2015-04-22_HYDROLOGY - M1987049 - Laserfiche WebLink

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Julia Keedy Bromley Lakes SWSP April 8, 2015 Page 6 • The period of the HCU analysis was 1942 to 1981. The study period is accepted by the SEO for this SWSP period, however for any future SWSP request the study period should be extended through present. If the 50 Polly Mann shares where were used by others in SWSPs those years can be excluded from the extended analysis. • The historical consumptive use was estimated using the Modified Blaney - Criddle methodology with the TR21 crop coefficients in the StateCU Consumptive Use Model. • Soil Conservation Service methodology for calculation of effective precipitation. • Assumed ditch loss of 20 percent • Available water storage capacity was estimated at 0.10 in /in • Temperature and precipitation data from the Fort Lupton 2 SE station (ID 3207) and Brighton 1 N station (ID 0950). • A maximum irrigation efficiency value of 65% was assumed. • The assumed irrigation efficiency will be accepted for this SWSP plan period; however any renewal request must provide information to support the claimed efficiency, including the,type of flood irrigation, soil properties, aerial photos, slopes, irrigation practices, technical references etc. • The historically irrigated lands were based on 46.1 acres of irrigation evenly split between alfalfa, corn, and pasture grass. For purposes of this SWSP the irrigated area and crop split will be accepted, however any future SWSP must provide documentation to support these assumptions. • For the irrigation water historically applied to the farm, a portion ran off the fields (surface return) and a portion seeped into the ground below the root zone of crops (deep percolation). Irrigation return flows were distributed with 67 percent attributed to deep percolation and 33 percent to surface runoff based upon conditions evidenced during site visits, discussions with irrigators and ditch company personnel, and a review of other studies and change cases within the basin. The surface runoff (tailwater) return flows are assumed to return to the South Platte River during the same month of diversion and thus they were not tagged to the river. The deep percolation was lagged to the river using the same AWAS software and the -following aquifer parameters: Distance from the centroid to the river (X) = 1,500 feet Alluvial aquifer width (W) = 18,500 feet Transmissivity (T) = 100,000 gallons per day per foot Specific Yield (S) = 0.2 Return flows associated with ditch loss were not included in this analysis since these losses will continue as water is conveyed through the ditch to the pit. Over a 40- year study period, the average pro rata diversion for the Polly Mann property was 179.2 acre -feet per year, which translates to a historic farm headgate delivery of 143.3 acre feet per year, or 2.87 acre -feet per share per year. In total, the historic consumptive use for the Polly Mann property was found to be 87.2 acre -feet per year, or 1.74 acre -feet per share per year. The surface water, or tailwater, runoff averaged 18.7 acre -feet per year and the deep percolation runoff averaged 37.5 acre -feet per year. The total return flows represent approximately 39% of the historical farm headgate delivery, or 1.12 acre -feet per share. The total farm headgate, return flows and net stream depletions associated with the RMCC's eleven shares used on the Tower Farm are presented on the attached Table 3B.