2015-08-06_HYDROLOGY - M1996049 - Laserfiche WebLink

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Mr. Raul Passerini, P.E. Page 6 June 24, 2015 Change of Use of Old Whetstone Sheep Creek Ditch Historically the Old Whetstone Sheep Creek Ditch irrigated approximately 28.85 acres of pasture grass at the Maryland Creek Ranch property as shown on the attached Figure A-4. Of this total, approximately 22 acres are currently wetlands created as mitigation for wetlands impacted by gravel mining operations. The remaining 6.85 acres have been removed from irrigation. The historical consumptive use of the irrigation supply for the 6.85 acres was quantified based on the average monthly diversion records for the period of 1966 through 2009 (adjusted to the total decreed diversion rate of 1.0 cfs), using the TR -21 Modified Blaney-Criddle Method with adjustment for elevation. Monthly temperature and precipitation data were taken from published records for Dillon 1 E station and the Green Mountain Dam weather station. The ditch loss from the headgate to the irrigated fields was assumed to be 5 percent and an irrigation efficiency of 60 percent was used. Water in excess of the irrigation requirement was added to the soil moisture bank, which was assumed to be 3 feet deep with a water holding capacity of 0.15 inches per inch. The average historical consumptive use from the water right in the Old Whetstone Sheep Creek Ditch for the 6.85 acres was estimated to be approximately 6.55 acre-feet, as shown on the attached Table 10 or 0.96 acre-feet per acre. The historical consumptive use based on average years during the study period was compared to the historical consumptive use for the dry years for 1977 and 1994. The dry year historical consumptive use for 1977 and 1994 was estimated at 1.27 acre-feet per acre, therefore for the purpose of this SWSP the study period average consumptive use of 0.96 acre-feet per acre was selected. Change of Use of McKay Ditch Historically McKay Ditch irrigated approximately 90 acres of pasture grass at the Maryland Creek Ranch property as shown on the attached Figure A-4. Of this total, 66.2 acres have been permanently removed from irrigation due to gravel mining operation as shown on the attached Figure A-5. The historical consumptive use of the irrigation supply for the 66.2 acres was quantified based on the average monthly diversion records for the period of 1964 through 2009 (adjusted to the total decreed diversion rate of 18.67 cfs), using the TR -21 Modified Blaney-Criddle Method with adjustment for elevation. Monthly temperature and precipitation data were taken from published records for Dillon 1 E and the Green Mountain Dam weather stations. The ditch loss from the headgate to the irrigated fields was assumed to be 10 percent and an irrigation efficiency of 60 percent was used. Water in excess of the irrigation requirement was added to the soil moisture bank, which was assumed to be 3 feet deep with a water holding capacity of 0.15 inches per inch. This junior water right in the McKay Ditch (appropriation October 1, 1926) was historically called out by the Shoshone water right. Historically the water rights within the Colorado River Basin that are junior to the Shoshone water right have been allowed to divert without curtailment because of releases of water from the HUP in Green Mountain Reservoir. Once the junior water in the McKay Ditch is changed for augmentation purposes it will no longer benefit from the Green Mountain Reservoir releases under the HUP. Therefore, for the purpose of this analysis, and based on the historical call of the Shoshone water right, it was assumed that the McKay Ditch was out -of -priority beginning July 1 of each year, and no historical consumptive use credits for the Mc Kay Ditch were used for the period of July - November of each year during the study period. The historical consumptive use from the water right in the McKay Ditch for the 66.2 acres was estimated to be approximately 43.36 acre-feet, as shown on the attached Table 11 or 0.65 acre-feet per acre.