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<br />1)02258 <br /> <br />Chapter II <br /> <br />Development of a Physically Based Distributed <br />Parameter Rainfall Runoff Model <br /> <br />pertinent information. As model simulations are performed, the user can create "run time" plots. <br />These plots display the behavior of model variables as they change through time during a model <br />simulation, assisting the modeler in calibrating and visualizing model processes. All model <br />variables within the system are available for these run time plots. The system also generates <br />statistics for user selected model variables. Additionally, the system has optimization and <br />sensitivity analysis capabilities. Such features assist the modeler in testing and calibrating a <br />physical-process model. <br /> <br />PRMS source code has been written in a modular fashion to be compatible with the MMS <br /> <br /> <br />framework. PRMS within the MMS framework consists of 14 physical-process modules, each of <br /> <br /> <br />which embodies a physical-process algorithm. The utilities contained in MMS greatly enhance a <br /> <br /> <br />modeler's ability to develop, calibrate, and analyze PRMS models. <br /> <br />MMS has been developed by the USGS, the Center for Advanced Decision Support for Water and <br />Environmental Systems, Reclamation, and other Federal and non-Federal entities. Funding for <br />MMS development was provided, in part, from the Gunnison Climate Study to facilitate the <br />optimal development and utilization of Gunnison Climate Study rainfall runoff models. MMS is <br />currently being maintained by the USGS in Denver, Colorado. <br /> <br />DEVELOPMENT OF THE MODEL HYDROLOGIC RESPONSE UNITS <br /> <br />The first step in constructing a PRMS model is the development of HRU's for the watershed being <br />modeled. Traditionally, HRU's have been developed by using topographic maps, along with maps <br />or images which depict land cover, geology, soils, or other physical features in a watershed. Lines <br />are then drawn on these maps to partition the watershed into areas which are deemed to be <br />homogeneous with respect to hydrologic response. <br /> <br />In the Gunnison Model, however, this traditional method was abandoned in favor of a <br /> <br />computerized approach using Geographic Information Systems (GIS's). Because the HRU is a <br /> <br /> <br />critical spatial element in PRMS, it was feil HRU's could be developed more efficiently and <br /> <br /> <br />effectively using GIS technology. <br /> <br />9 <br />