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EXHIBIT A <br /> Scope of Work <br /> CRDSS Yampa Daily Model <br /> Background and Purpose <br /> The Colorado Water Conservation Board(CWCB)has need for a model to estimate daily flows in the <br /> Yampa basin, over the CRDSS extended data period (1909— 1996). Currently, CWCB executes the <br /> CRDSS Yampa monthly model and selected results are disaggregated to daily by the U.S. Fish and <br /> Wildlife Service (USFWS). It is believed that a model that simulates on a daily time step may deliver <br /> more accurate results, but it is not clear whether the improvement in accuracy warrants the additional <br /> work required to develop a daily database of input data. <br /> The purpose of this work effort is threefold: 1)to test several approaches to creating a daily model, to <br /> determine benefit gained from increased input accuracy; 2)to develop user documentation that discusses <br /> advantages and disadvantages of a daily time step when developing and using the CRDSS Water <br /> Resource Planning Models; and 3) to develop a daily time step model of the Yampa basin using an <br /> efficient approach to input data development. <br /> Task 1 - Develop equivalent daily return flow factors <br /> Purpose: A daily return flow fraction that results in 50 percent of unconsumed diversions returning <br /> within the month is not equal to 0.50 divided by the number of days in the month, as noted in the current <br /> Statemod documentation. The purpose of this task is to develop daily return flow factors that result in <br /> approximately the same monthly returns as those used in the Yampa monthly model. <br /> Approach: Using the State's stream depletion analysis program, compute daily return flow factors for <br /> the aquifer properties and distance to the stream that were originally used to develop the return flow <br /> factors in the current monthly Yampa model. If the properties used originally cannot be obtained, Boyle <br /> will estimate aquifer properties by running the depletion analysis program for a range of values to re- <br /> create the monthly return percentages. The estimated parameters will then be used in a daily analysis. <br /> Deliverables: Memo describing the daily return flow factor issue, as well as approach and results to <br /> determining a daily return flow factors for the Yampa basin model. <br /> Task 2—Pilot study <br /> Purpose: The purpose of this task is to explore sensitivity of different approaches to developing daily <br /> data,without investing in a large-scale model. This pilot study in a small basin will also demonstrate the <br /> workability of different approaches from the point of view of the CDSS tools, including Statemod, the <br /> DMI's and the Mixed Station Model. <br /> Approach: Boyle will first create a small scale monthly model which is a subset of the current CRDSS <br /> Yampa model, to be used throughout the pilot study. Then three different approaches to creating a daily <br /> model will be undertaken. In each case, the existing Calculated data set will be the starting point for all <br /> or most of the daily model input. Flow at the downstream terminus, as simulated in the three Calculated <br /> calibration runs, will be compared to historical flows to determine relative accuracy of the approaches. <br /> dailyampa.doc <br />