Appendix 2
CLARIFICATION OF THE EFFECTS MOORLAND GRIP
BLOCKING AND FLOOD RISK MANAGEMENT
BACKGROUND
1. A recent review of research on land management
and flood risk, carried out as part of the Government's Making
Space for Water initiative, concluded that we are unable to predict
the effects of land management strategies such as grip blocking
on flood risk management. The impacts of moorland management are
difficult to predict because of multiple land management interventions
that can occur within a catchment. For example, grip blocking
may be combined with changes in grazing practices or heather burning
in the same catchment. Therefore, without prior knowledge and
investigation of the catchment in question, predicting the effects
of management intervention on flood risk management would be very
uncertain.
2. The Environment Agency has noted that
Natural England's verbal evidence to the Committee suggested that
"15% is the estimate in attenuation that would reduce the
flow of water off the hill" where moorland drainage grips
are blocked. We understand from Natural England that this figure
was taken from a draft unpublished report commissioned by English
Nature in 2005 for two upland catchments in Yorkshire. Our own
view is that it is not appropriate to extrapolate the figure from
English Nature's draft report to suggest that extensive upland
grip blocking will give the reduction in flows suggested.
FUTURE POSITION
3. Research shows that grips in moorland
can capture large areas of water and siphon it off into the drainage
network. Flows in the grips can be up to two orders of magnitude
faster than overland flows. Consequently, in some situations,
the rate of runoff and therefore flood generation increases (Lane
et al, 2003). The majority of studies show an increase
in annual flood peaks following the creation of grips. However,
some have also shown a decrease.
4. Tools are being developed that help to
predict the effect of grip blocking on the timing and magnitude
of downstream runoff. Modelling has also helped dictate which
grips should be blocked to achieve maximum impact on flows downstream.
These should help in the future to target land management approaches
which more effectively deliver public benefits.
REFERENCES
Environment Agency (2007). Making Space for Water—R&D
Update—Review of the impact of land use and management on
flooding; Final Report, March 2007.
Environment Agency (2008). Making Space for Water—The
role of land use and land management in delivering flood risk
management; Final Report, January 2008.
Lane, S N, Brookes, C J, Hardy, R J, Holden, J, James,
T D, Kirkby, M J, McDonald, A T, Tayefi, V and Yu Dapeng (2003).
Land Management, flooding and environmental risk: new approaches
to a very old question, Forthcoming in Proceedings of Paper presented
as CIWEM national conference, September 2003.
Environment Agency
March 2008
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