VALLEY — The San Luis Valley is blessed with groundwater aquifers that provide a significant and dependable water supply for approximately 6,000 high capacity wells and more than 12,000 domestic, stock and commercial wells.
Those aquifers depend heavily on recharge from the natural system, as well as leakage from the ditches and canals throughout the Valley.
Wells were constructed from the earliest days of settlement in the Valley; and in fact, the oldest appropriation of water in the San Luis Valley is a small domestic well in the Conejos area. No new non-domestic appropriations from the aquifers in the Valley have been allowed for 30 to 40 years depending on the aquifer and the area of the Valley being considered. The moratoriums on new wells occurred as a result of the State Engineer Office’s recognition that additional groundwater appropriations would cause impacts to those aquifers and surface streams.
Monitoring of the aquifers has been taking place for many years and there is an extensive network of wells that are measured to determine water levels in the shallow aquifer and aquifer pressures in the deeper confined or artesian aquifer. The Rio Grande Water Conservation District, along with the U.S. Geological Survey, has several different networks that are being measured, some wells as often as monthly, to determine what changes in the aquifers are occurring.
One of these well networks lies just north of the Rio Grande to several miles north of Center and from the foothills on the west to east of Highway 17 and covers the area of the Valley that is being irrigated intensively by sprinklers. Approximately 3,300 large irrigation wells draw their water from this area to irrigate approximately 170,000 acres of productive farmland. The Rio Grande Water Conservation District is actively studying this area with the measurement of approximately 27 wells in order to accurately monitor the change in the unconfined aquifer storage and to manage the shallow unconfined aquifer.
Recent drought conditions, with the lowest water year being 2002, have caused significant reductions in the natural runoff that recharges this study area, and have greatly reduced the diversions from the Rio Grande that normally provide approximately 275,000 acre-feet of additional recharge into this area. Recharge into the aquifer from those diversions occurs through infiltration from the ditches and from constructed recharge pits that introduce water into the aquifer.
Aquifer storage continues to decline even though the irrigated area within the study area has been reduced by approximately 20,000 acres over the last 12 years and recently by additional thousands of acres placed in fallowing and preventative planting insurance programs.
Graphs of the unconfined aquifer storage study show the changes that are occurring in the unconfined aquifer and are indicative of the significant reductions in storage that have occurred from changes in the hydrologic conditions over the last decade. Well pumping in the area has been reduced by approximately 20 percent in 2012, over the last several years because of management efforts of the well owners themselves and efforts of Rio Grande Water Conservation District’s Subdistrict #1.
Increases in the annual precipitation in the Rio Grande Basin would greatly help improve the storage levels in the unconfined aquifer, but much more needs to be done to insure the recovery of this aquifer. Subdistrict #1 is currently remedying injurious well depletions caused by subdistrict well pumping in the 2012 water year and will continue to do so.
It is very important that well owners be aware of the condition of the unconfined aquifer storage levels and what is needed to assure recovery of the aquifer and maintaining it in a sustainable condition.