FLO-2D is a two-dimensional finite difference model that simulates clear-water flood hazards, mudflows, and debris flows on alluvial fans and urban floodplains. Interactive flood or mudflow routing between channel, street, and floodplain flow is performed using a uniform grid system to describe complex floodplain topography. A quadratic rheological model, developed from field and laboratory mudflow data, enables appropriate simulations of flooding conditions ranging from clear water to hyperconcentrated sediment flows. Computer-aided design (CAD) graphics of predicted time-sequenced flood depths automates the delineation of flood hazards. Replication of the 1983 Rudd Creek mudflow in Utah demonstrates the capability of the model.