Effects of geological features on preferential flow on karst slopes in southwestern China

Abstract

The preferential flow phenomenon in karst mountains is subject to the influence of geophysical factors at the hillslope scale. Variations in geologic structure, stemming from hillslope orientation and slope position, impact the level of development of preferential flow. In this study, ground-penetrating radar (GPR) and field dye tracing experiments were applied on the south- and north-facing hillslopes to reveal the influence of slope aspects (south- and north-facing) and locations (uphill, mid-hill, and downhill) on preferential flow in a typical karst graben basin of Southwestern China. Results showed that the degree of preferential flow was higher on the north-facing hillslopes compared to the south-facing hillslopes, as indicated by the 3.6% higher preferential flow ratio (P_F) and 0.9% higher length index (L_i). For north-facing hillslopes, these two indices decreased with going uphill. There is a correlation between the geo-structural features reflected by GPR data and the indices (i.e., P_F and L_i) of preferential flow development. P_F and L_i were logarithmically increasing in relation to the radargram envelope parameters (i.e., maximum amplitude [Max_a] and total amplitude area [T_a]). A statistically significant correlation was found between the P_F and Max_a, T_a, and penetration depth (p < 0.01). The response of the envelope to preferential flow was attributed to 50.3% and 30.4%, respectively, indicating that these envelope properties effectively differentiate between south- and north-facing hillslopes. Our study provides a useful approach to advance the understanding of the influence of subsurface structure on preferential water distribution in the hillslopes of the karst area.