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surface water model In addition, 10 aggregated reservoirs were added to the model. The <br />aggregation process is documented in memoranda describing efforts under Tasks 7.1, 7.2 and 7.3. <br />Model Execution Sequence <br />Following development of input data sets to reflect the addition of aggregated structures, <br />StateMod was run using the three-step process described in the memorandum documenting Task <br />Phase la model development (Task 6.14). That is, the model was first executed in baseflow <br />mode, followed by data check mode, and finally the model was run in simulation mode. This <br />three-step process (baseflow, check, simulation) may be repeated numerous times during model <br />calibration efforts. <br />Phase 1b Model <br />As previously described, the Phase lb surface water for the Rio Grande Basin represents 100 <br />percent of the decreed surface water use along the Rio Grande and its tributaries (river impacts <br />associated with groundwater use are left in the gage). In this phase of development, the model <br />was executed in baseflow, check and simulation mode over the period 1950 to 1997. During this <br />period, historical flow observations at numerous gages, recorded water deliveries to diversion <br />structures, and historical reservoir end-of--month contents were used to develop baseflow <br />hydrologic conditions. The model was then run in simulation mode using historical diversions as <br />a surrogate for water demand. This "historical simulation" utilized numerous operating rules to <br />reflect water management practices over the study period. <br />Model calibration can be defined as simulating a system such that results agree reasonably well <br />with historical observations. The Rio Grande Surface Water Model was calibrated through <br />several adjustments to hydrologic conditions (baseflows) and operating rules. Efforts towards <br />calibration focused on three areas: comparison of historical to modeled diversion amounts, <br />comparison of historical to modeled stream flows, and comparison of historical to modeled <br />reservoir contents. The calibration period extended over the entire study period (1950 - 1997). <br />Due to improvements in data collection and changes in river administration, the most recent 20 <br />years of the study period were examined more closely. Calibration targets were chosen to <br />generally simulate conditions within 5 to 10 percent of observed conditions. <br />The steps used in the calibration process were as follows: <br />Diversions: <br />1 Compare simulated diversions to historical diversions to identify shortages <br />2 Determine reason for any shortage <br />3 If required, adjust proration factors, return flow pattern/location, operational rights <br />4 Regenerate baseflow and rerun simulation <br />Reservoirs: <br />1 Compare simulate EOM contents to historical EOM contents to identify differences <br />2 Determine reason for any EOM content differences <br />3 If required, adjust proration factors, operational rights <br />4 Regenerate baseflow and rerun simulation <br />C:Acdss\Task7-8.doc Phase lb Model March 17, 2000 -Page 2 of 10 <br />