Dynamics and removal effectiveness of residual saltwater with subsurface dams in a coastal aquifer
Abstract
Countermeasures against seawater intrusion (SWI) are critical to prevent coastal groundwater deterioration. Subsurface dams have been recognized as effective approaches to prevent SWI, but it is mostly likely to produce residual saltwater at the landside of the dam. Understanding removal mechanism and dynamic behavior of residual saltwater can facilitate aquifer desalinization, especially with the combined measures of subsurface dams and anthropogenic activities. This study performed laboratory-scale experiments and numerical simulations to investigate the dynamic process of residual saltwater trapped in the storage area upon construction of subsurface dams along with artificial discharge/recharge. The effects of subsurface dam design, aquifer properties as well as discharge and recharge rates on flow and salinity transport processes were explored in detail for a nearshore aquifer. Two indexes including the reduction rate of residual saltwater length (RRSL*) and the removal rate of residual salt mass (RRSM*) were developed in order to quantify the effectiveness of residual saltwater removal. This study newly revealed the desalinization mechanism of residual saltwater. The experimental and numerical results found that the subsurface dam needed a minimum height to achieve complete removal of residual saltwater. Moreover, a shorter subsurface dam achieved a faster removal rate of residual saltwater compared to a taller dam. It took much longer time for a taller dam to desalinize the residual saltwater in the upstream aquifer. Particularly, attenuation of the low-concentration saltwater was a quite slow process. Saltwater pumping or freshwater injection near the dam exhibited more effectiveness in desalinization than far from it. Findings from the study have significant implications in better understanding of residual saltwater removal mechanism and timescales for nearshore groundwater systems subjected to anthropogenic discharge/recharge.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFM.H24L..01Y