Logo image
Back
Describing soil hydraulic properties with sums of simple functions
Journal article   Peer reviewed

Describing soil hydraulic properties with sums of simple functions

P.J. Ross and K.R.J. Smettem
Soil Science Society of America Journal, Vol.57(1), pp.26-29
1993
DOI: https://doi.org/10.2136/sssaj1993.03615995005700010006x
url
Link to Published Version *Subscription may be requiredView

Abstract

Simple functions do not adequately describe the hydraulic properties of many field soils, particularly those with substantial macroporosity. By considering the soil pore-size distribution f(ψ) = ΣNi = 1 ψi fi (ψ) corresponding to the effective saturation S(ψ) = ΣNi = 1 ψi Si(ψ), where ψ is matric pressure head, the ψi are fractions of effective porosity, the Si(ψ) are simple water retention functions in common use, and fi(ψ) = S'i(ψ), we show that the relative hydraulic conductivity according to the Mualem model is Kr(ψ) = Sp[ΣΣNi = 1 ψi gi(ψ)/ΣNi = 1 ψi gi(0)]2, where gi(ψ) = εψ-xψ−1 fi(ψ) dψ and p is a pore interaction index. If the pores of the distributions do not interact, the appropriate relation is K(ψ) = ΣNi = 1 KsiKri(ψ), where Ksi is the saturated conductivity of distribution i and Kri = Sp[gi(ψ)/gi(0)]2. We note that the van Genuchten function S(ψ) = [1 + (−αψ)n]−m with the restriction m = 1 − 1/n leads to an infinite slope K'(ψ) at ψ = 0 unless n ≥ 2, which is unrealistic for field soils if a wide range of matric pressure heads is considered. Hydraulic conductivity near saturation is often expressed as K(ψ) = Ks exp(aψ). We introduce the function S(ψ) = (1 − αψ) exp(αψ), which gives, according to Mualem's model, a conductivity K(ψ) = Ks(1 − αψ)p exp[(p + 2)αψ] that approximates Ks exp(αψ) near saturation if a = 2α and is exactly equal if p = 0. As an example, a function using this model for one pore-size distribution and the van Genuchten model for the other was compared with a function using two van Genuchten distributions. The latter gave a slightly improved fit to water content and conductivity data for an aggregated soil.

Details

Metrics

23 Record Views
118 Times Cited - Web of Science

InCites Highlights

These are selected metrics from InCites Benchmarking & Analytics tool, related to this output

Citation topics
7 Engineering & Materials Science
7.133 Geotechnical Engineering
7.133.986 Unsaturated Soil Mechanics
Web Of Science research areas
Soil Science
ESI research areas
Agricultural Sciences
Logo image