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The question of sufficient water rights can be addressed in StateMod through the addition of "free <br />water rights" -junior priorities which allow ditches to divert under very higher river flows. <br />Insufficient supply is addressed by re-examining hydrology input files, re-configuring the model <br />network, and/or adjusting operating rules to make additional supply available. Calibration of the <br />Rio Grande Surface Water Model was achieved primarily through hydrology, network, and <br />operating rule adjustments. <br />With respect to model calibration, a Phase lc target was set to reduce basin-wide shortages to less <br />than 5 percent of total basin-wide diversions and, if possible, to improve over results of the Phase <br />lb model. Final Phase lc modeled demand shortages over the study period averaged <br />approximately 25,000 of per year, or roughly 1.5% of the average annual amount of water <br />diverted. Phase lb results showed basin-wide shortages averaging approximately 21,000 of per <br />year. Shortages from Phase lc results ranged from a high of 2.91% of total diversions to a low of <br />0.71%, which is slightly greater than Phase lb results (Attachment 2). <br />Shortages were also examined for each separate Water District and by river or stream to identify <br />any particular geographic areas with poorer calibration. Also shown in Attachment 2 are average <br />annual shortages for each of the eight water district. The greatest shortages as percent of <br />diversions was experienced in Water District 21 (Alamosa River and La Jara Creek). In fact, <br />nearly 50 percent of the average modeled basin-wide shortage (25,000 af) occurs in District 21. <br />The Phase lc model included a different representation of the Empire Canal (Commonwealth <br />system) than in earlier phases of model development. The Empire Canal is complicated in that it <br />originally diverts water from the Rio Grande (District 20), imports water to the Alamosa River, <br />then exports water again to La Jara Creek where it is diverted to serve Empire lands lying to <br />south. The large amount of modeled shortage occurring in District 21 is experienced in the <br />lowest reaches of the rivers, suggesting problems with return flow location assignments and/or <br />losses that are calculated during baseflow mode of model execution (the bottom of both creeks <br />are represented as no-flow nodes). An emphasis will be placed on this area to achieve better <br />calibration in subsequent modeling efforts. <br />Phase lc model results were generally consistent with those of Phase lb model runs and, with the <br />exception of District 21, demonstrate favorable calibration with respect to surface diversions. As <br />previously noted, representation of the Empire Canal system in both District 20 and District 21 <br />will continue to be refined during later stages of model development with the aim of improving <br />calibration of diversions and stream flows. <br />Modeled Reservoir Operations <br />Results of comparisons between historical EOM contents and simulated EOM contents are shown <br />graphically for each of the reservoirs explicitly represented in the model (Attachment 3). These <br />comparisons are shown both for the entire study period (1950 - 1997) and for the most recent <br />years (1978 - 1997). The current status of the HydroBase database requires significant data <br />filling for early years of the study period for reservoir records, and therefore more recent <br />comparisons are more meaningful. <br />The Rio Grande Surface Water Model includes numerous operating rules that define how <br />reservoirs are operated. For example, these rules define when, how much, and to which <br />downstream user(s) water should be released. The rules are based on information developed <br />during Task 4 of the RGDSS Surface Water Component study (interviews with local water users). <br />C:Acdss\Task8-8.doc Phase lc Model September 27, 2000 -Page 12 of 17 <br />