Journal of Food, Agriculture and Environment

Estimating unsaturated soil hydraulic properties in sloping lands by numerical inversion

Author(s):

Majid Raoof ^1*, Alireza Pilpayeh ²

Recieved Date: 2011-04-28, Accepted Date: 2011-10-10

Abstract:

Inverse solutions used an optimization algorithm to estimate the unknown parameters. Tension disk infiltrometer is a suitable instrument for determining the soil hydraulic properties such as hydraulic conductivity. In this study the tension disk infiltrometer data were used to estimate the unknown parameters of VanGenuchten (VG) soil water retention and Mualem-VanGenuchten (MVG) hydraulic conductivity models in different slope gradients including 0, 10, 20, 30 and 40 degree of slope. The unknown parameters, including θ_r , θ_s , α, l, n and K_S have been estimated by numerical inversion method using Hydrus 3D code. Initial estimates of unknown parameters were obtained from Rosetta code (for estimating θ_r , θ_s, α, l, n and K_S ) and Mualem report (for estimating ). Field experiments were carried out in a loamy soil with different slope gradients in Gonbad Research Station, Hamadan, Iran. For each slope gradient, infiltration experiments were conducted at tensions of 0, 6, 9 and 15 cm, using a tension infiltrometer disk. Totally 60 infiltration experiments in 5 treatments (slope gradients), 4 tensions and 3 replications were carried out. Results indicated that with increasing slope gradient, θ_s, K_S and values were decreased, θ_r values increased and α and l values had no regular trend. By increasing tension, the falling rate of θ decreased with increase in slope gradient. Unsaturated hydraulic conductivity also decreased with increase in slope gradient. The θ and values were estimated by numerical inversion method less than that measured for all slope gradients. The hysteresis effect and dependence of unsaturated hydraulic parameters together caused that numerical inversion underestimated the θ and values less than measured data.

Keywords:

Numerical inversion method, hydraulic conductivity, tension disk infiltrometer

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Journal: Journal of Food, Agriculture and Environment
Year: 2011
Volume: 9
Issue: 3&4
Category: Environment
Pages: 1067-1070

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