Scale-Constrained Estimation of Saturated Hydraulic Conductivity from Soil Texture and Porosity.

Estimates of median, 25%, and 75% quartiles of saturated hydraulic conductivity were given by Rawls et al. in 1998 for 12 soil textural classes with discrimination between low and high porosity soils in each class. The large database used in this work included almost 1000 published results of measurements. Inspection of sources of this data showed that samples of different sizes were used in different works. Soil hydraulic conductivity is a scale-dependent property, and can increase by half to one order of magnitude when support area increases one order of magnitude in laboratory conditions, whereas no substantial increase was often observed  when Ksat for large laboratory samples were compared with the field Ksat values. The objective of this work was to revisit the aforementioned database and to develop the estimates of soil hydraulic conductivity for the areas ranging from 20 cm² to 50 cm².  Using probability scale provided graphs of cumulative distribution  functions of Ksat that are relatively close to linear in the  probability range 5% and 95%. Most of  textural classes did not have enough data to characterize the distribution tails. A simple relationship cold be used to obtain the standard deviation of from logKsat from the distribution quartiles. The new table of Ksat values for textural classes in two porosity ranges provides less variable estimates. Decoupling scale effects and natural variability allows one to focus on derivation of scaling relationships suitable for the scale of a specific soil hydrology project.