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<br />. <br /> <br />. <br /> <br />EXlUBIT A <br /> <br />I~'" <br />\;'.", <br />,,-;. <br /> <br />SCDpe .of Work <br /> <br />CRDSS Yampa Daily Model <br /> <br />Background and Purpose <br /> <br />The Colorado Water Conservation Board (CWCB) has need for a model to estimate daily flows in the <br />Yampa basin, over):he 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 /> <br />The purpose of this work effort is threefold: I) 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 ofthe Yampa basin using. an <br />. . <br />efficient approach to input data development. <br /> <br />Task 1 - Develop equivalent daily return flow factors <br /> <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 /> <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 /> <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 /> <br />Task 2 - Pilot study <br /> <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 /> <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 detemline relative accuracy of the approaches. <br /> <br />dailyampa.doc <br />