Abstract
In the numerical investigation of saltwater transport in coastal aquifers, we need to correctly evaluate the hydrodynamic dispersion in the flow field. In this study, we focused on the role of dispersivity in the removal process of residual saltwater in a laboratory scale cutoff wall experiment. From a pulse-type fluorescent tracer injection experiment in a saturated porous media of glass beads with a mean diameter of 0.088 cm, the estimated longitudinal and transverse dispersivities were found to be 0.07 cm and 0.0025 cm, respectively. Numerical analysis of the saltwater intrusion and subsequent removal after cutoff wall installation using SEAWAT and the generated dispersivity ratio (αL/αT) of 28 reproduces well the measured salt concentration changes with time. Whereas, if a dispersivity ratio of 10 is used in the numerical simulation, transverse dispersion in the saltwater and freshwater mixing zone becomes large and the residual saltwater is removed faster than the laboratory experiment. Inversely, if 100 was used, the residual saltwater removal time took longer. The transverse dispersion is a key parameter in the mechanical dispersion of saltwater in the mixing zone after cutoff wall installation.
Highlights
Among several countermeasures to prevent saltwater intrusion in coastal aquifers, artificial subsurface barriers store and control groundwater and ensure a consistent extraction of freshwater without causing seawater intrusion
We focused on the role of dispersivity in the saltwater transport in the laboratory scale cutoff wall experiment
In our laboratory-scale study in a saturated porous media made of glass beads with a mean diameter of 0.088 cm, the longitudinal and transverse dispersivities, and their ratio were estimated using a pulse-type fluorescent tracer injection experiment to be 0.07 cm, 0.0025 cm, and 28 cm, respectively
Summary
Among several countermeasures to prevent saltwater intrusion in coastal aquifers, artificial subsurface barriers store and control groundwater and ensure a consistent extraction of freshwater without causing seawater intrusion. Luyun et al (2009) showed experimentally and numerically that residual saltwater trapped upon installation of these cutoff walls gradually retreated before being completely removed from the reservoir behind the cutoff wall. They observed slight differences in the time for complete removal between the experimental and numerical results. We focused on the role of dispersivity in the saltwater transport in the laboratory scale cutoff wall experiment. The objectives of this study are to determine the longitudinal and transverse dispersivities of a porous medium using fluorescein tracer test and to demonstrate their influence on saltwater movement after cutoff wall installation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
