New Mexico Geological Society Annual Spring Meeting — Abstracts

The shallow groundwater flow system of White Sands dune field, located within the Tularosa Basin of Southern New Mexico, likely stabilizes the base of the largest gypsum dune field in the world. The dune is saturated throughout nearly its entire accumulation thickness, resulting in a shallow water table (< 3 ft bgs) in the interdunal areas. Water table geometry and elevation play a critical role in controlling spatial extent of the dune field and accumulation thickness. The White Sands National Monument (WHSA) is concerned that lowering the water table may lead to increased scour and migration of the dune field, which could be unfavorable to the preservation of the flora and fauna that have adapted to survive there.  In response to projected increases in groundwater pumping in the regional Tularosa Basin groundwater system, changes in surface water use, and the threat of climate change, the WHSA is interested in understanding how these changes on a regional scale may impact the shallow dune field aquifer.

   We have collected hydrological, geochemical, and geophysical data in order to identify the water sources of that contribute to the dune field aquifer, and to assess interactions between the shallow aquifer with surface conditions and the basin-scale, regional system.  Vertical hydraulic gradients in the unsaturated zone, temperature, and water quality data indicate that local precipitation is a source of recharge to the dune field aquifer.  Additionally, geochemical and electrical resistivity data indicates a contribution of water from the regional Tularosa Basin groundwater system to the overlying saturated dune.

Mathematical modeling techniques are in use to characterize the relative importance of the sources of water to the dune filed aquifer, and to quantify the timescales on which changes may affect the shallow dune aquifer.  A 1-dimensional, dune-scale model uses the seasonal temperature fluctuations as a tracer to estimate the upward flow of water from the regional to the saturated dune.  We have also constructed a 2-dimensional, hydrologic model to attempt to characterize the regional groundwater flow regime near to the dune, as well as across the Tularosa Basin to a depth of 6 km.  Computed and observed salinity and groundwater residence times are the primary means of model calibration.  Preliminary results from the two mathematical models indicate the regional groundwater system does contribute flow to the dune aquifer.  Both dune- and basin-scale models will improve the understanding of the interaction of the shallow dune aquifer with the deeper basin groundwater and surface conditions.