Planning Library

Flood Risk and Water Glossary

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Breach of Defences A structural failure at a flood defence allowing water to flow through.
Catchment The area that is drained by a river or artificial drainage system.
Catchment Flood Risk Assessment and Management Study (CFRAMS) A catchment-based study involving an assessment of the risk of flooding in a catchment and the development of a strategy for managing that risk in order to reduce adverse effects on people, property and the environment. CFRAMS precedes the preparation of Flood Risk Management Plans (See also ‘Flood Risk Management Plans’).
Climate Change Long-term variations in global temperature and weather patterns, which occur both naturally and as a result of human activity, primarily through greenhouse gas emissions.
Coastal Erosion The gradual wearing away of the coastline through a combination of wave attack and, in the case of coastal cliffs, slope processes (e.g. high groundwater levels). This may include cliff instability, where coastal processes result in the periodic reactivation of landslide systems or promote rock falls.
Coastal Flooding Flooding from the sea which is caused by higher than normal sea levels and/or high waves resulting in the sea overflowing onto the land.
Consequence of Flooding Health, social, economic and environmental effects of flooding, some of which can be assessed in monetary terms, while other less tangible impacts are more difficult to quantify. Consequences depend on the hazards associated with the flooding and the vulnerability of receptors.
Conveyance Function When a river overflows its banks, it continues to flow over the flood plain, conveying water down-stream, as well as storing water where the flood plain may be obstructed and releasing it slowly.
Detailed Flood Risk Assessment A methodology to assess flood risk issues in sufficient detail and to provide a quantitative appraisal of flood hazard and potential risk to an existing or proposed development, of its potential impact on flood elsewhere and of the effectiveness of any proposed measures.
Estuarial Flooding Flooding from an estuary, where water level may be influenced by both river flows and tidal conditions, with the latter usually being dominant.
Flash Flood A flash flood is a rapid flooding of an area of land as a result of intense or extreme rainfall events or failure of infrastructure designed to store or carry water or protect against flooding and is distinguished from general flooding by the sudden onset.
Flooding Flooding is the overflowing of water onto land that is normally dry. It may be caused by overtopping or breach of banks or defences, inadequate or slow drainage of rainfall, underlying groundwater levels or blocked drains and sewers. It presents a risk only when people, human assets and ecosystems are present in the areas that flood. Flooding can also be referred to as ‘Inundation’.
Flood Defence A man-made structure (e.g. embankment, bund, sluice gate, reservoir or barrier) designed to prevent flooding of areas adjacent to the defence.
Flood Relief Scheme (FRS) A scheme designed to reduce the risk of flooding at a specific location.
Flood-Detention Reservoirs An embanked area designed to hold floodwater from areas upstream and release it slowly to reduce flooding downstream. Embankments may be constructed across a river or adjacent to a river, with flood flows being diverted into the reservoir area.
Flooding Directive The EU Directive 2007/ 60/ EC of 23 October 2007 on the assessment and management of flood risks which is aimed at integrating the way flood risk is managed throughout the European Union.
Flooding from Artificial Drainage Systems This occurs when flow entering a system, such as an urban storm water drainage system, exceeds its discharge capacity, becomes blocked or when the system cannot discharge due to a high water level in the receiving watercourse.
Flood Hazard The features of flooding which have harmful impacts on people, property or the environment (such as the depth of water, speed of flow, rate of onset, duration, water quality etc.).
Flood Hazard Assessment An assessment of the hazards that would arise from flooding, e.g. identifying where flooding would occur, how deep the water would be, how fast it would flow, how rapidly it would rise and how long it would remain.
Floodplain A floodplain is any low-lying area of land next to a river or stream, which is susceptible to partial or complete inundation by water during a flood event.
Flood Risk An expression of the combination of the flood probability or likelihood and the magnitude of the potential consequences of the flood event.
Flood Risk Assessment (FRA) FRA can be undertaken at any scale from the national down to the individual site and comprises 3 stages: flood risk identification, initial flood risk assessment and detailed flood risk assessment.
Flood Risk Identification A desk-based study to identify whether there may be any flooding or surface water management issues related to a plan area or proposed development site that may warrant further investigation.
Flood Risk Management (FRM) FRM combines the function of mitigating and monitoring flood risks and may include pre-flood, flood event or post-flood activities.
Flood Risk Management Plans (FRMPs) Plans which are developed in accordance with national flood policy and the EU Floods Directive and which provide the strategic direction for flood risk management decisions in a catchment. These will describe a range of traditional river or coastal defences to non-structural responses such as flood warning and resilience measures at property level.
Flood Storage The temporary storage of excess run-off or river flow in ponds, basins, reservoirs or on the floodplain.
Flood Zones A geographic area for which the probability of flooding from rivers, estuaries or the sea is within a particular range.
Fluvial Flooding Flooding from a river or other watercourse.
Freeboard Freeboard is a safety margin to account for uncertainties in water-level prediction and/or structural performance. It is the difference between the height of the flood defence or floor level and design flood level.
Groundwater Flooding Flooding caused by groundwater escaping from the ground when the water table rises to or above ground level.
Indicative Floodplain Map (IFM) A map that delineates the areas estimated to be at risk of flooding during an event of specified flood probability. Being indicative, such maps only give an indication of the areas at risk but, due to the scale and complexity of the exercise, cannot be relied upon to give precise information in relation to individual sites.
Initial Flood Risk Assessment A qualitative or semi-quantitative study to confirm sources of flooding that may affect a plan area or proposed development site, to appraise the adequacy of existing information, to provide a qualitative appraisal of the risk of flooding to development, including the scope of possible mitigation measures, and the potential impact of development on flooding elsewhere, and to determine the need for further detailed assessment.
Inland Flooding Any flooding away from the sea, the primary cause of which is prolonged and/or intense precipitation (or the failure of water-retaining infrastructure, such as burst water pipes or dam breaks).
Justification Test An assessment of whether a development proposal, within an area at risk of flooding, meets specific criteria for proper planning and sustainable development and demonstrates that it will not be subject to unacceptable risk nor increase flood risk elsewhere. A justification test is also undertaken as part of the development plan process in considering the location of future development, this forms part of the 'Strategic Flood Risk Assessment' (see below).
Likelihood (probability) of Flooding A general concept relating to the chance of an event occurring. Likelihood is generally expressed as a probability or a frequency of a flood of a given magnitude or severity occurring or being exceeded in any given year. It is based on the average frequency estimated, measured or extrapolated from records over a large number of years and is usually expressed as the chance of a particular flood level being exceeded in any one year.
Mitigation Measures Elements of a development design which may be used to manage flood risk to a development, either by reducing the incidence of flooding both to the development and as a result of it and/or by making the development more resistant and/or resilient to the effects of flooding.
Overtopping of Defences Failure of a flood defence or exceedance mechanism, when flood water reaches levels that are higher than the flood defence level and flows over the top of the structure. While the structure may remain stable, however, erosion of the landward face of the defence could cause the defence to collapse.
Pathways These provide the connection between a particular source (e.g. high river or tide level) and the receptor that may be harmed (e.g. property). In flood risk management, pathways are often ‘blocked’ by barriers, such as flood defence structures, or otherwise modified to reduce the incidence of flooding.
Pluvial Flooding Usually associated with convective summer thunderstorms or high intensity rainfall cells within longer duration events, pluvial flooding is a result of rainfall-generated overland flows which arise before run-off enters any watercourse or sewer. The intensity of rainfall can be such that the run-off totally overwhelms surface water and underground drainage systems.
Precautionary Approach The approach to be used in the assessment of flood risk which requires that lack of full scientific certainty, shall not be used to assume flood hazard or risk does not exist, or as a reason for postponing cost-effective measures to avoid or manage flood risk.
Receptors Things that may be harmed by flooding (e.g. people, houses, buildings or the environment).
Regional Flood Risk Appraisal (RFRA) A desk-based study to provide a broad overview of the source and significance of flooding across a region and identify potential conflicts with existing and proposed areas of development, thus highlighting areas where further studies will be required at county or city scale as part of development plan preparation.
Resilience Resilience relates to how a building is constructed in such a way that, although flood water may enter the building, its impact is minimised, structural integrity is maintained, and repair, drying & and cleaning and subsequent reoccupation are facilitated. Resilence can also be referred to as ‘wet-proofing’.
Resistance This relates to how a building is constructed to prevent flood water entering the building or damaging its fabric. Resistance can also be referred to as ‘dry-proofing’.
River Basin Management Plan (RBMP) As required by the EU Water Framework Directive (2000/ 60/ EC),the RBMP is a strategic plan for the long-term management of the River Basin District. It sets out objectives for water bodies, and in broad terms identify what measures are planned to meet these objectives, and act as the main reporting mechanism to the European Commission.
Run-Off The flow of water, caused by rainfall, from an area which depends on how permeable the land surface is. Run-off is greatest from impermeable areas such as roofs, roads and hard standings and less from vegetated areas – moors, agricultural and forestry land.
Sequential Approach The sequential approach is a risk-based method to guide development away from areas that have been identified through a flood risk assessment as being at risk from flooding. Sequential approaches are already established and working effectively in the plan-making and development management processes.
Site-Specific Flood Risk Assessment An examination of the risks from all sources of flooding of the risks to and potentially arising from development on a specific site, including an examination of the effectiveness and impacts of any control or mitigation measures to be incorporated in that development.
Source Source refers to a source of hazard (e.g. the sea, heavy rainfall).
Source-Pathway Receptor Model For there to be flood risk, the three components of flood risk - the source of the hazard, the receptors affected by the hazard and the mechanism of transfer between the two - must all exist.
Spatial Resolution Defines the density of information produced from the flood risk assessment process across the area of interest. A mosaic of flood risk data produced by different tools and base data, with a range of certainty in the output.
Strategic Flood Risk Assessment (SFRA) The assessment of flood risk on a wide geographical area against which to assess development proposed in an area (region, county, town).
Surface Water Management This activity focuses on the assessment and management of flood risk within the urban environment from sources primarily resulting from intense rainfall. Surface water management should understand the performance of the urban drainage network, where exceedance flow routes would form and what impact this would have. Solutions to surface water flood risk can involve green infrastructure provision to capture and direct these exceedance flows to lower vulnerable areas or open space. New development can provide solutions to reducing runoff not only from the proposed development but also from existing areas. This should be considered in the SFRA in critical areas where development is planned upstream of flooding hotspots.
Sustainable Drainage Systems (SuDS) A form of drainage that aims to control run-off as close to its source as possible using a sequence of management practices and control structures designed to drain surface water in a more sustainable fashion than some conventional techniques.
Vulnerability The resilience of a particular group of people or types of property or habitats, ecosystems or species to flood risk, and their ability to respond to a hazardous condition and the damage or degree of impact they are likely to suffer in the event of a flood. For example, elderly people may be more likely to suffer injury, and be less able to evacuate, in the event of a rapid flood than younger people.
Water Framework Directive (WFD) EU Water Framework Directive (2000/60/EC) is a framework established to protect all waters including rivers, lakes, estuaries, groundwater and coastal water, along with their dependent wildlife and habitats under a single piece of environmental legislation. The WFD focuses on: the protection and enhancement of all water, the involvement of the public, management of water bodies based on rivers/catchments, and the achievement of 'good status'.