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<br />01)1")540 <br /> <br />f <br /> <br />PROGRAM MElHODOLOGY <br /> <br />Basic Assumptions <br /> <br />The underlying principle in the operation of MODSIM is that <br />most physical water resource systems can be simulated as <br />capacitated flow networks. <br /> <br />The components of the system are represented in the <br />network as nodes, both storage (Le., reservoirs) and non- <br />storage (Le., river confluences, diversion points, and demand <br />locations) and links or arcs (Le., canals, pipelines, and natural <br />river reaches). <br /> <br />In order to consider demands, inflows, and desired reservoir <br />operating rules, several artificial nodes and linkages must be <br />created in such a way as to insure the fully circulating nature <br />of the network. It should be noted that the MODSIM user is <br />only responsible for setting up the real network. All artificial <br />nodes and links are added automatically by the model. <br /> <br />Important assumptions associated with MODSIM are listed as <br />follows: <br /> <br />1. All storage nodes and linkages must be bounded <br />from below and above (i.e., minimum and maximum <br />storages and flows must be given). The latter <br />bounds are allowed to vary over time in the model. <br /> <br />2. Each linkage must be unidirectional with respect to <br />positive flow. Possible flow reversals can be <br />modeled by assigning an additional reverse direction <br />link between two nodes. <br /> <br />3. All inflows, demands, and losses must accumulate at <br />nodes. Increasing the density of nodes in the <br />network thereby increases simulation accuracy, but <br />also increases computer time and data requirements. <br /> <br />10 <br />