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<br />Basic Concepts <br /> <br />. ,,('. ('Ill <br />Natural and Project Flow ~ ;1 i.:,' d <br />'~I <br /> <br />3 Basic Concepts <br />This section introduces the basic concepts used by HYDROSS. <br /> <br />3.1 Natural and Project Flow <br />Conceptually, "natural" flow is naturally accruing precipitation runoff and "project" flow is <br />stored water which would not be present in the absence of storage facilities. <br />Natural flow must be used in the month it appears, or not at all. Natural flows may be <br />withdrawn from the stream by demands with a natural water right; after all such demands have been <br />satisfied, the excess natural water (if any) may be withdrawn by demands with a project righi, or it <br />may be stored. <br />Project water is water which has been stored or otherwise appropriated for project use. <br />Under no circumstances may project water be withdrawn under a natural water right. <br />The above definitions contain the asymmetry that natural water may sometimes be <br />appropriated under a project right, but project water may never be appropriated under a natural right. <br />When you set out to define a model, remember that the functional asymmetry (what <br />HYDROSS actually does with the labels) is more important than the motivating concept. Feel free to <br />bend the conceptual definitions to achieve the desired result, but never forget how the different types <br />of water are treated. <br /> <br />3.2 Demands <br />HYDROSS recognizes four kinds of demands for water. <br /> <br />3.2.1 Instream Flow Reauirement: An instream flow requirement (IFR) is a demand <br />that requires a flow (specified by a monthly table) to be maintained in the stream at the station. <br />An IFR may have either a natural right or a project right, but not both. <br />Water is water to an IFR, and either kind of water (natural or project) will work to satisfy it. <br />Only a project IFR may demand the release of stored water. <br />Water flowing through an IFR is not withdrawn from the stream, and is available for use <br />anywhere below the IFR station. <br /> <br />3.2.2 Power Reauirement: A power requirement is similar to an instream flow <br />requirement, but in this case the monthly table gives the power required; the flow required is <br />calculated (by HYDROSS) from the reservoir content (head) and efficiency data. <br />Power plants may occur only at reservoirs. All reservoir releases are assumed to go through <br />the power plant, so natural water will work as well as project water in satisfying the demand. <br />Power requirements are always project demands, and may require release of stored water. <br />Water used to satisfy a power demand is not withdrawn from the stream, and is available for <br />use anywhere below the power plant. <br /> <br />March 25, 1991 <br /> <br />HYDROSS 4.1 <br /> <br />Page 15 <br />