 km); 

� Flood risk layer: Risk assessment for NUTS3 areas. 

NUTS areas (Nomenclature of Territorial Units for Statistics) are administrative divisions 

for all European member countries that were introduced in 1998 and for which four different 

levels of detail exist. A detailed description of the development of the maps by JRC is 

shown in given on the website of JRC 30 . As an example, the flood hazard map is reproduced 

in Figure 5.2. This map is based on an algorithm calculating the elevation difference of a 

location with the nearest river, along the hydrological flow path. The potential flood risk is 

determined by the difference in elevation and the estimated extreme water level of the 

nearby river. Further details on the methodology is given in the report on the website 

referred to earlier. In the future a higher resolution DEM will be used together with model 

simulations to obtain more reliable results. 

In Figure 5.3 the result is shown of a combination of a land use map (Corine 2000) and the 

European flood hazard map of Figure 5.2. Evidently the trend of increasing urbanisation in 

many parts of Europe has let to a major increase in flood hazard in those highly populated 

areas. 

30http://ies.jrc.cec.eu.int/fileadmin/Documentation/Reports/Land_Management/EUR_2006- 

2007/EUR_22116_EN.pdf 

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Figure 5.2 Flood hazard map of Europe (WDNH – JRC) 

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Figure 5.3 Overlay of the Corine land cover map and European flood hazard map 

5.2 Comrisk and Safecoast 

An example of cooperation between neighbouring countries on coastal flooding can be 

found in the related Comrisk and Safecoast projects, both under the auspices of the EU. 

Comrisk (Common strategies to reduce the risk of storm floods in coastal lowlands) was 

started in 2002 and has already been finalized 31 . It was carried out by eight coastal risk 

management authorities from Belgium, Denmark, The Netherlands and Germany. Various 

studies were carried out as part of the project and the project was finalized with an 

international conference in April 2005. 

The Safecoast project 32 forms the follow-up action to Comrisk and started in July 2005. 

The interesting aspects of these projects in view of this Atlas is the opportunity to bring 

more unity in the technical background for the production of flood maps, as well as the 

layout of the maps themselves. The projects deal with about 40,000 km 2 of floodprone 

coastal area and focuses strongly on the safety of the North Sea coast taking into account the 

expected increase of flooding danger due to climate change, with a planning horizon to the 

year 2050. Figure 5.4 shows the floodprone area along the North Sea, covered by the 

Safecoast project. 

Also in this project, the most important aim in view of transboundary issues in flood 

31 http://comrisk.hosted-by-kfki.baw.de/ 

32 http://www.safecoast.org/ 

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mapping is the comparison of different flood risk assessment methods and the goal to arrive 

at a common ground for the planning of the coastal defence. 

Figure 5.4 Study area of the SAFECOAST project 

A similar EU-funded project is FRAME (Flood Risk Management in Estuaries: Sustainable 

New Land Use in Flood Control Areas), which does have some mapping issues as well 

(such as a ‘Best Practice Manual’), but it is considered outside the scope of this Atlas. 

Information on the FRAME project can be found on the internet 33 . It is part of a number of 

projects that deal with the North Sea Programme and details on related projects are found on 

the internet page of this Programme 34 . 

5.3 ELLA 

The ELLA (Elbe-Labe Preventive flood management measures by transnational spatial 

planning) project is another example of an EU-financed flood-related project which deals 

with transboundary issues 35 . One of the aims is the preparation of flood maps with a number 

of examples on transboundary rivers, especially the Rhine and the Elbe rivers. The project is 

carried out with partners from Germany, Czech Republic, Austria, Poland and Hungary. The 

results of the transboundary flood mapping are available on a special internet site 36 , with 

access to maps for the Rhein, Weser and Elbe (Labe) river basins, the latter being in fact the 

result of the ELLA project. By clicking on the Rhine river, a next interactive internet site is 

33 http://www.frameproject.org/ 

34 http://www.interregnorthsea.org/default.asp 

35 http://www.ella-interreg.org/ 

36 http://www.floodmaps.de/FloodServer/ 

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opened 37 , which gives access to series of flood maps for this river (Figure 5.5). This is in 

fact part of the Flood Information System, which has been set up within the framework of 

the ESA project GSE RISKEOS 38 . Additional technological developments are being done 

within the project EC IP PREVIEW 39 . An important objective is the standardized 

delineation of flood hazard and flood risk maps. To the extent of their availability, the map 

service shows the outline and/or inundation depths of a 100 year flood and an extreme flood. 

Also shown are the damage potentials of at least one of these events. Additional information 

includes the outlined areas of recent flood events, which were derived from satellite 

imagery. Also available are historical flood maps. The service is completed by landuse data. 

Figure 5.5 Interactive site for flood maps of the Rhine river basin 

As an example, flood extension and damage potential maps are shown for the transboundary 

region along the Dutch – German border in Figure 5.6 and Figure 5.7. The legend to these 

two maps is shown in Figure 5.8. The two maps show the location where the Rhine river, 

after passing the Dutch border, splits into various branches. In green the region is shown that 

would be flooded in an extreme event, with water flowing along a different Northern route 

from the Rhine in Germany directly overland towards one of the Rhine branches (“IJssel”) 

in the Netherlands. 

Other combinations of flood map items and land use are possible, but the combination of 

land use map and damage map is not easy to distinguish (too many items on the map and 

mixed colours not included in the legend), although this would be the most interesting 

37 http://www.floodmaps.de/FloodServer/go?FrameLoaderActionSprache=en 

38 www.risk-eos.com 

39 www.previewrisk.com 

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combination. 

Figure 5.6 Flood extension map for Rhine river along Dutch – German border 

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Figure 5.7 Damage potential map for Rhine river along Dutch – German border 

Figure 5.8 Legend to the flood extension and damage potential map 

The flood mapping of the Elbe (Labe) river of the ELLA project is a good example of a 

transboundary effort for Germany and the Czech Republic. However, this is less interesting 

as an example in this Atlas as the boundary region between the two countries, being a 

mountainous area, does not exhibit any major flood threat. It does use the same type of 

layout, though, for the two countries involved as was the case for the maps of the Rhine 

river. This is evident from the map example shown in Figure 5.9, which shows the flood 

extent for an extreme flood and a flood with a return period of 1/100 year, in combination 

with a land use map. 

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Figure 5.9 Combination of flood extension and land use map for the city of Dresden (ELLA project) 

5.4 FLAPP 

Another interesting EU-funded project is the 'Flood Awareness & Prevention Policy in 

border areas' (FLAPP). The project started in 2005 and is now in its final stage. One aspect 

of the project is the production of a ‘good practice book’, which in itself has various 

components. For the transboundary flood mapping issue, an important component is the 

production of the cross-border flood maps for the cities of Görlitz and Zgorzelec on the 

Nyssa river between Germany and Poland. Information on the project is provided on the 

internet site of FLAPP 40 . 

The Nyssa river forms the border between the towns of Görlitz and Zgorzelec, which were 

separated in 1945 through a redrawing of the borders after the Second World War. The aim 

of the project was to create a common hazard zone and flood information map on a scale of 

1:5,000 in 3 languages (English/German/Polish). The map contains the flood plains of 

different events (return periods of 1/20, 1/50, 1/100, 1/200 and 1/500 years) which have 

been taken form the Saxon flood control plan for the Nyssa elaborated in 2004. Furthermore 

additional information with regard to endangered infrastructure, municipal planning and 

calamity defence are displayed on the map. In this map flood risk in a certain area is 

displayed via hazard zones (high, medium, low and residual risk). These zones are 

determined through overlapping intensity and frequency of a flood event. The map can be 

used to communicate flood risk to the public and to integrate information on flood risk into 

spatial planning of the municipalities. An example of part of this map is shown in Figure 

40 http://www.flapp.org/cmsEN/cms/index.asp?itemId=328 

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5.10, showing the flood extension for the various return periods. It is not clear whether the 

‘Hqextrem’ refers to the 1/500 year return period. There is also information on evacuation 

problems on this map (indication of a bridge in red that is flooded for an event with a return 

period of more than 1/200 year). 

Figure 5.10 Example of a transboundary map of the Nyssa river from the FLAPP project 

5.5 IKRS 

Regarding transboundary flood mapping the most important product from the International 

Commission for the Protection of the Rhine is the Rheinatlas (2001). The maps of this Atlas 

are available on the internet 41 . The maps themselves are accessible through a clickable PDF 

file 42 . As an example, both a flood extension and a damage potential map are shown for the 

transboundary region of the Rhine river at the Dutch – German border (Figure 5.11 and 

Figure 5.12). The legends to the two types of maps are given in Figure 5.13 and Figure 5.14. 

Although these maps are similar to those produced by the Flood Information System (see 

Figure 5.6 and Figure 5.7), the maps of the IKRS give the damage potential in quantative 

terms (Euro / m 2 ), while the Flood Information System gives only a relative (qualitative) 

scale (see legend in Figure 5.8). As such the maps of the IKRS are far more detailed and 

provide the user with a better level of information. 

41 http://www.rheinatlas.de/ 

42 http://www.iksr.org/index.php?id=302&type=0# 

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Figure 5.11 Flooding extension map for the Rhine river at the Dutch – German border 

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Figure 5.12 Damage potential map for the Rhine river at the Dutch – German border 

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Figure 5.13 Legend of the flooding maps of IKRS 

Figure 5.14 Legend of the damage maps of IKRS 

5.6 SAFER 

The SAFER ((Strategies and Actions for Flood Emergency Risk Management) project aims 

to develop innovative strategies and prevent and mitigate fluvial and coastal flood damage 

by working with organisations and agencies at different levels. The five partner regions 

involved in the project work are adopting a common approach in implementing these 

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strategies. The project is approved under the INTERREG IIIB NWE Programme and partfunded 

by the European Union (ERDF). A component that is related to transboundary flood 

mapping is the Workpackage ‘Hazard Mapping’, which aims at producing a common 

methodology to produce and provide flood hazard information to all the partners. Examples 

of the results of this work package can be found already elsewhere in this Atlas, e.g. for the 

German region of Baden-Württemberg (see Chapter 4.8.1), who is the lead partner in this 

project. An example of a map that is drawn according to the SAFER hazard mapping 

methodology is shown in Figure 4.43 for the Neckar river. 

5.7 TIMIS 

Transnational Internet Map Information System (TIMIS) Flood is a contribution to a 

uniform EU policy for flood protection and is meant to become a model for other regions 

with transnational flood issues. TIMIS focuses on both flood hazard mapping and flood 

forecasting for the border region of Luxembourg, Germany and France. 

In Figure 5.15 the extent is shown of the TIMIS project for both flood hazard mapping 

(approx. 22,500 km 2 >90 rivers and >3000 km length of river) and flood forecasting (about 

55,000 km 2 ). The project will produce by the year 2008 transnational hazard maps on a scale 

of 1:25,000, showing four hazard stages and a transnational GIS on flood for hazard, 

forecasting and warning. The maps are accessible through an interactive internet site 43 

(Figure 5.16). An image of the future GIS environment for flood-hazard related information 

is shown in Figure 5.17. 

Figure 5.15 Extent of the region of the TIMIS project 

43 http://www.timisflood.net/en/ 

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Figure 5.16 Internet page for the viewing of interactive flood hazard maps from the TIMIS project 

Figure 5.17 Example of the GIS environment of TIMIS for accessing the flood-related information 

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An example of a map produced by TIMIS is shown in Figure 5.18 for a tributary of the 

Mosel river in Luxembourg. This is another example of the flood hazard map on a 

transboundary river, where the same map layout and legend is used on both sides of the 

border (see also Chapter 4.8.5 on Rheinland-Pfalz). The maps are produced using the 

following information: 

� High-precision DTM 

� River cross-sections 

� Hydraulic modelling 

� Hazard classification using four hazard levels. 

The four hazard levels are determined by specific combinations of intensity, velocity and 

frequency of the events. The legend of the hazard levels is shown in Figure 5.19. 

Figure 5.18 Flood hazard map for a tributary of the Mosel river in Luxembourg 

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Figure 5.19 Legend of the four hazard classes used in the TIMIS project 

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6 Insurance maps 

6.1 CatNet 

CatNet is an interactive map tool from the insurance company Swiss RE 44 . It contains 

information on a number of natural hazards, including tornados, earthquakes, ‘European 

winterstorm peak gust’, hail, volcanoes, etc., but also flood risk and is regarded as a first 

attempt at a Worldwide Natural Hazard Atlas 45 . The CatNet flood zones are based on a wide 

variety of heterogeneous sources. Therefore, depending on the country, either storm surge 

and/or fresh water flood zones are displayed. The main page of the interactive hazard atlas 

of CatNet is shown in Figure 6.1 and the selection menu in Figure 6.2. The CatNet is 

accessible for external users who do have to register before they can use the information, but 

only for a trial period of 8 weeks, after which it is a commercial service. 

Figure 6.1 Main user graphical user interface of CatNet 

44 http://www.swissre.com/ 

45 http://www.esri.com/news/arcuser/0402/swissre.html 

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Figure 6.2 Selection of three bordering countries to extract information on flood hazard in CatNET 

CatNet covers a number of European countries. The flood risk information is included for 

the following countries (with short description of their content): 

� Belgium 

Freshwater flood zones are calculated by Swiss Re’s proprietary multiple regression 

approach. Zones describe naturally flooded areas affected every 100 years. The effect of 

flood protection measures was not taken into account and flood zones along canals are not 

depicted. 

� Czech Republic 

Fresh water flood zones are calculated by Swiss Re’s proprietary multiple regression 

approach. Zones describe naturally flooded areas affected every 50, 100, 250 and 500 years. 

The effect of flood protection measures was not taken into account and flood zones along 

canals are not depicted. 

� Germany 

Fresh water flood zones for 10, 50 and 200 year water levels are available. Original data for 

10 and 50 year flood zones have been calculated by Institut für Angewandte 

Wasserwirtschaft und Geoinformatik (IAWG), Ottobrunn; Germany. Orginal data for 200 

year flood zones have been calculated by Institut für Angewandte Wasserwirtschaft, 

Munich, Germany. 

The zones for Germany are the result of hydraulic calculations carried out for a river 

network with a total length of around 50,000 kilometres. The calculations were conducted 

using a Digital Elevation Model (DEM) with a horizontal resolution of 50*50 metres. They 

do not take flood protection measures into account, i.e. the 10 and 50 year zones are rather 

too conservative. The flood zones depicted may vary from those in the ZÜRS software (see 

Chapter 6.5) provided by the German Insurance Association (GDV). 

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There is also information available on the Elbe flood event of August 2002. 

� Italy 

Freshwater flood zones are calculated by Swiss Re’s proprietary multiple regression 

approach. Zones describe naturally flooded areas affected every 100 years. 

� Hungary 

The 100 year and 1000 year zones are based on the 1977 series of ‘Magyarország 

árvízvédelmi terképei, VITUKI, 1977’ maps at 1:100,000 scale, which were transferred by 

VITUKI to a digital format. Areas inundated every 50 years were subsequently introduced 

by Swiss Re. 

� Netherlands 

The zoning reflects the design level of the 53 areas defined by the dike ring system 

(dijkringgebieden) in the Netherlands, as published by the ‘Meetkundige Dienst’, afd. GAT, 

Delft, 1996. The protection level of the diked-in areas exceeds 1000 years. Elevated areas 

outside the dike-in areas are classified as ‘no data’. 

� Slovakia 

Fresh water flood zones are calculated by Swiss Re’s proprietary multiple regression 

approach. The zones describe naturally flooded areas affected every 20, 50, 100, 250 and 

500 years. The effect of flood protection measures was not taken into account and flood 

zones along canals are not depicted. 

� United Kingdom 

The scope of the flood zones in the UK is limited to areas affected by coastal hazards 

(saltwater flooding) and based on a study by Dr. J.C. Doornkamp of the University of 

Nottingham in 1996. 

There are also maps and data for Argentina, Israel and the USA. 

If we look at the geographical coverage of the CatNET it is evident that this is another 

example of a transboundary flood mapping as the combination of the Czech Rebublic, 

Slovakia and Hungary form one continuous region for which the flood maps are available. 

An example is shown in Figure 6.2. 

Examples of flood maps available in the CatNET system are shown in Figure 6.3 for 

Slowakia (which shows the transboundary coverage with Hungary south of Slovakia) and in 

Figure 6.4 for Germany (Sachsen-Anhalt). 

In general the cartographic layout of the maps is attractive and easy to read, but the level of 

detail does not allow the user to acquire a very precise level of detail in the information. The 

use of the colours, starting from dark blue for low return period (1/20 yr) to grey for high 

return periods (500 yr and larger) is unusual and does not provide the user with an intuitive 

idea of increased danger level. However, in practice this grey colour represents those 

regions that are not threatened by river flooding, or at least not by any major river. 

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Figure 6.3 CatNet map example: flood risk mapping in Slovakia 

Figure 6.4 CatNet map example: flood risk mapping in Sachsen-Anhalt (Elbe river) 

6.2 Austria 

HORA is an example of a successful public private partnership (PPP) on flood risk zoning 

and mapping in Austria. Following massive damages after heavy rainfalls and flooding in 

summer 2002 in Austria, insurance industry and public authorities in Austria under guidance 

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of the Ministry of Agriculture (Lebensministerium) and the Austrian Insurance Association 

signed a PPP-contract (available in German and English) stating a common project for the 

development of a public, common and admission-free risk zoning tool (internet access via 

Lebensministerium). Common goal was to create an open risk zoning platform for flood and 

earthquake. Public authorities were delivering GIS basis data, modelling and development 

was done by insurance and reinsurance industry. No direct exchange of any sort took place, 

the common result is open to the public since June 1st 2006. 

Local risk zoning and mapping is for several regions already available on the HORA system 

as well.. One can choose the option under "Legende", if more detailed public information 

(than probabilistic zoning for 25000 km river length in HORA) is already existing and 

HORA has got public access to this local or regional zoning-information (e.g. for the region 

of Carinthia). There one can see the risk zones in different colours (yellow and red instead 

of blue). 

From the point of view of the insurance industry, at a later stage, HORA is expected to 

develop into a PML (Probable Maximum Loss)-assessment system for underwriters and risk 

managers. The fully working public system will be dedicated for individual information 

(and work for insurance industry as a second source of risk information). 

The information from the HORA project is available on the internet 46 . An impression of the 

interactive internet site is shown in Figure 6.5. After starting up the map server for the 

HORA site, a disclaimer is shown in red font with the text (in German): “I have read the 

copyright statements and accept them as legal disclaimer”. This statement need to be 

accepted by the user before the maps can be accessed. The maps give a delineation of 

flooding areas on river catchment level for about 25.000 km of river length on scales 

varying from 1:10.000 to 1:50.000. The return periods shown on these maps are 1/30 yr 

(zone 1), 1/100 yr (zone 2) and 1/200 yr (zone 3). The information is not yet available for 

the entire country. 

46 http://geoinfo.lfrz.at/website/egisroot/services/ehora2/viewer.htm 

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Figure 6.5 Interactive Internet site for the flood hazard map of the HORA project in Austria 

Figure 6.6 HORA window for location of airport of Innsbruck with legend 

Users can enter their address information and find out the potential flood risk of their 

property. Examples of the maps are shown in Figure 6.7 (with topographic map) and Figure 

6.8 (with satellite image) for the area of the airport of Innsbruck. 

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Figure 6.7 Example of flood extension map for airport of Innsbruck (with topographic map background) 

Figure 6.8 Example of flood extension map for airport of Innsbruck (with satellite image background) 

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6.3 Czech Republic 

In the Czech Republic an exceptionally well-developed tool has been made available which 

allows the user to assess the flood risk at any location in the country using a map-based 

user-interface (Figure 6.9). This system, called FRAT (Flood Risk Assessment Tool), is now 

used by almost all property insurances in the Czech Republic, allowing them to identify 

high exposed risks and more accurately price flood risks. 

Figure 6.9 FRAT User Interface 

The tool was developed by Swiss Re, as the leading reinsurer and developer of catastrophe 

models, and MMC, the leading provider of GIS (Geographic Information System) 

technology 47 . It can now price selected properties according to their flood risk exposure and 

can also be used as a basis for improved flood accumulation reporting and control. The tool 

is designed as a stand-alone software solution (CD-ROM) and offers two basic functional 

modes: 

� The user, for instance, a risk manager or insurance agent, enters data on the property 

location using the full address (street, house number, and city). The address, or part 

thereof, is located and transformed into geographic coordinates, which are used for 

zoning analysis. 

� The system generates information on the flood risk exposure of the selected location and 

displays it on-screen. The tool distinguishes six different flood risk zones (zones 1 to 6, 

ranging from very low to very high risk), and the historically observed maximum flood 

boundary. The result is also translated into the CAP (Czech Insurance Association) 

47 http://www.swissre.com/INTERNET/pwswpspr.nsf/alldocbyidkeylu/ULUR-5QBJKQ 

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format for designating tariff zones. 

During the past few years, a Swiss Re team of hydraulic engineers, hydrologists, GIS 

specialists and statisticians developed statistical methodology to derive flood risk zones 

based on detailed digital terrain models (DTM). The prediction success of the methodology 

prompted Swiss Re to apply for a patent. 

� FRAT 1.0 flood risk zoning is based on the best DTM available in the Czech Republic. 

The DTM features a horizontal resolution of 10m, i.e. a reading is generated for every 

10m of elevation. 

� Due to the high impact of local factors, such as river defences or roads which are not 

reflected in the high resolution DTM, the high frequency flood risk (zone 6) is not 

derived by the statistical methodology but by detailed processing on the part of MMC. 

Figure 6.10 Example of geo-coding at city level and at street level 

An example of the outcome of FRAT, in the form of a risk map, is shown in Figure 6.11, 

with a distinction into four (out of maximum six) hazard zones with increasing severity of 

flooding. 

In August 2006 the FRAT 2.0 has been released. The new version of Flood Risk Assessment 

Tool, which focuses on property insurance risk assessment is distributed on DVD ROM 

media and contains address database for whole territory of the Czech Republic. The Address 

database is used for address verification and for geocoding of the property location. The 

product offers extended set of detailed city plans, covering in total over 160 cities of the 

Czech Republic. 

The FRAT system is not freely available as it is a commercial product. Swiss Re and MMC 

have decided to offer FRAT 1.0 CD-ROMs for a nominal fee to Czech clients of Swiss Re, 

the Czech Insurance Association (CAP) and to all companies within CAP. Other insurance 

companies with insured interests in the Czech Republic can gain access to the application by 

written request to Swiss Re or MMC. 

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Any map base – in most cases scale 1: 10 000 

Description of the zones: 

Zone 1 – out of probable max. flood 

Zone 2 – up to possible max. flood 

Zone 3 – up to average 50 years flood 

Zone 4 – up to average 20 years flood 

Figure 6.11 FRAT results with flood map showing hazard zones with four steps of severity 

An interesting development is the application of this technology to China. Flooding is one 

of the major threats to life and property in China, but to date, the insurance industry has had 

to depend on experience-based ratings, which have been unreliable especially for very large 

and infrequent events. Further information is provided on the internet site of Swiss-RE. 


Although the layout of the maps is clear and serves its purpose for insurance applications, 

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the choice of the colour green for risk zones is not intuitive as it suggests safety where this 

may be misleading. It does also conflict with the use of green for land use (wooded areas). 

6.4 France 

In Figure 6.12 and Figure 6.13 images of typical screens of an intranet website 48 are 

displayed developed for dissemination and use by insurance companies of public natural 

zoning data, by a organization dedicated to natural risk knowledge and prevention, for the 

whole French insurance market. 

The information is available for consultation with GPS coordinates or downloading of 

datasets with relevant metadata (as available from public authorities). Further treatment of 

the data for more industry specific use of the public zoning is under development at the level 

of the organization and/or at the level of each company. 

Depending to the existing public data on each location, the flood extension reflects either 

the highest historical one or classified in terms of floods being ‘exceptional’, ‘frequent’ or 

‘very frequent’ without details on actual return periods, if not delivered by public 

authorities. 

So far, the indication of urbanization is provided from the relevant themes of the CORINE 

Landcover land use data base. 

Figure 6.12 Screenshot of flood extension data sets made available to insurance companies in France (large 

area of Avignon, mainly on the Rhone river, indicating the urban areas affected) 

48 http://www.mrn-gpsa.org/accueil.php 

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Figure 6.13 Screenshot of flood extension data sets made available to insurance companies in France (three 

flood occurrence zones displayed for the area of Cavaillon, indicating the urban areas affected) 

Information provided on these type of maps: 

1. Map Titles : classification of flood zones 

2. Type of map: "Flood hazard zoning map, to be used by French insurance market" 

3. Responsible authorities / sources : 

a) Flood extension data sets: "waterway-data by the services of the French Ministry of 

Ecology and Sustainable development water authorities; 

b) Referential: selected themes of CORINE Landcover, with other references to be 

added according to specific needs, 

c) Intranet geoservice developer ; ARMINES on Kheops 

d) Project manager : MRN for French insurance associations 

4. Date of publication: MRN intranet geoservice in operation since mid 2006, with steady 

upgrade with new public data according to their availability 

5. Scale: maps are freely scalable on the screen according to data sets scale 

6. Explanation of legend: according to public data sets 

7. Stage of program: further development for added value services in process, but 

depending to future the evolution of insurance scheme. 

6.5 Germany 

In Germany a numeric tool for classification of flood zones developed by German insurance 

association (GDV) is available (Figure 6.14) under the name ZÜRS Zonierungssystem für 

Überschwemmung, Hochwasser und Rückstau. 

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Figure 6.14 Classification of flood zones update ZÜRS49 2006 – area of flood hazard (Regensburg) 

The following information is available on this type of maps: 

1. Map Title : Classification of flood zones update ZÜRS 2006 – area of flood hazard 

(Regensburg) 

2. type of map: "Flood hazard zoning map, produced and used by the insurance market in 

Germany" 

3. Responsible authorities / sources : 

a) waterway-data by the German water authorities; 

b) maps by "NAVTEQ"; 

c) flood-zoning by "IAWG", 

d) programming and additional data by "ESRI", "con-terra" and "geomer"; 

e) supervisor and project manager: "German insurance association, GDV" 

4. date of publication: ZÜRS Version 2.0.12; released August 2006 

5. scale: 1:21.151 (scale of this special map as seen on the maps footer, ZÜRS-maps are 

freely scalable) 

6. explanation of legend: 

a) GK 4, high hazard: flood at least once in 10 years 

b) GK 3, moderate hazard: flood at least once in 10-50 years 

c) GK 2, low hazard: flood at least once in 50-200 years 

d) GK 1, very low hazard: flood rare than once in 200 years or never 

e) B, additional information: small river 

7. stage of program: first release of ZÜRS in 2001, ZÜRS 2.0.12 is the fourth release since 

then. 

49 Zonierungssystem für Überschwemmung, Rückstau und Starkregen 

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6.6 Italy 

In Italy the insurance association (ANIA) provides flood hazard maps for insurance 

purposes via CEA, the European insurance and reinsurance federation. The maps show the 

flood extension according to different return periods. They are produced under the 

responsibility of the Public Basin Authorities or ANIA itself under a special (SIGRA) 

project 50 . The official internal release is planned for June 2007 and no public release has yet 

been established. The maps are produced on a scale of 1:25,000 to 1:5,000 for the SIGRA 

project maps. In Figure 6.15 an example of a screenshot of a flood hazard map is shown. In 

general the layout of the maps is straightforward, although the use of green is unusual as it is 

normally associated with safety. Nevertheless it is used here for the floods with the lowest 

return period (50 years), i.e. the highest threat of inundation. 

Figure 6.15 Example 1 of Regione UMBRIA/Provincia di Perugia/Comune di Torgiano 

Legend of the map: 

Green return period = 50 years 

Blue return period = 200 years 

Red return period = 500 years 

6.7 USA 

Although this Atlas is restricted to examples of flood mapping in the EU countries, as a 

reference the extensive mapping program in the USA is very interesting to include in this 

50 http://www.ania.it/sist_inf/prog/sigra/index.asp 

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chapter on flood mapping for insurance purposes since this program started already in 1969. 

The program, called National Flood Insurance Program (NFIP), is a Federal program 

enabling property owners in participating communities to purchase insurance protection 

against losses from flooding 51 . This insurance is designed to provide an insurance alternative 

to disaster assistance to meet the escalating costs of repairing damage to buildings and their 

contents caused by floods. Participation in the NFIP is based on an agreement between local 

communities and the Federal Government that states if a community will adopt and enforce 

a floodplain management ordinance to reduce future flood risks to new construction in 

Special Flood Hazard Areas (SFHA), the Federal Government will make flood insurance 

available within the community as a financial protection against flood losses. 

The program is administrated by FEMA (Federal Emergency Management Agency) which 

identifies flood hazard areas throughout the U.S. and it's territories by producing Flood 

Hazard Boundary Maps (FHBMs), Flood Insurance Rate Maps (FIRMs), and Flood 

Boundary & Floodway Maps (FBFMs). Several areas of flood hazards are commonly 

identified on these maps. One of these areas is the Special Flood Hazard Area (SFHA) or 

high risk area defined as any land that would be inundated by a flood having a 1-percent 

chance of occurring in any given year (also referred to as the base flood). The high-risk area 

standard constitutes a reasonable compromise between the need for building restrictions to 

minimize potential loss of life and property and the economic benefits to be derived from 

floodplain development. Development may take place within the SFHA, provided that 

development complies with local floodplain management ordinances, which must meet the 

minimum Federal requirements. Flood insurance is required for insurable structures within 

high-risk areas to protect Federal financial investments and assistance used for acquisition 

and/or construction purposes within communities participating in the NFIP. 

An important distinction is made between FHBMs and FIRMs. A Flood Hazard Boundary 

Map (FHBM) is based on approximate data and identifies, in general, the SFHAs within a 

community. It is used in the NFIP's Emergency Program for floodplain management and 

insurance purposes. A Flood Insurance Rate Map (FIRM) usually is issued following a flood 

risk assessment conducted in connection with the community's conversion to the NFIP's 

Regular Program. If a detailed assessment, termed a Flood Insurance Study (FIS), has been 

performed, the FIRM will show Base Flood Elevations (BFEs) and insurance risk zones in 

addition to floodplain boundaries. The FIRM may also show a delineation of the regulatory 

floodway. After the effective date of the FIRM, the community's floodplain management 

ordinance must be in compliance with appropriate Regular Program requirements. Actuarial 

rates, based on the risk zone designations shown on the FIRM, are then applied for newly 

constructed, substantially improved, and substantially damaged buildings. 

The FIRM is the basis for floodplain management, mitigation, and insurance activities for 

the National Flood Insurance Program (NFIP). Insurance applications include enforcement 

of the mandatory purchase requirement of the Flood Disaster Protection Act, which "... 

requires the purchase of flood insurance by property owners who are being assisted by 

Federal programs or by Federally supervised, regulated or insured agencies or institutions 

in the acquisition or improvement of land facilities located or to be located in identified 

areas having special flood hazards" (Section 2 (b) (4) of the Flood Disaster Protection Act 

of 1973). In addition to the identification of SFHAs, the risk zones shown on the FIRMs are 

51 http://msc.fema.gov/ 

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the basis for the establishment of premium rates for flood coverage offered through the 

NFIP. 

The Standard DFIRM Database presents the flood risk information depicted on the FIRM in 

a digital format suitable for use in electronic mapping applications. The Standard DFIRM 

database is a subset of the Enhanced DFIRM Database that serves to archive the information 

collected during the flood insurance study. 

In the maps a number of types of areas are distinguished using a coding. The most important 

codes used are: 

Zones AE: Areas subject to inundation by the 1-percent-annual-chance flood event 

determined by detailed methods. BFEs are shown within these zones. Mandatory flood 

insurance purchase requirements apply. 

Zone AH: Areas subject to inundation by 1-percent-annual-chance shallow flooding 

(usually areas of ponding) where average depths are between 1 and 3 feet. BFEs derived 

from detailed hydraulic analyses are shown in this zone. Mandatory flood insurance 

purchase requirements apply. 

Zone AO: Areas subject to inundation by 1-percent-annual-chance shallow flooding 

(usually sheet flow on sloping terrain) where average depths are between 1 and 3 feet. 

Average flood depths derived from detailed hydraulic analyses are shown within this zone. 

Mandatory flood insurance purchase requirements apply. 

Zone A99: Areas subject to inundation by the 1-percent-annual-chance flood event, but 

which will ultimately be protected upon completion of an under-construction Federal flood 

protection system. These are areas of special flood hazard where enough progress has been 

made on the construction of a protection system, such as dikes, dams, and levees, to consider 

it complete for insurance rating purposes. Zone A99 may only be used when the flood 

protection system has reached specified statutory progress toward completion. No BFEs or 

flood depths are shown. Mandatory flood insurance purchase requirements apply. 

Zone AR: Areas that result from the decertification of a previously accredited flood 

protection system that is determined to be in the process of being restored to provide base 

flood protection. Mandatory flood insurance purchase requirements apply. 

Zones X: Areas identified in the community FIS as areas of moderate or minimal hazard 

from the principal source of flood in the area. However, buildings in these zones could be 

flooded by severe, concentrated rainfall coupled with inadequate local drainage systems. 

Flood insurance is available in participating communities but is not required by regulation in 

these zones. 

Zone D: Unstudied areas where flood hazards are undetermined, but flooding is possible. 

No mandatory flood insurance purchase requirements apply, but coverage is available in 

participating communities. 

The flood maps can be used by a graphical user interface (Figure 6.16). In Figure 6.17 an 

example is given of the flood maps that are produced by FEMA as part of NFIP. 

An overview of all flood information and links to maps in the USA is available on the 

internet 52 . 

52 http://www.floodsmart.gov/floodsmart/pages/index.jsp 

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Figure 6.16 User-interface of the NFIP for selection of flood maps 

Figure 6.17 Example of the FEMA – NFIP flood insurance maps (Colorado – Boulder County) 

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7 Evacuation maps 

7.1 Germany – Hamburg 

For the city of Hamburg, detailed information is available on the internet 53 on the activities 

that are being implemented for the purpose of flood protection. Maps are available for 

several parts of the city 54 on flood hazard and the evacuation routes. On Figure 7.1 a 

detailed map is shown of part of the city (Wilhelmsbrug) with an indication of the 

evacuation zones corresponding to different water levels (6.5m and 7.5m), the location of 

evacuation locations (‘Fluchtburgen’, indicated with ‘F1….8’), emergency residences 

(‘Notunterkünfte’, indicated with ‘N1…4’) and busstops (‘H’) from where evacuation 

busses will depart. The maps are accompanied by an extensive description of the expected 

situation in case of flooding and detailed advice to the general public how to act in such 

circumstances. 

This is a good example of a well-planned information package for urban population in a 

very large city. The information is well-presented and easily accessible, although the files 

themselves may prove large for slow-speed internet connections. 

53 http://fhh.hamburg.de/stadt/Aktuell/behoerden/stadtentwicklung-umwelt/bauen- 

wohnen/hochwasserschutz/start.html 

54 http://fhh.hamburg.de/stadt/Aktuell/behoerden/inneres/katastrophenschutz/service/merkblaetter/start.html 

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Figure 7.1 Part of the map with flood protection and evacuation zones of the city of Hamburg with (German) 

legend 

7.2 Japan 

In Japan municipalities are obliged to inform their inhabitants on the flood risk conform the 

Flood Fighting Act, established in 2001. Since 2005 the municipalities are also obliged to 

take a pro-active attitude by distributing flood risk and inundation maps freely among the 

inhabitants in order to increase the flood-preparedness and, as a secondary goal, to 

contribute to the spatial planning within the municipality. The flood maps are prepared in 

two steps: 

1. the Ministery of Land, Infrastructure and Transport and the prefecture (for resp. 

nationwide and regionally adminstred river basins) determine the flood-prone areas; 

2. the municipalities produce the Flood Hazard Maps. 

The flood maps are produced following a nationwide standard that is determined by the 

Ministry, which e.g. establishes the inundation depth classes (0 – 50, 50 – 100, 100 – 200, 

200 – 500 & > 500 cm) and the corresponding colour codes. The choice of those depth 

classes is based on ‘human characteristics’: 

� 0 – 50 cm: most houses will stay dry and it is still possible to walk through the 

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water; 

� 50 – 100 cm: there will be at least 50 cm of water on the ground floor and electricity 

will have failed by now; 

� 100 – 200 cm: the ground floor of the houses will be flooded and the inhabitants 

have either to move to the first floor or evacuate; 

� 200 – 500 cm: both the first floor and often also the roof will be covered by water. 

Consequently evacuation is the logic choice of action now. The same applies, 

evidently, for the depth class > 500 cm. 

Similar to the situation in e.g. the Netherlands, the flood inundation maps are based on 

hydrodynamic calculations for several scenarios of possible locations of dike failure. The 

final map is based on the scenario that would cause the maximum number of victims, i.e. a 

worst case approach. The return period of the flood that is shown on the maps depends on 

the region as a function of potential damage. 

Once such maps have been made on municipal level, the municipality adds local 

information that is relevant for evacuation, such as the location of shelters, important 

buildings, evacuation routes, etc., as well as information on the items that should be taken 

along during an evacuation. On some maps space is left for the user to draw a personal 

evacuation route map based on the particular situation of the person or family. 

Al the maps are distributed free of charge to the public on scales of 1:5.000 to 1:10.000, and 

in some cases they can be downloaded from the internet. It is the task of the municipality to 

keep the maps up to date. 

Examples of flood maps that are available to the public are shown in Figure 7.2 for the city 

of Toshima, using the depth inundation classes mentioned above. As in most cases the 

legend is only given in Japanese, although in some cases an English legend is provided. 

Further information on the preparation of the map is given on the internet 55 . On this site all 

relevant information is given necessary for evacuation in case of flooding, including the 

addresses of the shelters. 

Other examples are shown in Figure 7.3 and Figure 7.4. Especially the latter gives 

indications of shelters, temporary shelters (which probably have fewer resources for a long 

duration stay), boundaries of evacuation areas, the location of flood warning speakers and, 

contrary to general custom, an indication of roads that should NOT be used for evacuation. 

The map also provides expected flood depths, although no indication is given to which 

return period this applies, and the limits of a recent historical flood. Although this map has 

some interesting features that are hardly ever found in other evacuation-type maps (like the 

earlier mentioned location of ‘flood warning speakers’), the topographical layout on the 

scale presented is not sufficiently clear to be used in practical situations. It may be used, 

though, for preparation purposes as a training for flood situations. Further information can 

be found on the internet 56 . 

55 http://www.city.toshima.tokyo.jp/english/bousai/hazardmap/index.html 

56 http://www.icharm.pwri.go.jp/html/docu/jan_20_22_2004_ws/pdf_output/hiroki.pdf 

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Figure 7.2 Part of flood depth map for the city of Toshima in Japan 

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Figure 7.3 Evacuation map for the Japanese city of Sukagawa 

Figure 7.4 Example of a flood hazard map with indications of evacuation roads 

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7.3 Netherlands 

An example of an evacuation map in the Netherlands is shown in Figure 7.5 for polders 

along the Rhine river near Germany. This maps shows clearly the mandatory evacuation 

routes, including indication of one-way converted roads, closed entrances and exits, and are 

a easy to interpret by the general public. 

In Figure 7.6 the simulation of the expected flood extension for the region of “Land van 

Maas en Waal” (see also Chapter 4.14) is translated into a decision-support map that shows 

the areas that will either remain dry, reach a water level that leaves the first flood of 

dwellings dry and those areas that will reach such water depths that evacuation will be 

required. In order to take decisions on the best evacuation routes, a map is produced that 

shows the time of arrival of the inundation front with a depth of 50 cm at the various types 

of infrastructure (especially roads, see Figure 7.7). Depending on the decision up till which 

depth roads or other escape routes are still safe to use, maps with the arrival time of dfferent 

inundation depths can be produced. 

Figure 7.5 Example of an evacuation map for the Netherlands with indication of obstructions and lane 

direction and closed entrances and exits 

Figure 7.6 Basis for decision making on evacuation (expected inundation depth) 

Figure 7.7 Time of arrival of the inundation front of 50 cm depth at infrastructure (roads/elevated areas) 

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7.4 USA 

7.4.1 Mississippi 

Similar to the comments made on insurance maps, there are a number of very interesting 

examples of evacuation maps that can be used as examples for the development of 

evacuation maps in Europe. In the USA the evacuation routes are published both by state 

and central on a clickable map of the entire country 57 . 

In the maps from the USA reference is often made to the ‘contraflow’ principle, i.e. the 

reversing of the normal traffic flow direction to change an ordinary two-direction road into a 

one-direction (evacuation) road to increase its capacity. Special maps are prepared for such 

occasions that are referred to as ‘contraflow maps’. An example is given in Figure 7.8 for a 

part of the State of Mississippi 58 and a detailed map of a road crossing prepared by the 

Mississippi Department of Transport is shown in Figure 7.9 59 . 

Figure 7.8 Hurricane evacuation routes in Mississippi state with indication of ‘contraflow’ roads 

57 http://www.ibiblio.org/rcip/evacuationroutes.html#sbs 

58 http://www.gomdot.com/cetrp/hurricane_evac_routes.pdf 

59 http://www.gomdot.com/cetrp/hurricane_evac_routes.pdf 

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Figure 7.9 Example of detailed maps prepared for road crossings in case of ‘contraflow’ situations 

7.4.2 Florida 

The State of Florida produces a number of very clear and attractive evacuation maps. An 

example is shown in Figure 7.10. This evacuation map is accompanied by a text with an 

indication of the ‘best’ evacuation route for each of the villages in the region. The colours 

refer to expected hurricane / storm surge force (category 1 – 5). 

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Figure 7.10 Evacuation map for a part of Florida 60 

7.4.3 Louisiana – New Orleans 

Evidently after the impact of the hurricane Katrina, New Orleans has become a focus of 

attention in terms of flood prevention. Detailed evacuation maps are available for the all of 

the state of Louisiana (see e.g. Figure 7.11) 61 , with for each road crossing a special map that 

60 http://www.firstcoastnews.com/weather/stormtrack/evacuation_map.aspx 

61 http://www.dotd.state.la.us/maps/ 

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indicates the contraflow plan and detailed instructions for the evacuation by car (Figure 

7.12). 

Figure 7.11 Part of an evacuation map for Southwest Louisiana 

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Figure 7.12 Detail of contraflow at a road crossing (reference to map on Figure 7.11) and detailed instructions 

Another example of an evacuation map for the city of New Orleans, including a phased 

evacuation plan, is given in Figure 7.13. Very detailed instructions are available in case of a 

hurricane threat, with emergency shelter information points, agency contact information, 

radio frequencies, a guide on how to make a ‘family communication plan’ and even a 

chapter on ‘preparing your pets’. 

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Figure 7.13 Part of evacuation map of area of New Orleans with phased evacuation plan 

7.4.4 California – Sacramento 

A very interesting example of a combination of a flood depth map and a combined rescue / 

evacuation map is available for the County of Sacramento in California, including the city 

of Sacramento itself. Various detailed maps showing hypothetical levee breaks, inundation 

levels and the time it would take for waters to rise in affected neighbourhoods, and rescue 

and evacuation zones have been made available on the internet 62 . For a specific failure 

location two types of maps can be downloaded: 

� Flood Depth Maps: show where the water would flow over time and how deep it would 

get given the hypothetical flooding scenario. 

� Rescue and Evacuation Route Maps: show rescue areas, evacuation areas, and 

potential evacuation routes. 

� Rescue areas, in red, indicate places where water has the potential to reach a depth 

of at least one foot after two hours from the time of a levee failure. People would 

not be able to drive out and likely would be stranded and require rescue. 

� Evacuation areas, in yellow, indicate places, depending on where the levee breech 

occurs, that could fill from 1 to 26 feet of water within 10 days, giving most people 

time to get out safely. Flood depth details are specified on each map. 

� This map also portrays potential evacuation routes (in green) and which evacuation 

routes would become inundated over time. 

A total of 18 sets of maps are available. Examples of both types of maps, with the 

corresponding legends, for the American – River Arden region, are shown in Figure 7.14 

62 http://www.msa.saccounty.net/waterresources/floodready/?page=maps 

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and Figure 7.15. 

Detailed maps are also available for some of the other States in the USA, especially New 

Jersey 63 and South Caroline 64 , but provide no extra information compared to the maps 

already shown in this Chapter. 

63 http://www.nj.gov/njoem/plan/evacuation-routes.html 

64 http://www.dot.state.sc.us/getting/evacuation.shtml 

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Figure 7.14 Flood depth map of the county of Sacramento, with indication of location of hypothetical levee failure and inundation process in time 

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Figure 7.15 Rescue and evacuation route map of the county of Sacramento, with indication of location of hypothetical levee failure and passable routes in time 

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8 Final Remarks 

In the present document a large number of examples of floods maps are shown, produced by 

various European countries. The aim of this document is to provide the reader with 

illustrative examples of various types of flood maps that might form an inspiration for future 

mapping efforts. As a kind of final remarks, in this section some do’s and don’ts are 

formulated regarding the flood information that can be presented in these type of maps. 

In some occasions map examples are described as being very clear and/of as an example of 

an excellent flood map. Evidently these are the subjective opinions of the compilers of this 

document and the users are invited to browse through it and form a personal opinion that 

may be brought forward within the context of EXCIMAP. 

Although in Chapter 1 a number of different types of flood maps are mentioned, not all 

these types are equally well presented. 

Most countries have flood extent maps. This flood extent should be related to a specified 

flood frequency. Frequencies used in the maps vary from 1/30 to 1/10.000. Most countries 

use only 2 or 3 different frequencies (e.g. 1/100 and 1/1000, or the less accurate “frequent” 

and “exceptional”), Flanders seventeen (2, 5, 10, 15, 20, 25, 30, 40, 50, 75, 100, 150, 200, 

250, 300, 500 and 1000 years). England & Wales distinguish between floods originating 

from the sea (1/200) and flood from rivers (1/100), while Ireland gives an indication of the 

uncertainty of the flood extent. Maps become difficult to read when flood extent is presented 

in iso-lines (instead of coloured surfaces) or when current velocities are presented is arrows 

(that may merge together with parallel current lines). 

Often flood extent for different frequencies is presented in one map. Increasing intensities of 

blue, suggesting increasing flood depth, represent the most frequent flooded (deeper) areas 

(like England & Wales, Finland, Germany). Flood depth maps may be presented for one 

representative flood frequency, e.g. 1/100. An interesting example is from Japan, in which 

the flood depth intervals are such that it contains “danger/how to act” information for 

individuals. In France maps exist that also present flood duration. 

Information on historic floods is shown on maps from France, Finland and Ireland. With this 

type of information one should be aware that since this flood event floodwave 

characteristics and floodplain topography may have changed considerably and that therefore 

this historic flood may not representative for present conditions. However, this information 

is valuable to increase flood awareness. 

Flood hazard maps, indicating where the combination of current velocity and waterdepth 

may be dangerous, are published in England& Wales. Austria uses the more or less 

comparable dragforce parameter. In Rheinland-Pfalz (Germany) and Switzerland this 

velocity-depth information is related to frequency, expressing this hazard information in a 

more sophisticated way for professional users. The dominant colours for this type of hazard 

information are red, orange and yellow. 

In terms of flood risk maps, official maps indicating potential damage are rare. The only 

examples are from Germany (Rheinland-Pfalz, Sachsen). Italy, Spain and Switzerland have 

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official risk zone maps. These maps are based on the probability of flooding in combination 

with the land use sensitivity /vulnerability to flooding. In Italy and Switzerland this risk 

zonation relates to spatial planning regulations and construction requirements. Specific 

vulnerability maps are available in England & Wales (social vulnerability of the population) 

and Sachsen (Germany) (vulnerable services, like hospitals). 

A special group of flood maps comprise the insurance maps, which are used as a basis for 

both the general user, to check on the liability of his/her property to flooding, and the 

insurance companies to assess the actual risk of flooding. These maps contain information 

on flood risk, represented as flood extent probability on damage potential. 

Evacuation maps are slowly becoming more usual, although most of them are still produced 

outside the EU. USA and Japan have a large tradition on this and may be valuable when 

European countries start to prepare these maps. Examples are found in Germany and also 

the Netherlands. These maps concentrate on how to act when a flooding threat becomes 

evident (evacuation routes, location of refuge/shelters, etc.), often combined with 

recommendations on what to take with you. Sometimes those maps are combined with 

“threat” information (potential flooding depth / flood extent depending on hurricane force). 

Apart form flood information (the core of the map of course) some additional information is 

essential for a proper use of the map: adequate title, date of publishing, responsible 

authority, orientation of the map, scale (preferably with a scale rod, to avoid confusion 

when printing or copying maps on other scales), relevant topographic information (roads, 

railways, buildings, cadastral information (e.g. in Austria)). Interesting opportunities arise 

when combining flood maps with Google Earth, however care should be taken to avoid an 

overload of topographic information in this way. 

Other desirable information is a small set-in map to locate the mapped area. Some Finnish 

maps indicate the area covered by the model calculation. In addition the map from Finland 

has a nice example of a Disclaimer. 

Another issue is language: in some instances English is used instead of the local language, 

but it is recognized that the use of English, especially on the publicly accessible internet 

sites, may limit the access to the information for those people with limited knowledge of 

English and the local language is preferred. The use of two languages may make the legend 

too large or difficult to read. An option is evidently to provide a translation of the map labels 

in English, especially on the internet sites. 

With maps presented digitally on a computer care should be taken that the legend remains 

readable, especially with (scanned) files of original hardcopies. Still many maps will be 

printed as well (A3 as most frequent maximum size), which requires that map and legend 

are printed on the same page. 

The Atlas shows for some of the maps a wide variety of layouts. When accompanied by a 

clear legend this may not be a problem, however for transboundary catchments / maps it is 

advisable that a certain level of uniformity is accomplished. Nice examples of such an 

approach are shown in the Chapter 0 on transboundary flood mapping. 

Apart from the large number of different types of layout, that will be evident when browsing 

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through this document, it is important to realize that the differences in layout are only the 

outside of the discrepancies between the various maps that according to their titles might 

assume to show the same information (e.g. flood extension for a certain return period). More 

important than the differences in layout are the different methodologies that are used for the 

production of the flood maps. Although the return period used is the same, the actual 

calculation method may be very different and is often not apparent from the map. However, 

even in cases where background documents do explain the technical details of the 

calculations, there are too many differences in the approaches followed by the various 

agencies that the maps would possibly become comparable or, at border locations where 

they present a continuous line of information, show the same results. And although in theory 

it would be possible to use one and the same methodology, it is unlikely that the same 

results would be generated for e.g. border stations as the underlying data are often 

contrasting and/or the length of the measurement series are different for stations in 

neighbouring countries. 

This demand for uniform approaches not only holds for border areas, but also for maps 

prepared for different purposes within a country, e.g. national programmes, EU 

demonstration projects and reinsurance purposes. Because of these initiatives different maps 

may exist, all presenting some type c.q. aspect of flood risk information. 

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Atlas of Flood Maps

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