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Model Calibration <br />The CRPM was calibrated over the period 1970 through 1990. This period was selected because it <br />comprises the entire modeling study period and it reflects a period in which the Rio Grande Compact <br />was administered as it generally is administered today. <br />Several different tests were performed during calibration. These tests included 1) a comparison of <br />modeled diversions to observed diversion amounts over the same period; 2) a comparison of <br />modeled flows at La Sauces to observed flows at La Sauces over the same period; a comparison of <br />modeled (calculated curtailment percentages) versus historical curtailment percentages; and 4) a <br />comparison of modeled storage contents in Platoro Reservoir to historical contents. <br />Comparisons to historical Platoro Reservoir contents were very favorable during initial calibration <br />efforts, with seasonal differences typically less than one percent. Comparisons to historical <br />diversions, on the other hand, were not in good agreement initially and resulted in considerable <br />effort to investigate the cause of large differences, then make adjustments to several model <br />parameters. The differences were eventually attributed to several sources including errors in <br />diversion records and unaccounted stream gains and losses. Comparisons to historical deliveries at <br />La Sauces, i.e. Compact deliveries, were excellent, and differences were typically less than 2 or 3 <br />percent annually, but less than 1 percent over the 21 year study period. <br />Adjustments to the CRPM during calibration included changes to individual ditch efficiencies and <br />return flow amounts, incorporation of a variable stream flow loss function dependent on river stage, <br />and incorporation of a loss factor to represent water consumption by phreatophytes growing along <br />the river banks. After these changes were made, calibration was generally within 5 percent on an <br />annual basis for all diversion structures combined, although comparisons for several individual <br />ditches were still poor. This was attributed to some degree to variations in water demand which are <br />behavioral in nature rather than water use decisions based strictly on legal and physical supply. <br />Model Use <br />To date the CRPM has only been used by the CWCD in support of their application for direct flow <br />storage in Platoro Reservoir. Under this application, model scenarios were developed to compare <br />diversion amounts by individual ditches with and without the ISA program. The results of these <br />model scenarios suggested that little, if any, injury would result to other ditches not participating in <br />the program. The Water Court has approved the CWCD's application with a retained jurisdiction <br />period over which to further evaluate the program, and the ISA program was initiated in 1991. <br />Strengths and Weaknesses of the Model <br />Positives <br />• 10-day seasons (i.e. time step, represents 10-day Compact administration) <br />• Represents every ditch on the Conejos system <br />• Very good, accurate representation of the Rio Grande Compact administration <br />• Detailed representation of direct flow storage at Platoro (ISA program) <br />• Represents Norton Drain and Closed Basin exchange to Platoro <br />• Includes both simulation and optimization capabilities <br />Negatives <br />• 10-day seasons (i.e. time step, can overstate resolution of results) <br />• Difficulty with individual ditch calibration on 10 day increment <br />• Does not represent groundwater use (wells) <br />C:\cdss\Task3Mem.doc Review Previous Modeling Efforts Apri16, 1999 -Page 7 of 11 <br />