STUDY TO IDENTIFY PRACTICAL MEASURES TO ADDRESS FLOODING ON THE CLARE RIVER VOLUME 1 - REPORT JUNE 2010 CONSULTING ENGINEERS Sherwood House, Sherwood Avenue, Taylor’s Hill, Galway Suite D4, The Cubes Offices, Beacon South Quarter, Sandyford Dublin 18 Report Control Sheet FORM 214 Rev 002 Business Management System Client Office of Public Works Project No. 2138//07/10 Project Title Clare River Flood Study – Volume 1 Report Title Study to Identify Practical Measures to Address Flooding on the Clare River Rev. Status Author(s) Reviewed By Approved By Issue Date 0 Draft 1 C. Lyons - - 27 May 2010 To TC 1 Draft C. Lyons - - 2 Draft C. Lyons M. Joyce 23 June 2010 3 Final Draft C. Lyons M. Joyce M. Joyce 27 June 2010 4 Final C. Lyons MJ Gannon M. Joyce 9 July 2010 5 Minor C. Lyons M. Joyce M. Joyce 23 July 2010 amendments to Final Report Control Sheet Page 2 TABLE OF CONTENTS VOLUME 1 Executive Summary .......................................................................................................................... 5 1. Introduction ........................................................................................................................ 4 1.1. ......... Background.............................................................................................................................................................. 1 1.2 .......... Methodology........................................................................................................................................................... 2 2. Catchment Characteristics ................................................................................................... 3 2.1...........The Clare River Catchment................................................................................................................................... 4 2.2…….. The section of the Clare River catchment pertinent to this Study.................................................................. 6 2.3…….. The section of the Abbert River catchment pertinent to this Study ............................................................... 7 2.4…….. Control of water levels in Lough Corrib Lower and the Corrib River channel ........................................... 7 2.5...........The operation of the Weir Barrage and its effect on high lake levels....................................................... 8 2.6...........Catchment Geology and Hydrogeology.........................................................................................................13 2.7...........Ecology ...................................................................................................................................................................14 2.8...........Meteorology..........................................................................................................................................................14 2.9...........Urbanisation and Land Use Zoning...................................................................................................................15 2.10 ........Heritage .................................................................................................................................................................17 2.11 ........Historical Flooding................................................................................................................................................17 2.12 ........November 2009 Flood Event.............................................................................................................................27 3. Data Collection ................................................................................................................ 38 3.1. ......... General ..................................................................................................................................................................39 3.2. ......... Hydrometric Data.................................................................................................................................................39 3.3. ......... Meteorological Data ...........................................................................................................................................40 3.4. ......... Operational Data.................................................................................................................................................40 3.5. ......... Surveys ...................................................................................................................................................................40 3.6. ......... Anecdotal Evidence..............................................................................................................................................44 4. Flood Flow Estimation ....................................................................................................... 48 4.1. ......... Introduction ............................................................................................................................................................49 4.2 .......... Statistical Flood Frequency Analysis.................................................................................................................49 4.3 .......... Statistical Analysis of Lower Lough Corrib Flood Levels at Anglinham Gauge (30089).......................51 4.4 .......... River Corrib Flood Flow Magnitude (Wolfe Tone Bridge Gauge (30061) .............................................52 4.5 .......... Flood Peak Estimation of River Clare at Claregalway (30012)................................................................53 4.6 .......... Flood Peak Estimation of River Clare at Corofin (30004)...........................................................................54 4.7 .......... Flood Peak Estimation of River Clare at Ballygaddy Tuam (30007)........................................................55 4.8.......... Discussion of Flood Frequency Results ..............................................................................................................56 4.9 .......... Flood Growth Curve ............................................................................................................................................56 4.10 ....... FSR Catchment Characteristics Index Flood method for ungauged catchments.......................................57 4.11 ....... Donor Station Analysis for Abbert River..........................................................................................................59 Table of Contents Page 3 TABLE OF CONTENTS 4.12 ....... Climate Change Allowance................................................................................................................................60 4.13 ....... Summary of Flood Estimation Results................................................................................................................61 5. Hydraulic Analysis ............................................................................................................ 63 5.1. ......... Introduction ............................................................................................................................................................64 5.2 .......... Model Development.............................................................................................................................................64 5.3 .......... Model Calibration................................................................................................................................................66 5.4 .......... Sensitivity of Flooding at Claregalway to Lough Corrib Lake Levels........................................................69 5.5 .......... Modelling of Flood Alleviation Measures........................................................................................................69 5.6 .......... Model Results.........................................................................................................................................................77 6. Flood Damage Analysis .................................................................................................... 78 6.1. ......... General .................................................................................................................................................................. 91 6.2. ......... Flood Mapping ..................................................................................................................................................... 91 6.3. ......... Assessment of Impact of Flooding .....................................................................................................................91 6.4. ......... Outline Flood Risk Assessment............................................................................................................................98 7. Alleviation Options ........................................................................................................... 90 7.1. ......... General ..................................................................................................................................................................91 7.2. ......... Potential Alleviation Options..............................................................................................................................91 7.3. ......... Summary of Initial Viability Screening of Measures .................................................................................