Draft Catchment Flood Risk Management Plan
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Draft Catchment Flood Risk Management Plan February 2010 Lee Catchment Flood Risk Assessment and Management Study Draft Catchment Flood Risk Management Plan Acknowledgements In early 2006, the Office of Public Works (OPW), Cork City Council and Cork County Council commenced work on a Catchment-based Flood Risk Assessment and Management Study (CFRAM Study) for the Lee Catchment, as a means of addressing the high levels of existing flood risk around the River Lee, its tributaries and estuary, and the potential for significant increases in this risk in the future. In August 2006, Halcrow Group Limited were appointed as lead consultants for the Study. The Lee CFRAM Study was the first pilot CFRAM Study for the new Flood Risk Assessment and Management Programme, which is at the core of the delivery of the new Flood Policy adopted by the Irish Government in 2004, shifting the emphasis in addressing flood risk towards a catchment-based, pro-active approach for identifying and managing existing, and potential future, flood risk. The Lee Catchment Flood Risk Assessment Management Study (CFRAMS) and the Catchment Flood Risk Management Plan (CFRMP) have been prepared by Halcrow Group Ireland Limited under the supervision of the OPW and its partners, Cork City Council and Cork County Council. Halcrow Group Ireland has had support from MarCon Computation International Ltd, J B Barry & Partners and Brady Shipman Martin. An in-house OPW Project Management Team managed the work of the Consultant on the Study. A Project Steering Group, which included representatives from OPW, Cork City Council, Cork County Council and the Environmental Protection Agency, was responsible for overseeing and directing the Study, and reviewing key outputs and deliverables. OPW wishes to acknowledge the endless support and advice of these Steering Group representatives, as well as the input from a wide range of Stakeholders and other interested parties. Sincere thanks are also extended to the Project Team at Halcrow Group Limited and their sub-consultants for their expertise, commitment and cooperation. MarCon Computations International BRADY SHIPMAN MARTIN Ltd i Lee Catchment Flood Risk Assessment and Management Study Draft Catchment Flood Risk Management Plan The project team would like to acknowledge and thank the data suppliers who have contributed to the project. These are listed in the table below: Data suppliers Central Statistics Office Coastal Marine Research Centre Cork City Council Cork County Council Department of Agriculture Fisheries and Food Department of the Environment Heritage and Local Government Electricity Supply Board Environmental Protection Agency Forest Service Geological Survey of Ireland Health Service Executive Hydrographic Surveys Ltd Maltby Land Surveys Ltd Marathon Oil Met Éireann Mott Mac Donald Pettit National Parks and Wildlife Service OPW PM Group Port of Cork RPS Group South West Regional Fisheries Board South Western River Basin District Southern Health Board Teagasc TJ O’Connor and Associates University College Cork ii Lee Catchment Flood Risk Assessment and Management Study Draft Catchment Flood Risk Management Plan Table of contents Table of contents iii Executive Summary viii 1. Introduction and background 1 1.1. Background ............................................................................................................ 1 1.2. Aims and scope...................................................................................................... 2 1.3. Flood risk management policies ............................................................................ 3 1.3.1. National flood risk management policy................................................................ 3 1.3.2. Flood risk management and planning.................................................................. 4 1.3.3. Flood risk and the Water Framework Directive.................................................... 6 2. Involving external parties 7 2.1. Overview ................................................................................................................ 7 2.2. Provision of information.......................................................................................... 7 2.3. Stakeholder consultation........................................................................................ 7 2.4. Public consultation ................................................................................................. 8 2.5. Final consultation stage ......................................................................................... 9 3. Catchment overview 10 3.1. Extent of the Lee catchment ................................................................................ 10 3.2. Topography, geology and soils ............................................................................ 12 3.3. Land use and land management ......................................................................... 13 3.3.1. Land types and land management .................................................................... 13 3.3.2. The Carrigadrohid and Inniscarra hydroelectric power dams............................ 14 3.4. Hydrology and tides ............................................................................................. 15 3.4.1. Hydrological cycle .............................................................................................. 15 3.4.2. Drainage system ................................................................................................ 16 3.4.3. Rainfall and hydrometric data ............................................................................ 18 3.4.4. Groundwater ...................................................................................................... 18 3.4.5. Tides and surge ................................................................................................. 19 3.4.6. Catchment response.......................................................................................... 21 4. Flood hazard assessment 22 iii Lee Catchment Flood Risk Assessment and Management Study Draft Catchment Flood Risk Management Plan 4.1. Introduction .......................................................................................................... 22 4.2. Historic flood hazard ............................................................................................ 22 4.3. Current flood hazard ............................................................................................ 23 4.3.1. Sources of flooding ............................................................................................ 24 4.3.2. Flood probability, modelling and extents ........................................................... 24 4.3.3. Flood mapping ................................................................................................... 27 4.3.4. Description of current flood hazard.................................................................... 28 4.4. Future flood hazard.............................................................................................. 32 4.4.1. Introduction ........................................................................................................ 32 4.4.2. Drivers................................................................................................................ 33 4.4.3. Description of future flood hazard...................................................................... 34 4.5. Groundwater flood hazard for Cork City .............................................................. 38 4.5.1. Potential flooding mechanisms, their occurrence and impact ........................... 38 4.5.2. Future flood hazard............................................................................................ 39 5. Flood risk assessment 40 5.1. Introduction .......................................................................................................... 40 5.2. Economic flood risk.............................................................................................. 40 5.2.1. Economic damages to properties ...................................................................... 40 5.2.2. Risk to infrastructure.......................................................................................... 42 5.3. Social flood risk .................................................................................................... 44 5.4. Risks to the environment...................................................................................... 46 5.5. Existing flood risk management ........................................................................... 47 6. Flood risk management options 49 6.1. Introduction .......................................................................................................... 49 6.2. Flood risk management objectives ...................................................................... 54 6.3. Option assessment process................................................................................. 54 6.3.1 Screening........................................................................................................... 54 6.3.2 Formulation of options ....................................................................................... 56 6.3.3 Detailed option evaluation.................................................................................. 56 6.4. Production of cohesive options ............................................................................ 62 iv Lee Catchment