2025-09-10_HYDROLOGY - M1994005 - Laserfiche WebLink

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Colona Pit SWSP Page 5 of 13 September 10, 2025 Total Depletions Total estimated depletions are 55.0 acre-feet/year. Lagged Depletions A Glover stream depletion model was used to calculate lagged depletions to the Uncompahgre River, assuming steady state conditions. The following parameters were used in the model: transmissivity (T) = 50,000 gallons per day per foot; specific yield (SY) = 0.15; distance from the centroid of the pit to the river (X) = 2,000 feet; and distance from the aquifer boundary through the pit to the river (W) = 5,000 feet. The Unit Response Function (URF) developed using the Glover analysis and the above parameters are shown on attached Appendix C1. Total lagged depletions are estimated to be 55.0 acre-feet/year, as shown on attached Table 2 and Appendix C2. Out-of-priority depletions were determined based on the percentage of days the Gunnison River fell below 750 cfs during the year 2002 (worst case scenario), as shown on attached Table 3. Out-of-priority lagged depletions are approximately 32.26 acre-feet/year. Replacement Water Ouray Ditch HCU Credits The primary source of replacement water for this pit during the irrigation season of April through October is consumptive use credits from the dry-up of 29.2 acres historically irrigated by 2.5 shares in the Ouray Ditch (WDID 4100549). Based on Ouray Ditch diversion records, assuming a ditch loss of ten percent (10%) and an irrigation efficiency of fifty percent (50%), the average annual historical consumptive use (HCU) associated with the Applicant's 2.5 shares is estimated to be about 49.1 acre-feet/year, as shown in the attached Table 3. A portion of the water diverted to irrigate the 29.2 acres property historically accrued to the Gunnison River in a form of surface and groundwater return flow. The Applicant has previously completed a delayed depletion analysis to determine the amount and timing of