Hydrogeological characteristics of foot caves in a karst peak-forest plain in South China

Abstract

In karst areas of South China, isolated peaks in peak-forest plains often have foot caves near the water table. Originally, foot caves are formed by surface water on the plain flowing through the peak foot into the underground during the rainy season. Later, surface water might not flow into some foot caves anymore, but foot caves still connect with groundwater. Understanding the role of foot caves is important in comprehending regional groundwater flow and in controlling the damage caused by groundwater flow in cave sites. This study employed a multi-electrode resistivity method to locate karst voids or caves at Zengpiyan cave site, Guilin City (Guangxi Province). Boreholes were used to detect karst features, tracer tests were adopted to assess the flow path and velocity of groundwater, and hydrological observations were conducted on site to reveal groundwater changes. Of the 26 boreholes drilled, 14 found underground caves, with heights ranging from 0.3 to 17.5 m. Groundwater was stored and flowed in four distinct media zones: concentrated flow zone (CFZ), highly fractured zone, cave sediment zone, and matrix-with-fractures zone, in which the foot caves constitute the primary groundwater flow zone. The CFZ was characterized and found to have a minimum hydraulic slope of 0.2%. Thus, the study succeeded in identifying hydrogeological characteristics of foot caves in a karst peak-forest plain and a hydrogeological model of the foot caves was developed. The methodology provides a basis for flood control and groundwater pollution prevention in the hydrogeological unit in which foot caves are located.