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Aerial view of Lake Mead

Surplus and shortages

The elevations in Lake Powell and Lake Mead are intended to rise and fall to capture excess water in high flow years and to buffer against dry years (or droughts).

The Secretary of the Interior is responsible for delivering water from Lake Mead to the Lower Basin States and Mexico. Shortages and surpluses of water are based upon Lake Mead's elevation.

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.

However, thanks to the success of community conservation efforts, per capita water use has declined significantly and Southern Nevada is not currently using its full Colorado River allocation.

Interim Guidelines

In response to the severe Colorado River Basin drought conditions, the Secretary of the Interior in 2007 issued a Record of Decision for Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated Operations for Lake Powell and Lake Mead. The Interim Guidelines define the availability of Colorado River water for use in the lower basin based on Lake Mead’s water surface elevation.

Per the Interim Guidelines, the Secretary of the Interior would base a shortage declaration on projections of Lake Mead water levels as determined by the U. S. Bureau of Reclamation's Colorado River modeling efforts. The projection forecast is determined annually in August.

Interim Guidelines
Lake level elevation (above sea level) Nevada shortage reduction Arizona shortage reduction
1,075 feet 13,000 acre feet 320,000 acre feet
1,050 feet 17,000 acre feet 400,000 acre feet
1,025 feet 20,000 acre feet 480,000 acre feet

The guidelines also created a new type of surplus called Intentionally Created Surplus. The Water Authority has water resources available for use under rules for Intentionally Created Surplus and other agreements.

Domestic surplus

Under the provisions for "domestic surplus," when Lake Mead's elevation is above 1,145 feet, the Southern Nevada Water Authority will have access to an additional 100,000 acre-feet of water per year to meet customer demands. In the future and until the Interim Guidelines expire, the Water Authority will use domestic surplus water when it is available and needed to meet demands.

Flood control surplus

The Secretary of Interior also may allocate additional water to control or alleviate flood potential along the Lower Colorado River.

The Water Resource Plan does not assume the availability of flood control surplus water during the planning horizon. However, the Water Authority will use this resource as a priority when it is available.

Intentionally created surplus

Intentionally Created Surplus (ICS) was created by the Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated Operations for Lake Powell and Lake Mead in 2007. The primary purpose of ICS is to encourage the efficient use of Colorado River water, increase storage in major system reservoirs, increase surface water elevations in Lake Mead, and help to minimize or avoid the potential for declared shortages.

There are five ICS categories:

  • Tributary Conservation ICS
  • Imported ICS
  • System Efficiency ICS
  • Extraordinary Conservation ICS
  • Bi-National ICS

Tributary Conservation and Imported ICS enable the Southern Nevada Water Authority to develop some of its surface and groundwater rights located in Nevada by allowing these rights to flow into Lake Mead in exchange for ICS credits. These credits can be used under any operating condition, including shortage (as a Developed Shortage Supply), and are converted to Extraordinary Conservation ICS if they are not used in the year they are created.

The SNWA also can participate in Colorado River conservation and efficiency programs in exchange for System Efficiency ICS, Extraordinary Conservation ICS and Bi-National ICS credits. These credits can be accrued in a variety of ways, such as land fallowing, canal lining, desalination and other efficiency projects that save Colorado River water that would otherwise be lost. These ICS credits are stored in Lake Mead and can only be used during normal operating conditions.

Aerial view of the Brock Reservoir
The sign at Coyote Springs
Aerial view of the Muddy River where it empties into Lake Mead
Aerial image of the Yuma Desalting Plant
Warren H. Brock Reservoir System – System Efficiency ICS

The Warren H. Brock Reservoir (formerly known as Drop 2) storage project was constructed to capture U.S. Colorado River water that would otherwise go unused in the Lower Basin and pass into Mexico. This System Efficiency ICS project provides Southern Nevada with 400,000 acre-feet of ICS credits; no more than 40,000 acre-feet are available for consumptive use each year through 2036.

Photo credit: U.S. Bureau of Reclamation

Coyote Spring Valley Groundwater – Imported ICS

The SNWA has developed 9,000 AFY of its Coyote Spring Valley Groundwater rights as Imported ICS by conveying the water to Lake Mead for credit.

Virgin and Muddy Rivers – Tributary Conservation ICS

The Water Authority has developed a portion of its Muddy and Virgin river surface water rights as Tributary Conservation ICS by conveying these rights to Lake Mead for credit. Approximately 14,700 AFY in permanent rights and 17,600 AFY in leased rights have been acquired.

Photo credit: U.S. Bureau of Reclamation

Yuma Desalting Plant – System Efficiency ICS

The SNWA collaborated with partners in 2009 to support funding of the Yuma Desalting Plant Pilot Project. The purpose of the project was to test the viability of resuming operation of the facility, which ceased in 1993 due to flood damage. In exchange for participation, the SNWA received 3,050 System Efficiency ICS credits.

Photo credit: U.S. Bureau of Reclamation

For details about the ICS projects, see Chapter 3 of our Water Resource Plan.

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