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<br />00lG7~ <br /> <br />7.2 Routing the Water Th.r~_u_!l..h the System <br /> <br />The CRSM simulates flow through the basin on a monthly time frame, <br />starting at the upstream end of the basin and proceeding to the <br />downstream end. Simulation is done reach by reach in an order specified <br />by the basin configuration, which is input to the model. Within a reach, <br />computat ions are made at each sequencf! poi nt starting at the upstream <br />end of the reach. <br /> <br />At the beginning of each monthly time increment, the flow at every <br />sequence point is considered to be zero. In other words, the model <br />assumes all storage of water is in the reservoirs, that no water is <br />stored in the river. Water occurs in the river only as it is routed <br />through the system each month. <br /> <br />A sample river basin is shown on figure 7.1. Each sequence point is <br />either an inflow, a demand, or a reservoir. A typical order of pro- <br />cessing sequence points is given by the numbers on the figure. As the <br />model moves from sequence point to sequence point, the procedure is <br />basically to add inflows to the flow in the river, subtract demands from <br />the flow in the river, and operate reservoirs to store and release <br />water. <br /> <br />The first sequence point in a reach is always an inflow point. When the <br />first sequence point of a reach is processed each month, a value called <br />"flow in the river" is set to zero. On figure 7.1, point 1 is the first <br />sequence poi nt of Reach 1-7. As thi s reach is processed each month, the <br />model first sets the flow in the river to zero. The model then adds the <br />inflow at point 1 to the flow in the river. Next, the model adds the <br />inflow at point 2 to the flow in the river. The model then subtracts <br />the demand at point 3 from the flow in the river, and so on. When the <br />entire Reach 1-7 is processed, the flow in the river computed at point 7 <br />is saved as an inflow to point 25. When Reach 22-30 is processed, point <br />25 will be processed as an inflow using the flow in the river computed <br />at point 7 as the inflow amount. <br /> <br />Inflow points can be hydrology inflows, return flows, flows from <br />upstream reaches, or flow check points. These terms are defined as <br />follows. Hydrology inflows are points where monthly values of flow and <br />salt are introduced into the basin. These inflows can be either actual <br />flows or intervening gains and losses. These inflows get their monthly <br />values from the hydrology input data file, which is described in sec- <br />tion 5. Return flows are the portions of demands that are diverted but <br />are not consumptively used. These flows are returned to the river at an <br />inflow point downstream of the demand, but not necessarily to the same <br />reach as the demand. Return flows can also be lagged to return up to <br />10 months after the actual diversion. Flow check points are simply <br />points used to check the salinity of the flow against maximum and mini- <br />mum constraints. <br /> <br />Demand points are points where water is removed from the river. If <br />there is not enough flow in the river to meet the demand, designated <br /> <br />31 <br />