Laserfiche WebLink
<br />Climate <br /> <br />The Moapa Valley Subevaluation Unit is in an arid climatic regime. <br />The frost-free season (in the irrigated area) averages about 240 days. <br />Based on observations at Lake Mead since 1936, the average annual evaporation <br />from a free water surface is 80 inches. Evaporation rates are highest <br />during July, August and September when 10 to 12 percent of the total evapora- <br />tion occurs each month. At Over~on, the December mean temperature is <br />450 F. while the July mean is 85 F. The precipitation in the irrigated <br />area varies from three inches during an average year to about six inches <br />in a wet year and comes in the form of rain primarily in the winter months. <br />A few summer convective storms are likely to occur and can cause serious <br />problems such as flooding, crop damage, and erosion. <br /> <br />Water Resource <br /> <br />Muddy River water has been used for irrigation in Moapa Valley since <br />the latter 1850's. The mineral content of the water makes it undesirable <br />for domestic use. <br /> <br />Surface Water - The surface water supply originates from Muddy River <br />Springs in Upper Moapa Valley and flows about 25 miles to the southeast <br />where it empties into Overton Arm of Lake Mead, just south of Overton, Nevada. <br />The mean annual discharge measured below Muddy River Springs at Moapa USGS <br />Gaging Station in 1977 was 32,670 acre-feet with 39 years of record. The <br />gaging station at Glendale which measures the streamflow to Lower Moapa <br />Valley had an average annual discharge in 1977 of 32,750 acre-feet with <br />27 years of record. Tributary areas contribute little water. Less than <br />five percent of the average annual flow is produced by surface runoff from <br />summer storms. Runoff from Meadow Valley Wash and California Wash only <br />occur during infrequent large convective storms. <br /> <br />Ground Water - In Upper Moapa Valley 3,920 acre-feet of ground water <br />is pumped for irrigation and cooling at Nevada Power electrical generating <br />plant. Little pumping in Lower Valley occurs because the quality of the <br />water is poor. Ground water samples from wells in Moapa Valley reflect <br />the presence of geologic formations containing soluble and moderately <br />soluble minerals, such as halite (sodium Chloride) and gypsum (calcium <br />sulfate). Sodium and calcium are the principal positive ions found in <br />the ground water while sulfate and bicarbonate are the predominant negative <br />ions. <br /> <br />Water Use - The major use of water is by irrigated agriculture in <br />Moapa Valley. Large volumes of water are also consumed by phreatophytes <br />and by evaporation. The reuse of water in onfarm systems is minor. The <br />effect of water reuse on irrigation efficiency is small. The principal <br />reuse of water consists of irrigation runoff, return flows, and power <br />plant return flow in the Upper Valley being delivered to the Lower Valley <br />for irrigation. Some 7,035 acres of wetland supporting phreatophytes <br />(of which 1,559 acres are riverine) use an estimated 3,200 acre-feet of <br />water annually. Salt cedar and arrowweed provide a li,mited amount of <br />nesting for song birds. <br /> <br />002692 <br /> <br />12 <br />