CRDSS_Task1_15-5_EvaluationofProgramMODSIM

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entire reservoir for purposes of evaporation and seepage loss computations and total storage diversions and releases. The children represent the individual accounting modules for multiple priorities and/or ownerships. Losses are prorated among the subset storage accounts. MODSIM also can be operated to attempt to achieve certain target storage contents which can be user specified for purposes of hydropower production, flood control, etc. Exchanges . The MODSIM network can be set up to include water rights exchanges on the river, including a situation where storage water is released into the network at one location (node), and a like amount is diverted by another ditch at an upstream location. Such an exchange can be assigned its own priority number (cost) and would be limited to the available flow in the intervening reach of the river after satisfying rights that are senior to the exchange (exchange potential). Exchanges can also occur between one demand node (direct diversion) to another direct diversion node, but may require additional iterations to confirm that no other water rights are being injured by the exchange. Return Flows . MODSIM has the ability to calculate return flows which result both from diversions at a demand node or reservoir node. Because the model solves the entire system network simultaneously, it can account for return flows that accrue to the system during the same time-step as well as lagged return flows from diversions in prior months. Return flow patterns can be described by the user either as a percentage of the diversion or in the form of a return flow table. Return flows can be assigned to accrue to multiple nodes in the network. Calibration and Virgin Flows . As part of the calibration process, MODSIM is capable of quantifying unregulated inflows to the network using actual historic data for diversions, reservoir change in storage, imports/exports, and gaged stream flow data, together with an estimate of the return flows. The network is then solved, forcing the network to quantify the unregulated inflows necessary to match the recorded stream flow measurements (the unregulated, unmeasured inflow being the only remaining unknown in the mass balance). This unregulated inflow is then stored for use in subsequent simulation runs. MODSIM can also be operated to develop "virgin flows" for the network. This is accomplished by using the unregulated inflows, determined during the calibration process, and then by turning off the historic diversions and storage and allowing the network to solve. This has the effect of removing the depletions attributable to man's activities from the historic stream flows. Calculation of virgin flows will require additional work effort by the CRDSS Project Team; however, that effort is consistent with the effort required for other models (with the exception of BESTSM, with its internal module for virgin flow simulation). Other Issues Additions and Modifications . The input format for MODSIM is structured to allow for the addition of nodes (diversions, reservoirs, in-stream flow rights, etc.) in a relatively straight forward manner. Discussions with persons familiar with MODSIM applications indicated that there is a wide range of flexibility for simulating different allocation scenarios by manipulation of the initially constructed network, i.e., adding nodes to represent specific issues. MODSIM is robust in that the model "as is" can handle most simulation requirements without the necessity of writing additional FORTRAN source code. Ease of Understanding . As compared to water allocation models such as BESTSM and HYDROSS, the logic of MODSIM is more difficult for the everyday water user to understand because of the 3 A275 05.10.94 1.15-5 Fosha, Hyre