Statistical distribution of hydraulic conductivity of rocks in deep-incised valleys, Southwest China

Characterizing the hydraulic conductivity distribution in aquifers is fundamental for groundwater models, solute transport and hyporheic exchange. Based on a total of 13,397 borehole packer test data collected at 12 high dam sites in Southwest China, the statistical distribution of hydraulic conductivity of rocks in this deep-incised valley area was investigated using hypothesis test, regression analysis and semi-variogram analysis, showing that the hydraulic conductivity of igneous and metamorphic rocks at various depths in the study area follows a log-normal distribution within 600 m depth. The vertical variation in hydraulic conductivity K [m/s] and standard deviation of lgK with depth d [m] can be best described by the power function K = 2 x 10(-6) d(-0.48) and the logistic function sigma(lgk) = 0.6/[1 + (d/428)(4.7)]. It is deduced that the decreasing degree of weathering and unloading from ground surface to unaltered fresh rocks leads to reduction in the geometric mean of hydraulic conductivity by about 1-2 orders of magnitude. The hydraulic conductivity of rocks in the study area is more controlled by geologic structures of various origins and scales and less by lithology. The compiled data and analysis presented in this study provide a reference for calibration of catchment hydrological models as well as parameterization of surface water-groundwater interactions in mountainous regions.