Numerical investigation of seawater intrusion and retreat in coastal aquifers

Seawater intrusion is a transient process, but the transient behavior of this phenomenon has received less attention due to human limitations to acquire numerical and experimental results. The influence of decreasing and increasing of the freshwater head on the saltwater wedge and the mixing zone movement was simulated using SUTRA code. To acquire and analysis simulated resulting, automated algorithm was planned in MATLAB. In order to more study the saltwater movement, changes in the three indicators of wedge toe length, wedge area and wedge height were measured over the time. The results demonstrated that the wedge area behavior is similar to the wedge toe length under transient condition. In the case of seawater intrusion, the wedge height reaches the steady state conditions sooner than the two other indicators, while in the retreating case, all the three indicators are stopped almost together. Also, the results showed that the mixing zone expanded at the primary stages of the retreating, but whit passage of time condensed again until it finally reaches its original state at the beginning of the intruding case. Sensitivity analyzes demonstrated that the rate of seawater intrusion and retreat does not affect the mixing zone thickness in the steady condition.