New Mexico Geological Society Annual Spring Meeting — Abstracts

Water table levels have been monitored at least yearly in 5 to 10 wells in the Sunshine Valley of northern Taos County since 1955 by the USGS, NMOSE and TSWCD. Water level was lowest in 1955, rose significantly in the decades of the seventies and eighties and has declined slightly since the mid nineties. These wells had water tables at approximately 50 to 200 feet below the ground level, from aquifers mostly in Q – T fan and alluvial clastics. They are located one to five miles west of the Sangre de Cristo mountain-front. The water table slopes gently westward at less than 100 feet/mile from the mountain front recharge area to the Rio Grande gorge. Precipitation has been gauged near the town of Red River, 10 miles east of Sunshine Valley, for the last 60 years. The precipitation record shows a low period in the fifties and sixties, followed by increased precipitation in the seventies and eighties, and a decrease since the mid-nineties. Thus the groundwater levels appear to reflect twenty-year climate changes seen in the recharge area. No groundwater age dates are available in the area of these wells, but an analogy to the Taos Valley to the south suggest residence time should be less than ten years. C14 dates from springs and wells near the Rio Grande have ages greater than 1000 years, suggesting a mix with much older ground waters from west of the Rio Grande and/or local recharge sources in the western Sunshine Valley. Abrupt level changes in individual wells are caused by cessation or resumption of irrigation. Recent well irrigation in the northern Sunshine Valley does not seem to lower the water levels. Acequia irrigation near Cerro and Costilla may be helping to maintain groundwater at higher than expected levels. Water table mapping in 1959 and 2009 appear similar and long-term changes are within the 50-foot contour intervals used in both.