A hillslope-scale experiment to measure lateral saturated hydraulic conductivity

Abstract

One of the most challenging parameters in hillslope- and watershed-scale, distributed, hydrologic models is the lateral saturated hydraulic conductivity (Ks). In this paper, we present a methodology to determine the hillslope-scale lateral Ks above a moderately deep sloping restrictive layer in an 18 x 35 m hillslope plot using perched water level measurements and drain tile outflow data. The hillslope-scale lateral K s was compared to small-scale Ks measured with small soil cores and the Guelph permeameter. Our results show that small-scale K s measurements underestimate the actual hillslope-scale K s. The hillslope-scale Ks measurements were 13.7, 4.1, and 3.2 larger than small soil core measurements in the A, B, and E horizons, respectively. We argue that the gap between small-scale and hillslope-scale Ks within the same porous medium is foremost a measurement problem. Data analysis provided the Ks distribution with depth, showing a sharp decrease in Ks within the first 0.1 m of the soil and an exponential decline in Ks below 0.1 m. The distribution of K s with depth was best described by a double-exponential relationship. Overall, results indicate the importance of macroporosity, perhaps of biological origin, in determining Ks at a hillslope scale.