Recycled Water Flow Changes From the SARS-CoV-2 Pandemic in Southern Nevada: Forecasting Improvements and Hydrodynamic Modeling

Abstract

The Las Vegas Wash (the Wash) provides a mechanism for delivering recycled indoor water used in the Las Vegas Valley, NV to the most downstream basin of Lake Mead. The Wash introduces different water quality to Lake Mead, including higher nitrogen and phosphorus concentrations, and it may contain constituents common to urban runoff including microbial organisms and trace contaminants. A strong link has been established between the residential population of the Las Vegas Valley and the mean annual flowrate in the Wash; however, with the onset of the SARS-CoV-2 pandemic in 2020, significantly reduced tourism led to reduced flow in the Wash. This work expands previous modeling efforts which project Wash flowrates based on population projections by incorporating tourism numbers, using the individuals employed in hospitality as a surrogate. The resulting model suggests that mean yearly Wash flowrates could increase 20.6%–23.2% (between 1.95 and 2.19 $m^3/s)$ by 2060, compared to 2022 levels. Numerical simulations of Lake Mead show that these increased Wash flowrates are not expected to have a significant thermal influence on either the drinking water intake (Intake) or Hoover Dam outflows. The Wash delivers about ${10}^3$ MW of heat into Lake Mead, while heat transfer at the Intake and Hoover Dam water columns was two orders of magnitude less. Wash water concentration and salinity increased in the simulations at the Intake and Hoover Dam outflows, respectively, by at most 0.91% and 1.3%.