Flood Frequency Estimates on Alluvial Fans

A uniform method has been presented for the determination of flood flow frequencies on alluvial fans. The method is based on geomorphologic principles, and has general applicability. There are three basic assumptions underlying the proposed method. The first assumes that a log Pearson III distribution applies to the distribution of flood flows at the apex. The second basic assumption is that each event forms a single channel and flow remains in that channel throughout the event. The third basic assumption is that flood channels are distributed uniformly across any contour. The concept is basically reasonable, but it ignores the fact that equally valid assumptions concerning placing of channels and placing of centers of channels would result in different probabilities, particularly within one stream width of the edge of an alluvial fan.