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<br />MEMORANDUM <br />TO: File <br />FROM: Meg Frantz and Linda Williams <br />SUBJECT: CDSS Daily Yampa Model -Task 2 Pilot Study <br />Objective <br />September 28, 2001 <br />The CDSS Water Resources Planning Models to date have been monthly time step models. Aware that <br />monthly models do not capture daily variations in streamflow and call regime, the State enhanced <br />Statemod to operate on a daily time step. The code is highly flexible, allowing several different <br />approaches to daily operation, including both disaggregation and permitting the user to supply daily <br />input for some or all variables. The purpose of the Daily Yampa Model pilot study was to: <br />... expiore the sensitivity of different approaches to dtvelopirig daily data, without investing in a <br />large-scale model. This pilot study in a small basin will also demonstrate the workability of different <br />approaches from the point of view of the CDSS tools, including Statemod, the DMI's, and the Mixed <br />Station Model. <br />Approach <br />Boyle created one monthly model and three daily time step models of the Elk River, a tributary of the <br />Yampa River, above the Clark gage. The three daily models represented three different levels of <br />complexity to the development of daily input files: <br />• "Average Daily Model" -Statemod sets daily baseflows, demands, and reservoir targets to the <br />average value for the month during each simulation day <br />• "Daily Pattern Model" -Statemod distributes monthly baseflows according to the distribution of <br />daily flows for a historical gage specified by the user; demands and reservoir targets are set as in the <br />Average Daily Model <br />• "Daily Input Model" -Statemod computes daily baseflow using daily gage, diversion, and reservoir <br />content information provided as input; for simulation, Statemod distributes monthly demand and <br />reservoir targets to daily by interpolating linearly between monthly values <br />The three approaches are summarized in Table L <br />TaskMem2Final.doc F3OYLE <br />