JBA Consulting - Kerry County Council

Sneem Area Flood Relief 

Pre-Feasibility Study 

Final Report 

September 2010 

Kerry County Council 

Roads & Transportation Section 

County Buildings 

TRALEE 

Co Kerry

2010s4114 - Sneem Pre-feasibility study Final Report v1.docx

JBA Office 

JBA Consulting 

24 Grove Island 

Corbally 

Limerick 

Ireland 

JBA Project Manager 

Elizabeth Russell 

Revision History 

Revision Ref / Date Issued Amendments Issued to 

Draft Report v1 / 19 July 2010 Initial Issue 

Draft Report v2 / 23 August 

2010 

Draft Final Report v3 / 24 


Draft Final Report v4 / 29 


Final Report v1 / 29 


Contract 

Chapter 7 completed 

Minor textual changes 

Minor changes to Chapter 8 

Final QA check and minor 

textual changes 

John O'Halloran, Kerry 

County Council 

John O'Halloran, Kerry 

County Council 

Padraic Teahan, Kerry County 

Council 





This report describes work commissioned by Kerry County Council by letter dated 29 April 

2010. Kerry County Council’s representative for the contract was John O'Halloran. Elizabeth 

Russell of JBA Consulting carried out this work. 

Prepared by .................................................. Elizabeth Russell BSc MSc 

Project Manager 

Reviewed by ................................................. Ross Bryant BSc MSc MBCS CEnv C.WEM 

MCIWEM 

Senior Analyst 

Approved by ................................................... Mark Morris BEng CEng CEnv MEI MCIWEM 

MICE MIOD 

Purpose 

Director 

This document has been prepared as a Pre-Feasibility Report for Kerry County Council. JBA 

Consulting accepts no responsibility or liability for any use that is made of this document other 

than by the Client for the purposes for which it was originally commissioned and prepared. 

2010s4114 - Sneem Pre-feasibility study Final Report v1.docx i

Acknowledgments 

Thanks to John O'Halloran and Padraic Teahan, and the Kenmare Engineering Area Staff, of 

Kerry County Council for their assistance and inputs during the site visit and throughout this 

project. 

Copyright 

© JBA Consulting Engineers and Scientists Limited 2010 

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A printed copy of the main text in this document will result in a carbon footprint of 181g if 

100% post-consumer recycled paper is used and 231g if primary-source paper is used. 

These figures assume the report is printed in black and white on A4 paper and in duplex. 

JBA is a carbon neutral company and the carbon emissions from our activities are offset. 

2010s4114 - Sneem Pre-feasibility study Final Report v1.docx ii

Contents 

1. Introduction .......................................................................................................... 1 

1.1 Commission ........................................................................................................... 1 

1.2 Report Structure .................................................................................................... 1 

2. Study Area ............................................................................................................ 3 

2.1 Sneem Catchment ................................................................................................. 3 

2.2 Flood History .......................................................................................................... 4 

3. Data Collection ..................................................................................................... 7 

3.1 Available Data ........................................................................................................ 7 

3.2 Site Visit ................................................................................................................. 7 

3.3 Site Survey ............................................................................................................ 7 

3.4 Property Survey ..................................................................................................... 8 

4. Flood Risk Mapping ............................................................................................. 9 

4.1 Hydrology ............................................................................................................... 9 

4.2 Fluvial Hydraulic Modelling .................................................................................... 10 

4.3 Tidal Flood Mapping .............................................................................................. 11 

5. Flood Risk Assessment ...................................................................................... 13 

5.1 Flood Mechanisms ................................................................................................. 13 

5.2 Flow Constraints .................................................................................................... 17 

5.3 Flood Defence Assets and Maintenance ............................................................... 17 

5.4 Flood Extents ......................................................................................................... 18 

5.5 Flood Depths and Frequency ................................................................................ 19 

5.6 Property at Risk ..................................................................................................... 21 

5.7 People at Risk ........................................................................................................ 22 

5.8 Infrastructure at Risk .............................................................................................. 22 

5.9 Environment at Risk ............................................................................................... 22 

6. Flood Mitigation Options .................................................................................... 23 

6.1 Introduction ............................................................................................................ 23 

6.2 Options Appraisal .................................................................................................. 23 

7. Cost Benefit Analysis .......................................................................................... 31 

7.1 Option Costs .......................................................................................................... 31 

7.2 Flood Damages and Benefits ................................................................................ 31 

8. Recommendations ............................................................................................... 35 

8.1 Short Term Actions ................................................................................................ 35 

8.2 Medium Term Actions ............................................................................................ 35 


List of Figures 

Figure 2-1 The Sneem and Owreagh catchments - overview ..................................... 3 

Figure 2-2 View from Sneem Bridge ............................................................................. 4 

Figure 2-3 Flooding of the GAA ground, October 2008 .............................................. 5 

Figure 3-1 Survey extents .............................................................................................. 7 

Figure 4-1 Typical catchment descriptors ................................................................... 9 

Figure 4-2 Inflow Points and Cross Sections .............................................................. 10 

Figure 4-3 Cross Sections and “Boxes” in JFLOW® .................................................. 11 

Figure 4-4 Virtual Tide Gauge Network ........................................................................ 11 

Figure 5-1 Flood mechanisms and flow routes ........................................................... 13 

Figure 5-2 Bank levels to the north of the GAA ground ............................................. 18 

Figure 5-3 Flood Zones A and B ................................................................................... 19 

Figure 5-4 Wrack mark in the Atlantic Gateway .......................................................... 20 

Figure 5-5 Depth bands for fluvial Flood Zone A ........................................................ 20 

Figure 5-6 Properties within Flood Zone A .................................................................. 21 

Figure 6-1 Flood mitigation measures .......................................................................... 24 

Figure 6-2 Channel maintenance and the Kenmare SAC ........................................... 25 

Figure 6-3 Berm around the Atlantic Gateway development ..................................... 26 

Figure 6-4 Reprofiling the river bank ............................................................................ 27 

List of Tables 

Table 5-1 Properties at flood risk .................................................................................. 21 

Table 7-1 Summary of option costs .............................................................................. 31 

Table 7-2 OPW Benefit Criteria ...................................................................................... 32 

Table 7-3 Summary of Financial Benefits - Options 3, 5 and 8 .................................. 32 

Table 7-4 - Summary of Financial Benefits - ................................................................ 32 

Options which are applied locally to the Atlantic Development ................................ 32 

Table 7-5 Objective Appraisal Matrix ............................................................................ 33 


Abbreviations 

2D Two Dimensional (modelling) 

AMAX Annual Maximum 

DTM Digital Terrain Model 

FEH Flood Estimation Handbook 

FSR Flood Studies Report 

FSU Flood Studies Update 

GIS Geographical Information System 

JBA JBA Consulting – Engineers & Scientists 

JFLOW 2-D hydraulic modelling package developed by JBA 

mOD Meters above Ordnance Datum 

OD Ordnance Datum 

OPW Office of Public Works 

QA Quality Assurance 

QMED Median Annual Flood (with return period 2 years) 

SAAR Standard Average Annual Rainfall (mm) 

SAC Special Area of Conservation, protected under the EU Habitats Directive 

WWTP Waste Water Treatment Plant 


This page is intentionally left blank. 


1. Introduction 

1.1 Commission 

JBA Consulting was commissioned by Kerry County Council in April 2010 to undertake a 

flood relief pre-feasibility study for Sneem. 

The aim of the study was to establish the causes, effects and feasibility of solutions to the 

recurring flooding in the vicinity of Sneem. 

The objective of the study was to identify and assess the likely viability, or otherwise, of 

potential flood mitigation measures for the Sneem catchment, incorporating an assessment 

of, among others, technical, economic, social and environmental issues. 

1.2 Report Structure 

This report aims to identify the flood extents within Sneem, assess the potential flood 

damages and provide an assessment of potential mitigation options. These aims are fulfilled 

through the following stages: 

Identification of the flooding sources and mechanisms, through site visits, topographic 

survey and analysis of historic flood reports; 

Development of flood hazard maps for flood zones A and B, as defined by 'the 

Planning System and Flood Risk Management' Guidelines 1 ; 

Assessment of the flood damage in terms of impact on property, critical infrastructure 

and environment; 

Identification and selection of options for mitigating or preventing flooding; 

Assessment of the risks associated with the proposed mitigation measures, including 

those that may increase the impact of flooding; 

Initial assessment of the environmental impact of the proposed measures; 

Estimation of the cost of the proposed measures; 

Recommendations for a programme of future works. 

1 DoEHLG and OPW, 2009, The Planning System and Flood Risk Management: Guidelines for Planning Authorities 

2010s4114 - Sneem Pre-feasibility study Final Report v1.docx 1



2. Study Area 

2.1 Sneem Catchment 

The River Sneem has a catchment of approximately 63km 2 to the Sneem Bridge, which 

marks the limit of the tidally influenced river (Figure 2-1 and Figure 2-2). This catchment 

incorporates over 130km of river including the Sneem itself and its primary tributary, the 

Ardsheelhane. The Ardsheelhane joins the Sneem approximately 1km upstream of Sneem 

town. 

A second river system drains into the tidal limits of the River Sneem, to the south of the 

bridge. The main river in this system is the Owreagh, which has a catchment area of 20km 2 

and a length of 7.7km, in addition to the numerous tributaries which contribute to its flow. 

The topography of the area plays an important role in influencing the speed and pattern of 

response to rainfall. The rivers in the Sneem catchment arise in the mountainous interior of 

south Kerry, at elevations of between 500 and 600 m OD, dropping to 5m OD in the town; this 

means water levels in the rivers can rise and fall very quickly, with flood waters receding in a 

matter of hours. As a result, water velocities both in channel and overland can be extremely 

fast, creating an increased risk to people and vehicles with little or no advanced warning. 

Figure 2-1 The Sneem and Owreagh catchments - overview 

Sneem 

Ordnance Survey Licence No: 2010/07/CCMA/KerryCountyCouncil 

© Ordnance Survey Ireland/ Government of Ireland 


Sneem is on the N70 Ring of Kerry, a primary tourist route, and the South East Kerry 

Settlements Local Area Plan (LAP) 2 recognises the importance of maintaining the attractive 

views currently experienced from the bridge (Figure 2-2). The LAP also notes that there are a 

number of parks throughout the town, which should be preserved. Considerations such as 

these, and the classification of the River Sneem as a candidate Special Area of Conservation 

(cSAC), will inform and influence the options available for the town. 

2.2 Flood History 

Figure 2-2 View from Sneem Bridge 

Sneem has a documented history of flooding, which has been raised in the Dáil, and in the 

Kerry County Council Chambers by the Elected Members on a number of occasions. The 

LAP notes that "there is a history of flooding at certain locations along the river", and this is 

further evidenced in the Tender Document, which recognises approximately 20 residential 

properties as potentially being at risk. The road infrastructure, agricultural and recreational 

land, including the GAA ground, is also liable to flood. Flooding is reported to occur at least 

annually, and can affect roads and surrounding land to a depth of approximately 300mm. 

Particularly severe flash flooding occurred in the area in October 2008, whilst in 2009 the 

GAA ground flooded five or six times (Figure 2-3), with water flowing across the road. On one 

occasion in 2009, waters reached in excess of 1m depth, and spilled across the wall 

surrounding the ground. There are anecdotal accounts of flooding incidents, and it is reported 

that the low lying land to the east of Sneem, including the site of the Atlantic Gateway 

development, 'have always flooded', and it is suggested the development may have been 

inundated a couple of times in the last four or five years. It is reported that the properties 

have been constructed approximately 1m higher than pre-development ground levels, which 

would remove them from the most frequent of flood events. 

It is also reported that there has been flooding of the neighbouring fields as long ago as 1948. 

2 South East Kerry Settlements Local Area Plan, Kerry County Council Planning Department, adopted February 

2008. 


Figure 2-3 Flooding of the GAA ground, October 2008 3 

The flooding of October 2008 resulted in inundation of the Derreenavurrig Road between the 

waste water treatment plant and the Owreagh River. Water backed up at the culvert and 

flowed down the road towards the treatment works. The flow velocity was such that the road 

surface was badly damaged and necessitated emergency road works by Kerry County 

Council. A local resident reported to the County Council that all properties beyond this point 

(in the region of 30 no.) were unable to travel the route to Sneem town as the road was 

"impassable by vehicles and very dangerous by foot due to the undermining of the surface 

leaving only an asphalt layer which would not support a vehicle". An incident of this severity 

had not previously been reported, but the waste water treatment plant is known to have 

flooded on numerous occasions. 

3 Photographs supplied by Kerry County Council 




3. Data Collection 

3.1 Available Data 

Kerry County Council made a range of data available for the study, including OSi mapping 

and National Height Model. Photographs of a 2008 flood event were also supplied. 

Digital catchment characteristic datasets, including the river network and SAAR, were used 

for the development of the flood maps. 

3.2 Site Visit 

Two site visits were undertaken by JBA Consulting on 26th April and 4 June 2010. John 

O'Halloran, KCC project manager was present on the second visit, and arranged a meeting 

with the Kenmare Engineering Area Staff. 

3.3 Site Survey 

As part of the project a threshold and topographic survey was commissioned from EMC 

Surveys. The survey extents are shown in Figure 3-1. 

Figure 3-1 Survey extents 




The survey included: 

33 no. threshold levels 

Road levels through Sneem 

Levels across the field adjacent to Atlantic Gateway development, the field to the 

south-west of the GAA ground and across the GAA pitch. 

Top of bank levels 

Bed levels in selected locations 

The survey allowed validation of the digital terrain model and the flood maps. 

3.4 Property Survey 

The property survey comprised the following stages: 

The property type was noted during the walkover survey; 

The threshold level of properties within, and immediately adjacent to, the 1000 year 

flood outline was surveyed (as detailed above); 

The properties were assessed in terms of flood risk vulnerability, based on the 

Planning System and Flood Risk Management Guidelines. 


4. Flood Risk Mapping 

The processes involved in the fluvial mapping can be divided into two stages: hydrology and 

hydraulic modelling. These are described in detail below. 

4.1 Hydrology 

The aim of the hydrology stage was to generate inflows for use in the hydraulic modelling. To 

generate inflows, catchment boundaries were delineated and catchment descriptors were 

calculated from a wide range of national environmental datasets, including: 

Digital Terrain Model (DTM); 

Vector data of water features (i.e. river centrelines and lakes); 

Teagasc General Soils Map of Ireland; 

Teagasc/EPA National Subsoils Map; 

CORINE Land Cover Data 2000; 

Met Éireann Annual Average Rainfall; 

OPW Hydrodata Annual Maxima (AMAX) series. 

Typical examples of these datasets are shown in Figure 4-1, below. 

Figure 4-1 Typical catchment descriptors 

Topography Annual Average Rainfall 

Ground Elevation 

Value 

1100mOD 

10mOD 

JBA Consulting developed in-house software tools to interpolate catchment descriptors from 

the environmental data, and an automated method for calculating design flows. This was a 

simplified version of the procedure used to automate the Flood Estimation Handbook (FEH) 4 

statistical method for the UK. This methodology is in line with that of the Flood Studies 

Update (FSU), which is currently under development by the OPW to replace the 1975 Flood 

Studies Report (FSR). 

These steps resulted in the creation of geographical information system (GIS) data that could 

be used to calculate design flows at most locations in Ireland. 

Using the GIS, index flows were generated at 300 m intervals along all watercourses with a 

catchment area of greater than 3 km 2 in areas of strategic importance, and greater than 10 

km 2 in all other areas. Annual Maximum flow data from the OPW’s Hydrodata website were 

used to adjust the index flows generated, by allocating “donor” gauges, whereby local gauges 

are used to compare and adjust index flows for a given catchment. 

The FEH Statistical Method was used to generate flows for different return periods (i.e. 100 

and 1000 year). In this method, growth curves are generated based on pooled gauge data, 

rather than using Regional Growth Curves. This provides a more reliable estimation of flows 

for different return periods. 

4 Flood Estimation Handbook, (Institute of Hydrology), 1999 

2010s4114 - Sneem Pre-feasibility study Final Report v1.docx 9 

SAAR 

Value 

3000mm 

1700mm

Once inflow points for an area were generated, they were checked manually to ensure that no 

river reaches were missing inflow points, and that no inflow points were located at 

confluences or within lakes. Flows were regenerated for any inflow points that were created 

or moved at this stage. 

Figure 4-2 below, shows an example of inflow points through Sneem. Flows were 

subsequently generated for these points. 

It should be noted that the flows derived are indicative; prior to undertaking works, a more 

detailed hydrological analysis, including deriving flows using a number of methods, and 

analysing the suitability of the donor sites should be undertaken. 

Figure 4-2 Inflow Points and Cross Sections 



4.2 Fluvial Hydraulic Modelling 

Cross sections were generated at each inflow point; the cross sections are used by JBA’s 2 

dimensional hydraulic modelling software, JFLOW® 5 , to define the area of DTM over which to 

route the flow. A box is created at each JFLOW® inflow point, the width and orientation of 

which are determined by the cross section. Once generated, cross sections were manually 

checked, to ensure suitable alignment and extension across the floodplain. 

Figure 4-3 below, shows typical cross sections generated along a river reach, and the boxes 

generated by JFLOW® to route the inflows across the DTM. 

Once the design flows had been developed, the flood maps were generated by simulating 

overland flooding, using JFLOW®. 

5 JFLOW® is a registered UK trade mark in the name of Jeremy Benn Associates Limited 


JFLOW® results were subjected to several iterations of manual checking and model rerunning, 

to remove anomalous results and irregular flow patterns, ensuring that results were 

realistic. 

The results were compared to reported flood extents and flow paths from previous events. 

4.3 Tidal Flood Mapping 

Figure 4-3 Cross Sections and “Boxes” in JFLOW® 

To map inundation from tidal flooding, a 10 km resolution numerical model was first 

constructed to simulate tide and surge processes for a virtual tide gauge network around the 

coast of Ireland for the period September 1957 to August 2003. Where tide gauge records 

were available, these were used to validate the simulated records. 

Figure 4-4 Virtual Tide Gauge Network 


Extreme sea levels were then generated for 200 and 1,000 year return periods. This process 

included joint probability analysis (tides and surges) and tide-surge interaction analysis. 

Using a level projection method, the extreme sea levels were interpolated between the 

simulated gauge stations, and outlines were created for the study area. 


5. Flood Risk Assessment 

5.1 Flood Mechanisms 

5.1.1 Rivers Sneem and Ardsheelhane 

Based on observations made during the site visits, anecdotal reports, the topographic survey, 

and the flood maps, the flood mechanisms and flow routes have been identified, and are 

shown in Figure 5-1. 

Numbers on the drawing and some photograph captions reference the numbers in the text 

below. Photographs of key locations are shown overleaf, note that not all numbered 

references have an accompanying photograph. 

Owreagh River 

Figure 5-1 Flood mechanisms and flow routes 

River Sneem 



River Ardsheelhane 

The River Sneem is joined by its primary tributary, the Ardsheelhane, upstream of the GAA 

pitch (1). This junction forms a 90 degree bend in the river, with flow constricted further by 

the presence of bed rock protrusions in the channel bed, and extensive vegetation growth on 

the banks. Flow was observed to slow considerably at this point in the river. Under flood flow 

conditions, water has historically overtopped the right bank to flow across the pitch (2) and 

exit through the gateway (3). In extreme events, water is reported to flood over the top of the 


wall of the GAA ground, at a depth of approximately 1m. The water flows across the road 

and inundates the field drain and surrounding floodplain as it follows a route to the north of 

the town centre (4). There is a 900mm diameter culvert below the road at the downstream 

end of the field drain (5). The water backs up at this culvert and flows across the N70 road 

adjacent to the Atlantic Gateway development, where it attempts to re-enter the field drain 

again. It is at this location that water of sufficient depth floods properties in the Atlantic 

Gateway development. 

A second flow route exists from the Owreagh River, to the south-west of the town. Water 

leaves the channel to flow across the floodplain on the right bank (6) in the direction of the 

Atlantic Gateway. It is reported that this situation is exacerbated during high tides, when 

water backs up in the channel and limits outflows from the land drain (7). 

Road bridge on the Sneem River upstream of 

the confluence with the Ardsheelhane 

(1) Constricted channel upstream of GAA ground 

Raised embankment and reprofiled field to the north of the GAA ground 

Below the confluence of the Sneem and Ardsheelhane - GAA ground on right bank 


(2) GAA ground (4) Field drain and neighbouring floodplain 

(5) 900 dia culvert upstream of the N70 (5) Secondary relief culvert upstream of the 

N70 

(5) View across the N70, where water would 

flow during a flood 

(5) 900 dia culvert downstream of the N70 


Field drain adjacent to the Atlantic Gateway 

Development 

5.1.2 Owreagh River 

Atlantic Gateway development 

A further source of flood risk is associated with the Owreagh River; the river is culverted 

below the Derreenavurrig Road adjacent to the waste water treatment plant (8). Flooding and 

road damage at this location was reported in October 2008. Since that time, a relief culvert 

on the right bank has been opened, thus increasing the capacity of the below road culvert. 

The relief culvert has 3 no. openings, which measure 800mm high by 1000mm wide (see 

photograph below). 

The QMED flow on the Owreagh River is estimated to be 32m 3 /s. A culvert with a minimum 

opening size of 10.3m 2 would be required to convey this flow without surcharge. In addition 

to this conveyance area, when designing a culvert 250-300mm should be allowed for siltation 

at the base of culvert, and 250-300mm freeboard above the design water level. In practice 

this means that if a culvert is 1.5m high, only 0.9 -1m of this height should actually be counted 

for conveying flood flow. 

The main culvert was inspected during the site visit and estimated to have an opening of 6- 

8m 2 . The combined opening of the main and relief culverts is approximately 8-10m 2 , which 

would provide sufficient capacity to convey approximately the QMED flow. 

(8) Owreagh River (8) Flood relief culvert at the Derreenavurrig 

Road 

The individual size of each of the three relief openings is smaller than would normally be 

recommended for a culvert, and it is likely that during a flood event these openings would 

become blocked by debris and vegetation. 

The results of the hand calculations suggest that a minimum of 3 no. 900mm diameter 

culverts would be required to provide conveyance for the 10 year, non-surcharged flow (45 


m 3 /s). A more detailed assessment of the culvert and channel will allow accurate sizing, 

based on a specific design and layout to be undertaken. 

5.2 Flow Constraints 

There are a number of constrictions and constraints to flow through Sneem: 

The previously highlighted location to the north of the GAA ground, where there is a 

considerable accumulation of sediment and vegetation growth in the channel and 

along the banks; 

Downstream of the confluence of the Sneem and the Ardsheelhane, and to the south 

east of the GAA ground, the river makes a second 90 degree turn. There is currently 

no evidence of water leaving the bank here, but care must be taken to ensure works 

upstream do not increase water levels at this bend; 

The bed of the channel through the centre of Sneem has significant rocky outcrops 

which act to constrict flow in several locations, particularly in the vicinity of the bridge; 

Downstream of the bridge the river is tidally influenced, which can cause the 

tributaries which discharge into this reach to back-up. 

Looking upstream through the Sneem Bridge 

5.3 Flood Defence Assets and Maintenance 

There are no formal flood defences in Sneem. However, informal works were undertaken 

following the extreme flooding in November 2009. This involved raising the height of the right 

bank to the north of the GAA pitch, where water overtops the banks. Since this work has 

been carried out there have been no periods of heavy rainfall, so it is not known if the work 

will be fully or partly successful. However, examination of the bank levels in this area 

indicates that the crest on the right bank (GAA side) is now higher, by some 0.4m, than the 

left bank (Figure 5-2). This indicates that water will either remain in channel or would 

preferentially flow over the left bank during future flood events. 

A more detailed assessment of the impact of this works should be undertaken to determine: 

The reduction in flood risk to the GAA ground, the land surrounding the field drain 

and the Atlantic Gateway and neighbouring properties; 

Any increase in flood risk downstream arising from flows being contained in channel. 


Figure 5-2 Bank levels to the north of the GAA ground 



No maintenance work is undertaken on the channel or its bank. It is reported that historically 

(30 or 40 years ago) the vegetation was cut, and gravel and silt was cleared from sections of 

the bed. Anecdotal reports suggest that incidents of flooding reduced significantly in the 

several years following a maintenance period. 

Kerry County Council have outlined that the frequency of inspection and maintenance of the 

road culverts is intermittent; it is noted that the gullies and road edge were being inspected 

and cleaned during JBA's site visit. 

5.4 Flood Extents 

The flood mapping methods discussed in Section 4 allow maps to be produced showing 

Flood Zones A and B (Figure 5-3), as defined by the Planning System and Flood Risk 

Management. 

Having identified the extents of flood zones A and B an assessment can be made of the 

property, environment and infrastructure which may be at flood risk. 


Figure 5-3 Flood Zones A and B 



5.5 Flood Depths and Frequency 

During the site visit, wrack marks were recorded on the internal walls of one of the properties 

in the Atlantic Gateway development. The internal flood depth was 0.15m (Figure 5-4, wrack 

mark highlighted in blue), which was calculated to correspond to a water level of 8.77 mOD 

(Malin head). Due to the lack of gauge record for the River Sneem and its tributaries, it is not 

possible to correlate this event with a return period. However, anecdotal evidence suggests 

that the properties at the Atlantic Gateway have flooded "a couple of times" since their 

construction approximately five years ago. Although the weather over the period has been 

particularly wet, this would suggest the development, or properties, are at risk from 

reasonably frequent events. 

An interrogation of the extent of the flood zones compared with the ground levels in the 

vicinity of the Atlantic Gateway indicates that the water level associated with Flood Zone A is 

approximately 9.3-9.5 mOD, with Flood Zone B being slightly higher (9.5-9.6 mOD). The 

topography in this part of the catchment means there is little difference in the extents of Flood 

Zones A and B. The depth of flooding varies depending on the ground height. An indication 

of the flood depths is provided in Figure 5-5, but it is noted that this is based on a coarse 

digital terrain model, and does not take into account the earthworks associated with the 

housing construction. 


Figure 5-4 Wrack mark in the Atlantic Gateway 

Figure 5-5 Depth bands for fluvial Flood Zone A 




5.6 Property at Risk 

To determine the number of properties at risk of flooding, a matrix was constructed based on 

the known depth of the most recent flood event, and the results of the threshold survey. This 

quantifies the number of properties which would be affected by a range of flood depths. 

The walkover survey confirmed that the lower lying properties (relative to the river channel) 

were located to the south-west of Sneem, in the vicinity of the Atlantic Gateway development. 

An interrogation of Flood Zone A shows nine properties to be at risk of fluvial flooding, and an 

additional four properties lie within Flood Zone B. All the properties within Flood Zone A, and 

all except one in Flood Zone B are located in the Atlantic Gateway development. 

Figure 5-6 Properties within Flood Zone A 

GAA Changing Rooms Atlantic Gateway Development 

One of the properties at risk is the GAA changing rooms and ancillary buildings. All the other 

properties at risk are residential, which, following the classification laid down in the Planning 

System and Flood Risk Management guidelines, makes them highly vulnerable to flooding. 

The changing rooms would be considered to be water compatible as they are associated with 

a playing field which is also in Flood Zone A. 

The flood level associated with the GAA pitch flooding is unknown, but the grounds are 

reported to flood several times a year, so inundation is likely to begin at a relatively low level. 

Table 5-1 Properties at flood risk 

Flood Level (mOD Malin) Number of properties at risk 

8.57 0 

8.67 2 

8.77 (recorded level) 2 

8.87 3 

8.97 3 

9.07 3 

9.17 6 

9.27 6 

9.37 (approx. Flood Zone A) 9 

9.47 (approx. Flood Zone B) 12 

9.57 13 

9.67 15 

9.77 20 


5.7 People at Risk 

Flooding of roads can cause an inconvenience to local residents and visitors alike. In Sneem 

flooding is generally shallow, and of short duration which reduces the impact and 

inconvenience of road blockage and closure for those wishing to travel. 

Where flood waters enter properties the impact on people is greatly increased. Even a few 

centimetres of flooding can cause damage to the building structure, furniture and other 

possessions, and may require new flooring, wall coverings and rewiring. Contamination due 

to flood water can have detrimental impacts on health, and the psychological pressure of not 

knowing if and when another flood will occur can place considerable strain on residents. 

5.8 Infrastructure at Risk 

There is a fire station, Garda station and primary school located on the N70 to the west of 

Sneem Bridge. None of these critical services are shown to be within the flood zones. 

As highlighted through the historic flood records, sections of both the N70 and the 

Derreenavurrig Road to the south of the town are at risk of flooding. 

The waste water treatment plant has also flooded on a number of occasions in the past. 

5.9 Environment at Risk 

The lower reach of the Sneem River forms part of the Kenmare River SAC. Flooding below 

the Sneem Bridge is tidal, and above the bridge is generally contained within the high, 

naturally rocky channel sides. The overland flow route from the GAA pitch is not through an 

environmentally designated site. 

However, the risks to the wider environment include contamination from the sewer and 

surface water systems. Flooding of the waste water treatment plant may cause 

contamination of water and the surrounding area. 


6. Flood Mitigation Options 

6.1 Introduction 

There are a number of flood mitigation options available to alleviate the risk of flooding in 

Sneem. These include one or a combination of the following (see Figure 6-1, below, for 

mitigation locations). More detail is provided for each option in the following sections, 

including an assessment of cost, environmental, construction and health and safety 

implications. 

1. Do nothing 

2. Install level / flow gauge and establish monitoring programme 

3. Periodic maintenance of the channel, including removal of in channel deposits and 

bank vegetation clearance 

4. Build a bank along the river bank upstream of the GAA ground to direct flows round 

the bend in the river 

5. Increase the capacity of the field drain which currently flows from the GAA ground 

past the Atlantic Gateway 

6. Build a berm around the Atlantic Gateway development 

7. Increase the capacity of the culverts (a) at the Atlantic Gateway and (b) near the 

Waste Water Treatment Works 

8. Re-profile the Sneem River 

9. Upstream Attenuation 

10. Retro-fit flood resistant and resilience measures to the properties at risk 

11. Relocate at risk properties 

This pre-feasibility study will allow a preferred option/suite of options to be developed. The 

detailed design stage of any option should include a more detailed study, including hydraulic 

modelling, to determine design capacity / levels, and give a better understanding of the 

impact the design may have on flood risk elsewhere. 

6.2 Options Appraisal 

6.2.1 Do nothing (1) 

This option is used to provide a baseline scenario against which the other options can be 

measured, and would assume any interventions and maintenance are stopped. In Sneem, 

where little or no maintenance is carried out, this option is also assumed to be a reflection of 

the current scenario. 

Under this option, residential properties, the GAA pitch and surrounding lands would continue 

to flood, and it is possible that the frequency and severity of flooding would increase both as a 

result of continued channel constriction and the likely impacts of climate change. 

There is no direct works cost implication associated with this option. 

As there is no requirement for construction or on-going maintenance, there are no health and 

safety implications for workers. However, the risks to the public and landowners during flood 

events would remain, and could increase over time. 

6.2.2 Install level / flow gauge and establish monitoring programme (2) 

There is currently no means of monitoring water flow on the River Sneem or its tributaries. In 

order to establish a quantitative record of water level or velocity, and the relationship these 

have with flow, it is recommended that a programme of monitoring is established at an 

appropriate site on the River Sneem, between the Sneem Bridge and the confluence of the 

Sneem and the Ardsheelhane. 


Figure 6-1 Flood mitigation measures 



The relationship between water level and flow rate within a river is complex and depends on 

control points. These are points within the river that control the relationship between depth 

and flow rate upstream, and for a short stretch downstream, of the point. Typical control 

points include weirs, sluice gates, or natural constrictions in the river. In the absence of 

structures or natural river constrictions, the control can be produced by a stretch of river. This 

applies at most flow measurement stations, and is the most cost-effective method for 

establishing a short term flow record on the Sneem. However, these natural points of control 

can move with changes in the flow rate and changes in the river cross section, thus changing 

the depth-flow rate relationship. A weir in the river causes a fixed control point and is 

desirable for this reason. However, the associated cost of weir installation is often prohibitive. 

Nationally, only 43 flow stations use weirs. 


There are a range of options available for the installation of a gauging station. The choice of 

option depends on the available budget, and the suitability of the channel for gauging. 

A basic level recorder/logger and staff gauge would provide a relatively inexpensive means of 

establishing a rated river section (

6.2.4 Build a berm around the Atlantic Gateway development (4) 

The majority of the properties at risk of flooding are located within the Atlantic Gateway 

development, so would benefit from a localised flood protection scheme. Such a scheme 

could comprise an earthen embankment to protect the development from flood waters (Figure 

6-3). Water would be routed back towards the field drain and the lower lying field on the right 

bank of the drain. Although this will result in the loss of a small quantity of floodplain behind 

the berm, the loss is unlikely to have a significant impact on flood frequency or levels 

elsewhere; the volume is very small when compared with the total volume of water and the 

area of the fields which are currently at flood risk. Full hydraulic modelling would allow the 

impact of loss of floodplain to be quantified. 

The embankment would tie in with existing higher ground levels, and should be carefully 

designed to allow access across the road whilst still providing a sufficient barrier to flow. 

Figure 6-3 Berm around the Atlantic Gateway development 



As this is a localised scheme, it would not protect the upstream GAA ground or properties and 

land outside the Atlantic Gateway development. 

Construction of the embankment would be reasonably straightforward, with the inclusion of 

the road and tying into the existing road levels adding an element of complexity. The 

maintenance requirements of the embankment would be low, and may include vegetation 

removal. Although it is possible that the embankment could be raised in line with climate 

change, the passage of the road may make this difficult 


The health and safety implications associated with construction are low. During operation, 

the safety of residents of the Gateway is secured whilst flood waters are lower than the 

embankment. However, the risks to the public and landowners during flood events outside 

the development, and those requiring access or egress from the Atlantic Gateway 

development would remain, and could increase over time. 

6.2.5 Build a bank along the river bank upstream of the GAA ground to direct 

flows round the bend in the river (5) 

This option would entail the construction of an embankment to the north of the GAA ground, 

to prevent flows leaving the channel at the bend. As discussed in Section 5.3, informal bank 

raising has taken place here in the last number of months. 

Prior to any further works being undertaken in this location the impact of the informal 

measures should be fully investigated; both through detailed hydraulic modelling and 

monitoring flow routes during future flood events. It is also important to ensure that 

remodelling the right bank will not increase the risk of flooding downstream as a result of 

increased water levels in the channel, or result in a re-direction of flows through the low bank 

behind the GAA changing rooms. 

This option has the potential to reduce flood risk through Sneem, including to the GAA 

ground, the arable land and residential properties, including the Atlantic Gateway. 

The health and safety implications associated with construction are low, and the risks for the 

population of Sneem are removed whilst flood waters are lower than the embankment. 

The cost of modelling the stretch of river will be approximately €20,000 (including survey). If 

the findings of the modelling demonstrate sufficient bank raising has been undertaken, then 

no further costs will be incurred. 

To provide a consistent level of protection along the river bank a small volume of fill may be 

required behind the GAA changing rooms; a low spot in the bank was identified in this 

location during JBA's site visit. 

Figure 6-4 Reprofiling the river bank 




6.2.6 Increase the capacity of the field drain which currently flows from the 

GAA ground past the Atlantic Gateway (6) 

Increasing the capacity of the field drain would provide a greater volume of flood storage, and 

thus reduce the depth and frequency of flooding of the adjacent fields. This will reduce the 

volume of water overtopping onto the road, and reduce the frequency of flooding of the 

Atlantic Gateway development. 

However, the reported frequency and depth with which the fields flood indicates that the drain 

would have to be enlarged considerably and lowering of the immediate floodplains may be 

required. 

This option has the potential to reduce flood risk to the Atlantic Gateway and neighbouring 

properties, and a proportion of the fields, but would not reduce risk to the GAA ground. 

Landscaping on such a large scale would also be highly damaging to the wetland habitat, and 

the changed flood regime and water levels could have longer term impacts on the wider 

ecology of the area. 

6.2.7 Increase the capacity of the culverts at the Atlantic Gateway (7a) 

This option could be undertaken as a standalone measure, or in conjunction with the 

enlargement of the field drain. The culvert below the N70 road is currently a 900mm pipe, as 

is the culvert downstream of the N70. 

As a standalone measure, increasing the culvert capacity would allow a greater flow of water 

through the culvert, and would decrease the frequency of overtopping of the road. The right 

bank of the field drain adjacent to the Atlantic Gateway development is lower than the left 

bank, so once the drain reaches capacity, water would preferentially flow onto the fields, 

rather than the development. Hydraulic capacity calculations would need to be undertaken to 

determine the required culvert dimensions. 

If the culvert was enlarged and the drainage channel capacity also increased, flood levels 

would be reduced upstream. Water would drain with a greater rapidity from the upstream 

fields, and would collect to an increased depth on the downstream fields. It is reported that 

the downstream field also floods as a result of water backing up from the Owreagh, so the 

interactions between the two events would need to be investigated to ensure water levels 

would not rise to flood the road and properties to the west, which are not currently shown to 

be at risk. 

Either of the variations of this option should reduce the risk of flooding to the Atlantic Gateway 

development, but would have no impact on the upstream GAA ground. The benefit to the 

fields is variable; those upstream of the road would flood to a lesser depth, but the frequency 

of flooding would remain largely unchanged. The speed of drainage from the fields would be 

enhanced. The land downstream of the road would flood to a greater depth. 

To provide flood relief to both the GAA ground, and the Atlantic Gateway this measure could 

be combined with the construction of a berm upstream of the GAA ground (4). 

The residual risks associated with reliance on a culvert to route flood waters away from the 

development are high; regular maintenance is required to ensure the culvert and its 

approaches remain clear. Should the culvert become blocked, flood risk is likely to revert to 

the pre-works scenario. 

6.2.8 Increase the capacity of the Derreenavurrig Road culvert (7b) 

An analysis of the current capacity shows that the culverts are sized to allow flows of 

approximately QMED pass through, although there is likely to be some water pooling on the 

banks upstream of the road. To increase the capacity of the openings to allow the 10 year 

flood pass without surcharging would require the construction of a minimum of 3 no. 900mm 

diameter culverts. Routine inspection and maintenance would also need to be undertaken to 

ensure the culverts remain clear. 

The preliminary site inspection indicated that this option may be constrained by space, or that 

clearance works would be required to allow the installation of the additional culverts. 


A more cost effective solution may be to create an on line attenuation area upstream of the 

culvert, which would allow water to discharge gradually through the culvert, rather than 

overtopping the road. 

6.2.9 Reprofile the Sneem River (8) 

To ensure extreme floods are contained in channel, reprofiling of the channel bed could be 

undertaken. This is a more invasive option than simply undertaking clearance associated 

with regular maintenance, and would involve removing bed rock from the channel floor and 

reshaping the channel sides to achieve a smoother and more regular profile. Ongoing 

maintenance would be required to retain the artificial profile. 

There are two constraints on this option. Firstly the impact of the works on the environment 

and ecology of the area; much of the works would take place within the Kenmare SAC. In 

addition, it is highly likely that the bridge structure in Sneem would require underpinning as a 

result of the removal of upstream bed materials. 

6.2.10 Upstream Attenuation (9) 

A number of the options detailed above result in the possibility of increasing the risk of 

flooding to Sneem town, either by increasing the velocity or volume of water contained in the 

channel. This risk may be mitigated by providing an on-line flood storage area upstream of 

the town. This may be achieved by lowering the bank levels upstream of the confluence of 

the Sneem and Ardsheelhane Rivers to create a flood attenuation area. As water levels in 

the river drop, the water on the floodplain will recede, resulting in a lower but more prolonged 

peak through the town. At this pre-feasibility stage, a conservative approach to flood 

frequency reduction has been adopted. This assumes all flow will be contained in the 

attenuation area upstream of Sneem, or in-channel. This would require an area with similar 

capacity to the fields which currently flood, estimated to be approximately 0.25km 2 , flooding to 

a depth of 0.5-1m. More detailed hydraulic assessment would allow this volume to be 

quantified more precisely, and allow a range of intermediate options, whereby some out of 

bank flooding is allowed, to be tested. 

This option has the advantage of offering flood protection to the whole town, but would result 

in inundation of lands which have not traditionally flooded, and which are in private 

ownership. 

The environmental implications are likely to be two fold; firstly a traditionally 'dry' area would 

be subject to periodic inundation, and the wetlands to the west of the town would flood less 

frequently. 

The creation of an area of standing water could create a risk to people, and also to livestock 

in the fields; the rapid catchment response time means there is unlikely to be sufficient time to 

warn the landowners of the flood. 

6.2.11 Retro-fit flood resistant and resilience measures to the properties at risk 

(10) 

There are a wide range of flood resilience (minimising the impacts of flooding, and 

maximising the speed and efficiency of recovery) and resistance (preventing the inflow of 

water to the property) products and design techniques available, but all are most costeffectively 

incorporated into the construction phase of developments. However, it is possible 

to undertaking retro-fitting to minimise the impact of future flood events. 

The cost of the option would depend on the exact nature of measures adopted, but could 

range from fairly low cost options, such as laying tiles on the ground floor and refinishing 

walls with water resistant concrete or plaster, to rewiring the property to ensure feeds are 

from the roof down. Flood gates across door ways are useful for resisting moderate depths of 

water (up to 0.6m), but rely on the resident having sufficient warning to operate the system. 

Whilst this option minimises flood damage to upgraded buildings, it is unlikely that all 'at risk' 

properties will be flood-proofed, particularly where funding is up to the private individual, and 

in cases where there is no history of flooding. There will also be no benefits to the GAA 

ground, or to the surrounding fields. 


The wider health and safety risks associated with flood waters are not dealt with, and where 

'resilience' has been adopted, there are still costs and risks associated with cleaning up after 

the flood waters have receded. 

6.2.12 Relocate at risk properties (11) 

If the level of risk to properties, particularly in the Atlantic Gateway, is deemed to be 

significant and likely to increase over time, the development could be abandoned, and the 

occupiers relocated. This option would only benefit those properties which are abandoned, 

and would provide no wider reduction in flood risk. Based on the advertised price for the 

properties in the Atlantic Gateway, this could amount to a loss to the developer of €200,000 to 

€300,000 per property, with nine properties lying within Flood Zone A. Demolition of the 

abandoned properties would also be required. 


7. Cost Benefit Analysis 

7.1 Option Costs 

The overall cost estimates for the various options contained within this report have been 

prepared in association with Kerry County Council staff and by utilising available works 

studies and recent drainage works costs. The cost options are summarised in Table 7-1. 

Table 7-1 Summary of option costs 

Option Cost (€) 

Do nothing 0 

Install level / flow gauge and establish monitoring programme 2,000 to 10,000 

Periodic maintenance of the channel, including removal of in channel 22,000 

deposits and bank vegetation clearance (cost is for one maintenance 

period) 

Build a bank along the river bank upstream of the GAA ground to direct 6,000 

flows round the bend in the river 

Increase the capacity of the field drain which currently flows from the 20,000 

GAA ground past the Atlantic Gateway 

Build a berm around the Atlantic Gateway development 9,000 

Increase the capacity of the road culvert at the Atlantic Gateway (2no. 17,000 

900mm pipes) 

Increase the capacity of the Derreenavurrig Road culvert (3no. 900mm 12,000 

pipes) 

Re-profile the Sneem River 150,000 

Upstream Attenuation (based on excavating 250,000m 3 ) 

> 750,000 plus land 

compensation 

Retro-fit flood resistant and resilience measures to the properties at risk 10,000 per property 

Relocate at risk properties 200,000 to 300,000 per 

property 

7.2 Flood Damages and Benefits 

7.2.1 Tangible Impacts 

The methodology used to calculate the benefits for a given flood risk management option is 

based on guidance provided by the OPW. If the capital value of proposed works for the 

scheme is under €500,000, OPW recommends the following approach: 

A standard €25,000 benefit should be applied for each residential property removed 

from the 100 year return period flood cell. Alternative cost benefits are provided 

based on other criteria; 

For each commercial property apply a benefit value equal to the local authority rates 

times a defined multiplier, which should be reviewed to ensure the flood benefits do 

not exceed the capital value of the property. In Sneem there are no commercial 

properties at risk, so a multiplier has not been defined; 

The full benefit to properties will be accrued only where the property is removed from 

the 100 year return period flood cell. Where the standard of protection to a property 

is increased, but it remains in the 100 year return period flood extents then the 

benefits will be accrued proportionately using percentages provided by OPW; 

The benefit to cost ratio of the scheme must be at least 1.5:1. 


Table 7-2 OPW Benefit Criteria 

Benefit (€) Criteria 

25,000 Per existing home flooded 

10,000 Per existing home at risk of flooding 

30,000 Per commercial premises flooded 

400 Per hectare of land continuously flooded for at least one month 

20 Per journey where a diversion greater than 30 minutes is caused by the flood 

160 Per day each home cut off by the flood 

It is assumed that the any works undertaken will have a 100 year standard of protection, so 

the full benefit given in Table 7-2 will be accrued. The OPW standard methodology does not 

specify benefits to recreational premises, so a benefit of €2,000 has been assumed. 

The only option which has no direct financial benefits is the installation of a flow gauge on the 

Sneem. However, the long term benefits, and advantages associated with building a local 

gauge record should not allow this option to be discounted on a cost-benefit basis. 

As all the residential properties are located in the Atlantic Gateway, the benefits would be felt 

if any of the remaining options were implemented; all the options are upstream of the Atlantic 

Gateway, so all would affect flood risk to the properties. The benefit to the GAA ground 

would arise under the implementation of options 3, 5 and 8, which are focused on reducing 

flood risk through the whole of Sneem. Although agricultural land and roads are flooded, the 

water recedes rapidly, so no significant benefit can be gained through these criteria. 

The financial benefits are summarised in Table 7-3 and Table 7-4. 

Table 7-3 Summary of Financial Benefits - Options 3, 5 and 8 

Criteria Number Benefit (€) 

Per existing home flooded 2 25,000 

Per existing home at risk of flooding 9 10,000 

GAA Changing Rooms 1 2,000 

Total Benefit 142,000 

Table 7-4 - Summary of Financial Benefits - 

Options which are applied locally to the Atlantic Development 

Criteria Number Benefit (€) 

Per existing home flooded 2 25,000 

Per existing home at risk of flooding 9 10,000 

Total Benefit 140,000 

Applying the OPW's benefit to cost ratio of 1.5:1 caps the cost of a potential scheme at 

between €93,000 and €95,000. Upstream attenuation, reprofiling of the river and relocation 

of at risk properties fall outside this benefit ratio, but the smaller scale options are justifiable. 

7.2.2 Intangible Impacts 

In addition to the financial benefits detailed above, it is important to consider the wider 

benefits of a scheme, or proposed works to the environment and wider community. 

Broad flood risk objectives have been defined, and are recorded in Table 7-5. 


Objectives 

Reduce 

frequency of 

flooding from 

the River 

Sneem and 

field drain to: 

Reduce 

frequency of 

flooding from 

the Owreagh 

to: 

Ensure no 

increase in 

flood risk to: 

Preserve the 

ecology of: 

Table 7-5 Objective Appraisal Matrix 

1. Do nothing 

2. Install level / flow gauge 

3. Periodic maintenance 

2010s4114 - Sneem Pre-feasibility study Final Report v1.docx 33 

4.Berm around the Atlantic 

Gateway 

5. Bank along upstream of the 

GAA ground 

6.Increase field drain capacity 

7a. Increase the capacity of the 

culvert sat the Atlantic Gateway 

7b. Increase the capacity of the 

Derreenavurrig road culvert 

8. Reprofile the Sneem River 

9. Upstream Attenuation 

10. Retro-fit flood resistant and 

resilience measures 

The GAA ground -- -- = -- ++ -- -- -- ++ ++ -- -- 

Agricultural land -- -- = -- ++ - = -- ++ - -- -- 

Atlantic Gateway -- -- = ++ ++ ++ + -- ++ ++ - ++ 

N70 -- -- = -- ++ - + -- ++ ++ -- -- 

Derreenavurrig 

Road 

-- -- = -- -- -- -- + -- -- -- -- 

WWTP -- -- = -- -- -- -- + -- -- -- -- 

Properties along 

the N70 

-- -- = -- ++ + + -- ++ ++ - -- 

Sneem town -- -- = -- = + + -- ++ ++ -- -- 

Kenmare SAC ++ ++ -- ++ - ++ ++ ++ -- - ++ ++ 

Wider environment 

(including wetland 

fields) 

++ ++ - ++ -- - = ++ -- - ++ ++ 

Upstream arable 

lands 

++ ++ ++ ++ ++ ++ ++ ++ = - ++ ++ 

Overall Assessment -- -- - -- ++ - + - - + -- -- 

Key 

++ Significant reduction in flood risk / considerable environmental benefits 

+ Reduction in flood risk / some environmental benefits 

= Modest reduction in flood risk / No environmental impact 

- Some reduction in flood risk / Negative environmental impact 

-- No reduction in flood risk (and risk is likely to increase in the future) / Very negative 

environmental impact 

11. Relocate at risk properties

This page is intentionally left blank 


8. Recommendations 

8.1 Short Term Actions 

Over the immediate / short term it is recommended that a river gauge is installed at a suitable 

location on the River Sneem. A monitoring programme of at least two years (and longer 

should a suitable range of floods not be experienced in this time) should be undertaken. This 

will provide the basis for a local set of flood data to be established. Ideally this will be 

telemetered, and could be linked to existing telemetry at the WWTP. 

In addition, advice on flood resilience measures for 'at risk' properties, and the cause of action 

to be followed during a flood event should be provided to local residents. There is a 

significant amount of information available on the subject from the OPW's website, 

www.flooding.ie, so a local awareness campaign building on this resource is recommended. 

A programme of channel maintenance, including bank top vegetation clearance will increase 

channel capacity in the vicinity of the GAA ground. It is unlikely that a moderate level of 

maintenance will increase flood risk downstream of the GAA ground. 

In addition, increasing the capacity of the field drain may alleviate risks associated with water 

backing up in the fields to the west of Sneem village. However, this would require agreement 

with affected landowners. 

Prior to any further engineering work being commissioned which relates to options 4, 5, 7a 

and 7b 6 , it is recommended that further, more detailed, hydraulic analysis and possibly a full 

hydraulic study is undertaken. 

8.1.1 Detailed Hydraulic Study 

A more detailed study would include for topographic survey of the river channels (at frequent 

intervals) and would include all structures. It should also include for OSi LiDAR data of the 

area, which would supplement the existing topographic and threshold survey data. 

The base data described above would allow for a 1D hydraulic model or a 1D - 2D linked 

hydraulic model to be constructed. The model would provide accurate estimates of existing 

channel and structure capacities and would allow for the investigation of alleviation options 

relative to chosen standards of protection. 

Depending on the scope of the required study the associated cost could be in the region of 

€20,000 to €50,000 including all survey and data costs. 

Data from the recommended installation of the river gauge would allow for greater confidence 

to be placed in the return period flows that are used to run the hydraulic model and hence the 

standard of protection that is afforded under any mitigation works. 

The longer the period of gauge data collection, the greater the confidence in the return period 

flows. 

8.2 Medium Term Actions 

Depending on the outcomes of the hydraulic modelling, further engineering works may be 

required. Of the options appraised, the most beneficial would be raising the bank heights to 

the north of the GAA ground (right bank), potentially combined with lowering of the left bank 

to encourage preferential flooding of the agricultural lands. However, this would require 

negotiation with, and agreement from, affected landowners under a consultation process. 

If none of the above engineering measures proved feasible then option 10 may have to be 

considered which would involve retro-fitting flood resistance and resilience measures to the 

properties at risk. 

6 Options 8 and 9 do not meet the current OPW cost benefit analysis criteria 


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