Ministerial guidelines
The Planning System and Flood Risk Management: Guidelines for Planning Authorities
Flood Zones A, B and C, the sequential approach and the Justification Test for development in areas at risk of flooding.
Department of the Environment, Heritage and Local Government and the Office of Public Works · November 2009 · 81 pages
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- achieving this objective, and set requirements for the OPW, DEHLG and local authorities in this regard. The OPW advises Government in relation to policy development and legislative requirements for flood risk management, and develops, coordinates and implements programmes and measures to reduce the national level of flood risk. These Guidelines have been developed as a direct response to the report above. A number of other policy documents have been published by the Government in recent years, which cover issues relevant to flooding. These include: :: Sustainable Development: A Strategy for Ireland (1997); :: National Climate Change Strategy (2000); :: Making Ireland’s Development Sustainable (2002); :: National Biodiversity Plan, 2002-2006; :: National Spatial Strategy, 2002-2020; :: A Framework for Major Emergency Management (2006); :: National Development Plan, 2007-2013; and :: National Climate Change Strategy, 2007-2012. The key messages arising from these documents are that: Government recognises the significance of flood risk and the need to integrate flood risk assessment and its management into the planning process in order to deliver a policy of avoidance or minimisation of potential future flood risk, and as part of a range of responses to flooding including risk evaluation, flood forecasting and warning, emergencyresponse systems and capital projects of an engineering nature; Proper planning and sustainable development may at the same time require in exceptional circumstances some development in areas of flood risk, provided that the issue of flood risk is managed appropriately; Implications for biodiversity should be considered at all stages of flood risk assessment and its management; Climate change is a dynamic process that requires a precautionary and flexible approach to ensure appropriate provision for, or adaptation to, its potential consequences; and Investment in flood risk management under the National Development Plan needs to be focused on the areas of greatest need through a strategically led flood risk management approach. 1.10 1.11 :: :: :: :: :: 3 Guidelines for Planning Authorities The Planning System and Flood Risk Management
- In addition, implementation of these Guidelines will need to be integrated with the ongoing implementation of relevant EU Directives on water quality and flooding that recognise the importance of managing the water environment on a catchment or river basin basis. In this regard, the Water Framework Directive (WFD)1 has established the overall concept of river basin management embodied in River Basin Management Plans (RBMPs) to enable all rivers and coastal waters to achieve good ecological status by 2015. River Basin Districts made up of groupings of local authorities have been established and are finalising the relevant management plans. The ‘Floods’ Directive2 requires Member States to undertake a national preliminary flood risk assessment by 2011 to identify areas where significant flood risk exists or might be considered likely to occur. Members States are also required to prepare catchment-based Flood Risk Management Plans (FRMPs), by 2015, that will set out flood risk management objectives, actions and measures. In Ireland, the OPW is responsible for overall implementation of the Floods Directive. Under the Floods Directive, the EU recognises the importance of land use management and spatial planning as a key tool in flood risk management. Preparation of River Basin Management Plans (RBMPs) under the Water Framework Directive, catchment-based Flood Risk Management Plans (FRMPs) under the Floods Directive and flood risk assessment within the planning process will in the longer term promote integrated river basin management and sustainable development. In addition, plans and projects arising from the integration of flood risk assessment into the planning process, must where there are implications for sensitive habitats, be subject to appropriate assessment of plans and projects under the Birds and Habitats Directives3 (see also paragraph 3.14). To recap, Fig. 1.1 summarises what integrating flood risk into the planning process is about. 1.12 :: :: 1.13 1.14 1Council Directive 2000/ 60/ EC of 23 October 2000 establishing a framework for Community action in the field of water policy (“the Water Framework Directive”) Official Journal L197/ 30-37. 2 Directive 2007/ 60/ EC of the European Parliament and of the Council of 23 October 2007 on the assessment and management of flood risk: Official Journal L288/ 27-34. 3 Council Directive 79/ 409/ EEC of 2 April 1979 establishing the Birds Directive on the conservation of wild birds and Council Directive 92/ 43/ EEC of 21 May 1992 establishing the Habitats Directive on the conservation of natural habitats and of wild fauna and flora. 4 1
- 5 Guidelines for Planning Authorities The Planning System and Flood Risk Management Fig. 1.1: Flood risk management and the planning system 1 3 3 3 3 3 4 4 4 5 5 2 National Spatial Strategy, National Planning Guidelines Flood Risk Management Guidelines Sequential approach, Strategic Environmental Assessment Sequential approach, dev. plan Justification Test, SEA Sequential approach, dev. plan Justification Test, SEA Sequential approach, dev. plan Justification Test, SEA / Env. Impact Assessment Sequential approach, dev. management Justification Test, EIA Regional planning guidelines Regional Flood Risk Appraisal, Catchment Flood Risk Management Plans Strategic Flood Risk Assessment, Catchment Flood Risk Management Plans City / county development plan Local area plan Strategic Flood Risk Assessment Site-specific Flood Risk Assessment Site-specific Flood Risk Assessment Master plan, nonstatutory plan, site brief Planning application Policy Documents / Instruments Flood Risk Assessment Technique Decision-making Tools Key Chapters n/a
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- Key Messages Flooding is a natural process and can happen at any time in a wide variety of locations. It constitutes a temporary covering of land by water and presents a risk only when people, their property and/or environmental assets are present in the area which floods. Understanding flood risk is an essential step in managing the associated impacts of flooding and in making informed decisions in addressing such impacts. The science is complex, and datasets are currently being enhanced by detailed studies. Therefore, these Guidelines recommend a staged approach. High level regional appraisals, strategic assessments at county/city level and more detailed site specific assessments of flood risk, taking account of the impacts of climate change, will need to be carried out by regional, local authorities and developers respectively. Types and causes of flooding Different types of flooding present different forms and degrees of danger to people, property and the environment, due to varying depth, velocity, duration, rate of onset and other hazards associated with flooding. With climate change, the frequency, pattern and severity of flooding are expected to change, becoming more uncertain and more damaging. There are essentially two major causes of flooding: Coastal flooding which is caused by higher sea levels than normal, largely as a result of storm surges, resulting in the sea overflowing onto the land. Coastal flooding is influenced by the following three factors, which often work in combination: :: High tide level; :: Storm surges caused by low barometric pressure exacerbated by high winds (the highest surges can develop from hurricanes); and :: Wave action which is dependent on wind speed and direction, local topography and exposure. 2.1 2.2 7 Flooding - Key Concepts
- Inland flooding which is caused by prolonged and/or intense rainfall. Inland flooding can include a number of different types: Overland flow occurs when the amount of rainfall exceeds the infiltration capacity of the ground to absorb it. This excess water flows overland, ponding in natural hollows and low-lying areas or behind obstructions. This occurs as a rapid response to intense rainfall and eventually enters a piped or natural drainage system. River flooding occurs when the capacity of a watercourse is exceeded or the channel is blocked or restricted, and excess water spills out from the channel onto adjacent low-lying areas (the floodplain). This can occur rapidly in short steep rivers or after some time and some distance from where the rain fell in rivers with a gentler gradient. Flooding from artificial drainage systems results when flow entering a system, such as an urban storm water drainage system, exceeds its discharge capacity and the system becomes blocked, and / or cannot discharge due to a high water level in the receiving watercourse. This mostly occurs as a rapid response to intense rainfall. Together with overland flow, it is often known as pluvial flooding. Flooding arising from a lack of capacity in the urban drainage network has become an important source of flood risk, as evidenced during recent summers. :: :: :: 8 2 Fig. 2.1: Principal causes and types of flooding Climate change: Increased intensity of rainfall over summer months Overland run-off and muddy flooding due to intense rainfall Groundwater flooding due to raised water table Surcharge sewer causes basement flooding Sewer exceedance flooding Urban creep (increased paved area) Blockage or sewer collapse Impervious paved area Direct overland flow and ponding in low spots (sinks) Flooding through alluvial soils Reservoir or canal breach
- Groundwater flooding occurs when the level of water stored in the ground rises as a result of prolonged rainfall to meet the ground surface and flows out over it, i.e. when the capacity of this underground reservoir is exceeded. Groundwater flooding tends to be very local and results from interactions of site-specific factors such as tidal variations. While water level may rise slowly, it may be in place for extended periods of time. Hence, such flooding may often result in significant damage to property rather than be a potential risk to life. Estuarial flooding may occur due to a combination of tidal and fluvial flows, i.e. interaction between rivers and the sea, with tidal levels being dominant in most cases. A combination of high flow in rivers and a high tide will prevent water flowing out to sea tending to increase water levels inland, which may flood over river banks. Flooding can also arise from the failure of infrastructure designed to store or carry water (e.g. the breach of a dam, a leaking canal, or a burst water main), or to protect an area against flooding (e.g. breach of a flood defence, failure of a flap valve or pumping station or blockage of a pipe or culvert). Because of the sudden onset, the impacts of this form of flooding can be severe and where appropriate should be assessed. Coastal erosion of both the foreshore and the shoreline itself is intimately linked with coastal flooding. The loss of natural coastal defences, such as sand dunes, due to erosion (or mechanical removal of sand) can increase the risk of flooding in coastal areas. Coastal erosion should therefore be considered in coastal areas within the planning process, although this issue is not specifically within the focus of these Guidelines. Increases in flood risk as a result of new development may be caused: Upstream by restricting the capacity and conveyance function of the watercourse and floodplain system; or Downstream by decreasing the volume available for flood storage on the floodplain, altering flow routes on the floodplain or by changes to the channel which can increase the flow discharged to downstream locations; and by increasing run-off due to changes in land management and introducing surfaces with reduced permeability, such as roads, roofs and car parks. 2.3 2.4 2.5 :: :: :: :: 9 River flooding in Clonmacnoise River and coastal flooding in Dublin, 2002 (Source: Dublin City Council) Guidelines for Planning Authorities The Planning System and Flood Risk Management
- Impacts of flooding Impacts on people and communities – Flooding can cause physical injury, illness and loss of life. Deep, fast flowing or rapidly rising flood waters can be particularly dangerous. For example, even shallow water flowing at 2 metres per second (m/sec) can knock children and many adults off their feet, and vehicles can be moved by flowing water of only 300mm depth. The risks increase if the floodwater is carrying debris. Some of these impacts may be immediate, the most significant being drowning or physical injury due to being swept away by floods. Floodwater contaminated by sewage or other pollutants (e.g. chemicals stored in garages or commercial properties) is particularly likely to cause such illnesses, either directly as a result of contact with the polluted floodwater or indirectly as a result of sediments left behind. Flood water may also hide other hazards for wading pedestrians, such as manhole openings where the covers have been lifted by flood flows. Those most likely to be at risk are those outdoors on foot or in a vehicle, in a tent or caravan, or in a building, such as a single-storey bungalow or below ground in a basement. The impact on people and communities as a result of the stress and trauma of being flooded, or even of being under the threat of flooding, can be immense. Long-term impacts can arise due to chronic illnesses and the stress associated with being flooded and the lengthy recovery process. The ability of people to respond and recover from a flood can vary. Vulnerable people, such as those who are old, disabled or have a long-term illness, are less able to cope with floods than others. Some people may have difficulty in replacing household items damaged in a flood and may lack the financial means to recover and maintain acceptable living conditions after a flood. The 2006 Framework for Major Emergency Management enables the principal response agencies such as An Garda Siochána, the Health Service Executive and local authorities to prepare for and make a co-ordinated response to a variety of major emergencies including flooding. A guidance and protocol document has been developed in conjunction with the OPW for responding to flood events (see http://www.mem.ie). 2.6 2.7 2.9 2.8 10 22
- Impacts on property - Flooding can cause severe damage to properties. Floodwater is likely to damage internal finishes, contents and electrical and other services and possibly cause structural damage. The physical effects can have significant long-term impacts, with re-occupation sometimes not being possible for over a year. The costs of flooding are increasing, partly due to increasing amounts of electrical and other equipment within developments. Sea-water flooding may cause additional damage due to corrosion. Impacts on Infrastructure - The damage flooding can cause to businesses and infrastructure, such as transport or utilities like electricity and water supply, can have significant detrimental impacts on local and regional economies. Flooding of primary roads or railways can deny access to large areas beyond those directly affected by the flooding for the duration of the flood event, as well as causing damage to the road or railway itself. Flooding of water distribution infrastructure such as pumping stations or of electricity sub-stations can result in loss of water or power supply over large areas. This can magnify the impact of flooding well beyond the immediate community. The long-term closure of businesses, for example, can lead to job losses and other economic impacts. Impacts on the environment - Significant detrimental environmental effects of flooding can include soil erosion, bank erosion, land sliding and damage to vegetation as well as the impacts on water quality, habitats and flora and fauna caused by bacteria and other pollutants carried by flood water. Flooding can however play a beneficial role in natural habitats. Many wetland habitats are dependant on annual flooding for their sustainability and can contribute to the storage of flood waters to reduce flood risk elsewhere. 2.10 2.11 2.12 11 Tolka Valley Wetlands, Dublin Guidelines for Planning Authorities The Planning System and Flood Risk Management
- Flood risk Understanding flood risk is a key step in managing the impacts of flooding. Flood risk is a combination of the likelihood of flooding and the potential consequences arising. These Guidelines recommend a staged approach to flood risk assessment that covers both the likelihood of flooding and the potential consequences. There are two components of flood risk that must be considered in applying this guidance in a consistent manner: Likelihood of flooding is normally defined as the percentage probability of a flood of a given magnitude or severity occurring or being exceeded in any given year. For example, a 1% probability indicates the severity of a flood that is expected to be exceeded on average once in 100 years, i.e. it has a 1 in 100 (1%) chance of occurring in any one year. Consequences of flooding depend on the hazards associated with the flooding (e.g. depth of water, speed of flow, rate of onset, duration, waveaction effects, water quality), and the vulnerability of people, property and the environment potentially affected by a flood (e.g. the age profile of the population, the type of development, presence and reliability of mitigation measures etc). Flood risk is then normally expressed in terms of the following relationship: Flood risk = Likelihood of flooding x Consequences of flooding 2.13 2.14 :: :: Construction of new masonry wall as part of OPW flood relief scheme in Kilkenny 12 22
Source Department of the Environment, Heritage and Local Government and the Office of Public Works: The Planning System and Flood Risk Management: Guidelines for Planning Authorities (November 2009) · Licence the publisher's termsText read from the publisher’s PDF; tables, maps and drawings do not survive as text, and page numbers are the PDF’s (its first page is 1). Check the original before relying on a passage.