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Olj33Z~ CHAPTER III POTENTIAL IRRIGATION DEVELOPMENT . The O'Neal Park area, including the reservoir site, consists of cretaceous beds which dip northward. These beds consist of sandy shales, interbedded sandstones, and coal seams of the Hesa Verde, Mancos shale, and Dakota formations. In valleys, swales, and bottom lands, these formations are covered by a soil mantle derived from the parent forma- tions and from glacial outwashes. This surface layer varies in depth from a few inches to an estimated 30 feet. Field observations did not indicate any problems in obtaining a watertight reservoir or satisfac- tory fOWldation for an earth-fill dam. It was assumed that satisfac- tory rock for foundation (probably shale) would occur at a depth of 15 feet on the abutments and 25 feet at the bottom of Perry Draw. Perry Draw Inlet Canal and Piedra Diversion Dam . The Perry Draw Inlet Canal would head at a diversion dam to be cOllstructed on the Piedra River approximately 6.5 miles upstream from the Bridge Ranger Station at an elevation of 8,295 feet. The canal would be 10.99 miles long with a capacity of 40 second-feet. It would consist of.9.29 mileo of u.~ined section, 1.65 miles of 3D-inch diam- eter steel siphon, a:1d a 270-foot chute. A wasteway would be located above the inlet to the siphon crossing Gordon Creek. The canal would intercept and divert flows of Big and Little Pagosa Creeks and other minor tributary streams. The canal alignment and cross sections were estimated from aerial photos with the aid of a stereoscope. Altimeter elevations of points that could be identified on the photos, estimated cross slopes, and type excavation were obtained in the field. The canal would generally be located on side hills with moderate to steep side slopes. A long siphon was provided to cross Gordon Creek and to avoid some steep shale side slopes, which indicate evidence 01 seepage and possible slipping. The inlet canal vould enter Perry Draw at a low saddle near the crest elevation of Perry Drav Dam. A chute would convey the water to dead storage elevation. The diversion dam on the Piedra River at the head of the Perry Draw Inlet Canal would be a concrete gravity weir with an earth section on the right abutment. The concrete overflow section would have a crest l;,ugth of 100 feet and vould rise 5 feet above strellIllbed. Maximum vater surface would be 5 feet above the crest of the overflow section. An additional 200 feet of earth dike, sluiceway, and headworks vould be pro- vided. Outlet Canals and Main Laterals . The Ant Hill Canal vould be about 9 miles in length. It would have an initial capacity of 20 second-feet and a terminal capacity of 5 second- feet. O'Neal Park Canal would be 6.2 miles in length. Its capacity would vary from 35 to 15 second-feet. The f1 ve main laterals would have a combined length of about 14 miles. Their capacities would vary from 15 to 2.5. second-feet. 20