Surface Water–Groundwater Interactions Between Irrigation Ditches, Alluvial Aquifers, and Streams

Abstract

Improved descriptions of surface water–groundwater interactions are required for enhanced water resource management in irrigated areas of the western U.S. We are conducting a research project to determine surface water–groundwater interaction effects on hydrologic budgets and water quality along the upper Rio Grande in New Mexico. This article reports on the initial phase of the project to ascertain the effects of unlined irrigation ditch seepage on shallow groundwater at the Alcalde Science Center in north-central New Mexico. Results from two seepage tests in which 60- and 80 m-long impoundments were established in the Alcalde Ditch indicate that under normal ditch flow depths about 11 cm/day seeps out of the Alcalde Ditch. Based on flow estimates over the 9 km length of the Alcalde Ditch, at least 5% of the total ditch flow seeps out of the ditch bed and banks during the irrigation season. Water level measurements from monitoring wells showed that within 1 month of the beginning of ditch flow, irrigation seepage caused a raised water table and orientation of flow paths towards the river. Specific conductance measurements of surface and shallow groundwater indicated that surface water was the origin of shallow groundwater. Seepage from earthen ditches such as the one in this study could possibly have multiple benefits: diluting agricultural chemicals or septic tank leachate in shallow groundwater, providing groundwater recharge to shallow wells, and providing delayed return flow to the stream thus maintaining in-stream flow after peak runoff periods.