The onset of the drought in the Colorado River has heighted the attention of the Southern Nevada Water Authority (SNWA) to the broader issue of climate change. Climate change impacts on the Colorado River may be significant. The majority of regional climate models project a more arid climate and reductions in Colorado River runoff. These reductions are expected to be in addition to natural-flow variability and temporary drought conditions. Changes in timing and frequency of rainfall may impact the River’s water quality and its treatability for drinking water supplies. The drought on the Colorado River has reshaped Lake Mead dramatically in the past 11 years. Water levels have dropped over 130 feet (40 m) and SNWA’s drinking water intakes have moved from an approximate depth of 210 ft (64m) when the lake is full, to an 80 ft (24 m) depth at current conditions. SNWA has an extensive water quality monitoring program in Lake Mead that was developed to track changes in water quality over time and provide an early warning system for water quality changes at the drinking water intakes. Samples are collected in Lake Mead and at all of the inflows, which include the Las Vegas Wash, the Muddy River, the Virgin River, and the Colorado River. SNWA has also become involved in a three dimensional modeling effort with another agency in the Las Vegas valley, the Clean Water Coalition. Flow Science Incorporated was tasked with developing a three dimensional model of Lake Mead for use as a predictive tool. The probabilities and consequences of adverse events (severe droughts, floods, changes in water quality) are often highly uncertain and potentially severe. The modeling tool helps SNWA in identifying and prioritizing key water quality threats and developing response and adaptation options that target the most significant risks to the drinking water supply. Modeling was used to select a new intake location and for evaluating the impact of wastewater effluent.
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