Beginning with a review of FEMA’s three phase approach, this chapter discusses numerical methods for predicting alluvial fan flooding with the focus on deterministic methods for unconfined flow. The limitations of the FEMA FAN model are outlined as background for discussing the important criteria for delineating fan flood hazards. Alluvial fan flood modeling requires an understanding of the potential sediment loading, flow path uncertainty, and flooding details such as rainfall, urban impacts, and hydraulic controls. An approach used worldwide for delineating flood hazards is recommended and some important considerations for alluvial fan flood mitigation are presented.
