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<br />0005~7 <br /> <br />Consumptive demands: <br /> <br />The other type of demand allowed in MODSIM is when all <br />water contributing to demand satisfaction in the model is <br />assumed to be consumptively used in the system. However, <br />the ability of MODSIM to consider stream-aquifer <br />interactions allows calculation of subsurface return flows to <br />the river due to inefficient application of water. <br /> <br />terminal demand nodes consumptively use the water diverted <br />to that node. Water specified for instream use, or flow- <br />through demand, bypass the node and are available for <br />downstream diversion. This is handled in the model in an <br />iterative manner. <br /> <br />- First the model allocates the water to all demand areas. <br />The allocated water for the flow-through demand node is <br />then treated as an unregulated inflow into a downstream <br />node, as specified by the user, for the next iteration. This <br />iteration procedure is also carried out within the channel <br />loss iteration loop. Flow-through demands <br /> <br />Artificial demand arcs: <br /> <br />An artificial demand arc links each real node (storage and <br />non-storage) with the artificial demand node. The lower <br />bound on this arc is set equal to zero, while the upper bound <br />is set equal to the demand associated with each real node. <br />The cost placed on each artificial demand arc is calculated by <br />the following equation: <br /> <br />(Cij)t =-[1000 - (DEMRij. 10)] (5) <br /> <br />18 <br />