Human Use of the River and Bosque 1800's to Present
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The rapid settlement of the Rio Grande Valley from the early 1800s to the present resulted in significant impacts on the aquatic and riparian ecosystems. Sediments eroded from adjacent upland areas as a result of overgrazing and deforestation were deposited in the river, causing riverbed aggradation (a rising riverbed relative to the surrounding floodplain). That, in turn, raised floodplain water table levels. The result was waterlogged soils of high salinity, which negatively affected cultivation; by 1926 only about 45,000 acres were being irrigated. Other human impacts during this period included the direct removal of native floodplain forests, hunting and trapping, grazing and pollution. |
Water-management facilities were increasingly constructed along the Rio Grande in the late 1800s and early 1900s. Several water-supply dams and reservoirs had been built in the Colorado headwaters of the Rio Grande by 1913, and Elephant Butte Dam, at the lower end of the Middle Rio Grande Valley, was completed in 1916. In 1925, the Middle Rio Grande Conservancy District (MRGCD) was authorized by the New Mexico state legislature to alleviate concerns over the decrease in irrigated land resulting from water shortages, poor drainage, inadequate irrigation facilities and periodic flooding. The MRGCD was designated to provide the middle valley with a complete and efficient irrigation system as well as drainage and flood-control facilities. |
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This resulted in the construction of El Vado Dam on the Rio Chama, six diversion dams or headings in the middle valley, 345 miles (555 km) of drainage canals, 181 miles (290 km) of river levees, 250 miles (400 km) of main irrigation ditches, and rehabilitation of nearly 400 miles (640 km) of old irrigation ditches. Construction was completed in 1936. These changes greatly reduced the waterlogging of valley soils and improved the distribution of irrigation water, allowing the productive agricultural business present in the valley today. However, a flood that breached and overtopped the levees in 1941 led to the belief that more extensive flood control was needed. To reduce the danger of future flooding, four dams (Abiquiu, Jemez Canyon, Galisteo and Cochiti) were constructed. Cochiti Dam was the last of these completed (in 1975) and its operation directly affects water levels along the middle valley. In addition to flood control, these dams were mandated for sediment retention, wildlife enhancement and recreation. Other changes included clearing the floodway, straightening the river channel, installing jetty jacks to stabilize the channel and protect levees and enlarging and adding to the levees. In 2000, about 73,000 acres (29,200 ha) were being irrigated along the Middle Rio Grande Valley.
