Response of the Rio Grande and shallow ground water in the Mesilla Bolson to irrigation, climate stress, and pumping

The EI Paso-Ciudad Juarez metropolitan area obtains its water from the Rio Grande and intermontane-basin aquifers. Shallow ground water in this region is in close communication with the surface water system. A major problem with both systems is salinity. Upstream usage of the water in the Rio Grande for irrigation and municipalities has led to concentration of soluble salts to the point where the surface water commonly exceeds drinking water standards. Shallow ground water is recharged by surface water (primarily irrigation canals and agricultural fields) and discharges to surface water (agricultural drains) and deeper ground water. The source of water entering the Rio Grande varies seasonally. During the irrigation season, water is released from reservoirs and mixes with the return flow from irrigation drains. During the nonirrigation season (winter), flow is from irrigation drains and river water quality is indicative of shallow ground water. The annual cycle can be ascertained from the inverse correlation between ion concentrations and discharge in the river. Water quality data indicate that the salinity of shallow ground water increases each year during a drought. Water-management strategies in the region can affect water quality. Increasing the pumping rate of water-supply wells will cause shallow ground water to flow into the deeper aquifers and degrade the water quality. Lining the canals in the irrigation system to stop water leakage will lead to water quality degradation in shallow ground water and, eventually, deep ground water by removing a major source of high quality recharge that currently lowers the salinity of the shallow ground water