Chapter 9: Road drainage and the water environment

8 Conclusion
The M1 Junction 19 Improvements scheme is considered to be at risk of fluvial
flooding as parts of the scheme are located within flood zone 3a, the 1 in 100
(1%) annual probability flood extents.
The proposed development is classified as essential transport infrastructure and
is only permitted in zone 3a if the Exceptions Test is satisfied.
Due to the location of the existing junction it is not possible to relocate this
development outside of the floodplain.
The Exception Test (PPS 25) has been completed for the development. The
development has been shown to have wider sustainability benefits by reducing
the stress, risk and travel time associated with driving between the M1 and A14.
The specific locations at fluvial risk are:
• The A14 on the eastern part of the scheme, specifically the embankment
shoulders, the highway deck is unaffected
• Bridleway Crossing 1 north of the A14 over the River Avon will be totally
submerged in the 1 in 100 year event
• Bridleway Crossing 2 between the M1 and A14 (southeast quadrant) will
be totally submerged in the 1 in 100 year event
To mitigate against the risk of increasing flooding downstream flood
compensation areas have been proposed. Dimensions of the compensation
areas can be found in Appendix D.
There will be a net total increase in impermeable area associated with the
scheme and thus a commensurate increase in highway runoff. To mitigate
against the effect of increased runoff in the River Avon, five attenuation ponds
have been proposed. The design has been developed in consultation with the
EA. Details of the attenuation ponds can be found in Appendix B.
It is recommended signage is incorporated at the bridleway crossing to inform
users of the risk of flooding
The scheme will involve deep cuttings for the Swinford Road underpass and the
A14-M1 link. This may result in groundwater seepage. To mitigate against this
risk filter drains and slope drainage are being considered by the contractor.
It is recommended that Severn Trent is pursued by the designers in respect of
their assets (water supply) which appear to pass through the site.
It is anticipated that the level of residual risk to the site, following the
implementation of all identified mitigation measures, will fully satisfy the
requirements of PSS 25.
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