Approximately 1,450 miles long, the Colorado River is the 3rd longest river in the Colorado. In addition to Colorado, the river flows through six other states and provides water for approximately 40 million people. These seven Colorado River Basin states—Arizona, California, Colorado, Nevada, New Mexico, Utah and Wyoming—negotiated The Colorado River Compact. This divided the basin into Upper Basin States (Colorado, New Mexico, Utah and Wyoming) and Lower Basin States (Arizona, California and Nevada). The focal point of the division is Lee’s Ferry, Arizona, ten miles below Glen Canyon Dam.
Supply and demand between the Upper Basin States (where most of the river’s water supply originates) and the Lower Basin States created discrepancies in the compact agreement. The Upper Basin States were concerned that the development of the Hoover Dam and other Lower Basin water projects would limit their future Colorado River water supply. Ultimately, Secretary of Commerce Herbert Hoover proposed that the Upper Basin and Lower Basin States split the estimated annual volume of 15 million acre-feet (MAF) and each receive 7.5 MAF of Colorado River water annually. This approach reserved water for future Upper Basin development and allowed planning and development in the Lower Basin to proceed. Approved by the General Assembly on November 24, 1922, the Colorado River Compact—also known as the “Law of the River”—provided an equitable division and apportionment of the Colorado River basin waters. The State of Colorado is entitled to approximately 50 percent of 7.5 MAF that is to be divided among the Upper Basin States.
The streamflows used when the appropriation was agreed upon are now considered too high when compared to longer term streamflow measurements and current streamflow trends. The difference is influenced by climatic and hydrologic fluctuations, changes in water resource management, and increased use, among other reasons. The USGS data shows the average annual volume at Lee’s Ferry was 12.4 MAF from 1895 through 2003, which is likely a more representative value than the 15 MAF total appropriation split between the Upper Basin and Lower Basin States. The States subject to the Compact have worked together to use Lake Powell and Lake Mead to meet the obligations and demands although there continues to be concerns over the water levels in these major reservoirs.
So what does that mean for the future? The major challenges in the Colorado River Basin in our state, identified in Colorado’s Water Plan, include finding balance for future demands for in-basin growth, transmountain diversion projects (TMD), and avoiding compact call deficits (which would limit the water use for water rights junior to the 1922 Compact; impacted water rights would include Denver Water’s Dillion Reservoir). Generally, the eastern slope of Colorado has the need for TMD projects to support the projected growth and preserve the option of future development of Colorado River water (and its tributaries). However, the western slope is generally concerned that the new TMD projects and western slope growth will overdevelop supplies. This overdevelopment could increase Colorado River Compact deficits and dwindle Colorado River reservoir storage, leaving critical minimum levels necessary at Lee’s Ferry and cause Compact-related water use curtailment.
If you are interested in learning more about the Colorado River, Colorado’s Water Plan or to discuss a project, contact us today.