Paper No. 40
Presentation Time: 6:45 PM
GROUNDWATER/SURFACE-WATER INTERACTION IN A LOSING REACH OF THE EL RITO WATERSHED
Understanding the interactions between groundwater and surface water is critical to the future sustainability of communities in semi-arid watersheds because streamflow is often the primary source of water for diversions, acequias, and irrigation. Recharge and runoff are largely seasonally limited to the snowmelt season. As a consequence, sustained streamflow through the remainder of the year often depends on a greater fraction of groundwater. This warrants further investigation into streamflow generation processes and groundwater/surface water interactions in semi-arid watersheds. For example, in the El Rito watershed, a mountainous, sedimentary watershed in northern New Mexico, groundwater/surface-water interactions are very complex and an overall losing trend in discharge emerges with increasing drainage area. The losing trend appears to emerge along an 8 km reach of the stream where both major extensional faults and numerous beaver ponds are present. Either or both of these features could potentially account for the increased loss of water along this reach; 1) enhanced losses of water due to evaporation and/or infiltration from beaver ponds, and 2) losses of water due to changes in permeability associated with the extensional faults. In order to test the first possible cause of water loss, we conducted high-resolution stream gauging and water sampling for chemistry at 14 sites along the reach. In order to test the second possible cause of water loss, we conducted resistivity surveys at 3 locations near and below the major extensional faults to quantify the impacts of the faults on the local groundwater water table. Two surveys were conducted at each location. Our data shows that beaver ponds are not responsible for the loss of water along this reach. However, the data from the resistivity surveys indicates that local groundwater tables are impacted by the faults and this may affect groundwater/surface water interactions along the losing reach.