Hydrology of autogenic percolation systems in some tropical karst outcrops, West Malaysia

This paper reports on the flow regimes of underground seepages in three tower-karst outcrops and in the Setul Boundary Range, West Malaysia. Groundwater movement in the tower-karst hills, which comprise very pure, massive marbles, is confined to vertical and subvertical joints. Although flow is primarily diffuse and the discharges of the majority of seepages correlate most closely with rainfall in antecedent periods of 1–16 days or more, some stormflow occurs along conduits in the upper parts of these aquifers. Many of these conduits appear to peter out at depth into tight rock fractures, thereby forming funnel-shaped underground reservoirs which serve to moderate discharge variations. In contrast, the limestones of the Setul Boundary Range are less pure and retain much of their original bedding. The presence of near-horizontal bedding plane fractures favours lateral groundwater movement and the development of integrated drainage networks within the rock. Compared with the tower-karst caves, seepage rates are generally higher and more responsive to short-term variations in rainfall. The marked difference in topography between the tower-karst hills and the Setul Boundary Range is largely attributable to the contrasted geohydrological properties of the limestones.