Saline intrusion through zones of high hydraulic conductivity associated with faults in coastal aquifers

Coastal aquifers are subject to contamination by saline intrusion in several regions of the world, notably in urban regions or near them, and the increase in demand for this resource aggravates this problem. In addition to this scenario, the presence of neotectonic faults implies an increase in the heterogeneity of the hydrogeological environment, which is reflected in variations in saturated thickness, hydraulic conductivity and exploited flow rates. In the east coast of northeastern Brazil, the Barreiras Aquifer, unconfined, compartmentalized by faults and, due to its high importance for regional water supply, is widely submitted to high rates of exploited flow. In this context, the objective of this research is to contribute to a better understanding on how a saline intrusion contamination can develop in the coastal aquifer, seeing that the main faults, these with a predominantly transtensional (striking NW-SE) and horizontal transcurrent (striking NE-SW) kinematic character, present themselves as zones of high hydraulic conductivities. The methods used consist of two-dimensional resistivity cross-section and a numerical model of dependent density flow using the SEAWAT software USGS. The 2D resistivity model allowed to characterize the fault locally and to support the construction of the numerical model by corroborating with the fault zone as a zone of high relative hydraulic and geoeletric conductivity. The simulations performed in the model developed in SEAWAT over 20 years reveal that there is a difference between the advance of contamination between faults. These results can be explained by the kinematic character. Variations in aquifer recharge between dry and rainy periods also show differences in the advance of saline intrusion. Therefore, there is a need for further research in these environments, seeking to develop an efficient management of water resources.

Keywords: coastal aquifers, faults, heterogeneity, hydraulic conductivity, saline intrusion, SEAWAT software.