Investigation of transient sea level rise impacts on water quality of unconfined shallow coastal aquifers

This study analyzes the impacts of 1 m gradual and instantaneous sea level rise combined with pumping activity on seawater wedge toe location in a shallow coastal aquifer located in the southern shores of the Caspian Sea. The gradual sea level rise scenario investigates the transition variation of seawater wedge toe due to linear and parabolic between the years 2015 and 2100. Moreover, the maximum value of saltwater intrusion due to variations in hydraulic conductivity and aquifer’s recharge rates is analyzed and compared with flux-controlled and head-controlled boundary condition systems. A tree model is also applied to develop a linear regression between the sea level rise and aquifer parameters derived from different real coastal aquifers in the literature. The results indicate that 1 m gradual sea level rise in the study area by the end of the year 2100 considering all 1320 pumping wells leads to a 6.5% depletion of freshwater volume. The results also show that the peak saltwater intrusion rate during nonlinear gradual sea level rise rises with increasing the aquifer depth and horizontal hydraulic conductivity and the time to reach the saltwater intrusion peak rate considering the current recharge rate of an aquifer is about 48 m. The maximum saltwater intrusion lengths estimated by the tree model are 48 m and 10.42 m for head-controlled and flux-controlled boundary conditions, respectively, indicating that the saltwater intrusion in the aquifer due to instantaneous seal level rise is closer to head-controlled boundary conditions.