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  • Writer's pictureMark L. Johnson

Know Your H2O-Part VII-Colorado River

Updated: Jul 11, 2021

Part VII provides the background on the Colorado River including; (1) General Description, (2) Law of the River, (3) Regulatory Quagmire, (4) Colorado River Basin Supply Demand Study and (5) Arizona's Colorado River Water Allocation.

The arid southwest could not survive without the Colorado River. The Colorado River supplies 36% of Arizona's water supply with the remainder coming from groundwater (40%), in-state rivers (21%) and reclaimed wastewater (3%). Therefore, understanding the Colorado River is critical.

Many common water resource terms will be explained but you can go to the Water Lingo Tab for more definitions and information. Reference photos are provided of waterworks facilities constructed and/or managed in CT, IL and CA and from other sources in AZ. Notes[1] containing references and supplemental information are provided at the end of the blog.


Colorado River

1.0 General Description

The Colorado River is 1,450 miles long. The watershed covers 246,000 square miles and includes portions of 7 states (Wyoming, Colorado, Utah, New Mexico, Nevada, California and Arizona) and a small portion of Mexico. It is interesting to note that most of the land in Arizona drains to the Colorado River. See Colorado River Basin Map (Map) below. [1]

The Colorado River region is rich with Indian heritage with 22 tribes living along or near the river. As America entered the 20th century, the Colorado River region attracted new settlers and the development of the Colorado River began.

Today, there are 15 dams on the main stem of the Colorado River that provide the lakes that service intakes which connect to tunnels, aqueducts and pipelines transporting water for municipal use and agricultural irrigation. Some of these dams also generate hydroelectric power.

The Colorado River supplies water to 40 million people for municipal use and to 5.5 million acres of land for agricultural irrigation.

2.0 Law of The River

As the West was settled, the fight for Colorado River water began and continues to this day. The Law of the The River is a series of compacts, laws, court decisions, decrees, minutes (Mexico) and regulations that define Colorado River water rights. The following timeline takes you through the key Law of the River events. The highlighted events directly impact Arizona.

As you can see from the timeline, Arizona has been in the thick of it from the very beginning. In fact, Arizona has been a very litigious player. Arizona v California is one of the most important and protracted (54 years) water-related lawsuits in American history.

Arizona receives its Colorado River supply via the Central Arizona Project (CAP) which was authorized in 1968 (30 years after California started receiving its allocation) and was completed in phases with the final phase to Tucson completed in 1993. CAP is a 336-mile aqueduct that starts on the Colorado River at Lake Havasu and extends all the way to Tucson. See Map above. A future blog will present the CAP in more detail.

I became familiar with the Law of the River as Director of Engineering for the Coachella Valley Water District (CVWD) in southern California. My responsibilities included representing CVWD at Colorado River meetings/negotiations with the California water agencies and other state water agencies. My experience indicates that there are only a handful of lawyers and water professionals that really know the Law of the River intricacies due to the long history and complexities. The rest of us have to dig deep to try to get the full picture.

3.0 Regulatory Quagmire

The Colorado River is controlled by the federal government. The federal agency that regulates the Colorado River is the United States Bureau of Reclamation (USBR). USBR falls under the Department of the Interior (DOI) along with other federal agencies shown in the chart below.

Any activity related to the Colorado River not only requires USBR involvement but also a number of the other federal agencies shown above. This is the federal nexus.

For example, my CVWD team was responsible for the Coachella Canal Concrete Lining Project. The Coachella Canal is a 123-mile aqueduct that brings Colorado River water to the Coachella Valley (CA) for agricultural irrigation and groundwater recharge. This project included concrete-lining the middle 35-miles of the Coachella Canal which was an earthen channel that had considerable leakage. The project required the involvement of USBR, Bureau of Land Management, US Fish & Wildlife Service and Bureau of Indian Affairs. And that was only the federal agencies. Yikes!

Each of the Basin States has its own agencies that coordinate with USBR on Colorado River issues. As we learned in Part VI, in Arizona that would be the Central Arizona Water Conservation District (CAWCD)(aka Central Arizona Project) and the Arizona Department of Water Resources (ADWR). Other Arizona agencies may also get involved depending on the issue.

Multiple federal, state and water agency involvement results in a huge Quagmire with little getting done quickly. In addition, I can tell you from experience that these agencies are usually at odds with each other and some of the leaders of these agencies are always trying to protect their turf.

4.0 Colorado River Basin Water Supply & Demand Study

In 2012, USBR published the Colorado River Basin Water Supply & Demand Study (Study) [2]. This is a very comprehensive study that examined the current and future water available from the Colorado River compared to the current and future water demands. Figure 1 below is taken from the study and shows that there is an annual imbalance (shortfall) of 3.2 million acre-feet (MAF) in 2060. You got it! There is more demand than water available.

The Study also included a rigorous set of strategies and a portfolio analysis to mitigate this imbalance. Strategies included melting icebergs, desalination of ocean water, import of Mississippi River water, water conservation, evaporation education and more. Costs ranged from $110/AF to $15,000/AF.

To my knowledge none of the strategies developed in the Study have been pursued.

The Quagmire is praying for rain!

5.0 Arizona's Colorado River Water Allocation

Despite all the litigation, Arizona's annual Colorado River water allocation is still 2.8 MAF. However, Arizona is subject to two allocation reductions related to the ongoing Colorado River Drought (Drought).

The Drought is serious and long-term. When I started work for CVWD in late 2004, the Colorado River System Contents (available storage in all reservoirs which totals 60 MAF) was 58%. On 5/4/20 the System Contents was 51%. In 15 years, the situation has not improved and has actually gotten worse.

Interim Shortage Guidelines were developed in 2007 as an initial response to the ongoing Colorado River drought (see Law of The River timeline). When the elevation in Lake Mead (Hoover Dam) drops to certain levels, then some of the Lower Basin States are required to reduce their Colorado River Supplies. You guessed it! Arizona takes the biggest hit.

I prepared the diagram below when the Interim Shortage Guidelines were being implemented. If Lake Mead gets to elevation 1,075' mean sea level (msl), Shortage Conditions (pink) begin. Arizona's normal 2.8 MAF allocation drops to 2.48 MAF (1,075' msl), 2.4 MAF (1,050'msl) and 2.32 MAF (1,025' msl). [3]

Lake Mead elevation was at 1,096' MSL on 5/4/20 which means the reservoir is 44% full and at the lower end of the Normal Operating Range (blue). Dry conditions this Spring could result in entering the Shortage Conditions in 2021.

Additional Shortage requirements were adopted in 2019. The USBR and Basin States determined that the Interim Shortage Guideline reductions were not enough as the Drought was not improving. The Drought Contingency Plan (DCP) supplements the 2007 Interim Shortage Guidelines. [4]

DCP-Table 1 (below) shows the additional hit that Arizona takes based on Lake Mead elevation. Now Arizona has to cut-back beginning at elevation 1,090' msl (0.192 MAF) and reduce its allocation by additional amounts as Lake Mead drops. For example, at elevation 1,045' msl, Arizona has to cut back an additional 0.240 MAF for a total of 0.640 MAF or a 23% reduction. At elevation 1,025' msl the total cut-back is 0.72 MAF for a 26% reduction.


  • Colorado River water represents 36% of Arizona's total water supply.

  • Arizona has been part of the Colorado River water feud since 1922 and has been a litigious player.

  • Law of the River defines Colorado River water rights.

  • Colorado River is regulated by the United State Bureau of Reclamation (USBR).

  • A huge Quagmire of federal, state and water agencies prevents any timely action on Colorado River issues.

  • Colorado River Basin Water Supply and Demand Study indicates an annual 3.2 MAF imbalance (shortfall) in 2060.

  • The Colorado River Drought is serious and long-term.

  • Arizona is subject to the 2007 Interim Shortage Guidelines and 2019 Drought Contingency Plan (DCP) reductions based on Lake Mead elevation and could reduce Arizona's Colorado River water supply by up to 26%.

This does not paint a rosy picture for Arizona. These facts lead one to the conclusion that Arizona should not rely on its full Colorado River allocation.


Upcoming Parts include; Central Arizona Project, Tucson Active Management Area (TAMA), Marana Water/Tucson Water & Conclusions



1 Comment

Janice Prezzato
May 11, 2020

Thank you for this well thought out overview on the Colorado River, as a water supply, and the current state of Arizona's dance with western states.

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