Validation of boundary layer solution for assessing mixing zone dynamics of saltwater wedge in a coastal aquifer

Abstract

In saltwater intrusion problems of coastal regions, the dynamics of narrower mixing zones are influenced by the amount of dispersive entrainment and its associated marine discharges. Modelling low-fresh water recharge and high-Peclet-number scenarios gives inaccurate results with the available methods. In this study, the physical accuracy of the BL solution provided by Paster and Dagan (2007) and Paster (2010) for such conditions is validated for discharge at outflow face and width of mixing zone (WMZ) with experimentally created datasets and further extended with numerical analysis to quantify the influence of dispersive entrainment on marine discharge and saline circulation. By comparing the measured and estimated saltwater outflows, the average transverse dispersion for all dimensionless freshwater flux rates (a) was calculated, and it ranged from 0.005 cm to 0.062 cm. The study showed that, for buoyancy-dominated, high Peclet number flow circumstances, the boundary layer solutions can be effectively used to predict the marine discharges up to a = 0.5. The combined effects of water flux and dispersion revealed that buoyant force has a considerable impact on the rate of saline circulation as it suppresses the dispersion. The findings lend credence to simplicity of the boundary layer solution in reducing numerical model convergence issues for field problems caused by low recharge and low transverse dispersion flow situations.