ČESKÉ VYSOKÉ UČENÍ TECHNICKÉ V PRAZE - ČVUT

storm.fsv.cvut.cz

ČESKÉ VYSOKÉ UČENÍ TECHNICKÉ V PRAZE - ČVUT

CZECH TECHNICAL UNIVERSITY IN PRAGUE

Faculty of Civil Engineering

Department of Irigation, Drainage and Landscape Engineering

Rainfall-Runoff Relationships

Assessment in Large Catchments – Case

Study Weisseritz

Part V.

Measures Effect Assessment

Project EMTAL – „Interdisziplinares Vrbundprojekt zum Einzugsgebiets-

Management fur Talsperren in Mittelgebirgslandschaften“ BMBF 02WT0337

Authors:

Coordinator: TU Bergakademie Freiberg; Prof. J.Matschullat

WG flood hydrology – CTU Prague

Ing. Petr KOUDELKA

Ing. Kateřina UHLÍŘOVÁ

Ing. Václav DAVID

Ing.Dr. Tomáš DOSTÁL

Doc.Ing. Karel VRÁNA, CSc.

Prague, 2006


1. Introduction and the goals of the project

The goal of this part of the EMTAL project was the impact assessment of channel

characteristics and flood-plain characteristics on flood wave routing. It should be the basis for

proof or disproof generally accepted opinion that stream rehabilitation (stream straightening

and deepening, channel lining, lowering the roughness of channel bottoms) and land-use

changes in flood-plains (mainly changes parcels for agriculturally used areas) causes higher

frequency of flood events and higher peaks of discharge during these situations. The other

aim was to prove or disprove opinion that stream rehabilitation can in some measure help

with decreasing frequency and intensity of flood phenomena. In summary the solving was

primarily aimed to small streams that belong to catchments with area smaller than 10 – 15

km 2 , because small stream rehabilitations are realized in these catchments nowadays.

2. Solution methodology

Solution approach of this part of EMTAL project could be divided into two sections

because this problem has been solved by two different attitudes.

Rainfall-runoff modelling focused on landscape and channel measures was considered

in the first case. Hydrologic model HEC-1 incorporated in hydrologic interface WMS 7.1 was

used for that. Computations were gone on two study catchments - Huckaback a Reichstädter

Bach. Landscape and channels measures were simulated in Höckenbach catchment. Influence

of land-use change, different size of channel cross-section, roughness changes of channels or

flood-plain areas were examined. In Reichstädter Bach catchment effect of dry reservoir –

polder on flood outflows was researched. (See Chapter 2.1)

The second approach concerned open channel flow modelling using hydraulic model

HEC-RAS. Number of scenarios relating to cross-section of stream channel and adjacent

flood-plain, longitudinal and transversal slope of the channel and Manning's roughness of the

channel and the flood-plain were simulated. (See Chapter 2.2)

2.1 Hydrologic modelling using HEC-1 in WMS

Input data, methodology, computations, results and conclusions that refer to the first

attitude will be presented in this section. It means the assessment of both landscape and

channel measures using rainfall-runoff model.

2.1.1 Catchments characteristics

Following text describes every further mentioned study catchment. Especially there

are specified those characteristics that are tightly connected to rainfall-runoff relations in

watersheds.

2.1.1.1 Höckenbach

Analyzed catchment of Höckenbach has to the outlet an area of 4.14 km 2 . As an outlet

the conclusion with the eastern branch of this stream in Ruppendorf was considered. This

2


catchment has a simple oblong shape with not developed stream network. The network

consists of the main reach and two source branches. The stream passes Beerwalde and

Ruppendorf where flood risk can be expectable. This catchment is moderately steep (aprox.

5.5 %) and elevations are within 377 and 505 m a.s.l while average elevation is 441 m a.s.l.

Most of the land within the catchment is agriculturally used. Aerial photo of the catchment

can be seen on the Fig. 1.

From land-use data statistics it is clear that the catchment of Höckenbach is more

agriculturally used than the other catchment of Reichstädter Bach. Arable land takes covers

more than 84 % of total catchment area. There is no important percentage of forest or

permanent grass within the catchment of Höckenbach. The land-use map of the catchment can

be seen on the Fig. 2. and the detail land-use distribution on the Fig. 3.

The soil information (Fig. 4) was for the catchment of Reichstädter Bach analyzed for

purposes of hydrological modelling using HEC-1 model when four hydrological soil groups

were needed. From statistical representation of soils using four hydrological soil groups it can

be seen (Fig. 5) that the most soils fall into the C group in this catchment. Soils from this

group cover ca 90 % of the catchment area. This group represents soils with lower infiltration

rates.

2.1.1.2 Reichstädter Bach

Reichstädter Bach catchment is characterized by quite simple oblong shape. The main

thalweg goes from south to north east. The total area of Reichstädter Bach catchment is 12.84

km 2 . This catchment is relatively much steep. The average slope in the catchment is

approximately 10.8 % based on slope analysis of raster digital elevation model with 10 meters

resolution. Elevations in the catchment are within 362 and 605 m a.s.l. while average

elevation is 483 m a.s.l.

Hydrographical network is not much developed and consists of one main stream

with several smaller tributaries. There is one bigger tributary which joins Reichstädter Bach in

lower part of Reichstädt from the left side. Most of buildings within a catchment are situated

along the stream channel what makes them vulnerable by floods.

From land-use data statistics value of more than 72 % was identified for arable land.

This value shows that this catchment is intensively agriculturally used. Percentage of pastures

or meadows is nearly 10 % and forests are not very much (about 6 %). The detail land-use

distribution of the catchment can be seen on the Fig. 7 and the land-use map on the Fig. 6.

From statistical representation of soils using four hydrological soil groups follows that

the most soils fall into the C group in this catchment. Soils from this group cover nearly 70 %

of the catchment area. This group represents soils with lower infiltration rates. The

distribution can be seen on the Fig. 9. and the soil map on the Fig. 8.

2.1.1.3 Blinka

Area of Blinka catchment is nearly 24 km 2 and its shape is also oblong. Length of the

Blinka stream is 12 km and goes from South to North West. The catchment is located in

elevation 210 – 350 m a.s.l.

3


From morphological point of view the area is not much dissected with relatively low

slopes. Statistical representation shows that almost 60% of total area has slope lower than 5%

and nearly 90% of area slope 10% lower.

From land-use data can be seen that this catchment is intensively agriculturally used.

Arable land fills more than 80%. Approximately 9% of total area is covered by grass,

orchards and gardens. More than 60% of arable land area was grown by corn in 2006 (Fig.

10).

Soil relations are relatively hydrological positive. Statistical representation shows that

more than 95% of soils belong to hydrological soil group B - it represents soils with middle

infiltration rates (0.06 - 0.12 mm/min). (Fig. 11).

2.1.2 Basic characteristics of applied simulation model

There has been used mathematical simulation tool WMS 7.1 for all hydraulichydrological

analyses within the catchment, which is complex interface for hydrological

analyses on GIS platform. The model has been developed by Environmental Modelling

Research Laboratory of Bringham Young University in cooperation with U.S. Army Corps of

Engineers Waterways Experiment Station in USA.

The model offers number of hydrological modules and methods (like HEC-1, TR-20,

TR-50, NFF, etc.) and further tools for digitalization and generation of Digital Elevation

Model (DEM). It also allows to simulate flood wave transformation trough channel routing

and in the reservoir or polder.

WMS uses GIS tools especially on ArcView a ARC/INFO platform. It’s possible to

import required layers as GIS layers or digitize them directly inside the system using its tools

and background pictures.

WMS model provides also good level of outputs visualization, which consists mainly

in presentation of calculated runoff hydrographs directly within the model, but also in

axonometric imaging or analytical hill-shading. [Brigham Young University, 1999]

2.1.2.1 Applied methods for rainfall-runoff modelling

SCS-CN method combined with unit hydrograph methods (Clark’s) were used for

rainfall-runoff modelling within the project and, using HEC-1 module of WMS simulation

interface. Method of Muskingum-Cunge has been selected to describe transformation of flood

wave routing trough channel. More details you can find in Part III. The catchment model has

been built based on following input data, which was generated or edited in GIS software

ArcView.

The basic input data that were used in case of mentioned methods above:

• Digital elevation model (DEM)

• Hydrological soil groups layer.

• River network.

• Land-use map

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• Hydrological data

• Cross-section of the channel stream and the flood-plain

• Manning roughness of the channel and the flood-plain

The last two inputs are required if the goal of the modelling is to assess the effect of

the channel and flood-plain area on transformation and routing of the flood wave. to have

parameters of the channel and possibly also flood-plain – mainly cross-sections, included of

roughness of the channel and flood-plain.

The same, for calculation of flood wave transformation by water reservoir or polder,

there is necessary to define the reservoir (volume-elevation and discharge-volume curves or

other parameters, where water volume and water level can be determined from). These values

were estimated from field survey as real values for real events modelling, and from catalogues

for scenarios and design rainfall events modelling.

You can find the details about methodology SCS-CN in Part III. and about polder

defining in next chapter.

Temporal distributions of discharge (hydrographs) are the outputs of surface runoff

simulation in all outlets of selected subcatchments.

2.1.2.2 Applied method for polder routing

Reservoirs in HEC-1 can be defined in few different ways, depending on the storage

routing techniques that need to be modelled. The effects of a detention basin on an inflow

hydrograph can be analyzed and an output hydrograph created in WMS using the Detention

Basin calculator. A level pool routing technique is used to determine the effects of storage

routing on an input hydrograph for given detention basin/reservoir parameters. Using the

principle of conservation of mass, the change in reservoir storage, S, for a given time period,

∆t, is equal to the average inflow, I, minus average outflow, 0.

S − S1

I1

+ I

2

O1

+

= −

∆t

2 2

2

O2

The defined storage vs. discharge relationships are used to iteratively solve for the end

of period storage and outflow.

The detention basin calculator requires three sets of input:

1. A hydrograph.

2. A storage-capacity (volume-elevation) relationship.

3. An elevation-discharge relationship.

When computing an outflow hydrograph an initial storage is used to account for any

volume of water that may be in the detention basin prior to the arrival of the inflow

hydrograph. If depth or elevation is known then the elevation vs. volume storage capacity

curve must be used to determine the initial storage. The storage-capacity and elevationdischarge

curves are plotted in the detention basin calculator (see Fig. 12). The way in which

these three inputs are defined from the detention basin calculator is documented in the next

three sections.

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2.1.2.2.1 Hydrograph

A hydrograph can be computed from any of the supported hydrologic models or as

imported from some other source.

2.1.2.2.2 Storage-Capacity Curve

There are three different methods for defining storage capacity: volume vs. elevation,

area vs. elevation, or known geometry. In all three cases a relationship between elevation and

volume will be computed. For the volume vs. elevation option this is explicitly defined. If

area vs. elevation is specified, then a corresponding volume for each elevation is computed

using the conic method. The conic method is illustrated in Fig. 13.

The volume between incremental areas A1 and A2 is computed using the following

equation:

h

∆ V = ( A1

+ A2

+

3

12

A1

A2

where:

∆V12 - The volume between areas A1 and A2.

Ai - surface area i.

)

h - vertical distance (E2-E1) between surface areas A1 and A2.

Ei - elevation of surface area i.

The same equation is used to compute the volume between each adjacent set of surface

areas, with the bottom area assumed to be 0. A TIN can be used to automatically create and

store for use in the detention basin calculator the elevation-volume relationship.

If the basin geometry option is chosen then an elevation vs. volume relationship is

computed directly from the geometry defined for the basin.

2.1.2.2.3 Elevation-Discharge Relationship

Discharge data for the basin/reservoir can be entered either by supplying an elevation

vs. discharge pairs, or by defining any number and combination of spillways (weirs), outlets

(orifices), and standpipes (weir-orifice combinations). If the Known-Discharge option is

chosen then it’s needed to enter a series of Elevation and Discharge values (you need the

same number of values in each series) to define the relationship. If the Discharge Structures

option is chosen you can add any number of weirs, outlets, and standpipes along with their

individual parameters. WMS will then compute an elevation discharge relationship with an

appropriate elevation step and display it in the detention basin calculator.

2.1.2.3 Input data preparation

Sources and preprocessing of the input data required for HEC-1 modelling are

described below.

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2.1.2.3.1 Digital elevation model (DEM)

The data layer which was available for project participants was dgm20_erg.shp. This

layer has a form of point vector layer. This information layer contains regular square net of

points. One or the attribute field contains information about elevation of points. Spacing of

points within this layer is 20 meters. Elevations are in attribute table stored with precision of

0.1 meters.

Digital elevation model was processed and created in ArcGIS environment. 3D Raster

elevation model was interpolated using tool Topo to Raster which is contained in an extension

Analyst. Resolution of resulting raster elevation model was set to 10 meters what is

sufficiently enough detail resolution for analyses that were planned to be done in frame of

EMTAL project. Because WMS prefers import of raster elevation data in form of ASCII

raster resulting model was finally converted into a file dem10.asc. For this purpose tool Raster

to ASCII was used. Triangulated Irregular Network (TIN) has been generated based on ASCII

raster in WMS. Distance of individual points within TIN was set to ca 20 m.

2.1.2.3.2 Hydrological soil groups layer

This layer has been based on digital soil map emtal_bkkonz_gesamt.shp. This data

layer was equipped by large database containing very detail soil information even for different

soil profiles. However, the information contained in the database was not homogeneous.

Therefore it was necessary to homogenize it. For this purposes mainly fields AGGNR and

BOART were used. The result was the map of soil texture units which was used for further

processing. Based on this map hydrological soil groups were assigned to single spatial units.

2.1.2.3.3 Stream network

Single streams have been manually digitized in WMS interface, based on an

information system ATKIS, orthophoto maps, DEM and field survey.

The stream network is other needed information which is required for purposes of

hydrological modelling. There was no specific data layer containing this information available

for EMTAL project participants. Therefore the information contained in land-use layer

fnutz_atkis_vollst.shp was used. However, this information had to be corrected and

supplemented by manual editing with use of aerial photography. Resulting layer of this

process was vector line layer containing hydrological correct stream network.

2.1.2.3.4 Land-use map

Land-use layer was created from fnutz_atkis_vollst.shp from an information system

ATKIS and has a form of a vector polygon file. For modelling purposes information stored in

a field NUTZ_G in form of codes was used and detailed field survey has been done.

Correction and editing of geometry of some features was necessary. Tool Intersect in ArcGIS

was used. There were classified in total number of categories (see Tab. 1). Layer of polygons

in file format *.SHP was imported into WMS model.

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Tab. 1 – CN catalogue used for both catchments

Lu_code

Land-use

CN for different soil type

A B C D

100 "urban areas" 61 75 83 87

110 "residential areas" 61 75 83 87

113 "gardens" 57 73 82 86

114 "parks, lanws" 39 61 74 80

120 "comunications" 82 89 92 93

121 "roads" 82 89 92 93

122 "paths" 72 82 87 89

123 "paths" 72 82 87 89

130 "industrial areas" 81 88 91 93

200 "arable land _ maize" 72 81 88 91

251 "small grain" 63 75 83 87

252 "small grain" 63 75 83 87

253 "small grain" 63 75 83 87

254 "small grain" 63 75 83 87

255 "small grain" 63 75 83 87

256 "small grain" 63 75 83 87

257 "small grain" 63 75 83 87

258 "maize" 72 81 88 91

259 "maize" 72 81 88 91

260 "rape" 65 76 84 88

261 "potatoes" 67 78 85 89

262 "potatoes" 67 78 85 89

263 "meadow" 49 69 79 84

300 "pastures or meadows" 39 61 74 80

310 "pastures or meadows" 39 61 74 80

320 "nonforested wetlands" 80 89 93 96

330 "swamps" 80 89 93 96

410 "streams" 100 100 100 100

420 "lakes" 100 100 100 100

510 "hedges" 35 56 70 77

550 "alleys" 43 65 76 82

610 "evergreen forests" 45 66 77 83

620 "deciduous forests" 36 60 73 79

900 "unknown" 100 100 100 100

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2.1.2.3.5 Hydrological data

Rainfall data from meteorological gauging station Weisseritz (Normal values - from

0.5 to 100 return period – duration 2 hours) were concerned as a primary source. Finally

precipitations of total depth 30, 40, 50, 60 and 70 mm and 2 hours time period were used for

scenarios modelling. These depths represent approximately normal values for 2 to 100 years

(See Tab. 2). Time distribution of the rainfall has been assumed as isosceles triangle, with

duration 2 hours, maximum intensity in the mid of duration and time step 15 or 5 minutes.

Time behavior of cumulative intensity of precipitations you can see on the Fig. 14.

Tab. 2 – Normal values of 2-hours precipitation in gauging station Weisseritz and depths

used in model

T – return period [years] 0.5 1 2 5 10 20 50 100

h N - height of precipitation [mm] 15 22.4 29.8 39.6 47.1 54.5 64.3 71.7

depth of precipitation used in model [mm] 30 40 50 60 70

2.1.2.3.6 Channel routing inputs

If the goal of the modelling is to assess the effect of the channel and flood-plain area

on transformation and routing of the flood wave, there is necessary to have parameters of the

channel and possibly also flood-plain – mainly cross-sections, included of roughness of the

channel and flood-plain. Höckenbach catchment was divided into 5 subcatchments that are

connected by 3 sections of the stream (see Fig. 15.) The total length of segments was ca

2.5 km 2 . These segments were defined by 2 channels S1-2, S3 on the base of terrain survey

(see Tab. 3). An example of cross-section is seen on Fig. 16.

Tab. 3 – Basic characteristics of stream channel sections

Section Channel width (m)

Channel depth (m)

1 1 0,5

2 1 0,5

3 1,5 1

Manning roughness coefficients were assigned on the basis of the terrain survey and

(Havlík, 1993). The values are:

Channel n k = 0.03 (natural small stream, straight clean channel),

Flood-plain n i =0.05 (flood-plain covered by sparse trees and bushes, dense weed)

The same, for calculation of flood wave transformation by water reservoir or polder,

there is necessary to input reservoir characteristics relating to storage and discharge. Storage

can be determined by storage-capacity (volume-elevation) curve or area-elevation curve or

9


known geometry. Discharge characteristics can be defined by discharge-elevation curve or

known discharge structures. For Reichstädter Bach catchment reservoir both curves were

derived.

2.1.2.4 Output data

Temporal distributions of discharge in form of hydrographs are the outputs of surface

runoff simulation in outlet points of all selected subcatchments. A catchment with result

hydrographs in WMS interface is seen on the Fig. 17.

2.1.3 Calculations – scenarios modelling

The goal of this task has been to present, how individual designed scenarios of landuse

and river network would influence surface runoff in case of theoretical rainfall events

with total depths 30, 40, 50, 60 and 70 mm. In the frame of calculations, hydrographs

corresponding to individual casual precipitation were made for all study catchments.

Complete hydrographs were compared graphically; their main characteristics were

compared tabular. Finally it was summarized in two types of graphs. The main characteristics

of hydrographs are: peak of discharge (m 3 /s), total volume of discharge (m 3 ) time of peak

(min).

This research should not be a pilot project of flood control but research of general

principles referred to all types of measures and outflow of precipitation from catchment.

Number of different scenarios corresponding to individual measures was considered. It’s

necessary to remind that these scenarios are theoretical and mainly unreal, but they express

extreme state of the phenomena.

HEC-1 model was used for this purpose. Details about methodology are mentioned in

Chapter 2.1.2.1.

Full spectrum of simulations for whole set of theoretical rainfall events was done and

is described in the next chapters.

2.1.4 Höckenbach catchment

Landscape and channels measures were simulated in Höckenbach catchment.

Influence of land-use change, different size of channel cross-section, roughness changes of

channels or flood-plain areas were examined. Outputs gained in VaV research project were

used for better results presentation and drawing general conclusion of basic principles. This

data were acquired by similar scenarios modelling in Blinka catchment in Czech Republic.

Short catchment description is included in chapter 2.1.1.3.

Simulated scenarios will be described in detail and some results will be presented in

the first chapter. Results will be arranged into hydrographs for runoff caused by precipitation

of 70 mm and 30 mm depth. This comparison is aimed to flow waves behaviour and

dissimilarity of runoffs caused by low and high intensity precipitation in particular. It is

supposed that temporal distribution of other hydrographs are similar to these two, it is

different only in peak value, its time and runoff volume. Mentioned hydrographs were

selected to present responds of significantly different intensities.

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For the rest of rainfall events (total depth 40, 50, 60 mm) the results of simulations are

presented in Chapter 2.1.4.2.1 and chapter 2.1.4.2.2.

Second chapter deals with comparison of all scenario results (caused by precipitation

of total depths 30, 40, 50, 60 and 70 mm). Peak flows and times of peak will be analyzed.

Every graph will figure results for one precipitation. This view compares all scenarios and

serves as a summary of peak flow decreases and shifts.

The third way of acquired result representation will be trends monitoring of the effect

of various measure types. Every scenario will be represented by one graph where results of all

precipitation will be included. From this point of view the influence of precipitation depth on

impact possibility of discharge in case of selected measures in selected profiles of

hydrographic network should be apparent.

Following types of design scenarios have been selected for modelling :

• Land-use changes

• Channel roughness modification

• Change of size and cross-section of the channel, change of inundated area roughness.

2.1.4.1 Detailed results for rainfall total depth 70 and 30 mm

As written above, the aim is to compare hydrographs individual scenarios. For more

general view, hydrographs caused by precipitation of 70 and 30 mm depth were chosen.

2.1.4.1.1 Land-use changes

It’s supposed that land-use changes have the most significant influence on runoff of all

natural measures in catchment. Affected are runoff characteristics, especially peak of

discharge and the total volume of discharge.

Then there have been following scenarios defined for simulation:

• LU0 - Real land-use - state from June 2005 (crops according to the field survey) – in

short “Real”.

• LU1 - Based on Real land-use but maize was replaced by small grain (positive crop

scenario) – in short “Small grain”.

• LU2 - all arable land is covered by maize (negative crop scenario) - in short “Maize”.

• LU3 - Conversion of all arable land on meadows (very positive scenario) – in short

“Meadows”. (very low probably scenario because of ratio of arable land in the

catchment but modelled as extremely positive alternative)

Channels and their roughness have been unchanged for these 4 scenarios.

Representation rates of concerned original land-uses in catchment can be seen for

reminding in Tab. 4.

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Tab. 4 – Land-use distribution in Höckenbach catchment

Land-use Area distribution (%)

Forest 6.4 %

Meadows and pastures 9.8%

Arable land 72.3 %

Other land 11.5 %

Total 100 %

Calculated (simulated) characteristics (runoff volume V [m 3 ] and peak discharge Q

[m 3 /s]) for individual scenarios and mentioned rainfall events can be seen in Tab. 5 and Tab.

6. Time variation of discharge is presented as hydrographs at Fig. 18 and Fig. 19.

Tab. 5 – Simulation results of land-use scenarios

LU0 LU1 LU2 LU3

Scenarios

/

Precipitation

depth (mm)

Q max

(m 3 /s)

Time of

peak

(hrs:min)

Outflow

volume

(m 3 )

Q max

(m 3 /s)

Time of

peak

(hrs:min)

Outflow

volume

(m 3 )

Q max

(m 3 /s)

Time of

peak

(hrs:min)

Outflow

volume

(m 3 )

Q max

(m 3 /s)

Time of

peak

(hrs:min)

Outflow

volume

(m 3 )

70 20.63 2:05 262282 19.96 2:05 255799 27.00 2:00 318854 15.62 2:10 213532

60 15.85 2:05 199561 15.23 2:05 194002 21.30 2:00 249615 11.60 2:15 157518

50 11.32 2:10 141304 10.83 2:10 136502 15.81 2:00 183677 7.94 2:15 106606

40 7.24 2:10 88772 6.85 2:10 84930 10.67 2:05 122444 4.71 2:15 62380

30 3.74 2:10 44520 3.46 2:10 41875 6.08 2:05 68089 2.12 2:20 27232

Tab. 6 – Simulation results of land-use scenarios – changes comparison to LU0 in %

Scenarios

/

Precipitation

depth (mm)

Q max

(m 3 /s)

Difference

of Q max

(%)

LU0 LU1 LU2 LU3

Difference

of outflow

volume

(%)

Q max

(m 3 /s)

Difference

of Q max

(%)

Difference

of outflow

volume

(%)

Q max

(m 3 /s)

Difference

of Q max

(%)

Difference

of outflow

volume

(%)

Q max

(m 3 /s)

Difference

of Q max

(%)

Difference

of outflow

volume

(%)

70 20.63 - - 19.96 -3% -2% 27.00 31% 22% 15.62 -24% -19%

60 15.85 - - 15.23 -4% -3% 21.30 34% 25% 11.60 -27% -21%

50 11.32 - - 10.83 -4% -3% 15.81 40% 30% 7.94 -30% -25%

40 7.24 - - 6.85 -5% -4% 10.67 47% 38% 4.71 -35% -30%

30 3.74 - - 3.46 -8% -6% 6.08 62% 53% 2.12 -43% -39%

Conclusions:

As can be seen from Tab. 5, Tab. 6, Fig. 18 and Fig. 19. both of peak discharge Q max

and runoff volume V has been influenced significantly by described scenarios. The rate of

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changes is directly connected with original land-use in the catchment. Big effect would have

been made by grassing of arable land or growing maize on every parcel.

Percentage rate is much more significant at less extreme event. Also time shift of peak

discharge is more significant in case of smaller event, but it is nearly negligible in comparison

with other scenarios.

2.1.4.1.2 Channel roughness change

The goal of the simulations was to assess the effect of channel parameters on flood

wave routing and transformation. It’s considered especially different roughness of channels

and flood-plains. It should include intensive agriculturally used or fallow flood-plain. The

primary purpose of last type of flood-plain is only just routing of runoff wave.

The channel characteristics were specified on the base of the field survey. There was

assumed trapezoidal cross-section channel and wide flood-plain for the simulations, with size

close to reality. For channel roughness changes n k and flood-plain roughness n i following

scenarios were modelled:

• R1

n k = 0,03 (natural small stream, straight clean channel),

n i =0,05 (flood-plain covered by sparse trees and bushes, dense weed)

• R2

n k = 0,05 (natural small stream, with meanders and deep pools and stones),

n i =0,1 (flood-plain – medium to high density of trees and bushes in summer conditions or

dense forest with high trees)

• R3

n k = 0,02 (open profile, concrete channel)

n i =0,03 (flood-plain - pastures without trees or bushes)

In Tab. 7 there are summarized the simulated runoff hydrographs and peak flow times

of all precipitations. There is an overview of time peak differences between individual

scenarios and the real one in tabular form (Tab. 8). Hydrographs for precipitations of depths

30 and 70 mm are presented on Fig. 20. Next graph (Fig. 21) represents result hydrographs of

similar scenarios from Blinka catchment. It means catchment where concentrated channel

flow is much longer and then routing could be more significant (even 1 hour).

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Tab. 7 – Simulation results of channel roughness scenarios

R1 = LU0 R2 R3

Scenarios

/

Precipitatio

n depth

(mm)

Q max

(m 3 /s)

Time of

peak

(hrs:min)

Outflow

volume

(m 3 )

Q max

(m 3 /s)

Time of

peak

(hrs:min)

Outflow

volume

(m 3 )

Q max

(m 3 /s)

Time of

peak

(hrs:min)

Outflow

volume

(m 3 )

70 20.63 2:05 262282 20.41 2:00 262180 20.94 2:10 262316

60 15.85 2:05 199561 15.69 2:05 199507 16.09 2:15 199620

50 11.32 2:10 141304 11.24 2:05 141175 11.55 2:15 141322

40 7.24 2:10 88772 7.17 2:05 88699 7.38 2:15 88834

30 3.74 2:10 44520 3.69 2:10 44547 3.80 2:15 44577

Tab. 8 – Simulation results of channel roughness scenarios – changes comparison to R1 in %

Scenarios

/

Precipitation

depth (mm)

Time of

peak

(hrs:min)

R1 = LU0 R2 R3

Time of

peak

shift from

R1

(hrs:min)

Time of

peak

(hrs:min)

Time of

peak

shift from

R1

(hrs:min)

Time of

peak

(hrs:min)

Time of

peak

shift from

R1

(hrs:min)

70 2:05 - 2:00 -0:05 2:10 0:05

60 2:05 - 2:05 0:00 2:15 0:10

50 2:10 - 2:05 -0:05 2:15 0:05

40 2:10 - 2:05 -0:05 2:15 0:05

30 2:10 - 2:10 0:00 2:15 0:05

Conclusions:

Channel roughness change has major effect on time shift of peak flow, as it is

documented in Tab. 7 and Tab. 8. Time shifts are more significant at less extreme event that

follows results of other studies. It doesn’t play such a big part in this case because of short

channel length (ca 2.5 km) unlike Blinka catchment (Fig. 21). The reduction effect of peak

flow rate is unimportant in both cases.

2.1.4.1.3 Change of channel cross-section area and change of flood-plain roughness

This case concerns mainly simulations of changes in cross-section area. Three channel

sizes were taken into account; it should represent trends of enlarging or decreasing channel

capacity. Trapezoidal channel cross-section of real size with wide flood-plain area has been

set as the primary state for simulation. There were following scenarios simulated:

• Cross-section area (in total 2 different profiles around whole catchment Chapter

2.1.2.3.6):

14


• Real cross-section (measured in the field) (Ch1)

• Doubled channel width and depth in comparison with original one (Ch2)

• Channel width and depth, reduced to ½ in comparison with real state (Ch3)

Following Manning roughness coefficients for channels and flood-plains were

considered:

• channel n k = 0.03 (natural small stream, straight clean channel),

• flood-plain n i =0.05 (flood-plain covered by sparse trees and bushes, dense weed)

In addition of that situation of small rough (rehabilitated) channel and rough

(overgrown) flood-plain (Ch3_R3) were simulated,

Channel roughness n k and flood-plain area n i :

n k = 0.05 for channel, n i = 0.100 in flood-plains (R3).

Time of peak results and their comparison are summarized in Tab. 9 and Tab. 10.

Hydrographs of causal precipitation (30 a 70 mm depths) can be seen on Fig. 22. On the next

picture (Fig. 23) there are hydrographs from Blinka catchment where similar scenarios were

simulated.

Tab. 9 – Simulation results of channel size scenarios

Scenarios

/

Precipitatio

n depth

(mm)

Q max

(m 3 /s)

Ch1 = LU0 Ch2 Ch3 Ch3_R3

Time of

peak

(hrs:min)

Outflow

volume

(m 3 )

Q max

(m 3 /s)

Time of

peak

(hrs:min)

Outflow

volume

(m 3 )

Q max

(m 3 /s)

Time of

peak

(hrs:mi

n)

Outflow

volume

(m 3 )

Q max

(m 3 /s)

Time of

peak

(hrs:min)

Outflow

volume

(m 3 )

70 20.63 2:05 262282 20.37 2:00 262273 20.73 2:05 262273 20.97 2:15 262235

60 15.85 2:05 199561 15.68 2:05 199631 15.94 2:10 199540 16.15 2:15 199528

50 11.32 2:10 141304 11.27 2:05 141305 11.45 2:10 141216 11.55 2:20 141211

40 7.24 2:10 88772 7.19 2:05 88830 7.32 2:10 88743 7.40 2:20 88766

30 3.74 2:10 44520 3.73 2:10 44536 3.77 2:15 44523 3.82 2:25 44573

Tab. 10 – Simulation results of channel size scenarios – changes comparison to Ch1 in %

Ch1 = LU0 Ch2 Ch3 Ch3_R3

Scenarios

/

Precipitation

depth (mm)

Time of peak

(hrs:min)

Time of

peak shift

(hrs:min)

from R1

Time of

peak

(hrs:min)

Time of

peak shift

(hrs:min)

from R1

Time of

peak

(hrs:min)

Time of

peak shift

(hrs:min)

from R1

Time of

peak

(hrs:min)

Time of

peak shift

(hrs:min)

from R1

70 2:05 - 2:00 -0:05 2:05 0:00 2:15 0:10

60 2:05 - 2:05 0:00 2:10 0:05 2:15 0:10

50 2:10 - 2:05 -0:05 2:10 0:00 2:20 0:10

40 2:10 - 2:05 -0:05 2:10 0:00 2:20 0:10

30 2:10 - 2:10 0:00 2:15 0:05 2:25 0:15

15


Conclusions:

By the same reason as in previous scenario (short channel length) the results show that

channel size changes have negligible influence on both peak of discharge and time of peak. In

case of Blinka catchment the results were more significant and important (Fig. 23). There

were differences of peak flow even 50 minutes to the real state, in case of small rough channel

even 3 hours. More important time shift of peak could be observed for smaller rainfall events

there. There can be very well seen that time shift of the peak flow due to changes in surface

runoff is significant for smaller channels, where inundated area is flooded more often and

earlier.

2.1.4.2 Results for all design rainfall events and conclusions

For all other design rainfall events (with the total depths 40, 50 and 60 mm), the same

scenarios have been simulated. All results are then presented in the form of general summary

graphs – 2 types. It has been focused on peak of discharge and its time. The graphs have the

same time interval 1:50 – 2:30 for the reason of time shift importance of discharge peaks. By

contrast and other knowledge summary graphs from Blinka catchment can be seen, too.

An overview of all alternatives, corresponding with legend of graphs is listed bellow:

Land-use change

Höckenbach

• LU0 - Real land-use - state from June 2005

• LU1 - maize replaced by small grain

• LU2 - all arable land is covered by maize

• LU3 - grassing of arable land – meadows

Blinka

• LU01 – real

• LU02 – meadows changed into arable land

• LU03 – grassing of arable land – meadows

• LU04 – afforestation of arable land and pastures and meadows – forest

Channel roughness changes

Höckenbach

• R1 - real

• R2 - rough

• R3 - smooth

Blinka

• D1 – real

16


• D2 – rough flood-plain

• D3 – smooth flood-plain

• D4 – rough channel

• D5 – smooth channel

Change of channel cross-section area and change of flood-plain roughness

Höckenbach

Blinka

• Ch1 – real,

• Ch2 – double sized,

• Ch3 – half size,

• Ch3_ R3 – half size and rough flood-plain

• K1 – real,

• K2 – double sized,

• K3 – half size,

• K3_D6 – half size and rough channel and flood-plain

2.1.4.2.1 Summary graphs – All scenarios

The first type of summary graphs is aimed to mutual comparison between all scenarios

for individual precipitations. So there is one graph for an individual precipitation event.

Peaks of discharge and its time are represented. Every set of scenarios is colourfully

connected in the graph. Summary graphs from Höckenbach catchment are on Fig. 24 - Fig. 28

and from Blinka catchment on Fig. 29 - Fig. 31.

Conclusions:

Expected influence and its trends are not very apparent from Höckenbach simulation

results. It’s caused particularly by small size of the catchment and short length of routing

channel. Following conclusions are especially evaluation of Blinka results that are more

significant.

From result comparison peak flow and its time of all scenarios (Fig. 24 - Fig. 31)

follows:

o knowledge of previous chapters is confirmed

o there is more important effect on peak flow rate and total volume in case of land-use

changes

o considering channel measures (changes of channel or flood-plain roughness, channel

cross-section) only time difference of peak flow is significant

o the intense precipitation the smaller time difference of peak flow in the frame of

individual scenarios – it stands for all sets of scenarios

17


o peak-flows accelerate if precipitation depth (intensity) increases (a constant time interval

in the graphs)

2.1.4.2.2 Summary graphs - Scenarios trends

The second type of summary graphs presents peaks of discharge and its time for

individual scenario sets. Values for the same precipitation were colourfully connected in the

graph. It signifies efficiency of given scenarios depending on precipitation rate. The influence

of precipitation rate on impact possibility of discharge in case of selected measures should be

apparent.

The graphs of land-use changes scenarios can be seen on the Fig. 32 and Fig. 33. The

lower precipitation, the smaller is difference in peaks of discharge from absolute point of

view but the bigger from relative point of view. The variance of peak flow times is also

decreasing with lower precipitation rate. The meaning of graph trends is evident; only results

of 2-years precipitation in Blinka catchment are defying. In this case discharges are too low

for routing simulation then the results can be misrepresented.

The trends of channel roughness changes are demonstrated on the graphs Fig. 34 and

Fig. 35. The results are influenced by channel roughness changes markedly in case of lower

precipitation. That concerns especially the time difference of individual peaks. From Blinka

results it is possible to trace that individual roughness scenarios are mutually shifting, because

their influences take effect for different discharges. For example peaks of smooth flood-plain

scenario (D3) are lagging against other scenarios with lower precipitation, while peaks of

smooth channel (D5) are getting sooner. It is similar for scenarios of rough flood-plain (D2)

or rough channel (D4). It is caused by water elevation for given discharges, specifically

wetted perimeter of the channel and the flood-plain.

Graph of cross-section changes scenarios can be seen on the Fig. 36 - Fig. 37. The

results show that, like in previous case, influence of channel size increases with smaller

precipitation, especially influence on time of peak. In this case it could be said that there is no

such a big mutual shifts as in previous case. Scenarios of small channel and rough flood-plain

(Ch3_ R3 or K3_D6) have the biggest routing effect. It is caused by early bursting the banks

and slowing down the runoff by rough flood-plain.

2.1.5 Reichstädter Bach catchment

Beside number of land-use scenarios modelling (Part III.) and some measures in

channels (Part IV.) technical measures influence was simulated too in Reichstädter Bach

catchment. In this case technical measures like dry reservoir (or polder) were considered. Its

influence on channel outflow is described in follow chapters. Computations were done in

hydrologic interface WMS 7.1. New outlet was incorporated into already working model of

watershed. This outlet should interpret given reservoir.

2.1.5.1 Location of the polder

The closer is the polder to protected place, the more effective is. Big part of outflow

from subcatchment is then managed. The aim was to locate the polder above the bigger part

of municipality Reichstädt in this case. It wasn’t easy to select an available place because of

following reasons. Mentioned village lies along the river as far 3.5 kilometres from the outlet

18


point of the catchment. A road is leaded near and parallel to the stream. The valley where the

stream flows has relatively steep side slopes. Options to locate the polder were very limited

because of these conditions. Adjacent road limited height of the dam and buildings confined

the possibly flooded area. Finally a locality that lies 2 km from the outlet point (elevation

402 m) was chosen. You can see the situation on Fig. 38 - Fig. 40.

2.1.5.2 Polder characteristics

The aim of this research was not the detailed solution of the body of dam, all

structures or technology etc. The possibility of placing the reservoir, its efficiency and the

influence of main reservoir characteristic on outflow hydrograph was researched. Considered

were these main characteristics of the polder: height of the dam, outlets, spillway and

reservoir volume.

Adjacent road limited height of the dam so it could be only 3 m high. Elevation of the

dam bottom is 401.85. The top of the dam is in 404.85 m a.s.l.

Circular outlet pipe was placed in the heel of the dam. Interior diameter was estimated

1.5 m that corresponds to discharge 6 m 3 /s if the water level is 3 meters above the outlet pipe

or This design was just first estimation. In reality more pipes of smaller diameters but similar

discharges would have placed there (even 3 pipes DN 1000 – 7.5 m 3 /s - the water level

2.5 m). The channel downstream has capacity ca 8 m 3 /s.

The spillway is in elevation 403.85 m, it means 1 meter under the top of the dam. Its

width is 10 meters and transfers (together with the outlet pipe) Q = 10.7 m 3 /s. Higher

discharge would go over the dam. It means if higher discharges are expected, the spillway

should be wider, even entire crest of the dam. From computation point of view there is no

problem that outflow is going over because what comes in, goes out. It would be similar if the

spillway was wider.

The reservoir volume – elevation curve was created automatically by WMS from

digital elevation model in the form of TIN. Area of flooded zone if water level is 3 m above

the dam heel is 7000 m 2 according to manual estimation from the map. Computed volume

appeared very small. The first reason is that the valley is too steep and the second is that given

digital terrain model is too rough to estimate volume of the reservoir even if it is accurate

enough to describe surface of the catchment. It could be considered that this volume is the

minimal in this locality. The height of dam is the other limiting condition. Polder

characteristics are following:

‣ Height of the dam – 3 m

‣ Heel of dam elevation – 401.847 m a.s.l.

‣ Crest of the dam elevation – 404.847 m a.s.l.

‣ Spillway elevation – 403.847 m a.s.l.

‣ Bottom outlet DN 1500

‣ Spillway length – 10 m

‣ Discharge if water level is 3 m – 10,68 m 3 /s

‣ Volume according to scenarios (see below)

19


These scenarios were considered:

‣ P0 – no reservoir

‣ P1 – reservoir whose volume is according TIN – minimal volume – V min

‣ P2 – reservoir whose volume is 3x V min

‣ P3 – reservoir whose volume is 10x V min

P2 should represent reservoir whose volume could be the maximal volume in reality. It

is possible if consider inaccuracy TIN and examples from other studies. It could be expected

that after accurate survey and possible terrain adjustment could be reached this volume in

reality.

P3 represents polder whose volume corresponds to reservoir with dam height 5 m and

volume 3x V min . This approach is very simplified but good for knowledge. It may be taken as

a hypothetical positive scenario. It was proceeded to make this scenario when no big effect for

higher discharge was shown in previous cases.

Elevation-discharge curve and volume-elevation curves of all scenarios could be seen

on the Fig. 41.

2.1.5.3 Results of calculations and conclusions

Simulation results are arranged into 2 tables (Tab. 11, Tab. 12) and 4 hydrographs

from point of reservoirs and 4 hydrographs from outlet point of the Reichstädter Bach

catchment. In the first table there are result peaks and its time, while the second table is

comparative and the values are compared with zero scenario P0 (no polder). Hydrographs

project polder routing of outflow wave caused by precipitations of 30, 50, 70 or 100 mm

depth. It can be seen on the Fig. 42 - Fig. 49.

Tab. 11 – Results of flood wave routing (transformation) by water reservoirs in point of

polder

Scenarios

/

Precipitation

depth (mm)

Q max

(m 3 /s)

P0 P1 P2 P3

Time of

peak

(hrs:min)

Q max

(m 3 /s)

Time of

peak

(hrs:min)

Q max

(m 3 /s)

Time of

peak

(hrs:min)

Q max

(m 3 /s)

Time of

peak

(hrs:min)

20 1.3 2:15 1.3 2:30 1.2 2:30 0.9 3:00

30 6.1 2:00 5.5 2:30 4.6 2:30 3.5 3:00

40 13.3 2:00 13.1 2:00 11.5 2:15 5.9 3:00

50 22.1 2:00 21.5 2:00 20.0 2:15 12.5 2:45

60 31.9 2:00 31.5 2:00 29.3 2:15 19.6 2:45

70 42.4 2:00 42.1 2:00 39.2 2:15 27.1 2:45

80 53.5 2:00 53.4 2:00 49.7 2:15 34.9 2:45

90 65.1 2:00 65.1 2:00 60.5 2:15 43.2 2:30

100 77.0 2:00 77.0 2:00 71.6 2:15 51.8 2:30

20


Tab. 12 – Differences of peaks of discharge for scenarios of polder routing P1, P2, P3 in

contrast to P0

Scenarios

/

Precipitation

depth (mm)

Q max

(m 3 /s)

P0 P1 P2 P3

Time of

peak

(hrs:min)

Decreasing

of Q max (%)

Time of

peak lag

(hrs:min)

Decreasing

of Q max (%)

Time of

peak lag

(hrs:min)

Decreasing

of Q max (%)

Time of

peak lag

(hrs:min)

20 1.3 2:15 3.6% 0:15 10.5% 0:15 31.3% 0:45

30 6.1 2:00 10.1% 0:30 23.5% 0:30 42.9% 1:00

40 13.3 2:00 1.3% 0:00 13.7% 0:15 55.2% 1:00

50 22.1 2:00 2.5% 0:00 9.4% 0:15 43.5% 0:45

60 31.9 2:00 1.3% 0:00 8.1% 0:15 38.4% 0:45

70 42.4 2:00 0.7% 0:00 7.6% 0:15 36.2% 0:45

80 53.5 2:00 0.3% 0:00 7.3% 0:15 34.8% 0:45

90 65.1 2:00 0.0% 0:00 7.1% 0:15 33.6% 0:30

100 77.0 2:00 0.0% 0:00 6.9% 0:15 32.6% 0:30

Results of the simulation for mostly all rainfall events approve, that reservoirs have

not very big impact of flood wave transformation, as volume of their retention capacity is

mostly not big enough and all free space is filled far before peak flow comes.

Specifically polder P1 (volume derived from TIN) is totally insufficient and its routing

effect is zero in almost all cases. Polder P2 (that could be considered the real) had also no

significant impact on runoff routing. Only polder P3 (its volume is corresponding to 10 x

volume of P1 or 3.3 x volume of P2 or volume like P2 but height of the dam ca 5 m) had

significant effect on runoffs especially the higher in contrast to the other scenarios.

Based on the results it could be claimed that polders P1 and P2 have too low efficiency

to realize them. Polder P3 has relatively positive influence on flood runoffs and its efficiency

could be even higher if bottom outlets had higher capacity. But because of terrain conditions

and other limitations would be very demanding to build a reservoir with such a big volume.

The reservoirs design should be of course optimized and there should be mentioned,

that presented scenarios are only very small example of nearly infinitive number of

alternatives and should only present how the model is able to handle water reservoirs.

2.2 Hydraulic modelling using HEC-RAS

The second approach concerned open channel flow modelling using hydraulic model

HEC-RAS. Number of scenarios relating to influence of channel and flood-plain modification

on flood wave routing were simulated. Methodology, computations, results and conclusions

will be presented in this section.

21


2.2.1 Description of applied Methodology

The applied method consists of modelling unsteady flow through the model river

reach. A lot of variants of the model river reach were designed. After the simulation hydraulic

variables were calculated and compared to each other. A mathematical model named HEC-

RAS was used for the simulation. In this part of the Emtal project a real river reach was not

used. The computations were performed by the model river reach and a flood-plain which

correspond to real rivers. During the simulations values of following parameters were

modified: dimensions of the stream-channel, stream-channel roughness, longitudinal slope of

the river bed and of the flood-plain and varied flood-plain land-use. An overview of used

scenarios, which combine different stream-channels, longitudinal slopes and so on, can be

seen in Tab. 14.

2.2.1.1 Cross-section of stream-channel

When doing water flow simulations two basic cross-section shapes were used for

stream cross-section. These two shapes should represent a regulated stream-channel and a

natural or rehabilitated stream-channel. A rectangle was used for the natural (rehabilitated)

stream and a trapezium for the regulated stream.

Trapezoidal cross-section has been nearly always used for stream regulation. A bed

length was between 0.6 m and 1.5 m, channel depth between 1.0 m and 1.5 m, and bank slope

between 1:1.5 and 1:1.75. A typical example of the stream training can be seen in the Fig. 50.

Therefore the trapezium cross-section was used for water flow simulations. Bed width was

1.2 m, channel depth was 1.2 m and bank slope was 1:1,75. All of these three variables were

constant.

A natural stream has often a rectangular cross-section. A width of the stream bed

varies from 1 – 3 m and channel depth is small. A typical example of the natural stream can

be seen in the Fig. 51. Therefore the rectangular cross-section was used for water flow

simulations. The bed width of the rectangular cross-section was 2.0 m and channel depth was

0.4 m.

2.2.1.2 Stream-channel line

The stream-channel line of natural streams is very variable and varies from straight

channel-line to meandering channel-line. However the meandering stream-channel line occurs

rarely for small streams in the central Europe. Therefore following three basic shapes (see

Fig. 52) of stream-channel line were used in the HEC-RAS simulation:

• fully straight stream-channel line,

• curved stream-channel line, ratio of the stream-channel line and the straight line

(sinuosity) is equal 1.25,

• “winding” stream-channel line, ratio of the stream-channel line and the straight line

(sinuosity) is equal 1.50.

22


2.2.1.3 Longitudinal slope of stream-channel line

Longitudinal slope of the stream-channel line is dependent on the sinuosity of the

stream-channel line and the longitudinal slope of the flood-plain. When doing water flow

simulations two values of the longitudinal slope of the flood-plain were used and these are

1.0 % and 3 %. Owing to sinuosity of the stream-channel-line (see chapter 2.2.1.2 and Fig.

52) the final longitudinal slopes of the stream-channel line was lower than the slope of the

flood-plain. The final slopes of the stream-channel-line range from 0.68 % to 2.0 % (see Tab.

13). These values are usual for wide range of streams (Ehrlich, 1992).

Tab. 13 – Used Longitudinal slope of stream-channel line depending on the sinuosity and

longitudinal slope of stream-channel line

Longitudinal slope of flood-plain

[%]

Sinuosity

[m/m]

Longitudinal slope of streamchannel

line

[%]

1.0

3.0

1.00 1.00

1.25 0.80

1.50 0.68

1.00 3.00

1.25 2.40

1.50 2.00

2.2.1.4 Flood-plain cross-section

When floods occur the water overflows banks and a lot of the discharge convey

through the flood-plain. Therefore a shape of the flood-plain is very important in light of

spring flood transformation. For example the flood-plain, which has narrow V shape, will

transform the peak flow certainly less than the flood-plain which has wide U shape. Therefore

the flood-plain, which has rectangular shape, was used in the simulation. Width of the used

flood-plain was 50 meters, transversal slope was zero and flood-plain sides were vertical. The

shape of the used flood-plain (see Fig. 53) was throughout the simulation the same.

2.2.1.5 Bed material and flood-plain cover, Manning’s roughness coefficients

Before water flow simulation can be performed the Manning’s roughness of the

stream-channel and the flood-plain have to be entered. The stream-channel roughness is

influenced by materials which make stream-channel bed and sides. Usually values of the

stream-channel roughness are from 0.015 (for concrete bed) to 0.060 (natural stream bed),

rarely to 0.150 (heavily weedy river reach with deep pools, temporary flood stream-channel

with trees and bushes). The flood-plain roughness is influenced by flood-plain land-use.

Usually values of the flood-plain roughness are from 0.025 for grass stand to 0.200 for

willows. Recommended Manning’s roughness can by found in a technical literature (Havlík,

1988).

Doing water flow simulation following values of Manning’s roughness were set to:

• 0.025, 0.1 and 0.7 for the trapezoidal stream-channel,

23


• 0.035, 0.1 and 0.7 for the rectangular stream-channel,

• and 0.7 for flood-plain.

Doing water flow simulation the value of Manning’s roughness was also set to 0.7.

The value 0.7 is unreal nevertheless was used because to estimating an influence of the high

value of Manning’s roughness to the spring flood transformation.

2.2.1.6 Calculation variants

The final number of calculation variants ensued from the combination of streamchannel

cross-sections, flood-plain cross-sections and longitudinal slope of the stream. The

total numbers of calculated variants were then 72. A summary of the calculation variants can

be seen in Tab. 14.

Tab. 14 – Summary of the calculation variants; in total 72 variants

STREAM-CHANNEL

Cross-section and

Manning’s roughness

Longitudinal

slope [%]

Cross-section

FLOOD-PLAIN

Manning’s

roughness

STREAM- CHANNEL LINE

1.0

n = 0.1

sinuosity =

1.0 m/m

sinuosity =

1.25 m/m

sinuosity =

1.50 m/m

n = 0.035

n = 0.100

n = 0.700

3.0

+

flat flood-plain

n = 0.7

+

1 : 1,75

1.0

n = 0.1

n = 0.025

n = 0.100

n = 0.700

3.0

+

flat flood-plain

n = 0.7

2.2.2 HEC-RAS simulation

A one dimensional mathematical model named HEC-RAS (Hydrologic Engineering

Centers River Analysis System) was chosen for the flow simulations. A detailed description

of the HEC-RAS can be found in the EMTAL report – part IV. Inputs, simulation processes

and outputs choosing will be described in this and following chapters.

The HEC-RAS computation proceeds in a few steps. Fist geometric data of a river

reach and of a flood-plain including Manning’s roughness coefficients have to be entered.

Second flow data and boundary condition has to be entered. During the second step the flow

computation regime should be selected. After that it is possible to make a plan in which the

geometric data and the flow data can be combined each other. Then the simulation can be

24


started. After the model has finished the flow computation outputs can be displayed in

graphical or tabular form.

2.2.2.1 Geometric data

The model river reach was chosen for the water flow simulation. A length of the

model river reach was 1000 m and a width of the flood-plain was 50 m. A river and a floodplain

morphology were entered by the 101 cross-sections (see Tab. 14). Distance between

contiguous cross-sections was from 10 m to 15 m in dependence on river sinuosity. When the

river sinuosity was higher than 1.0, the straight distance between the start ant the end of the

river reach was still 1000 m. The cross-sections were numbered from the downstream to the

upstream, from the zero to the 100.

Manning’s roughness coefficient equal to 0.025 was entered for the trapezoidal steam

cross-section. This value of Manning’s roughness is usual for stone pavement. For a

rehabilitated stream with the rectangular cross-section Manning’s roughness coefficient equal

to 0.035 was used. This value of Manning’s roughness is usual for natural stream with gravel

bed. In addition the values of Manning’s roughness 0.1 and 0,7 were used for both types

(natural and regulated) of the cross-sections. When the value 0.1 was used the spring flood

transformation was negligible. Therefore the value 0.7 was used although it is unreal value.

Nevertheless was used because to estimating an influence of the high value of Manning’s

roughness to the spring flood transformation.

For the flood-plain the Manning’s roughness values was set to 0.1. The value of the

Manning’s roughness was constant in the horizontal and vertical direction. This value of

Manning’s roughness is usual for flood-plain overgrown with few hushes. Analogous to

stream-channel cross-section also for the flood-plain the value 0.7 was used although it is

unreal value. Nevertheless was used because to estimating an influence of the high value of

Manning’s roughness to the spring flood transformation

2.2.2.2 Flow data and boundary conditions

The unsteady flow computation was chosen to perform flow simulation through the

model rive reach. Boundary conditions and an initial flow are required in the unsteady flow

module.

In the upstream (cross-section number 100) a flow hydrograph was chosen as a

boundary condition. The boundary condition hydrographs were taken from others flood

protection studies which have been worked up by authors of this report. These flood

protection studies were worked up on the catchments which have similar areas as the

catchments researched in the EMTAL project – part III and IV. Basic parameters of the used

hydrographs are shown in Tab. 15.

Tab. 15 – Basic parameters of the used hydrographs

Return period [year] 1 2 5 10 20 50 100

Peak discharge of flow

hydrograph

Volume of flow

hydrograph

[m 3 .s -1 ] 3.89 5.61 8.13 10.18 12.30 15.45 18.26

[m 3 .s -1 ] 40 858 58 065 82 005 102 915 123 347 154 586 180 600

25


In the downstream (cross-section number 0) “normal depth” was chosen as a boundary

condition. Normal depth is the slope of the energy level. The slope of the energy level was

approximated by stream bed slope or by slope of the flood-plain. (See Tab. 13). This

approximation simulates that the water level is parallel to the bed level.

Initial flow for all variants of the calculation was set to 0.1 m 3 .s -1 .

2.2.2.3 Calculation and choice of outputs

Once all of the geometric data and unsteady flow data have been entered, the

calculation plan can bee set out. The plan defines which geometry and flow date are to be

used, flow regime and how long a computing interval should be. The geometric and flow data

are described in the chapters 2.2.2.1 and 2.2.2.2. The computation interval was always 1

second. The mixed flow regime was selected for all simulations plans. After the model has

finished the flow computation results can bee seen in graphical and tabular format.

Modelling software HEC-RAS is capable to compute 255 variables. From the point of

view of the spring flood transformation only some of the variables are important. Therefore

only a few following variables were chosen as tabular outputs:

• Peak discharge,

• Time of a critical flood flow,

• Time lag of the critical flood flow time.

Chosen variables (see above) were evaluated at the downstream end of the model river

reach – at the cross-section No. 0.

HEC-RAS is capable to product a lot of graphical plots: river cross-sections with

marks of water level, energy grade level and critical depth, river profiles with the same marks,

rating curves of the cross-sections, and X-Y-Z perspective plot. The graphical plots are very

well-arranged but an accuracy of reading the level elevations is not to high. Therefore only

tabular outputs were used for an evaluation of the simulation results. Then graphs were built

up from the tabular outputs.

2.2.3 Modelling results

In the methodology 72 variants of calculation have been proposed. The calculations

were performed in the model river reach. The length was 1000 meters. The variants included

different shapes of a stream-channel, different stream sinuosity, and different Manning’s

roughness of the stream-channel and the flood-plain. Two longitudinal slopes (1 % and 3 %)

of the flood-plain were proposed. However during the computations it comes in sight that the

slope value of 3 % is too high to keep the computations stable. Therefore the variant in which

the value of slope was 3 % could not be simulated. Therefore only 32 variants can be

simulated. The influence of the change of longitudinal slope cannot be evaluated. However

the influence of the change of longitudinal slope has been researched in others studies (Vrána,

2006) and therefore the influence of the slope could be in a certain manner estimated.

Finally 32 calculation variants of unsteady flow were performed. The computation

results were processed to tabular form. The whole table is too big that it was not possible to

26


attach it to the report. Therefore only part of the table was printed out and attached (see Tab.

16). All tabular outputs are stored by authors ant there are available.

In the following text there are the comments to the modelling results for selected

flows:Q 5 , Q 20 , and Q 100 . These comments ensued from tabular and graphical outputs (see

Tab. 16 and Fig. 54 - Fig. 56) of this report and from knowledge which have been researched

in others projects (Vrána, 2006).

2.2.3.1 Results for Q 5

The influence of the sinuosity enhancement and the influence of the changes of the

cross-section shape, while the longitudinal slope is a constant (1 %), on the peak flow

decreasing is very small. When the real value of Manning’s roughness (it means n = 0.025 –

0.1 for the stream-channel, and n = 0.06 – 0.2 for the flood-plain) have been used, the peak

flow decreased by up to 2 %. When the unreal value of Manning’s roughness (it means n =

0.7) have been used, the peak flow decreased by up to 14 %.

By contrast the increasing the flood-plain roughness or the stream-channel roughness

has a high influence on the critical flood flow. The influence depends on a stream-channel

capacity.

Because a channel of the regulated stream is highly capacitive, discharge with return

period equals 5 years will not overflow. Therefore the flood-plain roughness has no influence

and the stream-channel capacity has high influence. When the value of Manning’s roughness

increase from 0.035 to 0.1 the time of critical flood flow extend by 20 minutes.

Because the channel of rehabilitated stream has low capacity discharge with return

period equal 5 years will overflow. Therefore the flood-plain roughness has very high

influence on a shift of the critical flood flow. When the value of Manning’s roughness

increase from 0.1 to 0.7 the time of critical flood flow extend by 27 minutes.

2.2.3.2 Results for Q 20

The influence of change of the stream or flood-plain geometry and the influence of

change of Manning’s roughness is for Q 20 similar toQ 5 .

When the real values of the roughness are using the sinuosity enhancement from 1.0 to

1.5 has no influence on peak discharge decreasing.

By contrast the flood-plain roughness has high influence on time of the critical flood

flow. When the value of flood-plain roughness of rehabilitated stream increase from 0.04

(grass-grown flood-plain) to 0.1 (scrubby flood-plain) the time of critical flood flow extend

by for about 50 %. When the roughness values increase from 0.1 to 0.7 the time of critical

flood flow extend two times. The situation for the Q 20 is similar to situation for Q 5 .

2.2.3.3 Results for Q 100

When the real values of the Manning’s roughness are used changes of the stream

sinuosity from 1.0 to 1.5 do not cause peak discharge changes. This is caused because during

the flood most of the water flows through the flood-plain without regardless of the stream

sinuosity.

27


For discharge with return period 100 years changes of flood-plain land-use has high

influence on a shift of critical flood flow. When the value of flood-plain roughness of

rehabilitated stream increase from 0.04 (grass-grown flood-plain) to 0.1 (scrubby flood-plain)

the time of critical flood flow extend by for about 42 %. When the roughness values increase

from 0.1 to 0.7 the time of critical flood flow extend by 150 %. When the value of flood-plain

roughness of regulated stream increase from 0.04 (grass-grown flood-plain) to 0.1 (scrubby

flood-plain) the time of critical flood flow extend by for about 35 %.

3. Conclusions

This conclusion confirms fact, that the floods existed always – mainly those disastrous

ones, which are subject of many discussions nowadays. It is very difficult to protect ourselves

against extreme flood and nearly the only way is either technical protection, including

retention storage capacities in water reservoirs and polders, increasing of water courses

channels capacity, construction of levees and so on. Such technical measures are very

sophisticated system, which always has to be assessed from point of view of possible failure

or breaking design capacity. On the other hand, there is alternative of respecting of floodplains

to be kept free and to allow the water courses flooding and damage less flood wave

routing trough flood-plain. The effect of non-technical flood control measures (like soil

conditions, land-use, landscape mosaic with acceptable proportion of the forests in good

shape, reasonable level of urbanization, good shape of stream channel and flood-plain with

possibility of flooding) is essential for smaller floods, concerning of return period and

extension. Therefore probably higher frequency of such smaller floods (concerning of both of

area and periodicity) in last years can be count to land-use changes.

Both attitudes have leaded to similar inferences. Based on number of simulations

provided, there is possible to formulate following general conclusions:

1. Proposed and used methodology for impact assessment of stream restoration on runoff

characteristics is appropriate and applicable to solving this problem.

2. Significant land-use change affects both of peak discharge and total runoff volume. This

measure is the most important (has the biggest effect) from all tested non-technical

measures. Relative effect nevertheless decreases with increasing externality rainfall

event.

3. Change of channel roughness affects mainly peak of discharge time shift (wave

transformation), the effect on total peak of discharge is negligible.

4. After stream rehabilitation the capacity of channel significantly decreases and the stream

velocity in the channel, too. It has positive influence on rehabilitated channel stability

during high discharges.

5. Remarkable time shift of peak discharge can be reached by water overflowing into

flood-plain areas, especially, if they have high roughness, what correspond mainly with

dense wooden type of vegetation. The effect of weed (plants) in the flood-plain is not

very big; as this vegetation will beat down and resulting roughness can be even lower.

Stream velocity significantly decreases in this case. The importance of flood-plain

characteristics increase with decreasing channel capacity. It corresponds with the fact,

that flood discharge will leave the channel earlier and then parameters of flood-plain can

be fully applied earlier, too.

28


6. Shape of flood-plain has negligible influence on channel flow.

7. Lengthening of stream channels has no influence on flood discharge because almost all

water goes through flood-plain without regard to channel rout.

8. Routing by channels is more significant if the channel in the catchment is longer. The

roughness takes its influence then. Oblong catchments have bigger routing by channel

than frond-shaped catchments.

9. Example of dry reservoirs implementation presented potential and also reserves in

affecting flood discharges by this type of measures. This type of measures nevertheless

requires more detailed theoretical analysis of general principles and relations.

10. There has been confirmed assumption, that the effect of flood control measures (those,

which were modelled) but mainly those non-technical ones, decrease quickly with rising

of extremity of rainfall (flood) event.

11. Generally, flooding caused by stream restoration can be applied only if there is no

danger of detriment health or property and where property rights are solved in the floodplain.

29


4. References

• Brigham Young University - Environmental Modeling Research Laboratory, 1999,

Watershed Modeling System, WMS 6.0 - Reference Manual.

• Doporučený standard technický, Hydrologické výpočty, soubor 4, č. 06, Praha 2001

• Dostál T. – David V. – Krása J. – Vrána K. – Váška J., 2003, Strukturovaný přístup

k odhadu produkce povrchového odtoku z území a předpovědní systém povodňové

ohroženosti, Vodní hospodářství 10/2003, str.269-272, 6319 ISSN 1211-0760.

• Ehrlich P. a kol., 1992, Metodika 9/1992: Prozatímní metodické pokyny pro obnovu

ekologické funkce upravených vodních toků s malým povodím. Praha: VÚMOP, 50 str.

• Havlík V. – Maršová I., 1988, Hydraulika: Příklady, ČVUT v Praze, Praha.

• Hrádek F. - Kovář P., 1994, Výpočet náhradních intenzit přívalových dešťů-metoda

redukce 1-denních maximálních srážkových úhrnů, Vodní hospodářství 11/12.

• http://www.hec.usace.army.mil/software/hec-ras/hecras-document.html

• Janeček a kol., 2002, Ochrana zemědělské půdy před erozí, ISV Praha.

• Janeček M., Váška J., 2001, Hydrologické výpočty v protierozní ochraně půdy;

Doporučený standard technický, skupina hydrologické výpočty DOS T 4/06/2001,

ČKAIT.

• Mistra S.K., Singh V.P., 2003, Soil Conservation Service Curve Number (SCS-CN)

Metodology, Kluwer Academic Publisher, Water Science and Technology Library,

Vol.42, London.

• Patera, A. - Váška, J. - Jakubíková, A. (ed.), 2003, Sborník z příspěvků z Workshopu

2003 - Extrémní hydrologické jevy v povodích, ČVUT v Praze, 332 s, ISBN 80-01-

02872-0.

• Vrána K. a kol., 2006, VaV-1D/2/20/II/04 – Vodohospodářská revitalizace a ochrana

před povodněmi, MŽP ČR, Praha.

30


5. List of figures

Fig. 1 – Aerial photo of Höckenbach catchment ........................................................................ 37

Fig. 2 – Map of land-use of Höckenbach catchment .................................................................. 38

Fig. 3 – Land-use distribution in Höckenbach catchment .......................................................... 38

Fig. 4 – Map of hydrological soil types of Höckenbach catchment ........................................... 39

Fig. 5 – Distribution of hydrological soil types in Höckenbach catchment................................ 39

Fig. 6 – Map of land-use of Reichstädter Bach catchment ......................................................... 40

Fig. 7 – Land-use distribution in Reichstädter Bach catchment ................................................. 40

Fig. 8 – Map of hydrological soil types of Reichstädter Bach catchment .................................. 41

Fig. 9 – Distribution of hydrological soil types in Reichstädter Bach catchment ...................... 41

Fig. 10 – Land-use distribution in Blinka catchment.................................................................. 42

Fig. 11 – Distribution of hydrological soil types in Blinka catchment....................................... 42

Fig. 12 – Detention Basins Dialog in WMS where Curves Storage-Capacity and Elevation-

Discharge are defined ......................................................................................................... 43

Fig. 13 – Conic Method for Volume Computations ................................................................... 43

Fig. 14 – Temporal distribution of precipitation cumulative intensity (total depth 30 – 70 mm

and time period 2 hours) ..................................................................................................... 44

Fig. 15 – Schema of topological tree – subcatchments of Höckenbach catchment.................... 44

Fig. 16 – Cross-section of channel – part S3 .............................................................................. 45

Fig. 17 – WMS 7.1 interface....................................................................................................... 45

Fig. 18 – Hydrographs of land-use changes scenarios in outlet point of Höckenbach catchment -

causal precipitations (70 mm and 30mm depth). ................................................................ 46

Fig. 19 – Hydrographs of land-use changes scenarios in outlet point of Blinka catchment -

causal precipitations (Normal values – 100 and 10 years). ................................................ 46

Fig. 20 – Hydrographs of channel roughness changes scenarios in outlet point of Höckenbach

catchment - causal precipitations (70 mm and 30mm depth). ............................................ 47

Fig. 21 – Hydrographs of channel roughness changes scenarios in outlet point of Blinka

catchment - causal precipitations (Normal values – 100 and 10 years).............................. 47

Fig. 22 – Hydrographs of channel cross-section changes scenarios in outlet point of

Höckenbach catchment - causal precipitations (70 mm and 30mm depth). ....................... 48

Fig. 23 – Hydrographs of channel cross-section changes scenarios in outlet point of Blinka

catchment - causal precipitations (Normal values – 100 and 10 years).............................. 48

Fig. 24 – Summary graph of all scenarios in case of precipitation depth 30 mm - Höckenbach.

............................................................................................................................................. 49

31


Fig. 25 – Summary graph of all scenarios in case of precipitation depth 40 mm - Höckenbach.

............................................................................................................................................. 49

Fig. 26 – Summary graph of all scenarios in case of precipitation depth úhrnem 50 mm -

Höckenbach......................................................................................................................... 50

Fig. 27 – Summary graph of all scenarios in case of precipitation depth 60 mm - Höckenbach.

............................................................................................................................................. 50

Fig. 28 – Summary graph of all scenarios in case of precipitation depth 70 mm - Höckenbach.

............................................................................................................................................. 51

Fig. 29 – Summary graph of all scenarios in case of precipitation N = 2 years - Blinka. .......... 51

Fig. 30 – Summary graph of all scenarios in case of precipitation N = 20 years - Blinka. ........ 52

Fig. 31 – Summary graph of all scenarios in case of precipitation N = 100 years - Blinka. ...... 52

Fig. 32 – Summary graph of land-use changes for all precipitation events – Höckenbach........ 53

Fig. 33 – Summary graph of land-use changes for all precipitation events – Blinka................. 53

Fig. 34 – Summary graph of channel roughness changes for all precipitation events –

Höckenbach......................................................................................................................... 54

Fig. 35 – Summary graph of channel roughness changes for all precipitation events – Blinka. 54

Fig. 36 – Summary graph of channel cross-section changes for all precipitation events –

Höckenbach......................................................................................................................... 55

Fig. 37 – Summary graph of channel cross-section changes for all precipitation events – Blinka.

............................................................................................................................................. 55

Fig. 38 – Schema of topological tree – subcatchments of Reichstädter Bach catchment........... 56

Fig. 39 – Polder position in Reichstädter Bach catchment ......................................................... 57

Fig. 40 – Polder locality – flooding if water level is 3 m ........................................................... 58

Fig. 41 – Discharge-elevation and volume-elevation curves...................................................... 58

Fig. 42 – Hydrographs of polder scenarios in polder point (precipitation 30 mm) .................... 59

Fig. 43 – Hydrographs of polder scenarios in polder point (precipitation 50 mm) .................... 59

Fig. 44 – Hydrographs of polder scenarios in polder point (precipitation 70 mm) .................... 60

Fig. 45 – Hydrographs of polder scenarios in polder point (precipitation 100 mm) .................. 60

Fig. 46 – Hydrographs of polder scenarios in outlet point (precipitation 30 mm) ..................... 61

Fig. 47 – Hydrographs of polder scenarios in outlet point (precipitation 50 mm) ..................... 61

Fig. 48 – Hydrographs of polder scenarios in outlet point (precipitation 70 mm) ..................... 62

Fig. 49 – Hydrographs of polder scenarios in outlet point (precipitation 100 mm) ................... 62

Fig. 50 – A typical regulated stream: trapezoidal shape of stream cross-section; bed and bank

foots are protected by concrete blocks................................................................................ 63

Fig. 51 – Typical natural stream: rectangular shape of stream cross-section ............................. 63

Fig. 52 – Three basic shapes of stream-channel line .................................................................. 64

32


Fig. 53 – Flood-plain cross-section used for calculation purposes............................................. 64

Fig. 54 – Hydrographs for trapezoidal river cross-section, longitudinal gradient 1.0 %, sinuosity

(length ratio) 1.0 and 1.5, Q 5 =8.13m 3 s -1 ............................................................................. 65

Fig. 55 – Hydrographs for trapezoidal river cross-section, longitudinal gradient 1.0 %, sinuosity

(length ratio) 1.0 and 1.5, Q 20 =12.25m 3 s -1 .......................................................................... 66

Fig. 56 – Hydrographs for trapezoidal river cross-section, longitudinal gradient 1.0 %, sinuosity

(length ratio) 1.0 and 1.5, Q 100 =18.26m 3 s -1 ........................................................................ 67

6. List of tables

Tab. 1 – CN catalogue used for both catchments ......................................................................... 8

Tab. 2 – Normal values of 2-hours precipitation in gauging station Weisseritz and depths used

in model ................................................................................................................................9

Tab. 3 – Basic characteristics of stream channel sections ............................................................ 9

Tab. 4 – Land-use distribution in Höckenbach catchment ......................................................... 12

Tab. 5 – Simulation results of land-use scenarios....................................................................... 12

Tab. 6 – Simulation results of land-use scenarios – changes comparison to LU0 in % ............. 12

Tab. 7 – Simulation results of channel roughness scenarios ...................................................... 14

Tab. 8 – Simulation results of channel roughness scenarios – changes comparison to R1 in % 14

Tab. 9 – Simulation results of channel size scenarios ................................................................ 15

Tab. 10 – Simulation results of channel size scenarios – changes comparison to Ch1 in %...... 15

Tab. 11 – Results of flood wave routing (transformation) by water reservoirs in point of polder

............................................................................................................................................. 20

Tab. 12 – Differences of peaks of discharge for scenarios of polder routing P1, P2, P3 in

contrast to P0....................................................................................................................... 21

Tab. 13 – Used Longitudinal slope of stream-channel line depending on the sinuosity and

longitudinal slope of stream-channel line........................................................................... 23

Tab. 14 – Summary of the calculation variants; in total 72 variants .......................................... 24

Tab. 15 – Basic parameters of the used hydrographs ................................................................. 25

Tab. 16 – Sample of HEC-RAS modelling outputs for flows with return period of 5, 20, and

100 years ............................................................................................................................. 68

33


Content

1. INTRODUCTION AND THE GOALS OF THE PROJECT.................................................... 2

2. SOLUTION METHODOLOGY.................................................................................................. 2

2.1 HYDROLOGIC MODELLING USING HEC-1 IN WMS...................................................................... 2

2.1.1 Catchments characteristics............................................................................................... 2

2.1.1.1 Höckenbach ................................................................................................................................ 2

2.1.1.2 Reichstädter Bach ....................................................................................................................... 3

2.1.1.3 Blinka ......................................................................................................................................... 3

2.1.2 Basic characteristics of applied simulation model ........................................................... 4

2.1.2.1 Applied methods for rainfall-runoff modelling........................................................................... 4

2.1.2.2 Applied method for polder routing ............................................................................................. 5

2.1.2.2.1 Hydrograph......................................................................................................................... 6

2.1.2.2.2 Storage-Capacity Curve...................................................................................................... 6

2.1.2.2.3 Elevation-Discharge Relationship ...................................................................................... 6

2.1.2.3 Input data preparation ................................................................................................................. 6

2.1.2.3.1 Digital elevation model (DEM) .......................................................................................... 7

2.1.2.3.2 Hydrological soil groups layer............................................................................................ 7

2.1.2.3.3 Stream network................................................................................................................... 7

2.1.2.3.4 Land-use map ..................................................................................................................... 7

2.1.2.3.5 Hydrological data ...............................................................................................................9

2.1.2.3.6 Channel routing inputs........................................................................................................ 9

2.1.2.4 Output data ............................................................................................................................... 10

2.1.3 Calculations – scenarios modelling................................................................................ 10

2.1.4 Höckenbach catchment ................................................................................................... 10

2.1.4.1 Detailed results for rainfall total depth 70 and 30 mm.............................................................. 11

2.1.4.1.1 Land-use changes ............................................................................................................. 11

2.1.4.1.2 Channel roughness change ............................................................................................... 13

2.1.4.1.3 Change of channel cross-section area and change of flood-plain roughness .................... 14

2.1.4.2 Results for all design rainfall events and conclusions............................................................... 16

2.1.4.2.1 Summary graphs – All scenarios ...................................................................................... 17

2.1.4.2.2 Summary graphs - Scenarios trends.................................................................................. 18

2.1.5 Reichstädter Bach catchment.......................................................................................... 18

2.1.5.1 Location of the polder............................................................................................................... 18

2.1.5.2 Polder characteristics ................................................................................................................ 19

2.1.5.3 Results of calculations and conclusions.................................................................................... 20

2.2 HYDRAULIC MODELLING USING HEC-RAS............................................................................... 21

2.2.1 Description of applied Methodology............................................................................... 22

2.2.1.1 Cross-section of stream-channel ............................................................................................... 22

2.2.1.2 Stream-channel line .................................................................................................................. 22

2.2.1.3 Longitudinal slope of stream-channel line................................................................................ 23

2.2.1.4 Flood-plain cross-section.......................................................................................................... 23

2.2.1.5 Bed material and flood-plain cover, Manning’s roughness coefficients ................................... 23

2.2.1.6 Calculation variants .................................................................................................................. 24

2.2.2 HEC-RAS simulation ...................................................................................................... 24

2.2.2.1 Geometric data.......................................................................................................................... 25

2.2.2.2 Flow data and boundary conditions .......................................................................................... 25

2.2.2.3 Calculation and choice of outputs............................................................................................. 26

2.2.3 Modelling results ............................................................................................................ 26

2.2.3.1 Results for Q 5 ............................................................................................................................ 27

2.2.3.2 Results for Q 20 .......................................................................................................................... 27

2.2.3.3 Results for Q 100 ......................................................................................................................... 27

3. CONCLUSIONS ......................................................................................................................... 28

4. REFERENCES............................................................................................................................ 30

5. LIST OF FIGURES .................................................................................................................... 31

34


6. LIST OF TABLES ...................................................................................................................... 33

APPENDIX – FIGURES AND TABLES............................................................................................ 36

35


Appendix – Figures and Tables

36


Fig. 1 – Aerial photo of Höckenbach catchment

37


Fig. 2 – Map of land-use of Höckenbach catchment

LU distribution - Höckenbach

0.4%

2.4%

6.8%

1.9%

0.2%

0.4%

3.1%

84.7%

Urban area

Comunications

Industry

Arable land

Pastures/meadows

Water

Woods

Forest

Fig. 3 – Land-use distribution in Höckenbach catchment

38


Fig. 4 – Map of hydrological soil types of Höckenbach catchment

Höckenbach - hydrological soil groups

D

7.3%

A

B

2.2%

0.2%

C

90.3%

Fig. 5 – Distribution of hydrological soil types in Höckenbach catchmen t

39


Fig. 6 – Map of land-use of Reichstädter Bach catchment

LU distribution - Reichstädter Bach

6.4%

6.4%

0.7%

0.5%

0.9%

3.1%

9.8%

72.3%

Urban area

Comunications

Industry

Arable land

Pastures/meadows

Water

Woods

Forest

Fig. 7 – Land-use distribution in Reichstädter Bach catchment

40


Fig. 8 – Map of hydrological soil types of Reichstädter Bach catchment

Reichstädter Bach - hydrological soil groups

D

8.5%

A

5.7%

B

16.7%

C

69.0%

Fig. 9 – Distribution of hydrological soil types in Reichstädter Bach catchment

41


LU distribution - Blinka

4.9%

1.5%

2.8%

2.5%

1.3%

0.6%

3.5%

82.8%

Urban area

Comunications

Orchands, gardens

Arable land

Pastures/meadows

Other

Woods

Forest

Fig. 10 – Land-use distribution in Blinka catchment

Blinka - hydrological soil groups

C

2.8%

D

0.5% A

0.5%

B

96.2%

Fig. 11 – Distribution of hydrological soil types in Blinka catchment

42


Fig. 12 – Detention Basins Dialog in WMS where Curves Storage-Capacity and Elevation-

Discharge are defined

Fig. 13 – Conic Method for Volume Computations

43


80

70

70 mm

60 mm

50 mm

40 mm

30 mm

60

Cummulative rainfall (mm)

50

40

30

20

10

0

0:00 0:15 0:30 0:45 1:00 1:15 1:30 1:45 2:00

Time (hrs:min)

Fig. 14 – Temporal distribution of precipitation cumulative intensity (total depth 30 – 70 mm

and time period 2 hours)

Fig. 15 – Schema of topological tree – subcatchments of Höckenbach catchment

44


3.5

3

2.5

2

1.5

1

0.5

0

0 5 10 15 20 25

Fig. 16 – Cross-section of channel – part S3

Fig. 17 – WMS 7.1 interface

45


Discharge Q (m 3 /s)

30

25

20

15

10

LU2 70 mm

LU0 70 mm

LU1 70 mm

LU3 70 mm

LU2 30 mm

LU0 30 mm

LU1 30 mm

LU3 30 mm

5

0

0:00 0:30 1:00 1:30 2:00 2:30 3:00 3:30 4:00 4:30 5:00 5:30 6:00 6:30 7:00 7:30 8:00

Time t (hrs:min)

Fig. 18 – Hydrographs of land-use changes scenarios in outlet point of Höckenbach

catchment - causal precipitations (70 mm and 30mm depth).

Discharge Q (m 3 /s)

50

45

40

35

30

25

20

15

LU02 100-years

LU01 100-years

LU03 100-years

LU04 100-years

LU02 10-years

LU01 10-years

LU03 10-years

LU04 10-years

10

5

0

0:00 4:00 8:00 12:00 16:00

Time t (hrs:min)

Fig. 19 – Hydrographs of land-use changes scenarios in outlet point of Blinka catchment -

causal precipitations (Normal values – 100 and 10 years).

46


Discharge Q (m 3 /s)

25

20

15

10

R3 70 mm

R1 70 mm

R2 70 mm

R3 30 mm

R1 30 mm

R2 30 mm

5

0

0:00 0:30 1:00 1:30 2:00 2:30 3:00 3:30 4:00 4:30 5:00 5:30 6:00 6:30 7:00 7:30 8:00

Time t (hrs:min)

Fig. 20 – Hydrographs of channel roughness changes scenarios in outlet point of Höckenbach

catchment - causal precipitations (70 mm and 30mm depth).

Discharge Q (m 3 /s)

50

45

40

35

30

25

20

15

D3 smooth flood-plain

D5 smooth channel

D1 normal

D4 rough channel

D2 rough flood-plain

D5 smooth channel

D3 smooth flood-plain

D1 normal

D4 rough channel

D2 rough flood-plain

10

5

0

0:00 4:00 8:00 12:00 16:00

Time t (h:min)

Fig. 21 – Hydrographs of channel roughness changes scenarios in outlet point of Blinka

catchment - causal precipitations (Normal values – 100 and 10 years).

47


Discharge Q (m 3 /s)

25

20

15

10

Ch2 70 mm

Ch3 70 mm

Ch1 70 mm

Ch3_R3 70 mm

Ch2 30 mm

Ch1 30 mm

Ch3 30 mm

Ch3_R3 30 mm

5

0

0:00 0:30 1:00 1:30 2:00 2:30 3:00 3:30 4:00 4:30 5:00 5:30 6:00 6:30 7:00 7:30 8:00

Tim e t (hrs:min)

Fig. 22 – Hydrographs of channel cross-section changes scenarios in outlet point of

Höckenbach catchment - causal precipitations (70 mm and 30mm depth).

Discharge Q (m

Dis charge (m 3 3 /s)

/s)

50

45

40

35

30

25

20

15

K2 100-years

K3 100-years

K1 100-years

K3_D6 100-years

K2 10-years

K1 10-years

K3 10-years

K3_D6 10-years

10

5

0

Time t (hrs:min)

0:00 4:00 8:00 12:00 16:00

Time t (h:min)

Fig. 23 – Hydrographs of channel cross-section changes scenarios in outlet point of Blinka

catchment - causal precipitations (Normal values – 100 and 10 years).

48


7.00

6.00

LU2

LU

R

Ch

Peak discharge Qmax (m3/s)

5.00

4.00

3.00

2.00

R2

Ch2

LU1

real

LU0

R1

Ch1

R3

Ch3

LU3

Ch3_R3

1.00

0.00

1:50 1:55 2:00 2:05 2:10 2:15 2:20 2:25 2:30

Time t (hrs:min)

Fig. 24 – Summary graph of all scenarios in case of precipitation depth 30 mm - Höckenbach.

Peak discharge Qmax (m3/s)

12.00

11.00

10.00

9.00

8.00

7.00

6.00

5.00

4.00

LU2

R2

Ch3

Ch2

real

LU0

R1

Ch1

LU1

R3

LU3

Ch3_R6

LU

R

Ch

3.00

2.00

1:50 1:55 2:00 2:05 2:10 2:15 2:20 2:25 2:30

Time t (hrs:min)

Fig. 25 – Summary graph of all scenarios in case of precipitation depth 40 mm - Höckenbach.

49


17.00

15.00

LU2

LU

R

Ch

Peak discharge Qmax (m3/s)

13.00

11.00

9.00

R2

Ch2

Ch3

real

LU0

R1

Ch1

LU1

R3

LU3

Ch3_R3

7.00

5.00

1:50 1:55 2:00 2:05 2:10 2:15 2:20 2:25 2:30

Time t (hrs:min)

Fig. 26 – Summary graph of all scenarios in case of precipitation depth úhrnem 50 mm -

Höckenbach.

24.00

LU

R

Peak discharge Qmax (m3/s)

22.00

20.00

18.00

16.00

14.00

LU2

Ch2

R2

LU1

real

LU0

R1

Ch1

Ch3

Ch3_R3

R3

Ch

12.00

LU3

10.00

1:50 1:55 2:00 2:05 2:10 2:15 2:20 2:25 2:30

Time t (hrs:min)

Fig. 27 – Summary graph of all scenarios in case of precipitation depth 60 mm - Höckenbach.

50


29.00

27.00

LU2

LU

R

Ch

Peak discharge Q max

(m 3 /s)

25.00

23.00

21.00

19.00

R2

Ch2

Ch3

real

LU0

R1

Ch1

LU1

R3

Ch3_R3

17.00

LU3

15.00

1:50 1:55 2:00 2:05 2:10 2:15 2:20 2:25 2:30

Time t (hrs:min)

Fig. 28 – Summary graph of all scenarios in case of precipitation depth 70 mm - Höckenbach.

2.00

1.80

1.60

D5

K2

arable

D3

D2

D4

LU

D

K

Peak discharge Qmax (m 3 /s)

1.40

1.20

1.00

0.80

0.60

real

K1

D1

K3

K3_D6

0.40

0.20

pasture

0.00

5:15 5:30 5:45 6:00 6:15 6:30 6:45 7:00 7:15 7:30 7:45 8:00 8:15 8:30 8:45 9:00 9:15 9:30 9:45 10:00 10:15

Time t (h:min)

Fig. 29 – Summary graph of all scenarios in case of precipitation N = 2 years - Blinka.

51


25.00

23.00

21.00

K2

D5

D3

arable

K3

D4

LU

D

K

Peak discharge Qmax (m 3 /s)

19.00

17.00

15.00

13.00

11.00

real

K1

D1

pasture

D2

K3_D6

9.00

7.00

forest

5.00

5:15 5:30 5:45 6:00 6:15 6:30 6:45 7:00 7:15 7:30 7:45 8:00 8:15 8:30 8:45 9:00 9:15 9:30 9:45 10:00 10:15

Time t (h:min)

Fig. 30 – Summary graph of all scenarios in case of precipitation N = 20 years - Blinka.

50.00

45.00

K3

D3 K2

D5

arable

D4

K3_D6

LU

D

K

Peak discharge Qmax (m 3 /s)

40.00

35.00

30.00

real

K1

D1

D2

pasture

25.00

20.00

forest

15.00

5:15 5:30 5:45 6:00 6:15 6:30 6:45 7:00 7:15 7:30 7:45 8:00 8:15 8:30 8:45 9:00 9:15 9:30 9:45 10:00 10:15

Time t (h:min)

Fig. 31 – Summary graph of all scenarios in case of precipitation N = 100 years - Blinka.

52


Peak discharge Qmax (m3/s)

30.00

25.00

20.00

15.00

10.00

5.00

lu2

lu2

lu2

lu1

lu1

lu2

lu2

lu0

lu0

lu1

lu1

lu3

lu0

lu0

lu0

lu3

lu3

lu3

lu 70 mm

lu 60 mm

lu 50 mm

lu 40 mm

lu 30 mm

lu1

lu3

0.00

1:50 1:55 2:00 2:05 2:10 2:15 2:20 2:25 2:30

Time t (hrs:min)

Fig. 32 – Summary graph of land-use changes for all precipitation events – Höckenbach.

50.00

45.00

40.00

lu02

lu01

lu 100-years

lu 50-years

lu 20-years

lu 10-years

lu 2-years

lu02

Peak discharge Q max (m 3 /s)

35.00

30.00

25.00

20.00

15.00

10.00

lu01

lu02

lu01

lu03

lu02

lu01

lu03

lu03

lu03

lu04

lu04

5.00

lu04

lu01

lu02

lu04

0.00

5:30 6:00 6:30 7:00

Time t (h:min)

Fig. 33 – Summary graph of land-use changes for all precipitation events – Blinka.

53


Peak discharge Qmax (m3/s)

25.00

20.00

15.00

10.00

5.00

R2

R3

R1

R2 R1

R3

R2 R1 R3

R2 R1

R3

R2 R1

R3

R 70 mm

R 60 mm

R 50 mm

R 40 mm

R 30 mm

0.00

1:50 1:55 2:00 2:05 2:10 2:15 2:20 2:25 2:30

Time t (hrs:min)

Fig. 34 – Summary graph of channel roughness changes for all precipitation events –

Höckenbach.

50.00

45.00

40.00

D3

D1

D5

D4

D2

D 100-years

D 50-years

D 20-years

D 10-years

D 2-years

35.00

D3

D5

D1

D4

Peak discharge Q max (m 3 /s)

30.00

25.00

20.00

15.00

D5

D3

D5

D3

D1

D1

D2

D4

D4

D2

10.00

D2

5.00

D3

D5

D2

D4

0.00

D1

5:15 5:45 6:15 6:45 7:15 7:45

Time t (h:min)

Fig. 35 – Summary graph of channel roughness changes for all precipitation events – Blinka.

54


Peak discharge Qmax (m3/s)

25.00

20.00

15.00

10.00

5.00

Ch2

Ch3

Ch1

Ch2

Ch1

Ch1

Ch2

Ch2

Ch3

Ch3

Ch1 Ch3

Ch1 Ch2

Ch3_R3

Ch3_R3

Ch3

Ch3_R3

Ch3_R3

Ch 70 mm

Ch 60 mm

Ch 50 mm

Ch 40 mm

Ch 30 mm

Ch3_R3

0.00

1:50 1:55 2:00 2:05 2:10 2:15 2:20 2:25 2:30

Time t (hrs:min)

Fig. 36 – Summary graph of channel cross-section changes for all precipitation events –

Höckenbach.

50.00

45.00

40.00

K3

K2

K1

K3_D6

K 100-years

K 50-years

K 20-years

K 10-years

K 2-years

K2

K3

35.00

Peak discharge Q max (m 3 /s)

30.00

25.00

20.00

15.00

K2

K2

K1

K1 K3

K1

K3_D6

K3

K3_D6

10.00

K3_D6

5.00

K2

K1

K3

K3_D6

0.00

5:30 6:00 6:30 7:00 7:30 8:00 8:30 9:00 9:30

Time t (h:min)

Fig. 37 – Summary graph of channel cross-section changes for all precipitation events –

Blinka.

55


Fig. 38 – Schema of topological tree – subcatchments of Reichstädter Bach catchment

56


Fig. 39 – Polder position in Reichstädter Bach catchment

57


Fig. 40 – Polder locality – flooding if water level is 3 m

Discharge Q [m 3 . s -1 ]

0.000 2.000 4.000 6.000 8.000 10.000 12.000

404.847

404.347

Elevation H [m]

403.847

403.347

402.847

1x volume

3x volume

402.347

10x volume

Discharge

401.847

0.00 10.00 20.00 30.00 40.00 50.00

Volume V [1000 m 3 ]

Fig. 41 – Discharge-elevation and volume-elevation curves

58


Discharge Q (m 3 /s)

7

6

5

4

3

2

P0 - no polder

P1 - min volume

P2 - 3x volume

P3 - 10x volume

1

0

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00

Time t (hrs:min)

Fig. 42 – Hydrographs of polder scenarios in polder point (precipitation 30 mm)

25

Discharge Q (m 3 /s)

20

15

10

P0 - no polder

P1 - min volume

P2 - 3x volume

P3 - 10x volume

5

0

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00

Time t (hrs:min)

Fig. 43 – Hydrographs of polder scenarios in polder point (precipitation 50 mm)

59


Discharge Q (m 3 /s)

45

40

35

30

25

20

15

P0 - no polder

P1 - min volume

P2 - 3x volume

P3 - 10x volume

10

5

0

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00

Time t (hrs:min)

Fig. 44 – Hydrographs of polder scenarios in polder point (precipitation 70 mm)

Discharge Q (m 3 /s)

90

80

70

60

50

40

30

P0 - no polder

P1 - min volume

P2 - 3x volume

P3 - 10x volume

20

10

0

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00

Time t (hrs:min)

Fig. 45 – Hydrographs of polder scenarios in polder point (precipitation 100 mm)

60


Discharge Q (m 3 /s)

10

8

6

4

P0 - no polder

P1 - min volume

P2 - 3x volume

P3 - 10x volume

2

0

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00

Time t (hrs:min)

Fig. 46 – Hydrographs of polder scenarios in outlet point (precipitation 30 mm)

Discharge Q (m 3 /s)

35

30

25

20

15

10

P0 - no polder

P1 - min volume

P2 - 3x volume

P3 - 10x volume

5

0

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00

Time t (hrs:min)

Fig. 47 – Hydrographs of polder scenarios in outlet point (precipitation 50 mm)

61


Discharge Q (m 3 /s)

70

60

50

40

30

20

P0 - no polder

P1 - min volume

P2 - 3x volume

P3 - 10x volume

10

0

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00

Time t (hrs:min)

Fig. 48 – Hydrographs of polder scenarios in outlet point (precipitation 70 mm)

Discharge Q (m 3 /s)

120

100

80

60

40

P0 - no polder

P1 - min volume

P2 - 3x volume

P3 - 10x volume

20

0

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00

Time t (hrs:min)

Fig. 49 – Hydrographs of polder scenarios in outlet point (precipitation 100 mm)

62


Fig. 50 – A typical regulated stream: trapezoidal shape of stream cross-section; bed and bank

foots are protected by concrete blocks.

Fig. 51 – Typical natural stream: rectangular shape of stream cross-section

63


Straight stream-channel

line

sinuosity 1.0

Curved stream-channel

line

sinuosity 1.25

"Vinding" stream-channel

line

sinuosity 1.50

Fig. 52 – Three basic shapes of stream-channel line

Fig. 53 – Flood-plain cross-section used for calculation purposes

64


Rectangular river cross-section, longitudinal gradient 1.0 %, length

ratio 1.0, Q 5 = 8.13m 3 s -1

Rectangular river cross-section, longitudinal gradient 1.0 %, length

ratio 1.5, Q 5 =8.13m 3 s -1

9

9

Discharge [m 3 .s -1 ]

6

3

Discharge [m3.s-1]

6

3

0

0

0:00 2:24 4:48 7:12 9:36 12:00 14:24 16:48 19:12

0:00 2:24 4:48 7:12 9:36 12:00 14:24 16:48 19:12

Time [h:min]

Time [h:min]

original hydrograph Nch=0.035,Nf=0.1 Nch=0.1,Nf=0.1

original hydrograph Nch=0.035,Nf=0.1 Nch=0.1,Nf=0.1

Nch=0.035,Nf=0.7

Nch=0.7,Nf=0.7

Nch=0.035,Nf=0.7

Nch=0.7,Nf=0.7

Trapezoidal river cross-section, longitudinal gradient 1.0 %, length

ratio 1.0, Q 5 =8.13m 3 s -1

Trapezoidal river cross-section, longitudinal gradient 1.0 %, length

ratio 1.5, Q 5 =8.13m 3 s -1

9

9

Discharge [m 3 .s -1 ]

6

3

Discharge [m 3 .s -1 ]

6

3

0

0:00 2:24 4:48 7:12 9:36 12:00 14:24 16:48 19:12

0

Time [h:min]

0:00 2:24 4:48 7:12 9:36 12:00 14:24 16:48 19:12

Time [h:min]

original hydrograph Nch=0.025,Nf=0.1 Nch=0.1,Nf=0.1

original hydrograph Nch=0.025,Nf=0.1 Nch=0.1,Nf=0.1

Nch=0.025,Nf=0.7

Nch=0.7,Nf=0.7

Nch=0.025,Nf=0.7

Nch=0.7,Nf=0.7

Fig. 54 – Hydrographs for trapezoidal river cross-section, longitudinal gradient 1.0 %, sinuosity (length ratio) 1.0 and 1.5, Q 5 =8.13m 3 s -1 65


Rectangular river cross-section, longitudinal gradient 1.0 %, length

ratio 1.0, Q 20 =12.25m 3 s -1

Rectangular river cross-section, longitudinal gradient 1.0 %, length

ratio 1.5, Q 20 =12.25m 3 s -1

16

16

Discharge [m 3 .s -1 ]

12

8

4

Discharge [m3.s-1]

12

8

4

0

0

0:00 2:24 4:48 7:12 9:36 12:00 14:24 16:48 19:12

0:00 2:24 4:48 7:12 9:36 12:00 14:24 16:48 19:12

Time [h:min]

Time [h:min]

original hydrograph Nch=0.035,Nf=0.1 Nch=0.1,Nf=0.1

original hydrograph Nch=0.035,Nf=0.1 Nch=0.1,Nf=0.1

Nch=0.035,Nf=0.7

Nch=0.7,Nf=0.7

Nch=0.035,Nf=0.7

Nch=0.7,Nf=0.7

Trapezoidal river cross-section, longitudinal gradient 1.0 %, length

ratio 1.0, Q 20 =12.25m 3 s -1

Trapezoidal river cross-section, longitudinal gradient 1.0 %, length

ratio 1.5, Q 20 =12.25m 3 s -1

16

16

12

12

Discharge [m 3 .s -1 ]

8

4

Discharge [m 3 .s -1 ]

8

4

0

0:00 2:24 4:48 7:12 9:36 12:00 14:24 16:48 19:12

Time [h:min]

0

0:00 2:24 4:48 7:12 9:36 12:00 14:24 16:48 19:12

Time [h:min]

original hydrograph Nch=0.025,Nf=0.1 Nch=0.1,Nf=0.1

original hydrograph Nch=0.025,Nf=0.1 Nch=0.1,Nf=0.1

Nch=0.025,Nf=0.7

Nch=0.7,Nf=0.7

Nch=0.025,Nf=0.7

Nch=0.7,Nf=0.7

Fig. 55 – Hydrographs for trapezoidal river cross-section, longitudinal gradient 1.0 %, sinuosity (length ratio) 1.0 and 1.5, Q 20 =12.25m 3 s -1 66


Rectangular river cross-section, longitudinal gradient 1.0 %, length

ratio 1.0, Q 100 =18.16m 3 s -1

18.26

Rectangular river cross-section, longitudinal gradient 1.0 %, length

ratio 1.5, Q 100 =18.16m 3 s -1

18.26

20

20

16

16

Discharge [m 3 .s -1 ]

12

8

4

Discharge [m3.s-1]

12

8

4

0

0:00 2:24 4:48 7:12 9:36 12:00 14:24 16:48 19:12

Time [h:min]

0

0:00 2:24 4:48 7:12 9:36 12:00 14:24 16:48 19:12

Time [h:min]

original hydrograph Nch=0.035,Nf=0.1 Nch=0.1,Nf=0.1

original hydrograph Nch=0.035,Nf=0.1 Nch=0.1,Nf=0.1

Nch=0.035,Nf=0.7

Nch=0.7,Nf=0.7

Nch=0.035,Nf=0.7

Nch=0.7,Nf=0.7

Trapezoidal river cross-section, longitudinal gradient 1.0 %, length

ratio 1.0, Q 100 =18.16m 3 s -1

18.26

Trapezoidal river cross-section, longitudinal gradient 1.0 %, length

ratio 1.5, Q 100 =18.16m 3 s -1

18.26

20

20

16

16

Discharge [m 3 .s -1 ]

12

8

Discharge [m 3 .s -1 ]

12

8

4

4

0

0:00 2:24 4:48 7:12 9:36 12:00 14:24 16:48 19:12

Time [h:min]

0

0:00 2:24 4:48 7:12 9:36 12:00 14:24 16:48 19:12

Time [h:min]

original hydrograph Nch=0.025,Nf=0.1 Nch=0.1,Nf=0.1

original hydrograph Nch=0.025,Nf=0.1 Nch=0.1,Nf=0.1

Nch=0.025,Nf=0.7

Nch=0.7,Nf=0.7

Nch=0.025,Nf=0.7

Nch=0.7,Nf=0.7

Fig. 56 – Hydrographs for trapezoidal river cross-section, longitudinal gradient 1.0 %, sinuosity (length ratio) 1.0 and 1.5, Q 100 =18.26m 3 s -1

67


Tab. 16 – Sample of HEC-RAS modelling outputs for flows with return period of 5, 20, and 100 years

Return period of flow

[year]

Characteristics of

stream-channel

Cross-section

Manning's roughness Peak flow Q delta Q delta Q Time of peak flow Lag time

[ - ] [m 3 .s -1 ] [m 3 .s -1 ] [%] [h:min] [h:min]

CS100 - start of the reach all 8.130 - - 4:10 -

Rectangular crosssection,

Length ratio =

1.0 CS0 - End of the reach

Nch=0.035,Nf=0.1 7.966 -0.164 -2.0 4:33 0:23

Nch=0.1,Nf=0.1 7.989 -0.141 -1.7 4:33 0:23

Nch=0.035,Nf=0.7 7.820 -0.310 -3.8 5:06 0:56

Nch=0.7,Nf=0.7 7.415 -0.715 -8.8 5:32 1:22

CS100 - start of the reach all 8.130 - - 4:10 -

5

Rectangular crosssection,

Length ratio =

1.5 CS0 - End of the reach

Nch=0.035,Nf=0.1 7.969 -0.161 -2.0 4:33 0:23

Nch=0.1,Nf=0.1 7.992 -0.138 -1.7 4:33 0:23

Nch=0.035,Nf=0.7 7.805 -0.325 -4.0 5:08 0:58

Nch=0.7,Nf=0.7 7.017 -1.113 -13.7 5:59 1:49

(Q 5 =8.13 m 3 .s -1 )

Trapezoidal crosssection,

Length ratio =

1.0 CS0 - End of the reach

CS100 - start of the reach all 8.130 - - 4:10 -

Nch=0.025,Nf=0.1 8.111 -0.019 -0.2 4:14 0:04

Nch=0.1,Nf=0.1 7.978 -0.152 -1.9 4:34 0:24

Nch=0.025,Nf=0.7 8.111 -0.019 -0.2 4:14 0:04

Nch=0.7,Nf=0.7 7.359 -0.771 -9.5 5:34 1:24

CS100 - start of the reach all 8.130 - - 4:10 -

Trapezoidal crosssection,

Length ratio =

1.5 CS0 - End of the reach

Nch=0.025,Nf=0.1 8.103 -0.027 -0.3 4:18 0:08

Nch=0.1,Nf=0.1 8.038 -0.093 -1.1 4:35 0:25

Nch=0.025,Nf=0.7 8.096 -0.034 -0.4 4:17 0:07

Nch=0.7,Nf=0.7 7.169 -0.961 -11.8 5:43 1:33

CS100 - start of the reach all 12.304 - - 4:00 -

Rectangular crosssection,

Length ratio =

1.0 CS0 - End of the reach

Nk=0.035,Nn=0.1 12.140 -0.164 -1.3 4:27 0:27

Nk=0.1,Nn=0.1 12.150 -0.155 -1.3 4:27 0:27

Nk=0.035,Nn=0.7 11.943 -0.361 -2.9 4:52 0:52

Nk=0.7,Nn=0.7 11.403 -0.901 -7.3 5:14 1:14

CS100 - start of the reach all 12.304 - - 4:00 -

20

Rectangular crosssection,

Length ratio =

1.5 CS0 - End of the reach

Nk=0.035,Nn=0.1 12.138 -0.166 -1.3 4:27 0:27

Nk=0.1,Nn=0.1 12.147 -0.157 -1.3 4:28 0:28

Nk=0.035,Nn=0.7 11.748 -0.556 -4.5 5:03 1:03

Nk=0.7,Nn=0.7 10.302 -2.002 -16.3 5:53 1:53

(Q 20 =12.3 m 3 .s -1 )

Trapezoidal crosssection,

Length ratio =

1.0 CS0 - End of the reach

CS100 - start of the reach all 12.304 - - 4:00 -

Nk=0.025,Nn=0.1 12.146 -0.158 -1.3 4:28 0:28

Nk=0.1,Nn=0.1 12.145 -0.159 -1.3 4:28 0:28

Nk=0.025,Nn=0.7 12.141 -0.163 -1.3 4:28 0:28

Nk=0.7,Nn=0.7 11.357 -0.947 -7.7 5:15 1:15

CS100 - start of the reach all 12.304 - - 4:00 -

Trapezoidal crosssection,

Length ratio =

1.5 CS0 - End of the reach

Nk=0.025,Nn=0.1 12.149 -0.155 -1.3 4:29 0:29

Nk=0.1,Nn=0.1 12.223 -0.081 -0.7 4:28 0:28

Nk=0.025,Nn=0.7 12.077 -0.228 -1.8 4:31 0:31

Nk=0.7,Nn=0.7 11.150 -1.154 -9.4 5:22 1:22

CS100 - start of the reach all 18.256 - - 4:00 -

Rectangular crosssection,

Length ratio =

1.0 CS0 - End of the reach

Nk=0.035,Nn=0.1 18.073 -0.183 -1.0 4:16 0:16

Nk=0.1,Nn=0.1 18.080 -0.176 -1.0 4:16 0:16

Nk=0.035,Nn=0.7 17.679 -0.577 -3.2 4:42 0:42

Nk=0.7,Nn=0.7 16.969 -1.287 -7.0 5:00 1:00

CS100 - start of the reach all 18.256 - - 4:00 -

100

Rectangular crosssection,

Length ratio =

1.5 CS0 - End of the reach

Nk=0.035,Nn=0.1 18.071 -0.185 -1.0 4:16 0:16

Nk=0.1,Nn=0.1 18.074 -0.182 -1.0 4:17 0:17

Nk=0.035,Nn=0.7 17.074 -1.182 -6.5 4:59 0:59

Nk=0.7,Nn=0.7 14.677 -3.579 -19.6 5:46 1:46

(Q 100 =18.26 m 3 .s -1 )

Trapezoidal crosssection,

Length ratio =

1.0 CS0 - End of the reach

CS100 - start of the reach all 18.256 - - 4:00 -

Nk=0.025,Nn=0.1 18.062 -0.194 -1.1 4:17 0:17

Nk=0.1,Nn=0.1 18.069 -0.187 -1.0 4:17 0:17

Nk=0.025,Nn=0.7 17.923 -0.333 -1.8 4:26 0:26

Nk=0.7,Nn=0.7 16.937 -1.319 -7.2 5:00 1:00

CS100 - start of the reach all 18.256 - - 4:00 -

Trapezoidal crosssection,

Length ratio =

1.5 CS0 - End of the reach

Nk=0.025,Nn=0.1 18.006 -0.250 -1.4 4:18 0:18

Nk=0.1,Nn=0.1 18.121 -0.135 -0.7 4:18 0:18

Nk=0.025,Nn=0.7 17.916 -0.340 -1.9 4:26 0:26

Nk=0.7,Nn=0.7 16.698 -1.558 -8.5 5:06 1:06

68

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