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<br />'" OU2023 <br /> <br />Basic Concepts <br /> <br />Station Items <br /> <br />3.6.4 Soill: Applicable only at stations with reservoirs. Spill occurs only when the <br />reservoir cannot hold the water, and will usually represent a flood condition. <br />A controlled spill occurs when the reservoir end~f-month content would otherwise exceed the <br />maximum content level for the month, defmed by a table on the RES card. At this point the reservoir <br />still has some control over the water, and will not release it if doing so would create a flood condition <br />downstream (defined as station flow exceeding channel capacity, defmed on the S1'2 card). <br />An uncontrolled spill occurs when the reservoir end~f-month content would otherwise exceed <br />the absolute maximum content level, defmed as the last (highest) entry in the content table of the <br />content-elevation-area-ilischarge curves for the reservoir. Conceptually the water is over the. top of <br />the dam and will flow downstream regardless of any damage it may cause. <br /> <br />3.6.5 Power: Applicable only at reservoirs with power plants. Power is computed <br />from discharge, and head and efficiency data furnished by tables called on the PWR card. It is <br />effectively computed at the station, which is just below the face of the dam. <br /> <br />3.6.6 IFR Satisfaction: Station flow is compared to the IFR requirement to determine <br />whether or not the IFR is satisfied. Water is water to an IFR, and it doesn't care if it uses natural <br />water or project water to satisfy its needs. <br /> <br />3.6.7 Available Flow: After all other demands have been satisfied (or as well as <br />possible), this value represents the excess water at the station which would be available for a low <br />priority diversion at the station. <br /> <br />3.7 Reach Losses <br />, In some instances, the stream channel between stations may be modeled as a canal, this is <br />used when there is no historical runoff for the reach, and the losses are best represented as a <br />percentage of the flow (as with diversion canals). <br />The mechanism for presenting this case to the model is to declare a reach efficiency table <br />(col 33-36 on the STA card), which the model handles much like a canal efficiency table for <br />diversions. It is like an other loss in that the reach loss has top priority in removing any water which <br />actually flows past the station, but there is also a mechanism for bringing part of it back later as <br />delayed return flow. <br />Note that reach losses occur after the water leaves the station. The reach efficiency <br />percentage of the station flow (natural and project) arrives at the next station downstream. <br /> <br />3,8 Flow To Next Station <br />After the station flow has been reduced by reach losses (if any), this is the flow (reponed as <br />natural, project and total) which actually reaches the next station and is reponed as "flows from <br />upstream" . <br /> <br />Page 20 <br /> <br />HYDROSS 4.1 <br /> <br />March 25, 1991 <br />