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<br />* streets are modeled as shallOlv rectangular channels. <br /> <br />* Runoff from overland flow in the upstream watershed can be <br />simulated and sediment can be added to the channel to <br />create a mudflow hydrograph a1: the fan apex. <br /> <br />* The outflow bridges and clJ.lverts is approximated by user <br />defined rating curves. Flow over adverse slopes and <br />backwater effects can be simulated. <br /> <br />* Runoff resulting from the effective rainfall on the <br />alluvial fan or floodplain can be simulated. <br /> <br />* The data file is created 1.i1:h AutoCAD'-DCA software. <br /> <br />The FLO-2D model has been designed in a modular form. The <br />subroutines have been separated from the main program for easy <br />modification. One of the subroutines performs a data check of the <br />grid system and ensures that common boundaries of contiguous grid <br />elements are identified correctly. Manning's n values and grid <br />elevations are checked for relativ,,~ magnitude. <br /> <br />To create a data file for the model, AutoCAD-DCA software is <br />used to discretize the potential flOlv surface into uniform grid <br />elements. Each grid element is assigned a representative <br />elevation, roughness factor, and a:!:"ea and width reduction factors. <br />The contiguous elements in each of the four pos!.ible flow <br />directions be must also be identif'ied. Linking with AutoCAD-DCA <br />has greatly improved the reliability and flexibil.ity of <br />manipulating the data file and has eliminated the tedious work <br />associated with creating an extensive grid system data file. <br /> <br />Separate subroutines determinE! the discharge flux between <br />adjacent channel or floodplain grid elements. Channel flow is <br />modeled one-dimensionally, using variable area cross sections. <br />Overland flow is modeled by a two-dimensional, diffusive wave <br />approximation of the momentum equat:ion which can distribute the <br />flow across the unconfined surface. If mudflows are being routed <br />in the channel, a separate subroutine is called that computes flow <br />velocity and determines the discharge flux. <br /> <br />streets are assigned a curb depth <br />east-west or north-south direction. <br />contain one or more streets in bot:h <br />dimensional street. flow. Streets <br />channels. <br /> <br />and located according to an <br />A given grid element may <br />directions simulating two- <br />are treated as rectangular <br /> <br />The overflow from a channel or street and the possible return <br />flow is computed in the channel-floodplain interface subroutine. <br />The computed velocity of either thE' outflow from, or the return <br />flow to, the channel or streets is based on the water surface <br />elevations. This interface routine distributes the flood flows <br />over the grid element containing tIlE! channel or streets. <br /> <br />17 <br />