2015-03-31_HYDROLOGY - M1999050 - Laserfiche WebLink

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Mr. Todd Williams, P.E. March 24, 2015 Page 3 of 6 Lesser of the water available for crop consumption or potential crop consumptive use if a full water supply was available. One -third (65.09 acre -feet) of the return flows from the use of the 4.0 shares were assumed to occur as surface return flows and the remaining two - thirds (130.18 acre -feet) were assumed to occur as subsurface return flows. Subsurface return flows were lagged to the river using the AWAS stream depletion model with the following parameters: • Distance from the irrigated property centroid to the river (X) = 3,300 ft •' Alluvial aquifer width (W) = 5,000 ft • Specific yield (S) = 0.2 • Transmissivity (T) = 50,000 (gpd /ft) The monthly net accretion/ depletion for the 4.0 BEDC shares were calculated as the monthly diversions available at the farm headgate, minus the surface return flow obligation and lagged subsurface return flow obligation for that month. The monthly net accretion/ depletion for the 2.5 BEDC shares to be delivered to recharge were calculated by pro - rating the monthly net accretion /depletion for the 4.0 BEDC shares. The expected volume of water available for diversion into the recharge pond for the subject 2.5 shares is 227.62 acre -feet per year. This figure represents the pro -rata average headgate diversion less a 10% ditch loss. The pro -rata historical consumptive use credit for the 2.5 shares is estimated to total 105.57 acre -feet for this plan period and the pro -rata return flow obligation for the 2.5 shares is estimated to be 122.05 acre -feet. The evaporation losses from the recharge pond (shown in Water Balance table) are estimated to total 19.52 acre -feet per year, resulting in a net amount of 208.10 acre -feet of water delivered to recharge. The lagged accretions from the Timnath- Connell recharge pond were estimated by the Applicant's consultant using the AWAS stream depletion model with the following parameters: • Distance from the recharge pond centroid to the river (X) = 3,500 ft • Alluvial aquifer width (W) = 5,300 ft • Specific yield (S) = 0.2 • Transmissivity (T) = 50,000 (gpd /ft) The lagged accretions to the Cache la Poudre River are estimated to total 302.21 acre -feet during this plan period. This amount includes deliveries to recharge from previous years. Pursuant to previously submitted accounting, 286.54 acre -feet were diverted into the recharge site during the 2012 irrigation season, 257.27 acre -feet were diverted into the recharge site during the 2013 irrigation season, and 502.69 acre -feet were diverted into the recharge site during the 2014 irrigation season. The summer and winter return flow obligations from the use of the 2.5 Box Elder Ditch shares will be maintained under this substitute water supply plan. A monthly breakdown of the stream depletions from the mining operation as well as the replacements made by the recharge accretion credits of the Box Elder Ditch shares are shown in the attached Water Balance table. Long Term Augmentation The final reclamation plan for this site includes both a lined reservoir and unlined ponds. The successful completion of a lined reservoir will eliminate long term depletions that would require a long term augmentation plan. After completion and approval of the reservoir liner this area must continue to be covered by a valid SWSP until the lagged depletions from mining operations are no Longer impacting the river. An unlined pond in addition to the recharge pond will remain on the site after final reclamation. The creation of a permanent unlined pond will result in long term evaporation of ground water which requires a long term augmentation plan. The Applicant is required to obtain a