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 (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 × 35 m hillslope plot using perched water level measurements and drain tile outflow data. The hillslope‐scale lateral Ks was compared to small‐scale Ks measured with small soil cores and the Guelph permeameter. Our results show that small‐scale Ks measurements underestimate the actual hillslope‐scale Ks. 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 Ks 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.