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<br />. <br /> <br />. <br /> <br />III. HYDROLOGIC MODELING <br /> <br />A. Studv Obiectives <br /> <br />The primary objective for the computer modeling effort <br />was to quantify the benefits achievable through operating the <br />OMID "check" structure and bypass channel to benefit junior <br />rights in the Grand Valley. <br /> <br />A secondary objective was to develop the model as a <br />useful tool in assessing the adequacy of water storage <br />facilities in meeting dry-year demands in the Grand Valley and <br />elsewhere in the Colorado River basin. <br /> <br />B. Method and AssumDtions <br /> <br />A daily accounting model was designed using LOTUS 1-2-3 <br />software and following the format of the U.S. Bureau of <br />Reclamation's Colorado River Accounting Sheets. The Colorado <br />River Accounting Sheets are maintained by the Bureau's Eastern <br />Colorado Projects Office and provide a daily record of <br />depletions, storage levels, replacement releases, and river <br />flow upstream from the Shoshone Power Plant in G1enwood <br />Canyon. The Bureau's records for April 1, 1977 through March <br />31, 1978 were transcribed onto the electronic spreadsheet and <br />expanded to account for changes in river administration since <br />1977. The result was a daily model entitled NATFLOW1 which <br />calculated the "natural flow" available to Grand Valley water <br />rights at Cameo. A second series of spreadsheets were <br />designed to look specifically at irrigation-season water <br />distribution within the "Cameo Call" water rights group. They <br />are titled CHKPLAN and extend from April 1 through October 31, <br />1977. <br /> <br />NATFLOW1 begins with historic 1977 river-flow and <br />diversion data, then makes adjustments to account for <br />relatively recent changes which are likely to affect water <br />availability in the future. 1977 was chosen because it was a <br />critically dry year for which good records were available. It <br />is often used when assessing adequacy of water supplies in the <br />Colorado River basin. It was necessary to alter the historic <br />1977 record because of four major changes: <br /> <br />- Replacement releases to account for out-of-priority <br />evaporation losses from reservoirs are now being <br />required in Water Division 5. No such releases were <br />made in 1977. <br /> <br />- A relatively junior (1940) hydroelectric power right <br />for 158 cfs at the Shoshone power plant is now being <br />administered. It was not administered in 1977. <br /> <br />- 10 - <br />