Memorandum submitted by Dr Nick Haycock
(FL 152)
We have concluded a review of the flooding in
South Worcestershire in association with the Wychavon District
Council and the Enviroment Agency. Flooding in the Village of
Sedgeberrow (River Isbourne that flows into the River Avon at
Evesham) resulted in 60 residents being airlifted and 93 homes
flooded to a depth of 2.5 metres. Water levels rose by 1.6 metres
in 20 seconds.
The analysis of the catchment and runoff regime
over the last 35 years suggests a marked degradation of runoff
regime. In the 1970s a 1:10 year flow was 26 cumecs, in 2000s,
this flow now equates to 38 cumecs. The result of land use change
and rapid arable development in the Isbourne catchment, especially
post 1975, appears to coincide with the largest shift in the the
runoff regime of the catchment. The net result is that a 2005
flood defence scheme for the Sedgeberrow village was designed
to 1:100 standard but the revised flow classification of the flood
regime, taking into account land cover changes, now places this
scheme as providing a 1:40 year level of protection. Flood flows
for given return periods have grown by 28-31% over the last 35
years for this catchment.
If the committee are interested in this work
and the implications and observations from a area that took the
full brunt of the 156mm that fell on the 20 July, please let me
know. The EA and ourselves have now classified the floods that
hit the village of Sedgeberrow as having a return period of 1:600
years. The met office identify this area as having the highest
rainfall depth of that day.
For your information, our company undertook
flood analysis and river scheme design work at Lewes (2000), Ripon
and Boscastle (2004) and has undertaken flood advisory work for
the National Trust, English Heritage and Royal Palaces for over
10 years. We have worked in association with many UK universities
and continue to provide specialist flood modelling work for Halcrow
and the main engineering consultants in the UK. Equally our small
team is the main technical advisors for the Venice Mainland Drainage
Authority. I hope there maybe an opportunity to supply evidence
to the Committee.
Dr Nick Haycock
November 2007
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