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<br />.' <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />.' <br />I <br />I <br />I <br />I <br /> <br />This formation extends over a large part of the drainage area. The sandstanes exposed on <br /> <br />the surface are badly weathered but are sufficiently hard and dense at various depths be- <br /> <br />low the present ground surface to support the dam and appurtenant structures. Shales and <br /> <br />claystones are exposed at the washed out area of the Starr Ditch headworks, about 3,000 <br /> <br />feet upstream of the dam site. <br /> <br />The flow in Elkhead Creek is derived largely from snow melt. About 65 percent <br /> <br />of the annual runoff occurs in the month of May. The spring runoff normally begins <br /> <br />during the middle of April, reaches a maximum in May and then declines as summer ad- <br /> <br />vances. The minimum flow occurs usually in September and then increases sl ightly during <br /> <br />the autumn months. <br /> <br /> <br />The principal features of the Elkhead Creek Dam Project are an earth embankment <br /> <br /> <br />dam on EI khead Creek, an out I et works condu it to provide irrigation rei eases to Storr <br /> <br /> <br />Ditch, an uncontrolled overflow type spillway of reinforced concrete, and a low level <br /> <br />outlet within the spillway ogee to permit reservoir evacuation. Elkhead Creek Dam will <br /> <br />have a maximum height of about 55 feet, a crest length of 930 feet, and a total embank- <br /> <br />ment volume of approximately 175,000 cubic yards. Releases through the outlet works <br /> <br />will be controlled by a guard gate at the control structure and will be discharged directly <br /> <br />into the spillway chute. The upstream slope of the dam embankment will be provided <br /> <br />with slope protection to guard against damage due to wave action and the downstream <br /> <br />face will be planted with grass for protection against erosion and for aesthetic reasons. <br /> <br />The operation of Elkhead Creek Dam will be primarily for recreational purposes <br /> <br />and except for seasonal flood flows will have a nearly constant water surface at the ele- <br /> <br />vation of the spillway crest. An irrigation outlet, which may be operated independently <br /> <br />of the reservoir, was provided at the left abutment to permit releases for the Starr Ditch <br /> <br />water right of 6.1 cubic feet per second. <br />-2- <br />