Global sensitivity analysis on a numerical model of seawater intrusion and its implications for coastal aquifer management: a case study in Dagu River Basin, Jiaozhou Bay, China

Abstract

Seawater intrusion (SWI) has triggered an accelerating process of freshwater contamination and significantly affected the soil fertility and local groundwater supply in the coastal area of Jiaozhou Bay, Shandong Province, China. This study establishes a three-dimensional numerical model based on SEAWAT code to simulate transient regional SWI to coastal aquifers in Dagu River Basin (DRB) adjacent to Jiaozhou Bay. The hydrogeological parameters in the SEAWAT model are calibrated and validated with the observed data of groundwater level and chloride (Cl−) concentration from 1 January 2010 to 1 June 2018. Also, global sensitivity analysis is used to evaluate the impacts of hydrogeological parameters (aquifer hydraulic conductivity and specific yield), along with sources/sinks consisting of recharge from precipitation infiltration and groundwater abstraction, on the SWI model. The sensitivity analysis results indicate that the progression of SWI is sensitive to the groundwater recharge from precipitation infiltration and the groundwater abstraction in the study area, while the hydraulic conductivity is of secondary importance. Furthermore, the baseline SWI model is applied to predict the extent of SWI under different scenarios considering the possible future precipitation and groundwater abstraction. It is shown that increased recharge and reduced groundwater abstraction could effectively lessen the extent of future SWI. As a case study, the research efforts on the regional SWI model are of critical importance for investigating the occurrence of SWI, identifying the factors most influential on the SWI process, and providing useful predictive information for SWI management in the DRB aquifer of Jiaozhou Bay.