Ecohydrological Controls on Flow Conveyance Losses of the Middle Rio Grande

The Middle Rio Grande experiences significant water loss in the reach from San Acacia to South Fort Craig, and while this quantity has been identified in the past, the cause of this loss remains unknown. This area is extremely important for transporting water from northern New Mexico to the southern part of the state and Texas. By examining this issue through both a hydrological and biological lense, the results can inform water management decisions, ecological considerations, and yield a better understanding of riparian corridor ecohydrology. Prior research points to two significant sources of loss, a hydraulic gradient draining surface water into the groundwater, and evapotranspiration in the summer months. We use several techniques in our research such as water table monitoring using data loggers in wells, soil moisture monitoring using probes, water quality and field chemistry parameters from surface and ground waters, soil gas flux, vegetation surveys, and remote sensing. It is our goal to investigate the interactions of the topography, hydrological conditions, weather, and vegetation to better define the processes that contribute to this conveyance loss. Hydrological 2-D modeling will build a better understanding of the interconnectedness between ground and surface water in the study reach using stage data. Remote sensing, in conjunction with vegetation survey data, can contribute to an estimate of water loss due to evapotranspiration of the surrounding riparian corridor. Preliminary results indicate a losing reach within the study area as groundwater coming in from the east flows underneath the Rio Grande and westward into the Low Flow Conveyance Channel. This is partly due to pre-existing hydrogeology, but surficial topography associated with 150 years of floodplain management has resulted in the river being perched above the floodplain. Monitoring shows a gradient of decreasing groundwater temperatures away from the Rio Grande. Depth to water appears to be a control on the source of transpired water, with additional information provided by soil moisture monitoring. With the knowledge gained from this study, better decisions can be made to minimize the impacts of the increasing human demand of water in the Rio Grande, and provide better protection for the delicate ecology in this semi-arid environment.