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).