Eletrorresistividade, água subterrânea, zonas costeiras, geofísica aplicada
Abstract
A geophysical survey using geoelectrical method was carried out on several coastal plains along the north coast of the State of São Paulo . These plains, corresponding to Baleia, Juréia, Juqueí, Una, Guaratuba, Boracéia, Maresias and Saí beaches, are small, urban tourist, areas under intense development. Water supply from the municipality is often not provided before most of the lots are occupied. Groundwater becomes the main source of water in most cases. Geologicaly the area is formed of Quaternary sediments covering the crystalline basement. These sediments, mostly sandy, contain silt and clay layers, which are sometimes saturated with salt water. The sediments present variable values of resistivities, depending of the surrounding topography. Large plains frequently contain salt water intrusions. Small plains, surrounded by high elevations, usually contain fresh water, even at greater depths, imposing high resistivities to the sediments. Telluric currents with high intensity were present at all investigated points, limiting MN spacing to a maximum of 4 meters. Due to the elevated soil humidity, contact resistance was low, allowing currents of 500 mA to flow in the ground using source voltages of about 500 V.
