Laserfiche WebLink
<br />"""' <br /> <br />o <br /> <br />"lI:t" <br />N <br />o <br />o <br /> <br />The river reach studied ends at the mouth of the river. The <br />depletion of the river consists of evaporation, irrigation diversions, <br />seepage to ground water, and final discharge into Lake Mead. Usually <br />during the summer months there is no surface water discharge to Lake <br />r1ead. Discharge to the lake usually resumes in the late fall as <br />irrigation diversion rates decrease. Peak flows in the river occur in <br />the spring and early summer as a result of snowmelt and rain in the <br />Upper Virgin River Basin. <br /> <br />Approximately 38,000 acre-feet of water are diverted into the <br />three main irrigation systems below Littlefield Springs each year. <br />During periods of low flows, typically in late June, July, and August <br />irrigation diversions at Mesquite and Bunkerville may completely <br />divert available streamflow. The Riverside Irrigation Group has water <br />available only when the two upstream irrigation districts flush silt <br />and sand accumulation from their ditches, which generally occurs <br />2 days out of the week. The existing flow and water quality records <br />for the Virgin River were deemed inadequate to analyze the natural <br />hydrologic system. The USGS has maintained a river gage at <br />Littlefield since 1929, but the gage downstream from the irrigated <br />areas monitored sporadically between 1971 and 1978 produced poor <br />di scha rge records because of the f1 uctua t i ng sandy bed of the ri ver. <br />This gage was later moved to its current location below Riverside. <br /> <br />To analyze the surface water flow, DRI divided the river into <br />five reaches and gaged the streamflow above and below each reach <br />monthly, coordinating the effort with the USGS gaging stations <br />monthly. At the same time, field electrical conductivity and pH <br />(acidity) of the surface water were measured at the gaging sites and <br />some sediment samples were collected. It was found that some reaches <br />of river gained while others lost water. The Littlefield reach, <br />immediately downstream from the USGS gage near Littlefield, showed no <br />measurable gain or loss. The Mesquite reach, an agricultural reach <br />containing the Mesquite and Bunkerville irrigated land, was <br /> <br />20 <br />