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HEC-1 parameters are edited from a master dialog which displays the currently defined data of a selected basin or outlet (in HEC card-style format) and allows the user access to the several user-friendly dialogs used to specify desired options. WMS includes the ability to define several of the advanced HEC-1 options (next section) such as time-area curves, lag times and times of concentration, and snow melt elevation zones using computed geometric parameters. Once a HEC-1 model has been defined, the HEC-1 model checker can be run to try and identify potential problems in the data prior to actually running the HEC-1 model. The model checker provides several hints (although it does not guarantee a successful run or that the answers will be correct) for correcting the data prior to running HEC-1. HEC-1 can be launched from within WMS and after completion, hydrographs can be displayed in the hydrograph window. Hydrographs from different sub-basins or from different runs of HEC-1 can also be overlaid for comparison. |
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Defining HEC-1 Unit Hydrograph Parameters One of the major difficulties in estimating runoff with unit hydrographs is coming up with reasonable values for required parameters. The Clark and Snyder methods used in HEC-1 have been shown to be reliable, but establishing the time of concentration and time area curves for the basin is difficult. WMS uses a TIN to define watershed and sub-basin boundaries. A topologic model of the watershed is always created in parallel to the development of the TIN. Once the TIN has been refined and all sub-basins established, the time of concentration (or lag time) can be defined from one of several equations. A user-specified equation can be defined if one of the given equations in the time of concentration dialog does not fit your basin. Time area curves for the Clark and Snyder Unit hydrograph methods are created by establishing a runoff distance for each triangle of the TIN. While time of travel to the outlet is a function of more than just the distance (slope, land cover, etc.), for many watersheds the distance of runoff provides an adequate relative measure of time of travel. Snow melt calculations in HEC-1 are simplified with WMS since the area in each elevation zone is easily calculated and supplied on the proper HEC-1 cards. With user-friendly dialogs, elevation thresholds are set and then areas are computed for each zone. |
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Watershed Modeling System (WMS) Overview |
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Scientific Software Group P.O Box 708188 Sandy, Utah 84070
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