A developer will need to demonstrate that:
- Within the site, the most vulnerable development (e.g. an electricity substation) is located in areas of lowest flood risk unless there are overriding reasons to use a different location.
- The development is appropriately flood resilient and resistant, including safe access and escape routes where required, and that any residual risk can be safely managed, including by emergency planning; and it gives priority to the use of sustainable drainage systems.
- They have considered the availability of water and water infrastructure for the lifetime of the development and designed responses to promote water efficiency and protect water quality.
Site Specific Flood Risk Assessments
Site-specific Flood Risk Assessments (FRAs) are undertaken by applicants when a planning application is submitted where flood risk is an issue. The National Planning Policy Framework (NPPF) states that FRAs should identify and assess the risks of all forms of flooding to and from the development and demonstrate how these flood risks will be managed so that the development remains safe throughout its lifetime, taking climate change into account.
The following guidance from the NPPF should be applied to all sources of flood risk:
- What is a site-specific flood risk assessment?
- What level of detail is needed in a flood risk assessment?
- Site-Specific Flood Risk Assessment: Checklist
As in most areas of development control, the best outcomes are secured through more proactive working and early, pre-application discussions between developers and development control planners. In this way the management of surface water can be carried out effectively and also contribute towards place making and good urban design.
|Start as early as possible||Assume a standard format and cost for all SFRAs|
|Undertake pre-application discussions||Use an SFRA to justify preconceived land allocations and housing targets|
|Ensure geographical scope suitable for the sequential test||Assume that the Environment Agency will produce an SFRA for you or has all the information|
|Consider all sources of flooding||Assume one is not needed if there’s no history of flooding|
|Consider current and future flood risk|
Surface Water Drainage Assessments
Although site specific Flood Risk Assessments may not be required for sites not identified as being at risk of flooding, there may still be a requirement to provide a Drainage Assessment in order to consider the impact the development may have on surface water management. For more information, please see our Surface Water Drainage page.
Groundwater Flood Risk Assessments
If properties have been affected by groundwater flooding or where the local planning authority has highlighted a potential groundwater flooding issue related to a potential development, this source of flood risk should be included within the site specific flood risk assessment. A conceptual model of the groundwater on site is often required to enable the risk to be assessed and to provide a basis for designing any required mitigation measures. Data on the geology, topography, historical land use and hydrology of the site should also be incorporated into the detailed groundwater flooding assessment.
Northamptonshire County Council, supported by ESI Ltd, has undertaken a study to assess the risk of flooding from ground water across the County. Due to license restrictions, extracts of this map can only be provided to developers at a scale of 1:125,000 with a supporting text summary of the risk for a particular site. This information is available through the Flood Data and Information Request service or the Technical Flood Advice service. Some guidance has been created setting out the level of detail that would be expected to be considered at each stage of planning for groundwater flood risk assessments, and advice on potential mitigation and avoidance measures. Although this guidance is predominantly for Local Planning Authorities, please refer to the Guidance For Planners on Groundwater Flood Risk in Northamptonshire for more information, or view the full study report in the Flood Library.
Standards of Protection – Local Requirements
Following the significant flooding to Northampton town centre in Easter 1998 improvements were made to the defences along the River Nene. In order to secure the level of protection afforded by the new defence, the standard set for new developments goes beyond the approved industry standards. All new development in the Upper Nene catchment must be designed for a flood with a 0.5% probability of occurring in any one year, including an appropriate allowance for climate change.
Residual Flood Risk
In any development there is a residual flood risk, which is the flood risk after all measures of risk avoidance, reduction and mitigation have been taken. Measures should be in place to manage and plan for the residual risk, such as through evacuation procedures.