THE SIGNIFICANCE OF PROCESSES ON ALLUVIAL FANS TO HAZARD ASSESSMENT

In laboratory conditions alluvial fans were developed and the spatial frequency distribution of active channels over various observation per iods was determined. By recording the development of the experimental alluvial fans on time-lapse video film, the main processes of fan form ation were observed: the channel entrenchment and aggradation process, and the channel migrating process which occurred as a result of conca ve bank erosion. These processes influence the short term flood risk a t a point, which was found to be a function of the absolute location o f that point on the alluvial fan, as well as of its location relative to the channel position, and of the shape of the alluvial fan and its slope condition. The long term flood risk is determined by the shape o f an alluvial fan and therefore it is a function only of the absolute location of that point on the alluvial fan. A method is suggested for formulation of risk maps on alluvial fans.