The Rio Grande's story
The Rio Grande is a river of many faces as it traverses the reach from its headwaters to the Gulf of Mexico.
Its genesis is the high alpine region at nearly 13,000 ft. in elevation on the Continental Divide in southwestern Colorado. Its water supply in the headwaters comes primarily from snowmelt runoff, with a small fraction of its annual flow coming from rainfall.
It then runs through the arid regions of the southern Colorado, New Mexico and west Texas and then into the subtropical regions the northern Gulf coast. The river is approximately 1,900 miles long.
The river is effectively two rivers. The Upper Rio Grande, in this instance is the reach from the headwaters to Ft. Quitman, Texas about 70 miles southeast of El Paso. The Lower Rio Grande is effectively from Presidio, Texas above Big Bend where the Conchas River out of Mexico joins the Rio Grande. This major tributary provides the primary flow for the Rio Grande in the lower reach, as the flows of the Upper Rio Grande are effectively diminished by diversions and very little if any water from the upper part of the basin reaches the confluence with the Conchas under normal circumstances.
This article will deal with the Upper Rio Grande reach as this is the portion of the river affected by the Rio Grande Compact. This federal and state law allocates the water of the Rio Grande above El Paso between Colorado, New Mexico and Texas. Depending on the annual flows of the river, the water is split between the three states pursuant to a schedule of deliveries written into the Compact.
The Rio Grande starts as a small spring and as it proceeds downstream it picks up a number of small tributaries and soon is a large stream and then a small river as it flows into the only main stem reservoir on the river in Colorado, Rio Grande Reservoir. This is a private reservoir which is used for irrigation and other uses.
The river then runs downstream and joins the South Fork of the Rio Grande and then towards to the San Luis Valley. On its way through the Valley, there are a number of diversions into irrigation ditches which divert the allocation of the Compact dedicated to Colorado. There are limits to how much Colorado can use and the remainder has to go on downstream to New Mexico which creates a portion of their water supply under their allocation from the Compact.
After running through the Rio Grande Gorge for a number of miles and joining a number of small tributaries in northern New Mexico, it runs into a large flood control reservoir above Cochiti Dam. The largest tributary to the river in New Mexico is the Chama River which enters the river just below that dam, delivers about one-third of the supplies for New Mexico. New Mexico then uses their allocation of Compact water for agriculture and municipal supplies through the central portion of the state. The cities of Santa Fe, Albuquerque, Socorro and others rely on the river as a source of supply.
The river then enters the largest reservoir on the Rio Grande in the Upper Rio Grande reach, the Elephant Butte dam and Reservoir. This reservoir is critical to the entire Rio Grande Basin as it holds and regulates southern New Mexico and West Texas allocation under of the Compact, generates hydroelectric power and provides protection for all three states’ water supplies.
Immediately below the Elephant Butte dam is Cabello Reservoir which serves as a regulating reservoir from the water running through the power generation station in Elephant Butte Dam. There are three large diversions from the River between Cabello Dam and El Paso that provide irrigation water to several tens of thousands of acres of highly productive land. El Paso uses a portion of Texas’s water allocation for municipal supplies. The American Dam diversion just upstream of El Paso serves many thousands of irrigated acres downstream of El Paso before the river gets to Ft. Quitman. The water allocated from the river to the Juarez, Mexico area by treaty with the US, is diverted at the International Dam just below the American Dam. The river is effectively dry below this point except for the water produced by several drains from both the US and Mexico sides of the river.
The water produced by the Rio Grande is used a number of times before it is all finally diverted. Returns flows from groundwater accretions, drain flows and many small tributary contributions along it length allow excess application and outfalls from different uses. The river works very hard for the people, farms, wildlife and riparian areas along this reach and is truly the life blood of this area of the arid west. It is under great pressure to serve an ever increasing demand for water supplies for many purposes and it will require very creative management to serve this Basin.
August 23rd marks the 100th year anniversary of the Rio Grande Reservoir. To celebrate, all Water 2012 August articles have been on the reservoir and the river. For all Water 2012 in the Rio Grande Basin articles, please visit www.rgwcei.org or www.water2012.org.
For the next three weeks, the Water 2012 display will be up at the Carnegie Library in South Fork. This is the last stop for the Water 2012 traveling display, so don’t miss it.