Research Theme

The hypothesis under test at Atrepo study sites is that increased floodplain roughness alleviates flooding by diffusing (lengthening) the peak of high magnitude hydrographs. Experimental results indicate that the (green) floodplain storage capacity responds beneficially to engineered roughness at critical points.  Such engineering can be modelled and comparisons drawn between watersheds of different characteristics, in particular relative floodplain areas and slope.

For reference:-

  1.  Full text of the 2D experimental Upper Severn Model is here 
  2. An ‘Urban’ Attenuation Study is here , and a
  3.  related ‘Wellbeing’ paper is here

Key to productive calibration of real hydrographs over such high-friction designer floodplains is the optimized coarseness of the array of nodes assembled to represent irregular rural features. Based on the experimental study, a terrain point-cloud can be degraded below  the relatively unproductive 37 nodes per hectare, provided  that strategic points remain anchored to vector break-lines at land-parcel polygonal (ie field) boundaries.  It is estimated that, using current technology, an average point budget of approximately 8-10 nodes/hectare will allow productive dynamic 2D analysis of  floodplain performance.

A typical high density point cloud (ie approx 37 nodes/hectare)

The coupling of sub-reach models hydraulically demonstrates the potential of 2D techniques for the evaluation of floodplains large enough to deliver significant downstream gain. Furtermore, confidence in such coupled hydraulic models can be enhanced by mid-reach calibration, in turn enabling on-line streaming of downstream forecasts.

A pragmatic  physical aim of Atrepo studies is to quantify and compare the storage capacity of a typical rural floodplain as its terrain roughness is increased and thereafter to quantify resulting downstream attenuation.  The main human aim is to enable communication of potential benefit in real time to inform riparian landowners and managers. In some cases,  the physical and human aspects of flood alleviation make uncomfortable bedfellows, but intransigence can be moderated by Ecosystem market mechanisms, and effective communication.

A typical stout ‘lateral’ hedgerow at an Upper Severn floodplain boundary where Q20 overbank flows are approximately 0.5m/sec x 1m deep

A tenet of the approach is that sustainable stout hedges in the path of floodwater form shallow weirs.  It is visualized (pragmatically defined) that dense stiff vegetation which creates a functional weir of approximately 0.1m – 0.2 m head will demand a width on the ground of between 1 m and 3 m (depending on local conditions).

Issues of riparian rights and agricultural cross-compliance are linked in the approach, as is a notion of competition between solution by attenuation and solution by resilience.




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