Transient Behavior of Saltwater Wedge and Mixing Zone in Head-Controlled Coastal Aquifer: Experimental Measurements and Numerical Modeling

Abstract

Article History: Received: 6 Dec. 2018 Accepted: 21 Feb. 2019 Saltwater intrusion is a transient process that affects the coastal aquifers quality and hydrodynamics. The transient behavior of the saltwater wedge (SW) and mixing zone (MZ) due to the changes of the inland freshwater head was investigated through experimental and numerical approaches using image processing technique and the numerical code SUTRA. To acquire data in the transient conditions, automated algorithms were designed and employed for both methods. Numerical simulations were extended to a reference problem of field scale for further study of the transient aspect of the saltwater intrusion phenomena. The results demonstrated that the behavior of SW area is significantly similar to the behavior of SW toe length in transient conditions. Also, in the advancing case, the SW height reaches the steady state condition much sooner than the SW toe length and the SW area, while in the receding case, all the three indicators are stabilized almost simultaneously. Furthermore, the results showed that the MZ expanded at early stages of the receding and after a while condensed again gradually until it finally reaches to its original state at the beginning of the advancing case. Although local velocity of brackish water toward sea boundary in the dilute region of the MZ is more than in the dense region, the flushing and mixing process causes to increase the MZ in the receding case. Sensitivity analyzes showed that the speed of SW advancing or receding does not affect the MZ thickness in a steady state condition.