Estimating fracture characteristics and hydraulic conductivity from slug tests in epikarst of southwest China

Abstract

Study region: Guizhou Province, Southwest China Study focus: This study aims to estimate the hydraulic conductivity (Kh) of the weathered rock fractures (epikarst) based on the best fitting of observed water head in 105 slug tests in the study sites. Specifically, comparisons of the estimated results from the analytical and numerical methods reveal the effects of changes in fracture flow conditions (e.g., steady and non-steady) on Kh for various fracture apertures and soil fillings. New hydrological insights for the region: The results comparatively show that Kh from the analytical solution of steady flow was significantly underestimated, and the numerical modeling of the non-linear and unsteady flow can improve the water head fitting when the Reynolds number (Re) > 17.27. The optimized Kh ranges 0.014–2673 m/d and the mean value of Kh is about 100 times the median value, suggesting that epikarst flow might be controlled by a limited number of larger fractures. Moreover, the soil filling in large fractures (>10 mm) creates a turning point of the exponential increase of Kh with d. Comparatively, the naturally full-filling fractures resemble the soil matrix with a low Kh, and the partial-filling fractures can create preferential flow around the soil-rock interfaces with a high Kh. These results fundamentally improve our understanding of water infiltration, retention, and availability for plant uses in the karst areas of southwest China.

Keywords

• Epikarst
• Rock fractures
• Hydraulic conductivity
• Slug test
• Southwest China