Guangxi is in a traditional karst region, where natural depressions caused by groundwater recession
and erosion are not uncommon.
The critical time is the time it takes the groundwater recession
curve to reach a stable shape after the recharge period.
The shape of the groundwater recession
curve (linear rather than concave or convex) after the 8 August rainfall event suggests that water movement from this aquifer is a combination of vertical and horizontal fluxes (Smith and Hebbert 1983).