AZ water allocations bump against limit of Colorado River flow

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The decades of compacts, laws, contracts and regulatory guidelines that are supposed to manage bordering states’ use of the Colorado River have come to be known collectively as the “Law of the River.” But the Law of the River could soon bump up against the laws of physics.

Ninety years after the first agreements were drawn up, and more than 50 years after the Supreme Court set water-use levels for Arizona and its neighbors, demand for Colorado River water continues to grow. But the amount of water flowing in the river, and the allotments of it to different users, remains the same.

In 2011, Arizona used more than 99 percent of its allotted 2.8 million acre-feet of water for homes, crops, recreation and businesses across the state. Add to that demand a proposal in Washington to allocate 20,000 acre-feet of river water to the Navajo and Hopi tribes and the state is bumping right up against the limit, if not going over slightly.

Trying to squeeze every last sanctioned drop from the exhausted river has an effect up and down the Colorado, from the reservations upstream to the croplands 1,000 miles downstream.

If left untouched by man, the river would deliver about 16.5 million-acre feet of water to the Gulf of California annually. But today only a fraction of that amount reaches the gulf.

The apportioning of the river began with the 1922 Colorado River Compact, a deal by seven Western states to divide the river and its tributaries into two basins, the Upper Basin and the Lower Basin. Each basin was allotted 7.5 million acre-feet per year under the compact, according to the Bureau of Reclamation.

In 1948, the Upper Basin states entered into an agreement allocating its 7.5 million acre-feet between Colorado, New Mexico, Utah and Wyoming.

When the Lower Basin states were unable to reach an agreement by 1952, Arizona went to the Supreme Court to force the issue.

Four years later, the court decreed that California was entitled to 4.4 million of the Lower Basin’s 7.5 million acre-feet of water, Arizona would get 2.8 million acre-feet and Nevada would get 300,000 acre-feet.

After the seven compact states took their shares from the river system, that left 1.5 million acre-feet annually to Mexico and, ultimately, the Gulf of California, an amount required under a 1944 treaty with Mexico.  (From the Tucson Sentinel 8-23-2012)