Chapter 9: Road drainage and the water environment

The extents of this problem are currently being investigated by the design team in
the form of additional ground investigation planned for August 2009. Once the
level of risk has been clarified, mitigation measures will be put in place to prevent
flooding from this source. At present, the proposed method of mitigation is to
control groundwater levels by installing a system of ditches and filter drains at the
highway boundary. Slope face drainage is also being considered to control water
seepages in deeper cuttings. All groundwater discharges will be managed and
released in a manner which will not increase flood risk elsewhere in accordance
with PPS25.
5.3 Mitigation of Surface Water Runoff (Overland Flows)
The impact of the scheme will be to reduce the total amount of surface runoff as
described in Section 3.4. No mitigation measures are therefore required.
5.4 Mitigation of Flood Risks from Artificial Drainage Systems
There are a number of culverts which convey small unnamed watercourses within
the limits of the scheme. Where embankments are being widened these culverts
will be lengthened. The design approach to these modifications is being carried
out as per DMRB methodology (106/04) for the design of culverts. A summary of
the culverts are given below:
Figure 4: Culverts within the scheme which require modification
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