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With respect to model calibration, a Phase lb 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 />la model. Final Phase lb modeled demand shortages over the study period averaged <br />approximately 21,000 of per year, or roughly 1.4% of the average annual amount of water <br />diverted. Phase la results showed basin-wide shortages averaging approximately 20,000 of per <br />year. Shortages from Phase lb results ranged from a high of 3.19% of total diversions to a low of <br />0.54%, which is a slight improvement over Phase la 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. Although most modeled shortages were <br />experienced in District 20 (Rio Grande mainstem) it actually represents the smallest amount of <br />shortage as a percent of total District diversions. The greatest shortages as percent of diversions <br />was experienced in Water District 25 (San Luis Creek and tributaries) -Phase lb included fairly <br />significant aggregate groups in this District, and the increased shortages may indicate the need for <br />adjustment to model hydrology. Phase lb model results were generally consistent with those of <br />Phase la model runs and demonstrate favorable calibration with respect to surface diversions. <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 which 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 />As shown in the graphs of Attachment 3, modeled EOM contents are quite favorable in <br />comparison to historic observations and are very similar to results from Phase la model runs. <br />Seasonal trends (fill/release) are evident in both time-series and match well in most cases. In <br />some instances, the model clearly reports releases from storage that apparently did not occur <br />historically and vice-versa. Modeled operations at Platoro Reservoir, for example, diverge from <br />historic beginning in the mid-1980's and continuing until the early 1990's -this is due to more <br />significant modeled releases over this period which may result from assumptions about reservoir <br />access by downstream ditches or basic hydrologic input data (proration factors, return locations, <br />etc.). EOM contents at Platoro, as well as other reservoirs will continue to be a focus of <br />calibration efforts in later stages of model development and as an updated HydroBase becomes <br />available. <br />C:Acdss\Task7-8.doc Phase lb Model March 17, 2000 -Page 8 of 10 <br />