From email from the Pagosa Area Water and Sanitation District:
When it comes to water in the west, the rule is “first in use, first in right,” which means those who could prove they put a quantifiable amount of water to beneficial use before their neighbors even arrived were generally granted a water right that says “I get mine before you get yours.” In the early years of the 20th century, the American West was rapidly changing. The lure of California and Arizona with endless days of sunshine had folks from the east packing their bags and heading west. California began to realize its potential as the center of western agriculture as it turned desert scrubland into fertile, well-irrigated farmland. To further this dream, California sought federal assistance to construct the “All American Canal” that would bring Colorado River water to the Imperial Valley on the US/Mexico Border.
Realizing that if California could prove that it needed and was fully utilizing all of this water, it could be granted rights that would constrain future growth in other states upstream; therefore, Colorado, led by local boy Delph Carpenter, proposed the idea of a treaty between all the states that rely on the Colorado River. This treaty intended to apportion the water equitably among the states to ensure that no state would be left high and dry. There are seven states in the Colorado River Basin – Wyoming, Colorado, Utah, New Mexico, Arizona, Nevada, and California. A line was drawn in the river at Lee’s Ferry, Arizona and the states were divided into two categories; upper basin and lower basin. Why Lee’s Ferry? Because there are no other major tributaries feeding into the Colorado below that point and because Lee’s Ferry was the only place one could cross the Colorado River for many miles in either direction. Lee’s Ferry lies approximately 16 miles south of present day Lake Powell.
Based upon the best scientific evidence available at the time, the delegates from the seven states agreed that the average annual flow of the Colorado River was 17.5 million acre-feet (i.e., an acre-foot is a unit of measurement specific to the water world and is comprised of 325,851 gallons or enough water to cover one acre of land under one foot of water). Under the 1922 Colorado River Compact, 7.5 million acre-feet (maf) were allotted “in perpetuity” to the three lower basin states – Arizona, Nevada, and California, and the four upper basin states – Colorado, Wyoming, New Mexico, and Utah presumably got the rest. Although the original intent of the agreement was to fairly split the resource among the states involved, concerns have surfaced that it would be impossible for the upper basin states to receive their fair share in the future. Because the upper basin states are the “supply” states, a gauging station was erected at Lee’s Ferry to ensure the lower basin states received their full 75 maf allotment over a 10 year rolling average. Should the compact obligations not be met, a “call” would be placed on the Colorado River where post-1922 water rights would be systematically suspended until the river flow rebounded.
The 1922 Colorado River Compact has been fought over since the day it was signed, yet it has withstood the test of time. This concludes the first part of an e-newsletter series on the 1922 Colorado River Compact, and future newsletters will discuss how this “call” could impact Colorado and the other upper basin states, the implications of the 1948 Upper Colorado River Basin Compact that redistributed water in the upper basin states, and the 1956 Colorado River Storage Project Act that ushered in an era of big dams and water buffalos.
More Colorado River basin coverage here.