appendix a - National Grid

8.3 Flooding from Land (Overland Flood Risk)
TEP on behalf of National Grid 13 of 21
King’s Lynn 400kV Connection
110488-FRA-R1(1)
Flooding from land can happen when intense rainfall, often of short duration, is unable
to soak into the ground or enter the drainage systems quick enough and is then run
quickly off land and result in local flooding.
Due to the relatively flat topography of the existing site, it is predicted that any rainfall
that cannot percolate into the ground immediately will sit above the saturated soil until
infiltration is possible. Localised ponding may present in heavy rainfall with more
extreme storm events.
8.4 Flooding from Groundwater
As quoted from the King’s Lynn & West Norfolk SFRA, flooding from groundwater is not
considered to be of strategic significance in King’s Lynn and West Norfolk. Therefore, it
is not anticipated that groundwater flooding poses a significant risk to the site.
8.5 Flooding from Sewers
Anglian Water record maps in Appendix G show that there is clean water pipe running
in High Road to the west of the site. There are both surface and foul sewer located to
the north of the site adjacent to the Low Road roundabout. There is also a foul sewer
running close to the northern site boundary. This sewer connects further east beyond
the Puny Drain.
There are no sewers from Anglian Water in the area where the overhead line and
pylons are to be built; therefore there is no risk of flooding from sewers within the site.
8.6 Flooding from Other Sources
It is possible that other types of flooding may affect the site that not mentioned above.
They are further discussed below.
8.6.1 Pumping Station
There is a risk of flooding from the failure of land drainage pumping stations. The Puny
Pumping Station is located within the site at NGR TF 60701502. This station pumps
water under the railway line through a culvert into an open drain to the River Nar where
it goes under the river via a siphon into an open drain which gravitates into the Flood
Relief Channel.
There is a risk that if the pumping station fails to operate, it can give rise to a residual
flood risk within the area. Any such flooding would be local and confined to low-lying
land as the area is relatively flat with minimal change in levels.
8.6.2 Direct Breach & Hazard Zone
There are currently flood defences along the River Great Ouse, the River Nar and a
defence running from east to west connecting the River Nar and the Great Ouse Relief
Channel, just to the south of the Dairy Farm and the Saddlebow House.