New Mexico Geological Society Annual Spring Meeting — Abstracts

The primary goal of this project is to quantify connections between the surface water and shallow groundwater systems in the Rio Grande valley between San Acacia and Elephant Butte Reservoir. The surface water system is dominated by the Rio Grande, the Low Flow Conveyance Channel (LFCC), and irrigation canals and drains. Groundwater and surface water samples were collected along several transects crossing the river and LFCC in February, June and October of 2002 and analyzed for major cations and anions and stable isotopes of oxygen and hydrogen.

Stable isotope data indicates that water in the shallow aquifer and the LFCC is primarily river water. Most groundwater between the river and the LFCC was characterized by a fairly constant water chemistry with TDS values between 380 and 420 mg L^-1, very similar to values for the Rio Grande, indicating that groundwater between the river and the LFCC is derived directly from river seepage. The water chemistry for groundwater to the west of the LFCC was highly variable with TDS values between 370 and 1240 mg L^-1 , which probably reflects the influence of irrigation recharge and water/mineral interactions. TDS values for the LFCC are slightly higher than those of the river, suggesting that much of the LFCC water comes from river seepage. However, the interpretation is complicated by several diversions that feed water into the LFCC.