ANALYSIS OF SINGAPORE’S OLD ALLUVIUM FORMATION AS A PROSPECTIVE GROUNDWATER REPOSITORY

Abstract

Singapore is a severely water-stressed nation that faces growing water supply challenges with the onset of climate change. To increase the nation’s resilience, Singapore has been exploring groundwater as a fifth “water tap”. A potential candidate for groundwater resource is the Old Alluvium formation in eastern Singapore. However, little is known about this geological formation, especially its distribution and internal structure. This study aims to analyse the Old Alluvium as a prospective groundwater repository. Various 3D geological models were constructed from borehole data to better understand the 1) spatial extent and boundary conditions, 2) lithofacies distribution, and 3) hydrofacies distribution in the Old Alluvium. The study predicted limited recharge from the surface due to overlying Kallang Formation and Fill, and potential recharge from Johor. Other key findings include an uneven Jurong Formation and Bukit Timah Granite basement below the Old Alluvium, and potential contact with the Sajahat Formation to the northeast. Three lithofacies regions were identified from the extremely complex lithology— a fines-dominated section in the southwest, a sand-dominated section in the east, and a gravel-dominated section in between. Hydrofacies-wise, the Old Alluvium consists of a large, structureless unit of low hydraulic conductivity which surround complex networks of medium conductivity and impermeable units. The models can provide useful tools for hydrogeologists to conduct flow experiments and engineers to plan site investigations, and can be extended to offshore areas as more borehole, seismic data, and site-specific hydraulic measurements become available.