Gallinas River Future Water Supply Operations Model

Challenge

The City of Las Vegas obtains the majority of its municipal water supply from surface flows of the Gallinas River. The Gallinas River is designated as an Active Water Resource Management (AWRM) area by the NMOSE, with flows apportioned to users in low flow years according to shortage sharing agreements administered by the NMOSE Water Master. Climate change has affected the water levels for waterbodies throughout the southeastern region of the United States. An operations model was needed to produce future drought scenarios that would then be used to develop water shortage strategies for low flow years. 

Solution

GGI, a division of GZA GeoEnvironmental, Inc.,  developed an Excel-based water operations model of the Gallinas River using historic flow records and incorporating future drought scenarios to develop shortage sharing proposals for the Gallinas River that would ensure the City’s ability to provide water in low flow years while also allowing sufficient water to remain in the river to satisfy acequia irrigators’ needs. 

The model initially incorporated additions to and withdrawals from the City’s two storage reservoirs (~500 ac-ft of storage) and pumping of the City’s well field during periods of drought. The model was subsequently expanded to evaluate the benefits of purchasing additional storage in Storrie Lake. Addition of Storrie Lake to the model allowed the City to make an informed decision on the amount of permanent storage to purchase in Storrie Lake that will provide added water security during extended drought periods in the future. Following the Hermit’s Peak Calf Canyon fire in 2022, which burned over 70% of the Gallinas River watershed, the model was further modified to take into account the inability to divert some post-fire flows due to increased turbidity in the river.

The model is utilized by GGI in conjunction with runoff forecasts prepared by the Natural Resource Conservation Service (NRCS) and short- and long-term precipitation forecasts prepared by the National Oceanic and Atmospheric Administration (NOAA) to provide the City with monthly updates on the outlook for runoff and storage during the spring runoff and summer irrigation seasons.  

Benefit

The forecasts are utilized by the City to make decisions on how to optimize reservoir operations to ensure that maximum water is kept in storage to be available during periods of low flow or, after the fire, highly turbid flow, on the Gallinas River. 
Additionally, the project demonstrates GGI’s ability to create and utilize river and reservoir models that incorporate surface water flows and groundwater pumping into an integrated representation of the flow system, and to conduct watershed yield investigation and analysis.