| Abstract: | The time required at a field site to obtain a few measurements of saturated hydraulic conductivity (Ks) will allow for many measurements of soil air permeability (ka). This study investigates if ka measured in situ (ka, in situ) can be a substitute for measurement of Ks in relation to infiltration and surface runoff modelling. Measurements of ka, in situ were carried out in two small agricultural catchments. A spatial correlation of the log‐transformed values existed having a range of approximately 100 m. A predictive relationship between Ks and ka measured on 100‐cm3 soil samples in the laboratory was derived for one of the field slopes and showed good agreement with an earlier suggested predictive Ks–ka relationship. In situ measurements of Ks and ka suggested that the predictive relationships also could be used at larger scale. The Ks–ka relationships together with the ka, in situ data were applied in a distributed surface runoff (DSR) model, simulating a high‐intensity rainfall event. The DSR simulation results were highly dependent on whether the geometric average of ka, in situ or kriged values of ka, in situ was used as model input. When increasing the resolution of Ks in the DSR model, a limit of 30–40 m was found for both field slopes. Below this limit, the simulated runoff and hydrograph peaks were independent of resolution scale. If only a few randomly chosen values of Ks were used to represent the spatial variation within the field slope, very large deviations in repeated DSR simulation results were obtained, both with respect to peak height and hydrograph shape. In contrast, when using many predicted Ks values based on a Ks–ka relationship and measured ka, in situ data, the DSR model generally captured the correct hydrograph shape although simulations were sensitive to the chosen Ks–ka relationship. As massive measurement efforts normally will be required to obtain a satisfactory representation of the spatial variability in Ks, the use of ka, in situ to assess spatial variability in Ks appears a promising alternative. Copyright © 2004 John Wiley & Sons, Ltd. |
