Analysis of structural lineaments in the fissural aquifers of the Forquilha and Vista Alegre catchments using remote sensing

The Brazilian semi-arid region presents fragility in terms of surface and groundwater resources due to the irregularity in precipitation regimes and the high evaporation rates. In this context, the communities and the stakeholders are conditioned to seek strategies to cope with droughts, and groundwater emerges as  an alternative supply. This demand requires detailed studies to understand fissural aquifers, given the circulation and storage of water in these aquifers is subject to the presence of structural discontinuities, in particular, influencing the variation of hydrodynamic characteristics and the salinity of wells. The area object of this study corresponds to the Forquilha and Vista Alegre Catchments, in the Ceará State, Northeast Brazil. The present research performed the identification and automatic extraction of the structural lineaments through remote sensing. PALSAR MDE images with 12.5 m spatial resolution and technical data from wells drilled in the region were used. This method promoted the identification of areas of interest for groundwater prospecting. The basins present intermittent drainages and low hydrogeological vocation. Lineaments with preferential NE-SW striking and WNW-ESE striking, in a secondary way, were identified, mainly associated with the drainages of the region. In Vista Alegre the relationship between flow rates and lineaments show a direct affinity. The wells reveal higher flow rates in the western region of the basin, where there is a zone of greater intersection of lineaments, moderate salinity and low variation of the static level in the rainy season. Preliminary results indicate poor interaction between surface and groundwater dynamics. At Forquilha, the relationship between structural features and the most productive wells occurs between structural intersections and drainage. Salinity and static level variation present direct interference in the rainy season, which is reflected in the reduction of the electrical conductivity. In this case, the interaction between the structures and the drainages is more coherent with respect to the lineaments, drainage direction and local relief. Therefore, knowing the structural context of a basin is a necessary increment for a more efficient and planned exploitation of groundwater resources, especially in semi-arid regions that are highly vulnerable to climate change.