The Colorado River is vitally important to the residents of the seven western states that share its drainage basin. It supplies irrigation and drinking water to more than 30 million people over an area stretching from Denver to San Diego. Unfortunately, the river is over allocated and over utilized and with the current drought we are reaching the point where who uses its water and how much they use will almost certainly have to change.

In order to understand how we’ve gotten to where we are today it is necessary to look back at how the Colorado River, one of the most regulated in the world, has been manipulated and managed since 1900. Prior to the twentieth century the Colorado ran free and was only utilized by those few people and settlements along the river that used minor amounts for irrigation and municipal purposes. The Colorado is one of the very few rivers in this country that has no major cities along its banks, although Las Vegas is only a few miles away. The river has never really been suitable for navigation, and the extremely hot summers along the lower reaches discouraged settlement. Most of the municipal use takes place outside the river’s drainage basin.

Hoover dam, with "bathtub ring" showing high water mark. Credit, Stacy Goss
Hoover dam, with “bathtub ring” showing high water mark. Credit, Stacy Goss
The first real change to the Colorado came in 1900 when the Imperial Land Company started diverting water from the river to the Imperial Valley for agricultural purposes. In 1905 the diversion canal was overwhelmed by the rivers’ spring flood and the river changed course and flowed into the Salton Sink for a year and created the Salton Sea. As the Imperial Valley boomed and became an important farm area, more and more water was diverted. By 1920 the other six states that share the Colorado River drainage basin became concerned that California might claim the entire flow of the river, and set out to assert their own claims. In 1928 the Colorado River Compact was signed. This compact divided the entire flow of the Colorado among the seven states. Mexico got nothing, and no provision was made for leaving anything in the river (in 1945 Mexico was allocated 1.5 million acre-feet in return for limiting Mexican diversions on tributaries of the Rio Grande). The quantity of water allocated to each state was based on then current and potential usage and ten years of flow data from the period shortly before the compact was signed. According to the data available at that time, the average annual flow was 17.5 million acre-feet. California got the largest share at 4.4 million acre-feet annually and Nevada the smallest at 300,000 acre-feet.

Until 1936 and the completion of Hoover Dam there was no storage capacity and no regulation of the river’s annual flow. Since 1936 a number of other dams have been built, including Glen Canyon Dam. Between them, Lakes Mead and Powell, backed up by Hoover and Glen Canyon Dams respectively have a storage capacity of about 60 million acre-feet. This volume equates to some four years of the total normal average flow of the river. During both the 1950’s drought and the filling of Glen Canyon Reservoir in the 1960’s the surface level of Lake Mead fell substantially, but no impact was felt by downstream users because Arizona and Nevada were using only a small portion of their allocations.

In the year 2000 the idea that the Colorado River could be completely consumed and unable to deliver its legal allocations seemed far-fetched. But in 2001 the current drought began and 2002 saw the lowest flows measured since record keeping began: just 25% of normal run-off. The level of Lake Mead fell precipitously and water managers began to take notice. With the exception of two very wet years, the drought that began in 2001 is still with us. The flow during the 2013 water year, which ended September 30, was 35% of average and the second lowest on record. The 2012 water year wasn’t much better with about 45% of average flow.

By 2005, it was apparent that the drought on the Colorado was not going away soon and the States and the Department of Interior’s Bureau of Reclamation, which manages the river, realized that changes to the compact were needed and began work on something called the Quantification Settlement Agreement, which was signed in 2007. This agreement laid out a framework for allocating water based on volume in storage and identified specific Lake Mead levels for the categories of surplus, normal condition, phase1 shortage, phase 2 shortage, etc. It also stipulated that except during times of surplus no State could take more than its legal allocation. The only state really affected by this stipulation was California, which had been diverting more than 5 million acre-feet as opposed to its 4.4 million acre-foot allocation.

Overlook of Lake Mead. Pyramid Island in the background at the waters edge is no longer an island. Credit, Stacy Goss
Overlook of Lake Mead. Pyramid Island in the background at the waters edge is no longer an island. Credit, Stacy Goss
The phase 1 shortage level for Lake Mead is 1075 feet above mean sea level. The lake surface currently (November 1, 2013) stands at 1104 feet above sea level and, barring a very wet winter, is expected to fall by about 25 feet by November 2014. This will mean the Bureau of Reclamation will be very close to declaring a shortage, which will require Arizona and Nevada to reduce their diversions from the river below their full allocations.

Starting in 2002 Las Vegas, which uses almost all of Nevada’s allocation, initiated a water conservation program, modest at first but ultimately quite aggressive. It has reduced Nevada’s consumptive use of Colorado River water from 330,000 acre-feet per year to 235,000 acre-feet per year. During this period the population of Las Vegas grew by 400,000 people. This is a remarkable accomplishment.

Approximately eighty percent of the Colorado’s water is used for irrigation. Major conservation efforts in that area are much more difficult, for a variety of reasons. First is cost; agricultural water is cheap, only a few dollars per acre-foot (about 326,000 gallons), due to the subsidies associated with federal water projects. Secondly, in order to thrive, plants need a certain minimum volume of water. In the hot summers of the interior deserts of California and Arizona that is a lot, about 5 acre-feet per acre per year, enough water to cover each acre of farmland to a depth of 5 feet if applied all at once. In addition, since there is a significant amount of salt in water from the Colorado (about 1 ton per acre-foot of water) which remains behind in the soil when irrigation water either evaporates or is transpired by plants, enough water must be applied to the soil to flush the salt through the soil into a drain system. The Salton Sea persists because it receives agricultural drain water from the Imperial and Coachella Valleys and the Mexicali Valley in Mexico.

Nearly a century ago Colorado River authorities made crucial decisions based upon inadequate information and naive assumptions. We are left with an overly-complex system further complicated by Western water law that says, first in time, first in right. Straightening out this tangle is a huge challenge. But under the duress of drought small changes are being made. It is in the interest of the three Lower Basin States, Arizona, California and Nevada plus Mexico to keep the water level in Lake Mead higher than 1075 feet above sea level so that there is not a declared shortage. Hence, there are several agreements in effect that allow conserved water to be stored in Lake Mead for later use. Prior to these agreements the situation was “use it or lose it.” There was no incentive to conserve water.

Based on current knowledge and projections the jobs of those charged with meeting the demands for Colorado River water will become increasingly difficult. We know from tree ring data that pre-historic droughts in the Colorado Basin have lasted as long as thirty years and that the twentieth century was the wettest century in the last two thousand years. Projections of future climate change suggest a drier, warmer climate with greater extremes in this region. We also know from recent experience that river flows are influenced by the previous year(s) precipitation because the soil acts as a sponge and the perennial flows are dependent on the level of saturation of that sponge. A “normal” year preceded by a dry year will have decreased river flows because part of the “normal” year precipitation will be consumed in re-saturating the soil sponge.

Is there any reason for optimism? Yes, I think there is, because we are starting to see some cooperation between the major municipal water purveyors. And Mexico is now partner in the discussions. But the 800-pound gorilla in the room is agricultural use. So far, the irrigation districts– speaking for farmers–haven’t shown much appetite for change. A drying, warmer climate will increase agricultural water demand. At some point we are going to have to re-consider how we use the water of the Colorado, an increasingly scarce and valuable resource.

John Hiatt, a desert activist living in Las Vegas, Nevada, is a member of the CNRCC Desert Committee and is a board member of Friends of Nevada Wilderness.