Repulsion driven by groundwater level difference around cutoff walls on seawater intrusion in unconfined aquifers.

Sci Total Environ

Technische Universität Dresden, Faculty of Environmental Sciences, Department of Forest Sciences, Chair of Forest Biometrics and Forest Systems Analysis, 01062 Dresden, Germany.

Published: May 2023

AI Article Synopsis

Article Abstract

Cutoff walls have been widely used to prevent seawater intrusion (SWI) in coastal regions. Previous studies generally concluded that the ability of cutoff walls to prevent seawater intrusion depends on the higher flow velocity at the wall opening, which we have shown is not the most critical mechanism. In this work, we implemented numerical simulations to explore the driving force of cutoff walls on the repulsion of SWI in both homogeneous and stratified unconfined aquifers. The results delineated that the inland groundwater level was raised by cutoff walls, which generated a significant groundwater level difference beside two sides of the wall and thus provided a large hydraulic gradient to repel SWI. We further concluded that by increasing inland freshwater influx, the construction of cutoff wall could result in a high inland freshwater hydraulic head and fast freshwater velocity. The high inland freshwater hydraulic head posed a large hydraulic pressure to push the saltwater wedge seawards. Meanwhile, the fast freshwater flow could rapidly carry the salt from the mixing zone to the ocean and induce a narrow mixing zone. This conclusion explained the reason that the cutoff wall can improve the efficiency of SWI prevention through recharging freshwater upstream. With a defined freshwater influx, the mixing zone width and saltwater pollution area mitigated with the increase of the ratio between high and low hydraulic conductivity values (K/K) of the two layers. This was because the increase of K/K caused a higher freshwater hydraulic head, a faster freshwater velocity in the high-permeability layer, and the prominent change of flow direction at the interface between the two layers. According to the above findings, we deduced that any way to increase the inland hydraulic head upstream of the wall would improve the efficiency of cutoff walls, such as the freshwater recharge, the air injection, and the subsurface dam.

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.scitotenv.2023.162535DOI Listing

Publication Analysis

Top Keywords

cutoff walls
24
hydraulic head
16
groundwater level
12
seawater intrusion
12
inland freshwater
12
freshwater hydraulic
12
mixing zone
12
freshwater
10
level difference
8
cutoff
8

Similar Publications

Want AI Summaries of new PubMed Abstracts delivered to your In-box?

Enter search terms and have AI summaries delivered each week - change queries or unsubscribe any time!