The Holderness coastline, some 30km of 20m high boulder clay cliffs is retreating at an average of 1.7m per year. The resulting yearly supply of one million cubic metres of sediment to the North Sea represents the largest single coastline source. The Holderness experiment monitored this transport of sediments away from Holderness over the period October 1994 to January 1995 and measured directly the component contributions to erosion, suspension and transport. This observational programme is now being used to develop algorithms and test simulations in the subsequent model development phase. Using detailed meteorological data available since 1960, simulated time sequences of coastal erosion and deposition will be compared with observational data on coastal retreat and accretion.