Predicting effects of gully blocking on Making Space for Water Project

David Milledge (Research Associate, University of Durham) A model to predict the effects of gully-blocking on flood risk; comparisons with a previous grip-blocking model. Presented by Martin Evans (Professor of Geomorphology, University of Manchester)

Results from experimental mini catchments will be used to create a model which will characterise the relationship between gully-blocking and flood risk (i.e. the amount and timing of peak water flowing down from the hill during storm events).

This can then be used to scale up from our experimental mini-catchments to predict the effect from the plateau as a whole, in addition to predicting the effect of using a different number of gully-blocks.

 A previous model “Topmodel” was used to predict the effect of blocking grips on flood risk. Surprisingly, this previous model predicted that the effect would be negligible. The reason for this is thought to be due to the pattern of grips, which run almost parallel to the contours of the slope. This pattern extends the journey time of the water as it is forced to run at an angle to the slope. Blocking these grips then simply forces the water more directly down the hill, which is a shorter route and faster, but the water also passes over micro topographical roughness of vegetation, which is slower. So the resultant effect of grip-blocking may be negligible due to these opposing effects.

The new model being generated in the present project will predict the effects of gully-blocking. This will also take into account the effects of saturation in the peat layer and route all the effects together to produce predictive hydrographs.

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