THE EFFECT OF RAINFALL INTENSITY ON SURFACE RUNOFF AND SEDIMENT YIELD IN THE GRAY DUNES ALONG THE DUTCH COAST UNDER CONDITIONS OF LIMITED RAINFALL ACCEPTANCE

Surface runoff and sediment yield in the grey dunes along the Dutch coast are rare events restricted to conditions of water repellency in summer. The sediment moves in mudflow-like tongues. From March 1989 to December 1990, weekly surface runoff and sediment yield have been measured on an experimental plot, along with a number of meteorological parameters. Rainfall intensity is more important than total amount of precipitation for the production of runoff and sediment. Rainfall intensity affects the erosion process in two ways: by supplying the large amount of water needed for the high water: sand ratio in the sand flow, and by providing the high frequency drop impact needed to maintain a high hydraulic pressure in the sand flow.