C150094 Long Hollow Dam Phase I Summary

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Long Hollow Dam and Reservoir Phase I Summary Report stream gauges, including the Long Hollow and Cherry Creek gauges installed in 1988. Based on 85 years of record at the Hesperus gauge, the study period was about 5 percent drier than average (see Table 5). The average annual La Plata River discharge at the Hesperus gauge for the study period was 27,577 AF, which ranks at about the 45th percentile on a scale from dry to wet. Flow data from the five stream gauges and diversion records for 18 irrigation ditches were used to create the model and develop a water balance for the La Plata River and its tributaries (see Figure 5). After calibrating the model with actual data, the model was used to simulate stream conditions in Colorado during the study period with and without the proposed LHR. The model simulated the ability of the LHR to fill in-priority. The model supplied water to New Mexico in an amount equivalent to the historic Compact call from New Mexico during the study period. Figure 6 depicts the LHR end-of-month storage that is anticipated under this operation plan (WWE, March 2004 : Based on historical Compact call conditions, LHR will fill 4 of 14 years, with an average fill of 3,540 AF/yr. LHR will release all or nearly all stored water in 10 of 14 years. �.- — -----The model also simulated the amount and timing of releases from LHR to deliver water to New Mexico at the Colorado-New Mexico State Line gauge, as required by the Compact, while allowing Colorado ditches on the La Plata River to divert in-priority by exchange without impacting Compact deliveries. A 300-AF Compact Reserve Pool in LHR was used to deliver water to New Mexico during the mid-summer low-flow period when the La Plata River in Colorado often must be administered as a split river. The incremental increase in diversions allowed by this exchange program benefits approximately 334 shareholders in the 18 ditches incorporated into the water allocation model (see Table 6). LPWCD irrigators have expressed support for allocation of the exchange water by priority. LPWCD will hire the necessary personnel to operate and maintain LHR. Records will be kept of LHR inflow, outflow (bypass amounts plus releases from storage), and remaining storage volumes for both.the Compact Reserve Pool and the remaining storage. Releases from storage 991-077.115 Wright Water Engineers, Inc. Page 18 July 2004