SUIR CATCHMENT FLOOD RISK ASSESSMENT AND MANAGEMENT STUDY HYDROLOGY REPORT Draft Final Report July 2015 Doc Ref: -1891_RP_ Hydrology Report Draft Final_Rev14 FRAM Section Engineering Services Office of Public Works River Suir CFRAM Study Hydrology Report 1891_RP_Hydrology Report ii Draft Final River Suir CFRAM Study Hydrology Report Document Control Sheet Client Suir Steering Group Suir Catchment Flood Risk Assessment and Management Project Title Study Document Title Hydrology Report Document Ref No: - 1891_RP_ Hydrology Report Draft Final This Document List of List of No of DCS TOC TEXT Tables Figure Appendices Comprises of the Following Pages 1 1 150 1 1 A to J Approved Office of Issue Rev Status Author(s) Reviewed By By Origin Date ON, NB, GG, Trim / 01 Draft SM CO’D Dublin ON, NB, GG, Trim / 02 Draft CO’D Dublin ON, NB, GG, Trim / 03 Draft CO’D, RK Dublin ON, NB, GG, Trim / 04 Draft GG CO’D, RK Dublin ON, NB, GG, Trim / 05 Draft CO’D, RK Dublin ON, NB, GG, Trim / 06 Draft CO’D, RK, CN, Dublin VF ON, NB, GG, Trim / 07 Draft CO’D, RK, CN, Dublin VF ON, NB, GG, Trim / 08 Draft CO’D, RK, CN, Dublin VF ON, NB, GG, Draft Trim / 09 CO’D, RK, CN, Final Dublin VF, SN 10 Draft ON, NB, GG, Trim / Final CO’D, RK, CN, Dublin 1891_RP_Hydrology Report iii Draft Final River Suir CFRAM Study Hydrology Report Final CO’D, RK, CN, Dublin VF, SN ON, NB, GG, Draft Trim / 11 CO’D, RK, CN, Final Dublin VF, SN ON, NB, GG, Draft Trim / 12 CO’D, RK, CN, Final Dublin VF, SN ON, NB, GG, Draft Trim / 13 CO’D, RK, CN, Final Dublin VF, SN ON, NB, GG, Draft Trim / 14 CO’D, RK, CN, AH 16/07/2015 Final Dublin VF, 1891_RP_Hydrology Report iv Draft Final River Suir CFRAM Study Hydrology Report EXECUTIVE SUMMARY The Office of Public Works and its partners, North Tipperary County Council, South Tipperary County Council, Kilkenny County Council, Waterford City Council, Waterford County Council, are undertaking a catchment-based Flood Risk Assessment and Management Study for the Suir catchment (Suir CFRAM Study). The main output from this study will be predictive flood maps and a Catchment Flood Risk Management Plan (CFRMP), which will identify a programme of prioritised studies, actions and works to manage the flood risk in the catchment. The plan will also develop a series of predictive flood which can be use as a decision support in relation to appropriate development planning. The Suir CFRAM study is one of four pilot projects of the national approach to flood risk management and is being undertaken in-house by the OPW. An extensive review of historic flood related documents has highlighted that there are a number of urban and rural areas at risk of flooding within the Suir catchment from both tidal and fluvial flood mechanisms. These areas are referred to as Areas for Further Assessment (AFAs) and will be the main focus of the study. The Suir CFRAM Study will identify both the existing and the potential future risk of flooding to communities. There are a number of drivers that can influence future flood risk in the Suir catchment; the main drivers have been identified as being climate change, afforestation and urbanisation. These drivers have been extensively investigated and two future flood risk management scenarios have been proposed, a Mid Range Future Scenario (MRFS) and a High End Future Scenario (HEFS). A review of flow, rainfall and tidal gauge data and historic flood documentation has identified a number of flood events which will be used to calibrate / verify the hydrology and hydraulic of the study. In addition, a detailed review of a number of river gauges in the catchment was undertaken. This review is published in a separate report titled ‘Suir CFRAM Study River Gauge Review Final Report’. A summary of the conclusions of this report has been included as Chapter 5 in this report. This report details the hydrological assessment that has been undertaken for this study with the objective of determining hydrological inputs for the Suir and its tributaries for specific present day and for the two future scenario design events, (i.e. MRFS and HEFS). The assessment is based on a review and analysis of historic flood information and use of meteorological and hydrometric records employing Flood Studies Update (FSU) and IH124 methodologies. 1891_RP_Hydrology Report v Draft Final River Suir CFRAM Study Hydrology Report The outputs from the hydrological analysis will be used in the subsequent hydraulic modelling phase of the study. The rainfall-runoff boundary units will be used to calibrate the hydraulic models to known historic flood events. Following from this, the design flows will be used to create flood maps for both present day and future scenarios. Furthermore, knowledge of the hydrological processes and historic flooding gained from this work will support the decision making process for the flood risk management options phase of the study. A flow chart outlining the hydrological analysis undertaken for the Suir CFRAM Study is presented on the next page. The relevant section of the report relating to each aspect of the analysis is included for ease of reference. 1891_RP_Hydrology Report vi Draft Final River Suir CFRAM Study Hydrology Report 1891 – SUIR CFRAM Study Hydrology Flow Chart Hydrological Calibration of 'Calibration Inflows' Generation of Design Inflows Rainfall Runoff model inflow predictions (all FSU Ungauged Catchment FSU Gauged Catchment points) Section 4 Characteristics Characteristics/ Gauged Data Section 7 Section 5 Historic/Observed flows (at Gauges) Section 4 River Gauge Review Section 5 Median Flow Pooling Group Adjusted Rainfall Runoff inflows (at Gauges (Qmed) Analysis/Growth THEN at all points) Generation Factor Analysis Section 6 Section 7.4 Section 7.5 & 7.6 Amax Series Section 6.2 Calibration Inflows to Hydraulic Models (all Generation of Peak Design points) Section 6 Flows Qmed Calculation Section 7.6 Section 7.3 Hydraulic Model Construction FSU Single Site Dependence Analysis Analysis Section 7.6 Hydraulic Model Construction Section 9.2 Suir Hydraulics Report Return Period Hydrograph Generation Flows Section 7.7 Section 7 Calibration of Hydraulic Model Flow/Level Data Observed flows (at Gauges) Section 4 Design Inflows to Hydraulic Section 6.5 Models Check Model flows (at Gauges) using Section 9.3 & 9.4 Calibration Inputs Section 6 Adjusted model parameters so Model flows Calibrated Hydraulic Models match observed flows Section 6 Section 6.7 & 6.8 Next Steps - Hydraulic Model Runs, Verify Hydraulic Models, Produce Flood Mapping - Suir Hydraulics Report 1891_RP_Hydrology Report vii Draft Final River Suir CFRAM Study Hydrology Report TABLE OF CONTENTS 1 INTRODUCTION .................................................................................................. 1 1.1 PURPOSE .........................................................................................................1 1.2 SUIR CFRAM ...................................................................................................1 1.2.1 Background..........................................................................................1 1.2.2 Study Objectives ..................................................................................3 1.2.3 Study Outputs ......................................................................................4 1.3 OBJECTIVES OF THE HYDROLOGICAL ASSESSMENT .............................................4 1.4 FORMAT OF THE REPORT ..................................................................................6 2 CATCHMENT DESCRIPTION ............................................................................. 8 2.1 CATCHMENT CHARACTERISTICS .........................................................................8 2.2 FLOODING HISTORY IN THE CATCHMENT .............................................................9 2.2.1 Waterford ...........................................................................................12 2.2.2 Carrick-On-Suir ..................................................................................12 2.2.3 Clonmel..............................................................................................13 2.2.4 Ardfinnan............................................................................................16 2.2.5 Templemore.......................................................................................17 2.2.6 Piltown ...............................................................................................17 2.2.7 Fethard...............................................................................................17 2.2.8 Coastal Flooding ................................................................................17 3 DATA COLLECTION ......................................................................................... 18 3.1 INTRODUCTION ...............................................................................................18 3.2 TOPOGRAPHICAL DATA ....................................................................................18 3.2.1 Floodplain DTMs ................................................................................18 3.2.2 Orthophotography ..............................................................................19 3.2.3 Channel and Cross-Section Survey....................................................19 3.2.4 Defence Asset Database....................................................................20 3.3 METEOROLOGICAL DATA .................................................................................20 3.4 HYDROMETRIC DATA