C150094 Reservoir Inflow Addendum

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Brice Lee December 20, 2002 Page 3 Hollow and Cherry Creek flows likely for a larger period would add increased error into the model. The modeled reservoir was not allowed to carry over storage from one year into the next. Only the minimum storage below the outlet structure is carried over from year to year in the model. Dry year benefits resulting from carry-over storage are not considered. The model cannot predict a futile call decision by the division engineer. It was assumed that all water upstream, no matter how small in amount, will be called downstream to satisfy senior water rights if required. The New Mexico Compact demand is modeled as the most senior water right or obligation. RESULTS OF THE ANALYSIS The modeled Red Mesa Reservoir end of month storage contents is presented in Figure 1. The reservoir filled to 4,072 af four out of 10 years. The reservoir filled to the 3,000 af level five out of 10 years. As discussed earlier, six out of 10 years during the 1989 through 1998 period were drier than average. Thus, given the relative dryness of the 10-year period of record used in the current model,these results are in line with previous estimates by WWE(see August 14, 2002 Report). The model results also show that the reservoir's ability to fill is not solely dependent upon annual flows in the Hesperus River. The pattern of river flows is an important component, especially during the New Mexico Compact period,when higher flows at the Hesperus Gauge result in higher demands for the compact at the state line. During the dry years (1990, 1994 and 1996)a majority of the reservoir's inflow occurs in March, with no inflows occurring during the summer months of May through September. Thus, during dry years,the reservoir storage depends on winter and early spring inflow. A review of the winter and early spring diversion record shows a substantial amount of water diverted during the winter and early spring(see Table 3 and Appendix C). Winter(October through March) diversion of water from the La Plata River ranges from 2,995 of(1990)to 6,728 of(1994)with a 10-year average of 5,801 af per year. The ability of the reservoir to fill would be enhanced by a reduction in winter water use in the river basin. If 1,500 af of storage could be gained from a reduction in winter water, the reservoir would fill seven out of 10 years. This water could later be used for direct diversion and exchange during the irrigation season.