Application of ground penetrating radar (GPR) to delineate clay layers in wetlands. A case study in the Soto Grande and Soto Chico watercourses, Doñana (SW Spain)

The potential utility of ground penetrating radar (GPR) in delineating the geometry of clay layers under two watercourses of the Doñana National Park (SW Spain) has been checked. The interpretation of the GPR profiles, calibrated with piezometers, shows the presence of two clay layer roughly continuous along some 2 km. The work allowed to gain insight about the watercourses relationship with groundwater. Up to now, watercourses in the area have been associated as a matter of fact to the intersection of the water table with the topography. But this work shows the existence of shallow, roughly continuous clay layers under the watercourses that may generate perched phreatic levels even if the regional water table is too deep to crop out. Thus, the GPR proved to be very helpful and suitable in supporting hydrogeological studies in wetlands.

Research Highlights
► GPR data have provided insight about the relationship between the watercourses and the groundwater in the wetlands of Soto Grande and Soto Chico watercourses (Doñana National Park, Spain).
► Two different clay levels at mean depths of about 2 and 4 m depth have been imaged.
► The shallowest clay level, roughly continuous, seems to have a fluvial origin. It controls the location and geometry of a local, perched water table.
► GPR has proven to be a useful tool to identify the existence and delineate geometry of clay layers under wetlands.