appendix a - National Grid

10 MITIGATION MEASURES
10.1 Context
TEP on behalf of National Grid 18 of 21
King’s Lynn 400kV Connection
110488-FRA-R1(1)
As the site is defended up to 1 in 50 year by the defence at the River Nar and up to 1 in
200 year by the raised defences on the River Great Ouse. Mitigation measures would
relate to the provision of drainage controls and residual flood risks.
10.2 Ground Levels
One of the most robust methods of removing a development from the floodplain is to
raise ground levels above the predicted design flood levels.
As the proposed development will mainly comprise of overhead lines supported by
pylons. It is not anticipated raising of the ground for these structures will be necessary.
However, other onsite compounds may need to be raised above the 1 in 100 year flood
level, which is currently provided at 2.27mAOD for the River Nar. A freeboard of 300mm
is recommended on top of this level. It is not anticipated that onsite compounds will
remain onsite once construction is completed. Therefore, it is not considered necessary
to include climate change in this case.
10.3 Flood Resilient Construction
Any development susceptible to floodwater should be constructed using the latest best
practice flood resilient construction techniques. These would include design features in
relation to the finish materials and the heights of service. This will ensure the site
remain operational and will reduce damage in the unlikely event of a breach in the flood
defence.
In general, the design should include reference to “Preparing for Floods” a DEFRA
publication (ref. 6) , CIRIA guidance C624 “Development and flood risk” (ref. 7) and the CLG
document “Improving the flood performance of new buildings” (ref. 8) .
However, as much of the onsite buildings will be temporary, it may be more cost
effective to place the buildings above flood level, where possible, than using flood
resilient constructions.
10.4 Flood Warnings
Flood Warnings are EA provision of advance warning of conditions that are likely to
cause flooding to property and potential risk to life.
Unfortunately, due to the existing agricultural nature of the site, the EA flood warning
system does not cover this area. The nearest Flood Warning Areas is in King’s Lynn,
directly to the north of the site and to the south, in the Parish of Wiggenhall St
Germans.