Overton Arm Basin and Virgin River Basin Water Quality Platforms
The Muddy River and Virgin River discharge into the Overton Arm of Lake Mead with a combined average annual flow of about 183,000 acre-feet (ac-ft).Water quality in these rivers is affected by return flows from irrigated agricultural fields, dairy operations, periodic storm-water runoff from seasonal thunderstorms, discharge of cooling water from power plants, and discharge of municipal wastewater from rapidly urbanizing areas in Mesquite, Nevada, and St. George, Utah. The effects of this discharge on localized water quality and limnology within the Overton Arm and Virgin River basins of Lake Mead are not well known.
In addition to these potential impacts, persistent drought conditions in the Colorado River Basin may impact the physical and chemical quality of water in the Colorado River, which provides over 95 percent of the inflow to Lake Mead. For example, the temperature of water released to the Colorado River from Lake Powell is expected to increase several degrees above average during the summer months; a result of the lake losing over 60 percent of its water volume during the drought. The impact that this warm water will have on Lake Mead, including fundamental properties such as the depth of the thermocline, and extent of the epilimnion, metalimnion, and hypolimnion, are not well understood.
Decreased water levels at Lake Mead are readily visible along the shoreline.
Five years of drought in the Colorado River Basin have reduced Lake Mead
to 60 percent of capacity and Lake Powell to less than 40 percent of capacity.
The water-quality platforms at Virgin Basin and Overton Arm will collect important data that will help assess the impact of inflow from the Virgin and Muddy Rivers and warm water releases from Glen Canyon Dam on the Virgin and Overton Arm Basins. These data also will help quantify changes in water quality that may be related to continued development along the Virgin and Muddy Rivers. Both platforms also are equipped with meteorological instruments. Water Quality and meteorological data collection began in February 2005.
