2013-04-01_HYDROLOGY - M1986079 - Laserfiche WebLink

Home Browse Search

Entit No. of Shares Chan.e Case Platte River Farms 12 SWSP 0202503 Aggregate Industries 22 SWSP 0202565 Read Mixed Concrete Co 11 Rick Parsons M &G SWSP March 28, 2013 Carlson has signed an affidavit on behalf of Platte River Farms dedicating their 12 shares to this SWSP. Tower Property Share Ownershi Page 3 of 7 The complete ownership and historic use data for the 45 shares used at the Tower property were found to be incomplete by the Applicant's engineer. Based on their research historic irrigation may have exceeded 200 acres. The analysis of the Polly Mann shares and the historical use analysis performed in 00CW202 and 01 CW258 show that Fulton Ditch shares were typically issued on the basis of about 1 acre of irrigated land per share. Therefore it is likely that there were once more shares used on the Tower property or that the 45 shares were not used to irrigate the full property. For the purposes of this SWSP only, the 12 Tower shares owned by Platte River Farms will use the Polly Mann consumptive use and return flow factors that are described below. The HCU analysis of the 50 Polly Mann shares was completed using the StateCU consumptive use model. The study period for the HCU analysis is 1942 to 1981 and is consistent with the study period used in the change case no. 00CW202 engineering report. This 40 -year period is representative of wet, average, and dry years and covers an era when the Fulton Ditch system was almost exclusively used for irrigation. Historical diversion data recorded for irrigation use were tabulated and the pro rata diversions attributable to the 50 shares were input into the CU model. A 20% ditch loss was assumed based on similar Fulton Ditch change cases and experience with various ditch systems in District 2. A maximum farm efficiency value of 65% was assumed based upon other change cases in the area and generally accepted ranges of efficiency values for furrow irrigation. 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 lagged to the river. The deep percolation was lagged to the river using the same AWAS software and aquifer properties as described in the Depletions section. 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. The average irrigation water requirement (IWR) for the Polly Mann property was found to be 93 acre -feet per year which was based on 46.1 acres of irrigation evenly split between alfalfa, corn, and pasture grass. 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 monthly HCU factors as a percentage of lateral deliveries and the winter time return flows as a percentage of irrigation season's consumptive use credits are as shown in the table below: