The Colorado River — an endangered water source for the southwestern U.S.
April 30, 2014
The Colorado River is the lifeblood of the southwestern part of our country, delivering snowmelt from the Rocky Mountains to southern California and Nevada, and nearly all of Arizona. This includes the major population centers of Los Angeles, San Diego, Las Vegas, Phoenix, and Tucson, which are home to one tenth of the U.S. population. But its ability to meet their water needs and the agricultural water needs of the area it serves is becoming increasingly uncertain, as a result of a combination of rapid population growth, expanding agriculture, a prolonged drought, and a series of unwise management decisions.
In 1920, in response to agricultural interests, which were beginning to be concerned about protecting irrigation water rights, a commission was convened to draw up a plan for the allocation of Colorado River water. The resulting plan, adopted in 1922, and known as "The Law of the River", has been in effect ever since.
However, the Law of the River contained two significant flaws. First, it was predicated on the limited river flow records that existed, covering only 24 years, which have since been recognized to have been a wet period in the river's history. Using that data, without seriously considering the possibility of lower flow periods, the Commission adopted 17.5 million acre-feet (MAF) per year as the average flow on which to base its allocation, apportioning 7.5 MAF per year each to the lower basin states (CA, AZ and NV), and the upper basin states (CO, UT, WY and NM), and 1.5 MAF per year to Mexico — with 1 MAF per year left over.
But between 1930 and 1980, the average flow was only 14.7 MAF per year — 1.8 MAF per year short of the allocated amount. But nothing was done to revise the allocation, even though by 1950, archeological evidence of prolonged severe droughts in previous centuries, confirmed by dendrochronological (tree ring) studies, indicated flows in the Colorado River as low as 10-12 MAF per year lasting for decades. But there was little concern, because the use of Colorado River water had increased from 6 MAF per year in 1920 to only 8.4 MAF per year in 1950, well below even the 10-12 MAF per year flow.
Second, the Commission failed to fully recognize the potential future increases in both population and agricultural water use. Growth trends should have been obvious — by 1960 water use had grown to 10.5 MAF per year, which if continued would reach 14.7 MAF per year around 1995 — which it has.
The upper basin states, especially Colorado, should have been alarmed. By some quirk in the Law of the River, the lower basin states were guaranteed their full allotment of 7.5 MAF per year regardless of how low actual river flows fell. So even at the assumed average flow of 14.7 MAF per year, the upper basin states would be allowed only 5.7 MAF per year instead of 7.5, requiring them to cut their use by 24 percent. If the flow drops to 13 MAF per year as currently predicted, Colorado would have to give up fully half of its allotment.
From the beginning, it was obvious that the seasonal variations in river flow were not in phase with seasonal irrigation needs. The solution was to build a dam and create a huge reservoir, so the Hoover Dam was authorized in 1928, and completed in 1935. It was such a major accomplishment that it started a frenzy of dam building in the West by the rising Bureau of Reclamation. The final dam on the main stem of the Colorado River was Glen Canyon, completed in 1965.
There are two drawbacks to these dams. One is that they create an evaporative loss equal to about 10 percent of the flow, reducing the available supply by nearly 1.5 MAF per year. The other, of catastrophic magnitude, is the sedimentation of the tremendous amounts of silt picked up by erosion and suspended in the roaring rivers and dropped into the still reservoir water behind the dams. Like a cancer, the silt steadily fills the reservoir, eventually rendering it useless — and there is no known cure. Accumulation in Lake Powell is proceeding at the rate of 45 million tons per year, equivalent to 30,000 truckloads per day! In effect, the Bureau of Reclamation has created a water empire in the West that is guaranteed to fail. It is not a question of whether, but when — 50 years, 100 years, 200 years? Then what will the West do for water?
The final lack-of-foresight error was allowing development of multi-million population centers in a desert.
— "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 firstname.lastname@example.org.