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Streamflows: <br />1 Compare simulated stream gage flows to simulated flows <br />2 Repeat diversion and reservoir steps until simulated gage flows approximate historical <br />Results - Baseflows <br />Final average annual baseflows for the Phase lb surface water model are summarized in Table 2. <br />Average monthly baseflows at seven key points along the Rio Grande and four key points along <br />the Conejos River are shown graphically in the Figures 1 and 2, respectively. It is interesting to <br />note substantial losses to the river system between the Rio Grande gages at Del Norte (USGS <br />08220000) and Monte Vista (USGS 08221500). Model results suggesting losses in this reach of <br />the Rio Grande averaging approximately 25,000 of per year are generally consistent with <br />observations of the District 20 Water Commissioners. The baseflow calculations also suggest <br />system losses in lower reaches during the non-irrigation season During peak runoff months and <br />throughout much of the irrigation season, baseflows, as expected, generally increase in the <br />downstream direction as the River gains from additional tributary inflow and return flow. <br />River losses consistent with District 22 Water Commissioners are also evident in the baseflows <br />calculated for the Conejos River and along its tributary the Rio San Antonio. Model results <br />suggest that the Conejos River system losses nearly 60,000 of between the Magote gage (USGS <br />08246500) and the LaSauces gage (08249000), inclusive of gains from the Rio San Antonio. <br />Numerous seepage studies conducted along the Conejos River by the Division 3 Engineer have <br />confirmed significant losses in this reach. <br />A component of the reporting during operation of the surface water model in baseflow mode is to <br />report on calculated negative flow values if they occur. Calculated negative flows can occur at a <br />gage in the baseflow model run if simulated return flows are greater than historical flow <br />observations adjusted for historical upstream diversions. In this event, StateMod resets the <br />calculated negative value to zero flow, and proceeds with the run. However, the warning of <br />negative flows can suggest the need for adjusting such things as return locations, return timing <br />patterns, and/or irrigation efficiencies. Calculated negative flows may also suggest less accurate <br />stream flow gage data. <br />Results of baseflow model runs for the Rio Grande model indicate calculated negative flow <br />conditions at 10 of the 53 gages represented. For the most part, the calculated negative flow <br />values are relatively small and infrequent (less than 5 percent of the time and less than 20 cfs). <br />However, calculated negative flows are more frequent and more substantial at two of the modeled <br />gages (08249000 and 08234500). Discussions with Division 3 staff confirm that these gages <br />periodically suffer from backwater conditions and/or channel profile shift that can reduce <br />accuracy of measurements. <br />C:Acdss\Task7-8.doc Phase lb Model March 17, 2000 -Page 3 of 10 <br />