Operations and Planning

The Arizona Department of Water Resources collaborates with the Bureau of Reclamation and representatives of the seven Colorado River Basin States to better prepare for Arizona’s long-term needs and by taking an active role in water use projections, monitoring of hydrologic conditions and Colorado River operations.  The Department also utilizes models prepared by Reclamation to evaluate various scenarios related to modifications in water use, hydrology, climate, water supply and demand and other factors within the Colorado River Basin.

The Colorado River system has experienced severe drought conditions for almost two decades. Further, the Basin runoff during this period is comparable with one of the lowest comparable periods in the paleo-hydrologic record that dates back over 1,200 years. As a result, water levels in Lake Mead, the primary storage reservoir for the Lower Basin states, and the entire Colorado River System reservoirs have been declining and projections indicate that this will continue into the foreseeable future.

As a result, water levels in Lake Mead, the primary storage reservoir for the Lower Basin states and largest of its kind in the United States, and reservoirs throughout the Colorado River System have been declining; projections indicate that this will continue into the foreseeable future. In addition, given the basic apportionments in the Lower Basin, the allotment to Mexico, and evaporation losses, Lake Mead annual outflow is about 1.2 million acre-feet more than the combination of annual releases from Lake Powell and local inflows between the two reservoirs.

Water deliveries to the Lower Basin States and Mexico are facilitated through releases from Lake Mead, while Lake Powell is operated to deliver water from the Upper Basin. As introduced under the 2007 Interim Guidelines below, water levels in these two reservoirs are coordinated to allow for better management of the Colorado River supply.

Three factors that significantly affect the water levels in lakes Powell and Mead are:

1. The hydrology of the Colorado River, such as the amount of precipitation (mostly as snowpack) that falls within the basin and the resulting runoff that flows into the river and reaches the reservoirs,
2. Colorado River water use, such as the amount of water needed for agricultural and urban purposes in both the Upper and Lower Basins, and
3. Colorado River reservoir operations per the "Law of the River."

As a result of these conditions, the Colorado River users have taken actions to protect Lake Mead’s elevation from dropping to critical levels.

Annual Operating Plans – In consultation with the representatives of the Governors of the seven Colorado River Basin States, Indian tribes, Upper Colorado River Commission, appropriate Federal Agencies and others interested in Colorado River Operations, the Bureau of Reclamation produces an Annual Operating Plan (AOP) for Colorado River Reservoirs that reports on both the past operations of the Colorado River reservoirs for the completed year as well as the projected operations and releases from these reservoirs for the coming year. Annual Operating Plans for Colorado River Reservoirs.

24-Month Study –  The monthly 24-Month Study reports present hydrologic descriptions and projected operations for the Colorado River system reservoirs for the next two years. Reclamation uses this model to provide current status and projected operation of the system on a monthly basis.  The 24-Month Study model is updated at the beginning of each month upon receipt of the monthly inflow forecast from Colorado Basin River Forecast Center (CBRFC). Under the 2007 Interim Guidelines, the August study model is the basis for the decision for Lake Powell and Lake Mead annual operations for the coming year.  The April study model is used to make potential adjustments to Lake Powell’s annual operation at higher reservoir levels. 24-Month Study Reports are available.

Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated Operations – The 2007 Interim Guidelines were a product of direction to Reclamation from the Secretary of the Interior to develop additional strategies for improved coordinated management of Colorado River system reservoirs. Development of these guidelines was spurred by the current drought period, system storage volatility, and growing demands on the Colorado River.  Each year under the Guidelines, the Secretary is required to declare the Colorado River water supply availability conditions for the Lower Basin States in terms of Normal, Surplus, or Shortage. While regulations and operations criteria had been developed for Normal and Surplus conditions, robust protocol for operation during shortage were not established. These guidelines provide greater certainty to future annual water deliveries, particularly under drought conditions.

Releases and diversions are made from Lake Mead to meet water deliveries in Arizona, California, Nevada, and Mexico, while Lake Powell is operated to deliver water from the Upper Basin to the Lower Basin. As part of the 2007 Interim Guidelines, water levels in these two reservoirs are coordinated to allow better management of the Colorado River supply.

Intrastate Drought Contingency Planning Implementation – The 2007 Interim Guidelines had proven to not be enough; despite their enactment, river flow projections in 2014 indicated that Lake Mead levels could drop to the point of seriously impacting power generation and water availability. To protect Lake Mead from dropping to these critical levels, and to improve the health of the Colorado River System, the Drought Contingency Plan (DCP) enumerates the sharing of reductions among the three Lower Basin States (Arizona, California, and Nevada) as well as the United States and Mexico. The DCP gives a greater degree of certainty to on-river communities, agriculture and Central Arizona water users, as well as those throughout the Basin regarding the longer-term reliability of the Colorado River.

Colorado River Basin Supply and Demand Study – The Colorado River Basin Supply and Demand Study characterized current and future water supply and demand imbalances in the Colorado River Basin and assessed the risks to Basin Resources. Resources include water allocations and deliveries consistent with the apportionments under the Law of the River, hydroelectric power generation, recreation, fish and wildlife, and their habitats, water quality (including salinity) and flow, as well as water-dependent ecological systems and flood control.  A full report on the Colorado River Supply and Demand Study is available.

Colorado River Simulation System (CRSS) – CRSS is the official long-term basin-wide planning model for the Upper and Lower Colorado Regions to simulate future Colorado River conditions.  Specifically, the model projects future river and reservoir conditions over a period of decades into the future.  ADWR can modify model inputs to simulate possible water planning or management strategies, such as conserving water in Lake Mead, to assess impacts to the system from such strategies. Here is more information on CRSS.