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The Middle Rio Grande Conservancy District (MRGCD) was formed in 1925 to manage the irrigation systems and control floods in the Albuquerque Basin. It is responsible for the stretch of river from the Cochiti Dam in Sandoval County in the north, through Bernalillo County, Valencia County and Socorro County to the Elephant Butte Reservoir in the south. It manages the Angostura, Isleta and San Acacia diversion dams, which feed an extensive network of irrigation canals and ditches. ==Background== The Pueblo people of the Rio Grande valley had developed primitive irrigation systems in the Rio Grande valley by the 10th century AD. These systems used a main ''acequia'' (shared irrigation ditch) into which water was diverted from the river, with secondary ditches leading off the main channel named for specific families. Maintenance of the main ''acequia'' would be a community responsibility. The Spanish arrived in New Mexico in 1598, and used Indian labor to extend the system of irrigation ditches. In 1848 Mexico ceded the territory to the United States. Railways arrived in 1880, bringing new settlers. The Federal government encouraged irrigation, which probably peaked in the early 1890s. After this there was a steady decline in irrigation due to "droughts, sedimentation, aggradation of the main channel, salinization, seepage and waterlogging". Part of the problem was caused by increased use of the river for irrigation in the San Luis Valley upstream in Colorado. Development and deforestation there caused silt to be washed into the river. Where the river widens and slows in the middle Rio Grande valley around Albuquerque the silt was deposited, raising the riverbed and the water table and causing waterlogging in the farmlands that border the river. By the time the Middle Rio Grande Conservancy District was founded in 1923, more than of farmland had become swamps or alkalia and salt grass fields. Floods were another hazard, often destroying whole villages. The ''acequia'' running through the city of Albuquerque, parallel to the river, had become an unsanitary drainage ditch, serving as a common sewer. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Middle Rio Grande Conservancy District」の詳細全文を読む スポンサード リンク
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