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reach, flow = infZow_tot- demand met - reach_losses. (3-26) <br />As above, demand_met in this equation is initially set equal to the demand calculated <br />above. However, if the reach_flow calculated in Equation 3-26 is below the minimum <br />required flow, then demand_met is reduced until this constraint is satisfied. <br />Shortage and Return Flows: <br />A shortage, in terms of ineeting M&I demand, occurs when demand_met is constrained <br />by the combination of available inflows and either reservoir or reach minimum storage <br />requirements. Shortage is calculated as: <br />shortage = demand - demand met. <br />(3 -27) <br />When there is no reuse occurring, the net return flow is simply the non-CU portion of the <br />used water or: <br />net returnFlow =(1 - percentCU annual) * demand met. (3-28) <br />However, when there is reuse, the calculations get slightly more complicated. For the <br />case where the net demand has been met (shortage = 0), the equation is: <br />net returnFlow = demand - percentCU annual * total use_annual <br />- reused water, (3-29) <br />where <br />reused water = Is` time reuse = extra CU * total reuse. (3-30) <br />In other words, the returned flow is equal to the delivered water minus the consumed <br />water minus the water that gets consumed during reuse. <br />For the case where there is a shortage, the equation is: <br />net returnFlow = demand met - percentCU annual * total use_annual <br />* demand met/demand - reused water, (3-31) <br />where reused water is calculated according to Equation 3-30, but extra_CU is calculated <br />as: <br />extra CU = demand met * percentCU source - percentCU annual * <br />total use_annual * demand met/demand. (3-32) <br />The underlying assumption in Equations 3-31 and 3-32 is that the percent CU in M&I <br />usage stays the same even during times of shortage. <br />10 <br />