Flood risk assessment
Flooding in the UK has been in the news recently particularly since the severe floods of winter 2000. Such events are often attributed to changing weather patterns due to climate change. This in part is true but for many cases it has been the lack of consideration of flooding during the development process that has resulted in problems.
Development on areas classified as ‘functional floodplain’ has resulted in a large number of properties at high risk of flooding. Also the effect of development elsewhere in the catchment on ‘downstream’ developments has also been neglected.
Climate change predictions, suggest that flood events will become more prevalent and more severe. With this in mind legislation has tightened in order to protect future development.
Planning Policy Statement 25 (PPS25) calls that flood risk is considered at all stages of the planning process. It recommends that all planning should be directed to an area of lowest potential risk. It also suggests that flood risk is considered during development design with particular attention to sustainable urban drainage systems (SUDS).
Will I be asked to undertake a flood risk assessment on my planning proposal?
The Environment Agency has undertaken flood mapping since 2000 for the whole of England and Wales. The mapping classifies Flood Zones 1, 2 and 3.
If the site where development is proposed lies within Flood Zone 2 or 3, the local planning authority may ask for a flood risk assessment to be undertaken.
If it is known that the site lies within an area of frequent historical flooding (particularly relating to groundwater which is not considered by the Environment Agency mapping), a flood risk assessment may also be requested.
What we do?
Apple Environmental can undertake flood assessments for potential developments at risk from fluvial, coastal and groundwater flooding. Our reports utilise Environment Agency modelling data and historic data to assess the likelihood and potential impacts of future floods and advise on mitigation strategies where required.
Further information
Environment agency flood zones
Flood zone three covers an area where, neglecting the effects of flood defenses the probability of flooding from the sea by a flood that has a 0.5% (1 in 200) or greater chance of happening each year or from a river by a flood that has a 1% (1 in 100) or greater chance of happening each year.
Flood zone 2 where the likelihood of flooding is 0.1% (1 in 1000) or greater chance of occurring each year.
All other areas are classified as Flood Zone 1 where the probability of flood from the sea or rivers is considered to be less than 0.1%.
Strategic flood risk assessments, which local authorities are required to undertaken under PPS25, separate Flood Zone 3 into flood zone 3a and 3b. Flood zone 3a represents an area where the probability of flooding is 1% and flood zone 3b is defined as functional flood plain where the probability of flood is considered to be 5% (1 in 20).
Planning Policy Statement 25 (PPS25)
PPS25 was developed to provide guidance to local authorities with the aim of ensuring that flood risk was considered at all stages the planning process to ensure that development is not placed within areas of high risk. The key aims of the policy are to assess, manage and reduce risk. This is achieved by:
- identifying land at risk and the degree of risk of flooding from river, sea and other sources in their areas;
- preparing Regional Flood Risk Appraisals (RFRAs) or Strategic Flood Risk Assessments (SFRAs) outlining policies for the location of development which avoid flood risk to people and property where possible, and manage any residual risk, taking account of the impacts of climate change;
- only permitting development in areas of flood risk when there are no reasonable available sites in areas of lower flood risk and benefits of the development outweigh the risks from flooding;
- safeguarding land from development that is required for current and future flood management e.g. conveyance and storage of flood water, and flood defences;
- reducing flood risk to and from new development through location, layout and design, incorporating sustainable drainage systems (SUDS);
- using opportunities offered by new development to reduce the causes and impacts of flooding e.g. surface water management plans;
- making the most of the benefits of green infrastructure for flood storage, conveyance and SUDS;
- re-creating functional floodplain;
- and setting back defences;
- PPS25 uses a sequential risk based approach to accessing the suitability of land for development.
PPS25 clearly sets out appropriate development for each zone. An example is residential development. This type of development is classified as a more vulnerable land use. PPS25 recommends that more vulnerable development should be restricted from zone 3b and only allowed in Flood Zone 3b if the exception test is past, allowed in Zone 2 as long as accompanied by a Flood Risk Assessment.