A novel approach for characterizing the mixing zone of a saltwater wedge

The mixing zone between freshwater and seawater in a coastal aquifer is an important transition region that controls regional groundwater flow dynamics and reactive transport processes. While experimental procedures have been developed to study the movement of salt wedges in aquifers, so far no one has attempted to exclusively map the mixing zone associated with the wedge in a laboratory-scale aquifer model. We propose a colorimetric experimental method, which employs the reaction between alkaline freshwater and acidic saltwater, to map the mixing zone. The experiment was completed in a two-dimensional aquifer model to simulate a steady saltwater wedge. We used the density-dependent flow model SUTRA to simulate these experimental results and to estimate the mixing parameters, i.e., dispersivity coefficients. The results show that the proposed colorimetric technique is a useful experimental approach to visualize and quantify the level of mixing in a saltwater intrusion experiment. Citation: Abarca, E., and T. P. Clement (2009), A novel approach for characterizing the mixing zone of a saltwater wedge, Geophys. Res. Lett., 36, L06402, doi:10.1029/2008GL036995.