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<br />communities in the area are St. George, about 17 miles to the south- <br />west and Cedar City, about 40 miles to the north. All project fea- <br />tures would be located within the general vicinity of the towns of <br />Hurricane and La Verkin which are immediately adjacent to the <br /> <br />springs. <br />2. Virgin River Flow. To fully understand the problems <br />involved in a water quality improvement program on the Virgin River, <br />it is necessary to look at the river from a point above La Verkin <br />Springs to its point of discharge into Lake Mead (Figure 1), <br />The Virgin River drainage is largely a semidesert area receiving <br />less than 15 inches of annual precipitation. Flows in the river are <br />irregular. The greatest part of the total annual flow occurs during <br />the winter and spring corresponding to greater precipitation and <br />snowmelt runoff over these months. However, high peak flows (flash <br />floods) primarily associated with thunderstorm activity, are known to <br />occur at any time. Records of the U. S. Geological Survey show flood <br />peaks as high as 22,800 cubic feet per second (ft3/s) at Virgin, Utah <br />(a 100-year flood is computed to be 23,550 ft3/s at this location), and <br />35,200 ft3/s at Littlefied, Arizona. High flows carry high sediment <br />loads. Sediment loads at the Virgin gage vary from a minimum of <br />8 tons per day to about 360,000 tons per day. <br />The Hurricane Diversion is a major irrigation diversion for the <br />Hurricane area (See Figure 1). Water is normally diverted from April <br />to mid-October. Water rights for this diversion are about 30 ft3/s <br />although reported diversions have frequently' exceeded 35 ft3/s. <br />Irrigation return flows reenter the Virgin River via the ground-water <br />system and Gould Wash. <br />The La Verkin Diversion Dam is located less than 1 mile down- <br />stream from the Hurricane Diversion Dam. Historically, this diversion <br />was operated solely for irrigation, but currently is also used by C P <br />National Corporation to supply water to a small (1 megawatt) hydro- <br />electric powerplant. The conveyance canal is presently capable of <br />handling 50 ft3/s. Irrigation diversions average about 10 ft3/s <br />during the irrigation season. <br /> <br />002512 <br /> <br />5 <br />