The Closed Basin Project
- Created on Thursday, 12 April 2012 14:51
- Written by Ken Beck
The impacts of drought and water shortages are something the Bureau of Reclamation works to manage throughout the West. Things are no different in the Closed Basin Project, where the bureau taps this precious resource to help Colorado deliver water to other Rio Grande Compact states and make important mitigation deliveries for local wildlife and recreation.
People in the San Luis Valley have likely heard about the closed basin and Closed Basin Project, but may not understand what these terms mean. A closed basin is a hydrologic basin without an outlet to another body of water. Precipitation that falls within a closed basin can only leave the basin naturally through evaporation or seepage.
In the San Luis Valley, the closed basin is north of Alamosa and Monte Vista and encompasses 2,940 square miles bounded by the San Juan Mountains to the west, the Sangre de Cristo Mountains to the east and Poncha Pass to the north. The towns of Center, Hooper, Moffat, Mosca and Saguache and Great Sand Dunes National Park are within the closed basin. The topographic low point or “sump area” of the closed basin extends from north of San Luis lakes to the Blanca Wildlife Habitat Area.
Major tributaries flowing into the closed basin are irrigation diversions from the Rio Grande, and also Carnero, La Garita, and Saguache Creeks from the west, San Luis Creek from the north, and North Crestone and Sand creeks from the east. This water spreads out across the valley floor where it evaporates or infiltrates the underground aquifer. Historically, the water table in the sump area was very shallow allowing groundwater to evaporate from the soil and to be consumed by vegetation (evapotranspiration).
In 1972, Congress authorized construction of the Closed Basin Project which spans 195 square miles of the sump of the closed basin from east of Alamosa to four miles south of Moffat. The purpose of the project is to salvage unconfined groundwater from the sump area that historically was lost to evaporation and evapotranspiration.
The value of the Closed Basin Project to the San Luis Valley is simple. It helps Colorado to meet commitments to New Mexico and Texas under the Rio Grande Compact of 1939. For every acre-foot of water produced by the Closed Basin Project, irrigators in the San Luis Valley get to keep an acre-foot of water for irrigation. Because Colorado receives credit for Closed Basin Project water, less curtailment is required for irrigators who have water rights on the Rio Grande or Conejos rivers.
The water has also helped the United States meet its commitment under a 1906 treaty with Mexico. Lawsuits have been filed against the United States and the state of Colorado in the past over downstream water shortages.
The Closed Basin Project, which is operated and maintained by the Bureau of Reclamation and currently employs 23 individuals, pumps water from the sump area through a network of shallow groundwater wells or salvage wells. This salvaged water is delivered through a 42-mile canal to the Rio Grande. The project also delivers water to the Alamosa National Wildlife Refuge, the Blanca Wildlife Habitat Area and San Luis Lake.
The Rio Grande Water Conservation District (RGWCD) provides civil maintenance on the Closed Basin Project.
A three person operating committee consisting of representatives of the Colorado Water Conservation Board, RGWCD and Reclamation oversees operation of the Closed Basin Project. The committee ensures operation within parameters outlined in the Rio Grande Compact regarding pumping restrictions and water quality requirements.
The authorizing legislation requires that operation of the Closed Basin Project shall not cause the water table to drop more than two feet in wells outside of the project boundary which existed prior to project construction. Water level data from a network of more than 350 monitoring wells throughout the closed basin is used to evaluate impacts from pumping. When drawdown limits are reached, the Operating Committee directs Reclamation to curtail pumping in impacted areas. Of the 170 salvage wells constructed, about 60 are out of production due to drawdown limitations.
The Rio Grande Compact also specifies that water delivered to the river cannot exceed 350 parts per million total dissolved solids (tds.) Because of this limitation, wells with very high tds concentrations cannot be utilized. Eleven wells are out of production due to water quality issues.
The Closed Basin Project’s original design estimate of 100,000 acre-feet per year has never been reached. Since 2000, the average output has been about 17,000 acre-feet per year. Factors such as aquifer depletions caused by an increase in irrigation well development, bio fouling of salvage wells, reduced recharge from irrigation ditches, and diminishing natural runoff as a result of persistent drought conditions impact project output.
The State Engineer is currently working toward well administration to replace depletions from irrigation well use. Data is being gathered to determine impacts of wells on the aquifer. The data will come from the Rio Grande Decision Support System model. The model will benefit the Closed Basin Project by establishing a sustainable pumping yield for the closed basin aquifer.
The Closed Basin Project will continue to play a role in managing a sustainable aquifer level while delivering water to the Rio Grande to meet compact requirements and protecting local water rights on the river system.
Ken Beck is a graduate of Utah State University with a degree in Agricultural Education and a masters degree in Agricultural Economics. He has worked for the Bureau of Reclamation (Bureau) for 29 years. He has been the manager of the Closed Basin Project since January 2008.
For more information on Water 2012 in the Rio Grande Basin, please visit www.rgwcei.org or www.water2012.org. Starting in May, Water 2012 will be hosting a series of tours around the San Luis Valley of ongoing projects that are sponsored by the Rio Grande Interbasin Roundtable. Please continue to follow the Water 2012 series or visit the website for tour dates and information. Contact Leah Opitz with any questions or comments.