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002028 Advanced Concepts Offstream Storage 5.1.4 Proiect Flows and Offstream Storal!e: Project (only!) return flows received at a point Upstream from the target reservoir are available for diversion before the flow reaches the reservoir. For project-right diversions, the sequence of allocation is: a) Allocate project water available between the delivery station and the end of the basin. b) Allocate natural water available between the delivery station and the end of the basin. c) Request a release from the control reservoir(s). d) As a last resort, allocate project water available between the delivery station and the next reservoir downstream. Case (d) works for project flows only. Project water stolen on its way to a r.eservoir will have to be made up from the reservoir, which is stored water and can be released only as project flow. Natural flows stolen in this manner could not be made up as natural flows. Case (d) is the -QNLY- way for a diversion to access off stream storage return flows before they reach the target reservoir. If you want these return flows to be useable before they reach the target reservoir, you must type the flows as 'project' on the RFL card; if the flows are typed as 'natural', they will be inaccessible until they reach the target reservoir (after which they will be available as project water). 5.2 Availab]e F]ow 5.2.1 Establishinl! Available Flow: Available flow at a station is determined by observing the flow at the station, and at each station downstream to the end of the basin. Generally, the smallest number so obtained is the amount available for diversion at the station in question. There are some exceptions to this general rule, occasioned by the way the model handles station losses and reach losses. These exceptions are discussed below in paragraphs 5.2.3 [Page 31] and 5.2.4 [page 31]. * Another exception is at a reservoir below the station where we are calculating available flow. In this case there is an implied station at the upper end of the reservoir where we must look at the inflow to the reservoir. If there is negative runoff, then the inflow to the reservoir may be smaller than either the outflow from the reservoir or the outflow of the upstream station; if so, the constraint will be the reservoir inflow. This constraint will not be obvious in any of the reports unless you specifically look at the reservoir inflows. To make the constraint more obvious, introduce a dununy station at the upstream end of the reservoir so that there is zero runoff at the reservoir station. 5.2.2 Diversions and Available Flow: Flow available for diversion depends on the type (natural or project) and the water right date of the proposed diversion. Natural-right diversions must consider natural-right demands (diversions or IFR's) of higher priority (earlier water right date). Natural-right diversions may take only natural flow; they may never take project flow. Natural-right IFR's may not demand project water (but see 5.2.1 below); however, if there is project water flowing at the station that water may be used to satisfy the IFR. Water is water when deciding if an IFR is short. Project-right diversions must consider project-right demands of higher priority when they propose to use project water; they may also take natural water after allowing for natural-right demands of all priorities. Only a project-right demand (diversion, IFR or power) may draw upon stored water. Reservoir seepage is project water. It is not available for diversion by demands at or above the reservoir. HYDROSS 4.1 March 25, 1991 Page 30