Karl Flessa, University of Arizona

A brief meeting of the waters: The science and policy of the first environmental flow to the Colorado River Delta

In most years since 1960, the Colorado River has not reached the sea. In 2014, 130 million cubic meters (105,000 acre-feet) of environmental water was delivered to the Colorado River Delta in Mexico during an eight week period that ended May 18, 2014. This “pulse flow” was the result of a new and temporary modification to the US-Mexico Water Treaty of 1944 that also calls for Mexico and the U.S. to share future shortages, allows Mexico to store water in a U.S. reservoir, and supports measures to conserve water. Teams of university, agency and NGO scientists from both countries are monitoring the bio-physical effects of the pulse flow. The pulse flow’s hydrograph was designed to mimic the spring floods that flowed in the era before upstream dams and diversions. Recruitment of native vegetation was most successful in sites that had been prepared in advance. The water table rose as much as 7 meters and returned to its previous level within six months. Remote-sensing documented a one-year increase in greenness. Bird surveys documented an increase in diversity and abundance, especially in the sites targeted for restoration. The river reached the sea, if only for a few days. NGOs are raising funds to supply another 65 mcm (52,000 af) for base flow to support new and existing vegetation and wildlife. The local community celebrated the water’s arrival. Despite widespread drought in western North America, media coverage and direct interviews in both the US and Mexico were strongly favorable.