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• Average basin-wide consumptive use of approximately 803,267 af. <br />• Diversions (Divert) and pumping (Pumping) over this period average 1.60 million af, <br />suggesting an average efficiency of approximately 50 percent. <br />• Losses (Loss), unconsumed diversions and pumping that do not return to the stream, <br />average approximately 533,766 of per year. <br />• Salvage (Salvage), well pumping that does not deplete the stream, average <br />approximately 438,788 of per year. <br />• Stateline flow (Stream Outflow) is approximately 350,721 af/yr. <br />It should be noted that while the water balance indicates a total stream outflow of averaging <br />350,721 of per year, flows at the bottom of the model network average only 328,897 of per year. <br />The difference, 21,823 of per year, is due to outflows from several small tributaries known not to <br />physically connect to the Rio Grande (e.g. San Luis Creek, Carnero Creek, La Garita Creek). <br />Summary <br />The Phase lc Rio Grande Surface Water Model has been completed. One-hundred percent of <br />decreed surface water and groundwater rights in the Rio Grande Basin, 12 explicitly modeled <br />reservoirs, 10 aggregated reservoirs and 28 instream flows are represented in the model. <br />Operations are characterized by approximately 300 operating rules. <br />Numerous calibration runs have been performed and several adjustments have been made to the <br />network structure and hydrology. The model calibrates quite well based on comparisons of <br />historical observations to modeled diversions, modeled reservoirs EOM contents and modeled <br />stream flows. Phase lc results showed a slight improvement in calibration over Phase la and <br />Phase lb results in most areas. <br />Comments and Concerns <br />Phase lc model results includes aggregations of reservoir with decreed absolute storage rights as <br />shown in HydroBase. Additional storage rights, specifically smaller stock ponds, may be decreed <br />in Division 3, but are not, at this point, represented in the model. Although it is likely any <br />additional storage rights represent a relatively small amount (volume) of storage, these rights <br />should be included in future model development. <br />The "historical simulation" calibration described herein that uses diversions for demands and end <br />of month contents as reservoir targets is appropriate for a sequential calibration approach and <br />certain "what if' applications. The "calculated calibration" that will be performed in Task 9 and <br />does not include these constraint limits should be expected to produce less favorable calibration. <br />Overall calibration in historical simulations was very favorable. However, calibration in certain <br />areas within the overall model network was less satisfactory. For example, calibration on La Jara <br />Creek and the Alamosa River indicated excess water simulated at the end of these rivers (these <br />rivers are generally known to run dry before they enter the Rio Grande). It is most likely that <br />excess water on these streams is due to errors associated with return flow assignments (both <br />locations and amounts). The current return flow assignments are based on results of the <br />preliminary RGDSS groundwater model. Rather than attempt to achieve better calibration on La <br />Jara and Alamosa, the State decided to wait for updated Groundwater Model results (and return <br />flow information) before attempting further calibration efforts in the Surface Water Model. <br />C:Acdss\Task8-8.doc Phase lc Model September 27, 2000 -Page 15 of 17 <br />