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<br />EXECUTIVE flUMKARY <br /> <br />A two-dimensional computer model, I'LO-2D, has been developed for <br />routing water and mudflows over u.nconfined alluvial fans and <br />floodplains. The model can simula.te flow in variable geometry <br />channels, overland flow in two-dimensions, and street flow. Flow <br />hydraulics for mudflows are predicted using viscous and yield <br />stresses as a function of sediment concentration by volume. <br />Options in the model have been d'=signed to simulate flow past <br />buildings and obstructions and through bridges. FLO-2D is linked <br />to AutoCAD-DCA software to create CL finite difference grid system <br />and extract grid element elevations. This has significantly <br />increased the speed at which a data file can be formulated and <br />revised. <br /> <br />The FLO-2D model was verified in three tests: 1) a comparison with <br />HEC-2 predictions for channel hydraulics; 2) a comparison with a <br />HEC-2 river overbank flow study; and 3) a correlation with field <br />data for the 1983 mudflow in Rudd Creek, Davis County, utah. All <br />three FLO-2D simulations displayed excellent correlation with the <br />chosen baseline conditions. <br /> <br />FLO-2D simulations were compared with the Federal Emergency <br />Management Agency (FEMA) procedure for computing flow hydraulics on <br />alluvial fans. Hydraulics predic'ted by FEMA I s guidelines were <br />found not to be conservative by comparison with FLO-2D predicted <br />hydraulics. It was concluded that flow hydraulics predicted with <br />the FEMA method were inappropriate for the design of flood <br />mitigation or for delineation of ha:r.ards on urbanized, channelized <br />or mudflow fans. The limitations of .the FEMA method are discussed. <br /> <br />FLO-2D has been applied to several projects including: delineation <br />of water and mudflow hazards on urban alluvial fans; prediction of <br />flood hydraulics for the design of flood containment structures in <br />an alluvial wash; flood hazard deli.neation resulting from split <br />overbank flows; and flood hazard delineation on a river floodplain. <br />Several of the projects were conducted for FEMA Flood Insurance <br />Studies (FIS) or to obtain a FEMA LE=tter of Map Revision (LOMR). <br />Some of the development and application of the FLO-2D model was <br />conducted under the auspices of FEl-'IA I S Region 8 office. <br />