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<br />ii <br /> <br />concentration of sediment. <br /> <br />FLO-2D requires a representation of the topography of the study area. This is <br /> <br /> <br />accomplished by establishing a network of nodes and assigningx-y coordinates and <br /> <br /> <br />elevations to each node, The nQdes must be placed in a rectangular grid with equal <br /> <br /> <br />spacing between nodes. A typical grid node spacing is 200 feet to 500 feet. <br /> <br /> <br />Decreasingthe node spacing increases the number of nodes and decreases the length <br /> <br /> <br />of time step used in the model. Both factors increase the model's run time, <br /> <br /> <br />Flow in the model is generated by simulating rainfall on each node in the study area <br /> <br /> <br />or by inputting a runoffhydrograph at select nodes. Rainfall and inflow hydrographs <br /> <br /> <br />cannot be used simultaneously, The amount and direction of overland flow is <br /> <br /> <br />calculated in eight directions - directly forward and backward, to each side, and in <br /> <br /> <br />the four diagonal directions. <br /> <br />Mud floods and mudflows are modeled using inflow hydrographs, The input data <br /> <br /> <br />contains the hydro graph data, flow versus time, and the concentration of sediment <br /> <br /> <br />conveyed by the flow, concentration by volume versus time. FLO-2D routes the <br /> <br /> <br />hyperconcentrated flows, tracking the sediment volumes through the system, <br /> <br /> <br />Changing sediment concentration, dilution effects, and the remobilizatioI! of deposits <br /> <br /> <br />are simulated at each node, Mudflow cessation and deposition can be predicted by the <br /> <br /> <br />model. Sediment concentration governs the movement of the fluid matrix. Quadratic <br /> <br /> <br />rheological equations are used to predict viscous and yield stresses as a function of <br /> <br /> <br />sediment concentration, <br /> <br />The model also accounts for the initial rainfall abstractions and infiltration, <br />Infiltration is estimated for each node using the Green-Ampt equation, <br />This model has several other applications and capabilities which were not used in this <br />study and will not be presented in this report. <br /> <br />Results generated by the FLO-2D model include outflow hydrographs at designated <br /> <br /> <br />nodes, maximum flow depths and velocities, and a summary of the total inflow, <br /> <br />10 <br /> <br />I, <br /> <br />! <br />