A methodological framework for the optimal design of injection barriers against seawater intrusion in coastal-rural regions

Abstract

Seawater intrusion (SWI) has nowadays evolved into a major problem for many coastal areas worldwide, adversely affecting both the environment and local economies. To alleviate its serious consequences, injection barriers are often employed as a countermeasure against SWI. However, planning proper injection strategies poses significant decision-making challenges in coastal aquifer management (CAM). In this context, this study investigates the applicability and effectiveness of constructing injection barriers to combat SWI, specifically aiming at designing optimal injection schemes. For this purpose, an advanced approach has been adopted that considers socio-economic factors associated with economic benefits in the agricultural sector and the implementation costs of injection, while incorporating the following components: (a) a hydro-economic model for investigating how groundwater salinity due to SWI advancement impacts farmers' profits; (b) a coupled simulation-optimization framework for maximizing farmers' profits at the farm level under various injection scenarios using different amount of water; (c) a cost-benefit analysis for assessing the economic viability of the applied scenarios by calculating the B/C (benefit/cost) ratio; and, finally, (d) an analysis focused on identifying the relationship between the B/C ratio and the amount of water used for injection. The ultimate goal is to determine the optimal water volume, at which economic benefits are equal to implementation costs (B/C = 1). Under this solution, benefits are maximized without costs exceeding them, thus ensuring the economic viability of injection. According to our results, an optimal water volume of 2.625*10⁶ m³/year allocated to the injection wells was determined. This allocation strongly depends on the spatial distribution of crops across agricultural parcels as certain injection wells were prioritized over others. In conclusion, this study provides valuable insights into the beneficial effects of injection barriers in combating SWI, while aiding operating managers in developing CAM strategies that are both cost-effective and acceptable to water users.