The shrinking Colorado River
Glenwood Springs, CO Colorado
Although the 1,450-mile long Colorado River is not the largest in the United States, it is the most thoroughly used and intensively regulated, because it is the major source of water for 30 million people and for the irrigation of millions of acres of vital agricultural land in the desert southwest.
Water in the Colorado River Basin is allocated in accordance with the Law of the River, originating in 1922 with the Colorado River Compact, which divided the 242,000-square-mile Colorado River drainage area into the Upper Basin and Lower Basin states.
The Upper Basin, totaling about 110,000 square miles, is made up of the 40 percent of Colorado west of the Continental Divide, the eastern half of Utah, the southwestern one-sixth of Wyoming, and a tiny corner of New Mexico.
The Lower Basin, totaling about 132,000 square miles, is made up of nearly the entire state of Arizona, a portion of southern Nevada (which includes the Las Vegas metropolitan area), and a narrow fringe of California bordering the Colorado River.
At the time of the Colorado River Compact, it was believed, based on about 25 years of flow records, that the average flow of the river basin was about 17.5 million acre-feet (maf) per year. The compact divided that into 7.5 maf for each of the two basins plus 1.5 maf for Mexico, with 1.0 maf left over. (One acre-foot is the amount of water that would cover one acre one foot deep, or 325,851 gallons; the main pool at the Glenwood Springs Community Center holds 300,000 gallons.)
The Lower Basin states were allocated fixed yearly amounts: California 4.4 maf, Arizona 2.8 maf, and Nevada 0.3 maf. (In 1922, the Las Vegas area population was less than 10,000.) The reason California, which has only 2.5 percent of the Lower Basin area, received nearly 60 percent of the Lower Basin’s allocation is because of the enormous irrigation water rights in the Imperial Valley that predated nearly all other water rights in the entire basin.
The joker in the deck is that the Lower Basin states were guaranteed fixed amounts, and if the yearly flow in the system falls below the 16.5 maf that was allocated, the shortfall would come out of the Upper Basin’s 7.5 maf. The allocation among the Upper Basin states was therefore made a percentage of what is left, with Colorado getting 51.75 percent, Utah 23 percent, Wyoming 14 percent, and New Mexico 11.25 percent.
Under this rule, Colorado definitely comes up on the short end. Colorado comprises 38 percent of the Upper Basin, and is where most of the water comes from. The Colorado River and its tributary, the Gunnison River, contribute 40 percent of the total flow in the system.
Add in flows in the White and Yampa Rivers, which together make up half of the flow in the Green River (which joins the Colorado River in Utah), and the flows in the Dolores River and the portion of the flow in the San Juan River that comes from Colorado, and you find that Colorado is the source of nearly two-thirds of the total flow in the entire Basin.
But Colorado is allotted only 3.88 maf (less than a quarter of the total flow). And even that is not guaranteed.
The period of record on which the allocations were based is now known to have been wetter than normal. The average flow is now thought to be about 14 .7 maf, which would leave only 5.7 maf for the Upper Basin states, of which Colorado’s share would be reduced to 2.95 maf. Will this be enough to meet the water demands of gas fracking and shale-oil extraction?
The consumption of Colorado River Basin water has increased steadily from 6 maf in 1925, until in 2003 it exceeded the supply for the first time, and it continues to do so. Last year’s high runoff helped, but this year’s snowpack, at only half of normal, will undo all of last year’s gain.
Every year, Colorado sends over 0.5 maf from the Fraser, Blue, Eagle and Roaring Fork Rivers east through the Continental Divide to the Front Range. The combination of what may be a prolonged drought and the exercise of more of their water rights by the Front Range cities to supply the needs of their growing populations, can deplete the flows in all of these streams to the point that there will no longer be enough water to support fish life.
Serious water conservation measures are desperately needed.
“As I See It” appears on the first and third Thursdays of the month. Hal Sundin lives in Glenwood Springs and is a retired environmental and structural engineer. Contact him at email@example.com.
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