2014-09-04_HYDROLOGY - M1977023 - Laserfiche WebLink

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Mr. Peter Foster, P.E. August 29, 2014 Replacement Page 3 The proposed source of replacement water for this pit during the irrigation season (April through October) is a portion of the Applicant's interests in the Seventy -Five Ditch. The Seventy - Five Ditch diverts water from Gunnison River and it was decreed in CA1325 (Priority No. 1) for 14 cubic feet per second ( "cfs "), to irrigate 560 acres, providing a duty of water of 1 cfs per 40 acres of land. United owns 31 percent of the senior water right in the Seventy -Five Ditch or 4.33 cfs which is proposed to be used as a replacement water source in this plan. Based on United's pro -rata ownership of the Seventy -Five Ditch, the 4.33 cfs could irrigate up to 173 acres. The State Consumptive Use model with the Upper Gunnison High Elevation Calibration Coefficient was used to determine the historical consumptive use for lands irrigated under the Seventy -Five Ditch, Priority No. 1. In addition, based on the decreed duty of water of 1 cfs per 40 acres of land, you determined the historical consumptive use for the lands under the Seventy -Five Ditch as 1.7 acre -feet per irrigated acre (Table 3). Based on the average depth to groundwater of approximately 5 feet below ground surface, the historical consumptive use for subirrigation was reduced by 15 percent, resulting in an adjusted historical consumptive use value of 1.5 acre -feet per acre. The gravel mining operations at Gunnison West Pit have resulted in the dry-up of 28 acres of the mining property outside of the pit ponds (Figure 6). Applying the adjusted historical consumptive use value of 1.5 acre -feet per acre to this area produces a historical consumptive use total credit of 41.3 acre -feet earned by the dry-up. This credit is more than sufficient to offset out -of- priority depletions of 14.7 acre -feet for each year of the plan period. The only major water right in the vicinity of Gunnison West is the Gunnison River Whitewater Course. The Gunnison West irrigated lands and associated return flows are located downstream of this Recreational In- Channel Diversion water right. The historical calling water rights downstream of the Gunnison West operation are the Gunnison Tunnel and the Redlands Power Canal. In 2002 the Gunnison Tunnel placed a call from July 7 to September 19 and from September 25 to September 27. The Redlands Canal has not historically placed a call, but could potentially place a call when stream flows are not adequate to meet their water rights. The Seventy -Five Ditch, Priority No. 1 water right is senior to both Gunnison Tunnel and Redlands Canal water rights. The Applicant asserts, per their discussion with Division 4 Engineer Bob Hurford, that the historical call period on the Gunnison River is limited to the period from July through September, during which the historical consumptive use credit exceeds depletions to the river. April and October are the only months in which plan depletions would not be exceeded by historical consumptive use, but with no call on the river, no water will be owed during those months. Blue Mesa Reservoir is located immediately downstream of the Gunnison West operation, with a decreed capacity of 1,064,744 acre -feet, and provides releases to Gunnison River for power and upper Colorado River storage purposes. The operation of the Blue Mesa Reservoir typically determines the downstream call regime, therefore the timing of return flows is not necessary to consider in this plan. This is because the timing of return flows will be offset by storage and operation of the Blue Mesa Reservoir, which does not require lagging of return flows to the river to avoid injury.