Chapter 9: Road drainage and the water environment

Non Technical Summary
Skanska Construction UK is currently leading the development of the M1
Junction 19 Improvements Scheme. The aim of the scheme is to relieve
congestion at the junction, make the roads safer and reduce journey times, whilst
minimising any environmental effects.
Jacobs UK Limited has been commissioned by Skanska Construction UK to
provide a Flood Risk Assessment (FRA) for the M1 Junction 19 scheme. The
purpose of the FRA is to ensure that flood risk and its management have been a
material consideration in the planning of this scheme, in accordance with the
Department of Communities and Local Government’s Planning Policy Statement
25: Development and Flood Risk (PPS25Planning Policy.
This specific FRA relates to the proposed M1 Junction 19 Improvements
Scheme. During the course of the FRA, the site has been investigated to
determine the risk from all significant sources of flooding and the impact they
could have on flood risk elsewhere. The key findings from the FRA are:
• The site is at risk from fluvial flooding. Part of the site (the A14 road) is
situated in Flood Zone 3a High Probability as defined by PPS25. The
proposed land use is classified as essential infrastructure therefore
passes the PPS25 Sequential and Exception Test. The proposed scheme
will displace the existing floodplain, this will be mitigated by introducing
floodplain compensation.
• Two bridleway crossings will be constructed below the Q100 flood
levels. The structures will be at risk from fluvial flooding, furthermore the
bridges will not be passable during high flows. Signage is recommended
to inform users of the risks of attempting to use the bridge during high
flows.
• The scheme will result in a net increase in highway runoff. To
mitigate against the effect of increased runoff in the River Avon a system
of attenuation ponds have been proposed and designed in consultation
with the Environment Agency.
• There is evidence of high groundwater tables relative to the
proposed finished road levels. This may result in groundwater seepage.
To mitigate against this risk extra filter drains and slope drainage is being
investigated by the contractor.
In summary, it is considered that if the proposed M1 Junction 19 improvements
are planned and designed in-line with the recommendations of this FRA all
associated flood risks can be successfully managed. The development will
therefore meet the requirements of the PPS25 Sequential Test and Exception
Test.