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Model Calibration <br />The Rio Grande model was calibrated over the period 1950 through 1967. This period was selected <br />because it is a period in which diversion records were readily available, and because it reflects a <br />period of little, if any, curtailment of diversions in the Del Norte to Alamosa reach to satisfy the Rio <br />Grande Compact. <br />Two different tests were performed during calibration. These tests involved 1) a comparison of <br />modeled diversions to observed diversion amount over the same period; and 2) a comparison of <br />modeled flows at Alamosa to observed flows at Alamosa over the same period. Comparison to <br />average annual historical diversion amounts revealed that model results were generally within 10 <br />percent for individual diversion structures, and within 1 percent for all structures combined. The <br />analysis to compare gaged versus modeled flows at Alamosa, which included estimates and <br />inclusion of return flows between Del Norte and Alamosa, also resulted in relatively minor <br />differences. The information developed from this latter analysis was then used to refine estimates of <br />ditch use efficiencies and return flow parameters to apply to modeled diversions. <br />Model Use <br />The Rio Grande model has been used to examine various water supply and use scenarios to analyze <br />storable flows at four potential storage sites. These scenarios included examining storable flows <br />with and without deliveries from the Closed Basin Project, and what was referred to as "Step One" <br />and "Step Two" modeled diversion scenarios. The Step One scenario simulated mainstem <br />diversions at levels similar to those recorded from 1950 through 1967. The Step Two scenario <br />simulated mainstem diversions at decreed water right levels. The model results were further used to <br />define storable flows resulting from Closed Basin Project exchange water, flood flows, Compact <br />debit water, and normal seasonal flows. <br />Strengths and Weaknesses of the Model <br />Positives <br />• Monthly time step -appropriate for model purpose <br />• Limited input and data requirements <br />• Relatively simple solution technique <br />Negatives <br />• Monthly time step -does not accurately represent Compact administration <br />• Simplification of diversion structures <br />• Simplification of water rights structure <br />• Does not represent groundwater use (wells) <br />Other Modeling Efforts <br />Several other modeling efforts were identified and documented in a memorandum for Task 3.1 of the <br />Surface Water Modeling Scope of Work. A detailed review of these efforts was not conducted <br />under Task 3.2 because it was felt they do not provide information that would be valuable or <br />beneficial in RGDSS surface water modeling. <br />Comments and Concerns <br />None <br />C:Acdss\Task3Mem.doc Review Previous Modeling Efforts Apri16, 1999 -Page 11 of 11 <br />