2017-04-04_HYDROLOGY - M1999050 - Laserfiche WebLink

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Timnath-Connell Substitute Water Supply Plan Page 3 of 7 March 31, 2017 The remaining 1.5 BEDC shares not used for recharge will continue to be used to irrigate the portion of the John Weitzel Farm still in agricultural production. The diversions available at the farm headgate for the 4.0 shares used on the John Weitzel property were estimated to total 365.20 acre-feet per year, and the historical consumptive use of the 4.0 BEDC shares was estimated to be 168.99 acre-feet. This quantification is based on the average headgate diversions for the Box Elder Ditch for the years 1950 to 2014, assuming 10% ditch loss and 55% field efficiency for flood irrigation. Historic consumptive use was determined as the lesser of the water available for crop consumption or potential crop consumptive use if a full water supply was available. One-third (65.40 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 (130.80 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 228.25 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 105.62 acre-feet for this plan period and the pro-rata return flow obligation for the 2.5 shares is estimated to be 122.63 acre-feet. The evaporation losses from the recharge pond (shown in Water Balance table) are estimated to total 20.82 acre-feet per year, resulting in a net amount of 207.43 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 248.91 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, 502.69 acre-feet were diverted into the recharge site during the 2014 irrigation season, 407.81 were diverted into the recharge site during the 2015 irrigation season, and 240.11 were diverted into the recharge site during the 2016 irrigation season. In addition in 2014, and 2015 long periods of no call on the Cache La Poudre River allowed for considerable amount of free river water to be delivered into the recharge pond beyond the historic yields of the 2.5 Box Elder shares. 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