As part of the planning process, Plymouth City Council as the Lead Local Flood Authority (LLFA) is consulted on surface water drainage and flood risk matters relevant to the development.
Most of Plymouth is a Critical Drainage Area, defined by the Environment Agency as an area where the existing drainage system is considered to be at, or close to, capacity. New developments in these areas require some drainage limitations to manage and reduce the risk of flooding downstream. For details of these critical locations, please consult Part 2 of the Local Flood Risk Management Strategy.
Lead Local Flood Authority requirements
All new developments need a surface water drainage strategy
All new developments require a surface water drainage system designed for up to a 1 in 100 year storm event (a design standard of 1:100 year return period) with an appropriate allowance for climate change (for rainfall, this is typically 50%).
See the Local Flood Risk Management Strategy for further guidance.
Flood risk assessment
All new developments (including change of use) that are at risk from flooding from rivers or the sea require a flood risk assessment that acknowledges the sources, scale and extent of flooding, including mitigation of these risks.
Guidance about flood risk assessments is available from gov.uk.
Part 2 of the Local Flood Risk Management Strategy includes guidance about flood protection.For single property developments that are not at risk from flooding from rivers or the sea, the LLFA have produced Pre-Application Standing Advice that summarises technical guidance requirements for surface water drainage. This is issued, if appropriate, by the LLFA during the pre-application planning process.
Climate change allowance
All new developments require a climate change allowance relevant to the life and type of the development. For rainfall, this is typically 50%, but should always be checked against the gov.uk guidance.