Laserfiche WebLink
demand = total use_annual. (3-18) <br />Storage: <br />For the reservoir source option, storage is calculated using a simple flow balance: <br />dS/dt = infZow - ou ~ow, (3 -19) <br />where S is the reservoir storage volume and t is time. In the model, this equation is <br />applied according to: <br />res vol = res vol~rev + infZow_tot - res release - demand met - evap (3-20) <br />where <br />demand met = demand (initially, see below) <br />and <br />(3 -21) <br />evap = evap_rate_annual(in./yr) * 365 / 12 *(res area~rev + res_area)/2 (3-22) <br />or <br />evap = evap_rate_annual(%vol) * (resyol~rev + res vol)/2. (3-23) <br />Since evaporation rates are a function of current reservoir volumes, Equation 3-20 is non- <br />linear. Therefore, the following steps are followed in solving for res_vol: <br />• Equation 3-20 is linearized by assuming evap = 0, <br />• If necessary, this value is used to calculate res_area (according to the user-defined <br />vol:area table), <br />• Equations 3-22 or 3-23 are applied to estimate evap, <br />• res vol is recalculated with Equation 3-20 using this estimated evap value. <br />If the calculated storage volume is greater than the reservoir capacity, then overflow is <br />calculated as: <br />res overfZow = resyol - res_capacity <br />and <br />res vol = res capacity. <br />(3 -24) <br />(3-25) <br />Alternatively, if the calculated storage is less than the user-defined storage minimum, <br />then demand met is reduced until the minimum storage limit is reached. If evap alone <br />causes the storage volume to drop below the minimum, then demand_met = 0. <br />For the reach source option, the instream flow is calculated as: <br />9 <br />