CHARACTERIZATION OF SHALLOW GROUNDWATER SYSTEMS IN EAST TEXAS FORESTED WATERSHEDS

Shallow groundwater systems were evaluated in Sabine County, Texas using well data and Capacitively Coupled Resistivity (CCR). A seven-acre watershed was investigated within the undivided Wilcox group, a Paleocene strata that consists mainly of mudstones, cross-bedded sands, and deltaic silts. A series of eight shallow, up to 12 meters deep, wells were installed in the watershed and continuously monitored for six months using pressure transducer data loggers to document temporal fluctuations in the water table. Slug tests conducted on these wells indicate that permeabilities range from 10^-3 cm/sec to 10^-5 cm/sec. CCR was conducted periodically to map variations in the water table across the entire watershed through a series of eleven transect lines. Depth of CCR penetration seen across the study area varied due to lithology, water content and topography, with and average depth resolution of less than ten meters.

Well and CCR data have been coupled to produce a hydrogeologic model for shallow groundwater flow in forested watersheds of East Texas. Vegetation, interfingering lithologies, and slope produce complex shallow groundwater behavior. Flora diversity across the study area induces heterogenous transpiration causing differential water table fluctuations. Interfingering of facies results in unique flow paths due to highly variable permeability structure. Significant variations in slope produce a wide range of hydrostatic head. The dynamic nature of forested watersheds in East Texas requires the development of complex groundwater models for resource management.