The winter of 2018-2019 yielded considerable snow fall amounts in the Rockies and the Sierra Nevada mountain ranges that feed the water supply for Nevada. Notwithstanding an excellent year for surface water runoff, however, reservoir levels have not necessarily rebounded from past drought years. In northern Nevada, the reservoirs on the Truckee River that store water for the Reno metropolitan area are projected to fill. In southern Nevada, however, the forecast is for reservoir levels to hover just above critical levels, below which a shortage is declared and a reduction in deliveries would occur.
Water Supply for Nevada’s Population Centers
Northern Nevada and southern Nevada differ in many respects, the source of their water supplies being just one of them. The Las Vegas metropolitan area relies almost exclusively on water from the Colorado River, which begins as snowmelt in the Rocky Mountains. Colorado River water makes up nearly 90 percent of the supply for southern Nevada’s 2 million residents. Currently, only 10 percent of southern Nevada’s municipal water supply comes from Las Vegas Valley groundwater.
The Reno metropolitan area relies primarily on the Truckee River for its water supply, which is delivered by the Truckee Meadows Water Authority (TMWA). The Truckee River flows out of Lake Tahoe in California and into Nevada, where it passes through Reno and then ends at Pyramid Lake. TMWA holds approximately 119,000 acre-feet of Truckee River rights to serve over 385,000 people and generate revenue from its hydroelectric facilities. TMWA conjunctively manages its water supplies through a combination of natural river flows, injection of treated surface water into aquifers, groundwater pumping, and releases of its upstream drought reserves.
Legal Framework for Water Deliveries
With the 1922 Colorado River Compact (Compact) as the legal keystone, the Colorado River is managed and operated under numerous compacts, federal laws, court decisions and decrees, contracts, and regulatory guidelines, which are collectively known as the “Law of the River.” The Law of the River apportions the water and regulates the use and management of the Colorado River among the seven basin states and Mexico. Lake Powell, behind Glen Canyon Dam, and downstream Lake Mead, behind Hoover Dam, are the storage reservoirs that serve the Lower Basin States, including Nevada. Nevada’s allocation under the 1922 Compact is 300,000 acre-feet per year, which is delivered by Southern Nevada Water Authority (SNWA) through a contract with the U.S. Bureau of Reclamation (Bureau).
In the nearly century since the 1922 Compact was entered into, the basin states and Mexico have largely avoided litigation, focusing instead on finding consensus over river operations. On December 13, 2007, the Secretary of the Interior signed the Record of Decision for the Colorado River Interim Guidelines for Lower Basin Shortages and the Coordinated Operations for Lake Powell and Lake Mead (Guidelines), which implement a new management regime for Lake Powell and Lake Mead. The Guidelines specify the amount of water that will be released from Lake Powell based on the elevations of both reservoirs and establish criteria for the Secretary to declare a shortage. Key to the Guidelines is a new concept called “intentionally created surplus” (ICS), which permits Lower Basin States to store water in Lake Mead for future use. ICS water is defined as water that has been conserved through an extraordinary conservation measure, such as land fallowing, seawater desalination or lining irrigation canals. The goal behind ICS water is to avoid a shortage declaration triggered by the lake levels dropping below established thresholds.
The Truckee River is one of the most heavily litigated waterways in the country. It is managed under the 1944 Orr Ditch Decree, which adjudicated ownership, priority, and relative rights to Truckee River water in Nevada, as amended by the Truckee River Operating Agreement “TROA”). TROA was signed by the states of Nevada and California, the United States, TMWA and the Pyramid Lake Paiute Tribe on September 6, 2008. Implementation of TROA began in December 2015.
TROA allows for more efficient and flexible use of available reservoir storage to provide benefits to fish and wildlife, municipal, industrial, and irrigation water users, including supplies for emergency conditions and worse-than-worst-case droughts. It resolved decades of litigation and promotes future cooperation through a dispute resolution process. TROA’s major innovation is the ability for major stakeholders to establish “credit water” in upstream storage reservoirs during times when it is not needed. The credit water can then be carried over into subsequent years and released as needed. Using “credit water,” TROA significantly increases the amount of upstream drought storage.
Effects of Drought on Water Storage
Since 2000, the Colorado River Basin has experienced historically dry conditions, causing the combined storage in Lakes Powell and Mead to reach its lowest level since Lake Powell began filling in the 1960s. Fifteen of the last 19 years have had below average unregulated inflow into Lake Powell. Lake Mead’s elevation has dropped more than 130 feet since 2000. Due to drought conditions in the Rockies, the 2018 runoff was the third-lowest on record inflow into Lake Powell. With the deepening drought, beginning in 2014, the Basin States began working on Drought Contingency Plans (DCPs) to reduce the likelihood that the reservoirs will decline to critical elevations.
As of April 29, 2019, Lake Powell was at 38% capacity, while Lake Mead stood at 41 percent capacity. The Bureau’s January 2019 model runs projected that cuts to water deliveries in the Lower Basin would occur in 2020 to avoid the reservoirs reaching critically low levels. If Lake Mead dips below 1,075 feet, the Secretary of the Interior could declare a shortage, meaning Nevada would be required to reduce its Colorado River allocation. The amount of allocation reduction depends upon Lake Mead’s elevation level.
The winter of 2018-2019 produced heavy snowfall in the Rockies, resulting in the Colorado River basin snowpack being 121 percent of average as of April 29, 2019. March precipitation in the Upper Colorado Basin was 175 percent of average. However, the hot and dry conditions of 2018 left parched ground throughout much of the basin, which is likely to soak up much of the run off. Although the Lake Powell inflow is forecast to be 128 percent of average, the reservoir levels are not anticipated to rebound significantly. Current forecasts project that, at the end of the 2019 water year, Lake Powell’s elevation will near 3,611.59 feet, which is 55 percent of capacity. The projected elevation of Lake Mead is 1,076.17 feet, just above the critical shortage level.
The Sierra Nevada Mountains that feed the Truckee River also experienced heavy snowfall, resulting in the basin having 179 percent of average snowpack as of April 29, 2019. Truckee River flows at the California/Nevada state line are expected to be 188 percent of average. In contrast to the situation in southern Nevada, all storage reservoirs on the Truckee River system are expected to fill, in part due to credit water that was stored in the last few years since TROA was implemented. Although northern Nevada also experienced a grave drought in 2018 and many dry years since 2000, the smaller basin size and shorter distances over which surface run off must travel to reach the Truckee River and its reservoirs, in addition to improved river management under TROA, have likely contributed to the excellent storage capacity that the region now enjoys
Conclusion and Implications
The concepts of “credit water” (under TROA) and “intentionally created surplus” (under the Colorado River Guidelines) both allow for reservoir storage that can be tapped in future times of need. Credit water stored in the Truckee River reservoirs since TROA implementation began in 2015 has assured that reservoirs will fill this year. In contrast, even though the Colorado River basin experienced a banner snow year, the lingering effects of 15 dry years are still apparent in Lower Basin reservoir levels. ICS and other management strategies are being implemented in an effort to prevent shortages and provide future stability in the face of drought.
(Debbie Leonard)
