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'"I I IV. WATER I ',I '1 ',j J ':.1 ,.-., ;:;J ~.,<~ ',',. .~, .~ d 'I A. Water Requirements The additional hay production as outlined in the previous section will require a consumptive use of 1059.4 additional water. In estimating the total project water requirement, the irrigation water re- quirement plus the losses incurred in storage, con- veyance, and operation of the system from the reser- voir to the fields must be considered. ("Irrigation Water Requirements", USDA-SCS Engineering Division, Technical Release No. 21, rev. Sept. 1970.) The parcels of land will be surface irrigated by water stored in the proposed Hyannis Peak Reservoir through release of the water into a ditch system. A delivery schedule is not presently available on a ditch-by-ditch basis, however it is common practice to irrigate during the months of May, June and July. Estimation of the irrigation water requirement considers a field application irrigation efficiency of 90%. Application losses due to surface runoff will be minimal due to use of a tailwater recovery system in which runoff is collected by gravity and allowed to flow to lower parcels. Additional application losses are expected due to evaporation and percolation. The resulting irrigation require- ment is thus estimated at 1177.1 acre-feet: 1059.4 ac-ft. consumptive use : 0.90 = field irrigation efficiency 1171.1 ac-ft. irrigation requirement The project water requirement further considers conveyance, storage and operational losses expected from the point of diversion (Hyannis Reservoir, middle fork of Arapahoe Creek and ditch headgates) to the delivery at the parcels. The conveyance los- ses include seepage, evaporation, and consumptive use by phreatophytes in the stream and ditch system. Stream losses are considered negligible due to the gaining stream, high natural gradient and shaded characteristics of this high elevation stream reach. Within the unlined ditch system, seepage and phreato- phyte use are the major factors contributing to con- veyance loss, Reduction of this loss through lining of the ditches in this remote area is considered cost prohibitive. Reservoir storage losses are through evaporation seepage, and phreatophyte use. Opera- tional losses through delivery in excess of demand is assumed to be normal with good management. The project water requirement, considering all of the above losses, is thus estimated to be 1801.7 acre- feet of storage. -8-