were not to cause the flow of the Colorado River at Lee’s Ferry to be less than 75 million acre-feet in any period of ten consecutive years (Goslin, 1978).

The compact cleared the way for federally funded, water-project development in the lower states, while allowing the upper states to develop at a slower pace without losing their water use rights. Since the 1890s, when direct stream flow measurements were made on the river, “the flow estimates on which allocations were negotiated in the 1920s were based upon data drawn from a relatively short and very wet period, and thus turned out to be overly optimistic” (NRC, 2007: 28). In fact, the gauge record shows that the 1905–1922 period had the highest annual flow volume of the 20th century, averaging 16.1 million acre-feet at Lee’s Ferry.

The Rio Grande, Colorado and Tijuana Treaty of 1944 between the United States and Mexico (59 Stat. 1219, T.S. 994) codified obligations of the United States to deliver water from the Colorado River to Mexico and guaranteed that the United States would deliver to Mexico 1.5 million acre-feet annually of the “waters of the Colorado River, from any and all sources” (IBCW, 1944).1 The treaty further provided that Mexico shall not acquire any right to water in excess of that amount thus preventing future Mexican demands for water as their agricultural water demands grew. The guaranteed 1.5 million acre-feet annual water delivery to Mexico was subject to reduction in the event of shortages or drought upstream in the U.S. portion of the basin. This treaty did not address water quality levels for the Colorado River water entering Mexico.

In 1949, the Upper Colorado River Basin Compact (63 Stat. 31) was signed, which apportioned water rights among the states with land in the upper basin. This compact details the rules and regulations for water-use curtailment during years when necessary to meet delivery requirements to the lower basin states under the Colorado River Compact. The compact specifies that the amount of water delivered at Lee’s Ferry be “measured by the inflow-outflow method in terms of man-made depletions of the virgin flow” at that location (Goslin, 1978).2 This compact also outlines agreements between member states (Colorado, Utah, Wyoming, and New Mexico) on the use of interstate stream water. Although technically part of the lower basin, a small portion of Arizona resides in the upper basin. That portion of Arizona was apportioned a fixed quantity of 50,000 acre-feet per year. The remaining water was divided as follows: Colorado with 51.75 percent, Utah with 23 percent, Wyoming with 14 percent, and New Mexico with 11.25 percent.


See waterplan.state.wy.us/BAG/green/briefbook/lor/lor-7.html (accessed March 31, 2010).


See Article VI of the Colorado River Compact at waterplan.state.wy.us/plan/green/techmemos/compacts.html (accessed March 31, 2010).

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