A SEMIEMPIRICAL INVESTIGATION OF THE INFLUENCE OF FLOODPLAIN STORAGE ON FLOOD FLOW

A simple model is used to assess the effect of floodplain storage on f lood flows, with a view to developing methods for general use in flood -frequency estimation. Recent floods on the River Severn at Montford a re 'unrouted' in order to determine the shape and magnitude of the hyd rographs, provided that there had been no overtopping and all flows ha d been contained within the banks. The model used to unroute the hydro graphs has, at its core, a relationship between water depth and floode d area derived from a coarse (50 m) digital terrain model developed fr om Ordnance Survey 1:50 000 maps. The implications for flood-frequency curves at sites downstream from significant flood-plain storage are d iscussed.