Policy CC/FM: Managing flood risk

1. Flood risk from all sources will be managed using the sequential, risk-based approach taking into account the impacts of climate change, set out in the National Planning Policy Framework and National Planning Practice Guidance. Development proposals, including change of use, will be supported where:

  a. The sequential test and, if necessary, the exception test have been passed and demonstrate that the development is acceptable, having regard to actual and residual flood risks from all sources and taking into account the impacts of climate change;

  b. Built development has been sequentially located within the site to avoid any areas of flood risk;

  c. The development does not lead to an increase in flooding elsewhere and, where, possible reduces overall flood risk;

  d. There is a safe access and escape route for future users of the development;

  e. The development does not affect the integrity of existing flood and surface water management assets;

  f. The ongoing maintenance and management of any necessary flood defences or flood mitigation measures have been agreed with the relevant bodies, and the necessary agreements are in place;

  g. The peak rate of run-off over the lifetime of the development, allowing for climate change, is no greater for the developed site than it was for the undeveloped greenfield site. Betterment must be provided on previously developed sites;

  h. The post-development volume of run-off, allowing for climate change over the development’s lifetime, is no greater than it would have been for the undeveloped site (if this cannot be achieved, then the limiting discharge is 2 litres per second for all events up to the 100-year return period event);

  i. The development is designed so that the flooding of properties in and adjacent to the development would not occur for a 1-in-100-year event, plus an allowance for climate change and in the event of local drainage system failure; and 

  j. finished floor levels are 300mm above the 1-in-100-year flood level (plus an allowance for climate change), and, where appropriate and practicable, 300 millimetres above adjacent highway levels.

2. Unless exceptional circumstances can be demonstrated, proposals in Flood Zone 3 (taking into account the effects of climate change) that would introduce a ‘highly vulnerable’ or ‘more vulnerable’ use at basement level or ground-floor-only level will not be permitted.

Managing Flood Water

3. If a proposal is considered to be acceptable within the 1% annual probability flood area (Flood Zone 3), taking into account the impacts of climate change, it must not decrease flood storage capacity, impair flow performance, accelerate flooding onset, or create unsustainable flood storage that requires ongoing silt removal, maintenance, or renewal.

4. If a proposal is within a functional floodplain (Flood Zone 3b), developers must ensure the floodplain’s capacity to store or move water is maintained or improved. Development will only be permitted where it results in no loss of floodplain performance.

Flood Risk Assessments

5. A site-specific Flood Risk Assessment (FRA) appropriate to the scale and nature of the development will be required for the following:

  a. All sites that include land within Flood Zones 2 and 3;

  b. Sites within Flood Zone 1 with a site area of 1 hectare or more;

  c. Sites within Flood Zone 1 in locations that are identified as being at greater flood risk in the future, taking into account the effects of climate change;

  d. Sites within Flood Zone 1 where there is a risk of flooding from surface water, or are designated as an area with critical drainage problems; and

  e. Sites with land that may be subject to other sources of flooding, where its development would introduce a use of higher flood risk vulnerability.

6. The FRA should consider all forms of flooding, taking into account the effects of climate change, and include an assessment of flood risk to and created by the proposed development. FRAs should also demonstrate how the development will be made safe for its lifetime, including, where appropriate, the mitigation measures that will be incorporated to manage residual flood risk.