HILLINGDON UNITARY DEVELOPMENT PLAN - London Borough ...

Surface Water Drainage and Flood Prevention
6.16 Strategic Planning Guidance notes that unless carefully sited and designed, new development can
exacerbate problems of flooding in areas downstream through an increase in run-off from additional roofs
and paved surfaces. Boroughs are advised therefore, in association with the Environment Agency, to take
into account in their UDPs the surface drainage consequences of new development, including the need to
protect the flood plain and urban washlands (SPG, para 68).
6.17 The Environment Agency has recently carried out extensive flood alleviation studies of the three
principal watercourses in the Borough, the River Pinn, the River Colne catchment (including the River
Frays, Duke of Northumberland River and the Grand Union Canal) and the River Crane catchment
(including both arms of Yeading Brook). The aim of these studies is to remove the risk of regular flooding
from existing development, and flood defence measures are being designed and implemented. However, in
order that the risk of flooding is not increased elsewhere it is essential that the level of future development
of the floodplain is strictly controlled, and that the capacity of the available flood plain is not reduced, or
the flow of water impeded. The Local Planning Authority will have regard therefore to the drainage
implications of new development and will liaise with the Environment Agency to ensure that proper
provision is made. In particular the Local Planning Authority will have regard to the Environment
Agency's advice on areas liable to flooding. These areas are shown on Figure 6.
OE7 IN THE AREAS LIABLE TO FLOODING PERMISSION WILL NOT BE GRANTED
FOR NEW DEVELOPMENT OR THE INTENSIFICATION OF EXISTING DEVELOPMENT
UNLESS A DEVELOPER IS PREPARED TO IMPLEMENT FLOOD PROTECTION MEASURES
AS PART OF THE PROPOSED DEVELOPMENT TO A STANDARD SATISFACTORY TO THE
COUNCIL, IN CONSULTATION WITH THE ENVIRONMENT AGENCY AND WHERE
APPROPRIATE, OTHER DRAINAGE BODIES.
OE8 PLANNING PERMISSION WILL NOT BE GRANTED FOR NEW DEVELOPMENT OR
REDEVELOPMENT OF EXISTING URBAN AREAS WHICH WOULD RESULT IN AN
INCREASED FLOOD RISK DUE TO ADDITIONAL SURFACE WATER RUN-OFF, UNLESS
THE PROPOSED DEVELOPMENT INCLUDES APPROPRIATE ATTENUATION MEASURES
TO A STANDARD SATISFACTORY TO THE COUNCIL, IN CONSULTATION WITH THE
ENVIRONMENT AGENCY AND, WHERE APPROPRIATE, OTHER DRAINAGE BODIES.
6.18 The Council acts as agents for Thames Water Utilities for the sewerage functions of the Borough.
Under the agency arrangement the Council has recently completed the Harrow Branch Relief Foul Water
Sewer to alleviate the foul flooding problem in the Ruislip area and other schemes are being investigated.
The most significant is likely to be a storm relief sewer for the South Ruislip area. Surface water run-off
generated by the development of a green field site or redevelopment of an existing built-up area can
exacerbate an existing flooding problem or may overload the existing surface water sewerage system. The
Council should therefore be consulted at an early stage about the drainage requirements for development
proposals.
OE9 IN CATCHMENTS WHICH HAVE A POTENTIAL FOR SEWERAGE FLOODING
PERMISSION WILL NOT NORMALLY BE GRANTED FOR DEVELOPMENT WHICH MAY
PRECIPITATE SUCH FLOODING OR FURTHER FLOODING, UNTIL SUFFICIENT
IMPROVEMENT HAS BEEN IMPLEMENTED TO ALLEVIATE THE PROBLEM.
OE10 IN AREAS OF POTENTIAL FLOODING OR INADEQUATE CAPACITY OF THE FOUL
AND SURFACE WATER SEWERAGE SYSTEM TO RECEIVE THE ADDITIONAL
DISCHARGE FROM THE DEVELOPMENT, A PHASED DEVELOPMENT MAY BE
REQUIRED TO MATCH THE PROVISION OF INFRASTRUCTURE SO THAT THE EXITING
SYSTEM IS NOT OVERLOADED TO THE DETRIMENT OF THE COMMUNITY AS A
WHOLE.
London Borough of Hillingdon Unitary Development Plan