Offshore Brackish Water Resources in Hong Kong: A Case Study on Lantau Island South

Abstract:

Paleo-fluvial deposits associated with Quaternary sea level low stands have been recognized in Hong Kong waters. An integrated geophysical and hydrochemical approach is adopted to study these sand and gravel deposits, which are likely to constitute regional offshore aquifers and hold brackish paleo-waters. Marine seismic reflection profiles from Lantau Island South, are studied to depict the three-dimensional configuration of the subsurface aquifer-aquitard system. Sedimentological evidence and geophysical properties of an offshore vibrocore drilled south of Lantua Island show a three-fold sequence, with two upper marine layers and a lowermost oxidized terrestrial layer. The shifts of depositional environments are attributed to the Holocene sea level rise. Hydrochemical analysis of the porewater from the core samples indicates the presence of brackish water in the lowermost layer and possible diffusion transport. High ammonium levels in porewater and acoustic turbidity in seismic profiles are resulted from biogenic activities. This study provides preliminary information for feasibility study on exploiting submarine waters as an alternative water resource in Hong Kong.