Scaling hydraulic properties of forest soils

Abstract

Abstract:For the purpose of characterizing spatial variability of soil hydraulic properties on a forested hillslope, ®ve diering scaling methods were examined using the data set for 30 undisturbed forest soils: scaling of water retention curves, scaling of hydraulic conductivity curves, and simultaneous scaling of both water retention and conductivity curves. For the scaling of conductivity curves and the simultaneous scaling, the soil-poretortuosity parameter in a conductivity model was either ®xed at a constant or treated as a ®tted parameter. Results showed that the set of scaling factors and reference parameters derived by the separate scaling of water retention curves was dierent from that derived by the separate scaling of conductivity curves. Moreover, the separate scaling methods resulted in large estimation errors in either eective saturation or conductivity. Optimizing the tortuosity parameter was eective in improving scaling results. It was concluded that the simultaneous scaling with a ®tted pore-tortuosity parameter was the best among the ®ve methods tested in this study. The obtained scaling factors obeyed the lognormal distribution rather than the normal distribution. The variance of log-transformed scaling factors at the forested hillslope was larger than those at many crop ®elds studied by previous studies. While a spatial dependence of soil hydraulic properties was suggested for the surface layer of the forested hillslope, hydraulic properties of the subsurface layer exhibited large variations even in a small distance.

On the use of the similar media concept for scaling soil air permeability

“…The respective mean and standard deviation was 1.03 and 0.23 for α a,i , and 0 and 0.23 for lnα a,i . The values of the standard deviations for α a,i and lnα a,i were smaller than previously reported values derived from soil water retention and hydraulic conductivity data (Warrick et al, 1977;Hopmans, 1987;Hendrayanto et al, 2000), probably due to the smaller number of sediment samples used in this study. Although those previous studies showed a log normal distribution of scaling factors, the Kolmogorov-Smirnov Test did not reject the null hypothesis that α a,i and lnα a,i were normally distributed at the significance level of 0.01.…”

“…In terms of the distribution of scaling factors from Dataset II, the respective mean and standard deviation for the HT model was 1.01 and 0.14 for α a,i , and 0 and 0.13 for lnα a,i . Again, the values of the standard deviations for α a,i and lnα a,i were smaller than the previously reported values derived from soil water retention and hydraulic conductivity data (Warrick et al, 1977;Hopmans, 1987;Hendrayanto et al, 2000).…”

“…The generalized reduced gradient method was used to optimize Eq. (10) with the geometric mean of the scaling factors assumed to be unity (Hopmans, 1987;Zavattaro et al, 1999;Hendrayanto et al, 2000): 11To evaluate the performance of each air permeability model, the root mean square error (RMSE) was used:…”

Scaling the Hydraulic Functions of A Water Repellent Sandy Soil

“…The results show a more equal distribution. Hendrayanto et al (2001) measured a much larger standard deviation for the scaling factor, but they scaled the hydraulic function for the whole profiles and not for a single horizon. They presented data for the variance of ln (a S ) of other studies which had measured scaling factors for the water retention.…”

Upscaling Hydraulic Properties and Soil Water Flow Processes in Heterogeneous Soils: A Review

“…Clausnitzer et al (1992) introduced a method to scale both hydraulic functions simultaneously, yielding a single set of scaling factors that then is consistent with the Miller similitude scaling relationships. They have shown that simultaneous scaling was not always as successful as independent scaling, whereas Hendrayanto et al (2000) found that simultaneous scaling was the best among five methods tested to scale the hydraulic properties of forest soils.…”