Shallow Water Integrated Geophysical Survey - A Case Study with Geological and Hydrogeological Consequences

Fresh water wetlands are usually sanctuaries to wildlife and important recharge areas for groundwater. In these areas, groundwater-surface water exchange occurs and it depends, among other factors, of local geology. Hence, management of these wetland areas should include detailed information about the local geology and hydrogeological particularities. To investigate these aspects, geophysical methods can be very a very useful tool to obtain information from concealed formations and assist in the minimization of environmental stresses. However, the use of geophysics in wetlands requires the design and construction of dedicated equipment and proper navigation and positioning techniques. The application of geophysical techniques in a sensitive wetland, Pateira de Fermentelos fresh water lagoon, is herein presented. For a successful survey equipment was specially designed and constructed, that is, a 65 m long resistivity floating multicable and a floating 24x24 m, coincident loop to be used with TEM equipment, as well as specific navigation procedures. The quality of the results show that these equipments can be used in other shallow water environments. These equipments allowed fast, efficient and accurate field operations. Modelling and interpretation of geophysical data provided most valuable information regarding geology, geological discontinuities and groundwater-surface water exchanges.