Select Committee on Environment, Food and Rural Affairs Minutes of Evidence


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 We understand from Natural England that this figure was taken from a draft unpublished report commissioned by English Nature in 2005 for two upland catchments in Yorkshire.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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