Rio Grande: Threat of Water Extraction

A high level of water extraction for agriculture and increasing domestic use threatens the Rio Grande. Most of the major tributaries and many of the lesser ones support substantial agricultural production.

Damming, high levels of evaporation, persistent drought and invasive species have exacerbated the high level of water extraction. Extensive networks of water diversions and dams control flows in both the Rio Grande and its key tributary, the Rio Conchos, without managing instream flow to sustain riparian habitat.

Currently, there are 100 large dams, 8 of which are on the main stem of the river, and there are 6 very large dams. Drought has caused crops to wither which has led to severe malnutrition among the Tarahumara Indians in the highlands of the Chihuahua.

The invasive species Salt Cedar, has proliferated through large portions of the Big Bend area (where the Rio Conchos joins the Rio Grande), and is known to consume large quantities of water. One monoculture of Salt Cedar is believed to have choked 150 miles of the river corridor downstream of El Paso/Ciudad Juarez and may be the most extensive infestation of this species in the world.
River water is diverted for irrigation in the El Paso/ Ciudad Juarez area, Eagle Pass/Piedras Negras area, and Rio Grande/Rio Bravo valley downstream from International Falcon Dam.

In 2005, 451,456,974 m3 (366,000 acre feet) were diverted from the middle Rio Grande during the irrigation season (Middle Rio Grande Conservancy District 2006). Although this is down from 1999, when total diversions in the middle Rio Grande were 837,869,606 m3 (679,268 acrefeet), nearly all of the irrigation water in the upper basin, is produced by snow pack.

Several years of low snow pack has dramatically lowered the volume of the most important reservoir on the mainstem, Elephant Butte Reservoir. With current level Irrigation accounts for more than 80% of all water taken from the river, but municipal needs are competing more and more as urban areas grow.

Along the Rio Grande mainstem, there are only 4 major cities, but the urban population is growing at a rapid rate of 2-4%. Water is also wasted through unnecessary diversion: the amount of water diverted and wasted by dams for irrigation increased by over 123,348,900 m3 (100,000 acre feet) per year from 1979-1998.

Historically, flows passing through Big Bend have varied considerably, but by the time the Rio Grande leaves El Paso, a city less than 1/3rd the length of the river at this confluence of the Rio Conchos, so much water has been diverted that the riverbed between El Paso and Presidio/Ojinaga often lies dry.

The highest daily flow recorded above the Rio Conchos confluence was 387,984 L/s (13,700 cubic feet per second) on June 1905. Pre-1962, the river’s average flow was 2.9 Km3/year (2.4 million acrefeet) and ocean-going ships used to be able to navigate at least 16 Km (10 miles) from its mouth.

In 2005, at the last gauge point before the sea, in Brownsville Texas, however, the average flow was 0.44 Km3/year. Between February and June 2001, the river failed to reach the Gulf of Mexico.

As a result of low water levels, the concentration of pollutants is so high that fish kills have occurred, and the lower Rio Grande is suffering from salinization. In fact, some marine fish species are invading as far as 400 Km upstream, and the increasing salinity of the river has already displaced 32 native freshwater fish species.

Irrigation accounts for more than 80% of all water taken from the river, but municipal needs are competing more and more as urban areas grow. Along the Rio Grande mainstem, there are only 4 major cities, but the urban population is growing at a rapid rate of 2-4%.

Water is also wasted through unnecessary diversion: the amount of water diverted and wasted by dams for irrigation increased by over 123,348,900 m3 (100,000 acre feet) per year from 1979-1998.
 / ©: WWF
Threat to the River: Over-extraction of water
© WWF

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