Description

FEMA guidelines for floodplain delineations on active alluvial fans allow use the FAN methodology, a stochastic model based on work originally published by Dawdy (1979). In 1985, FEMA contracted with DMA Consulting Engineers (DMA) to perform an analysis of their alluvial fan methodology. FEMA regards the DMA study as the computational link between Dawdy’s theoretical model and the FAN program, as well as a verification of the FAN methodology (Lenaburg, 2010). The stated purpose of the DMA report was to evaluate and verify two key assumptions in the FEMA alluvial fan methodology: (1) that the location of a stream path on a fan surface is random, i.e., a channel has an equal probability of occurring anywhere across the fan, and that (2) flow forms its own channel and remains in one channel throughout the flow event, except when a channel avulses (p. 1).