Analysing the Combined Effect of Barrier Wall and Freshwater Injection Countermeasures on Controlling Saltwater Intrusion in Unconfined Coastal Aquifer Systems

Freshwater recharge wells and underground flow barriers are among several methods proposed for controlling saltwater intrusion (SWI) into coastal aquifers. In this study, experimental and numerical studies were performed to determine the effect of using a flow barrier wall, a recharge well and a combination of these, to control SWI in unconfined coastal aquifer systems. The SEAWAT model was used to predict the SWI wedge and the behaviour of the retreating residual saltwater after installing the remediation measures. The results show that increasing the barrier wall embedment ratio (d(b)/d) from 0.44 to 0.67 led to an increase in the repulsion ratio (R) from 20.8 to 46.87%. Moreover, increasing the freshwater injection rate ratio (Q(i)/Q) from 0.22 to 0.56 increased the repulsion ratio (R) from 10.93 to 22.39%. Barrier wall embedment with ratios (d(b)/d) of 0.44, 0.51 and 0.57, combined with a freshwater injection ratio (Q(i)/Q) with a value of 0.56, achieved (R) of 41.14, 45.41 and 50.0%, compared with 20.8, 27.1 and 34.40% for the barrier wall only and 22.39% for freshwater injection only. Freshwater injection ratios (Q(i)/Q) of 0.22, 0.33, 0.44 and 0.56 combined with a barrier wall embedment ratio (d(b)/d) of 0.508 achieved repulsion ratios (R) of 33.9, 36.5, 39.0 and 45.42%, compared with 10.9, 15.6, 18.8 and 22.4% respectively for freshwater injection only and 27.1% for the barrier wall only. A combination of flow barrier and freshwater injection forced the saltwater to retreat and achieved values of R greater than either the barrier wall or freshwater injection separately.