A hillslope-scale experiment to measure lateral saturated hydraulic conductivity

One of the most challenging parameters in hillslope- and watershed-scale, distributed, hydrologic models is the lateral saturated hydraulic conductivity (K-s). In this paper, we present a methodology to determine the hillslope- scale lateral K-s above a moderately deep sloping restrictive layer in an 18x35 m hillslope plot using perched water level measurements and drain tile outflow data. The hillslope- scale lateral K-s was compared to small-scale K-s 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 K-s 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 K-s within the same porous medium is foremost a measurement problem. Data analysis provided the K-s distribution with depth, showing a sharp decrease in K-s within the first 0.1 m of the soil and an exponential decline in K-s 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 K-s at a hillslope scale.