The subsurface barrier is one of various engineering measures used to
prevent seawater intrusion in coastal regions which has been widely
applied. However, its two common types, the cut-off wall and the
subsurface dam, are both found to cause nitrate (NO3-) accumulation in
landward aquifers. In this study, numerical simulations were conducted
to investigate the mechanism of NO3- accumulation caused by the two
types of subsurface barriers, as well as the influence of several key
parameters, i.e. the infiltration NO3- concentration, the inflow DOC
concentration, the barrier height and the barrier location on the
performance of the subsurface barriers. The results showed that the
cut-off wall generally requires a large height to ensure a satisfactory
seawater prevention effectiveness, and it is more likely to cause NO3-
accumulation compared to a subsurface dam. On the other hand, despite
the subsurface dam may not result in the significant increase of NO3-
concentration in groundwater upstream, it cannot be applied to the areas
where SI has occurred due to the residual seawater problem. Moreover,
the construction of a cut-off wall results in a stagnation zone appeared
at the upper corner of the barrier, where accumulated NO3-
significantly. With the increase of the barrier height, the stagnation
zone expanded, leading to further increase of mean NO3- concentration in
the landward aquifer. Since the construction of a subsurface dam will
not generate such a zone, the subsurface dam generally has little impact
on NO3- accumulation.
A new physical barrier system for seawater intrusion control
