Laboratory Scale Simulation of Hydraulic Barriers to Seawater Intrusion in Confined Coastal Aquifers Considering the Effects of Stratification

Instability caused in fresh/salt water system in coastal aquifers due to overexploitation, produces the landward movement of the seawater wedge. Hydraulic barriers are created to reduce seawater invasion by injecting freshwater and raising aquifer's hydraulic head. Sensitivity of rate and location of water injection over the wedge length reduction were measured at two laboratory-scale sandboxes under hydraulic confinement. Homogeneous and stratified media were evaluated, being the latter case a prevalent condition in natural coastal aquifers [9]. Sandboxes disposed to simulate seawater wedge and afterwards, allow the injection through horizontal wells installed in a 10 cm x 10 cm mesh. The best hydraulic barrier performance was observed in the extreme point of wedge, 17.8% of reduction in homogeneous media and 78.9% in stratified media. Regarding rates of injection, the highest reduction of saltwater intrusion was achieved with the highest injection rate applied at one location. Stratification affects performance of hydraulic barrier, for stratified medium smaller injection rates were necessary to reduce saltwater intrusion. It could be also concluded that for stratified medium, injected freshwater caused almost a complete wash of the wedge at the layer of injection and layers of coarse grain size maintain traces of saltwater wedge at steady state attained after injection. On the other hand, contrast between layers of stratified media, caused important changes in thickness of mixing zone, increasing as dispersivities rise, K decays and layer thickness increment.