appendix a - National Grid

11 CONCLUSION
TEP on behalf of National Grid 20 of 21
King’s Lynn 400kV Connection
110488-FRA-R1(1)
Construction of the proposed pylons with associated overhead lines on the site will be
possible with careful consideration of the proximity of the pylons to the River Nar and
other water features in the area.
Other flood risks considered in this assessment included overland flow, groundwater,
sewer and existing infrastructure i.e. pumping stations have been assessed, and they
do not pose a significant flood risk to the site.
The proposal will result in minimal increase of impermeable area, hence limited
additional runoff of surface water. The limited volume of the additional surface runoff, as
a result of development, will percolate into the ground before they can reach and drain
into any water sources in the area. Therefore, It is not anticipated that additional
drainage system will be required.
The proposal will not impede flood flows and will have minimal impact on the flood
storage volumes, as any floodwater will flow through the pylon structure without
obstruction.
The nearest tower will be located at more than 60m from the flood defence in River Nar,
therefore they will have minimal impact on the defences. Even in the unlikely event that
a pylon falls over, it is unlikely to reach the existing flood defences due to the physical
distance between the towers and the riverbanks.
Pontoon crossings are proposed for pedestrian access across the River Nar. Pontoon
crossings will have less impact to the watercourse by having minimal construction in the
riverbed with effect to the river flow from pontoon crossing also minimised.
If works are required at the flood defence, the crest level of the defence should not be
lowered to more than the 1 in 100 year flood event for the River Nar with 600mm
freeboard included at 2.9m AOD. This is to ensure the local environment currently
benefiting from the flood defence will not be affected.
In summary, this assessment considers the site to be at low risk of flooding with flood
defences in place. Appropriate maintenance of the defences will ensure the residual
risk of flooding is minimised.
Tidal and fluvial flood risk will, however, increase to high risk with climate change
included. Even at high risk, it is not anticipated that the structure and operation of the
pylons will be affected during a flood event. The climate change event has also
assumed that the flood defences and other defence mechanism in the area remain
unchanged over the years and do not take into account any intermediate improvement/
bank raising to the flood defences and embankments in the future in accordance to the
Great Ouse Tidal River Strategy (ref. 9) .