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Lower Colorado River Water Accounting
History and Types of Reports

The Colorado River is the principal source of water for irrigation and domestic use in Arizona, southern California, and southern Nevada. The Consolidated Decree of the U.S. Supreme Court in Arizona v California (547 U.S. 150 (2006)) requires the Secretary of the Interior to provide detailed and accurate records of diversions, return flows, and consumptive use of water diverted from the mainstream of the Colorado River below Lee Ferry (lower Colorado River).

Colorado River Accounting and Water Use Reports

The Bureau of Reclamation provides records of diversions, returns and comsumptive use through publication of an annual report called the "Colorado River Accounting and Water Use Report: Arizona, California, and Nevada". This report, generally referred to as the "Water Accounting Report", tabulates measured diversions, measured and unmeasured returns, and consumptive use of each user taking water from the lower Colorado River. (Note:  Unmeasured returns -- flows that return to the river through the groundwater system – were not reported prior to 2002.  Unmeasured returns are calculated as a coefficient multiplied by the water user’s measured diversion amount.)

The Water Accounting Report has been previously titled:

  • Compilation of Records in Accordance with Article V of the Decree of the Supreme Court of the United States in AZ vs. CA dated March 9, 1964
  • Accounting for Colorado River Water Use within the States of Arizona, California, and Nevada

Beginning in 2002, the report was updated to include information supplemental to the requirements outlined in the Consolidated Decree. Additional sections were also added that contain information on activities and programs such as off-stream storage/interstate water banking, the Lower Colorado Water Supply Project, transfers made under the Colorado River Water Delivery Agreement, Inadvertent Overrun and Payback Policy, and Intentionally Created Surplus.

Estimates of Evapotranspiration and Evaporation along the Lower Colorado River

Since 1995, Reclamation has provided estimates of annual agricultural, riparian vegetation, and open water acreages and water uses along the lower Colorado River from Hoover Dam to the Southerly International Boundary with Mexico. This information is summarized in a report now called "Estimates of Evapotranspiration and Evaporation Along the Lower Colorado River."

This report has been previously titled:

A detailed history of the work that was performed related to the development of this remote sensing-based program is presented in the United States Geological Survey Water Supply Paper 2407. Reclamation uses evapotranspiration calculations to monitor water use by agricultural and riparian vegetation below Hoover Dam. These calculations may also be used to improve the unmeasured return flow coefficients used in the water accounting methodology, to help determine beneficial use estimates for Reclamation's water conservation program, and to assist in verifying conservation measures implemented for purposes of meeting payback obligations or creating Intentionally Created Surplus.

Contact: Paul Matuska
Updated: September 2014