The Adolfo Ruiz Cortines Dam, built in 1955 is a medium-sized reservoir, located in the Mexican state of Sonora; it provides water for the Río Mayo Irrigation district. At 1,100 million m3 it ranks the 25th largest reservoir in Mexico. In 1985 the dam overflowed reservoir forcing the evacuation of 20,000 people. Description and Statistics The main source of water supply for the irrigation district is the watershed of the Mayo River (hence the name Rio Mayo), which covers an approximate area of 11,000 km2. The river extends for approximately 350 km and averages 1,000 million m3 in streamflows. The hydraulic work used to secure the flows from the river is the ARC reservoir, also known as Mocuzari. The ARC reservoir was built in 1955 and its infrastructure consists of an earth- filled structure 81 m high above the river bed, 775 m long, and 10 m wide at the crest, and 440 m wide at the base. After an expansion project in 1968, the storage capacity increased from 1,100 million m3 to 1,300 million m3. The silting that occurs through the years has reduced the capacity. Of the 51 reservoirs in Mexico, the Adolfo Ruiz Cortines ranks 25th in size. The largest system is over 10,000 million m3 and the smallest is around 27 million m3 The mean inflows accumulation to the reservoir over one agricultural year is 1,034 million m3. The mean annual agricultural releases are 832 million m3. This number does not account for releases for municipal use (around 20 million m3), reservoir spills and evaporation losses. semesters. The first semester corresponds to the accumulation of inflows between October and March. This accumulation is important because it determines whether agricultural production occurs in the SS season. 30% of the annual accumulations occur in this semester. The second semester corresponds to the period April–October and is the most critical to replenish the reservoir. 70% of the inflows occur in this period. History In 1985 the dam overflowed reservoir forcing the evacuation of 20,000 people. Water then flowed towards the Pacific coast cut off the international highway and isolated several small towns. A highway was cut north of Navojoa, 240 miles from the U.S. border. Troops were deployed to help the evacuees, who left their homes after the Mocuzari Dam overflowed. As a consequence of droughts that occurred the Adolfo Ruiz Cortinez dam on the Mayo River in Sonora