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<br />Basic Concepts <br /> <br />, ,~1> ~~,,: ~\,it <br />~, u. .,".u <br />Station Action . . <br /> <br />3.5.3 Evaooration: Applicable only if there is a reservoir at the station. If the RES <br />card specified an evaporation table in col. 10-13, that table gives, in linear units, the depth of <br />evaporation per unit of surface area per month; thus the table value multiplied by the surface area of <br />the mean content of the reservoir is the volume of water lost to evaporation for the month. If there <br />was no table specified, there is no evaporation loss for the month. <br />Conceptually, this is similar to a low priority diversion in that it removes water from the <br />system but only after all other actions have been taken. <br />Also refer to the section for precipitation on reservoir surface (section 5.4 [Page 32]). <br /> <br />3.5.4 Content Chanl!e: Applicable only if there is a reservoir at the station. Content <br />change is defined as end-of-month content minus beginning-of-month content. If positive, the value <br />represents water withdrawn from the system into storage; if negative, the value represents water <br />released into the system from storage. <br /> <br />3.6 Station Items <br />Items measured at the station itself are: <br />Station flow <br />Discharge (reservoirs only) <br />Seepage (reservoirs only) <br />Spill (reservoirs only) <br />Power (power plants only) <br />IFR satisfaction <br />Available flow <br /> <br />3.6.1 Station Flow: Station flow is defined as inflow minus station action. <br />Conceptually, this is the flow at the station point itself after other losses and diversions have been <br />deducted, and before any IFR's have been satisfied. Station flow may be negative (inflow less other <br />loss); if so, the value represents the amount of water which must reach the station before we can even <br />consider a diversion. <br />If there is a reservoir at the station, the station flow is the sum of discharge, seepage and <br /> <br />spill. <br /> <br />3.6.2 Discharl!e: Applicable only at stations with reservoirs. This is the flow through <br />the outlet works. If there is a power plant at the reservoir, this is the flow which generates the <br />power. <br />Discharge has no natural/project designation; it may be either or both, and serves only to <br />indicate how the water got through the reservoir. <br /> <br />3.6.3 Seeoal!e: Applicable only at stations with reservoirs. Seepage is defined in <br />col. 43-52 of the RES card as a constant, by a monthly table, as a function of flow, or as a function <br />of mean reservoir content. If the definition is omitted from the RES card, seepage is assumed to be <br />zero. <br />Seepage appears immediately below the reservoir as project water. It is not available for <br />diversion at or above the reservoir, and will not contribute to power generation. <br /> <br />March 25, 1991 <br /> <br />HYDROSS 4.1 <br /> <br />Page 19 <br />