Modeling the Soil Water Retention Curves of Soil-Gravel Mixtures with Regression Method on the Loess Plateau of China |
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Authors: | Huifang Wang Bo Xiao Mingyu Wang Ming'an Shao |
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Institution: | 1. Beijing Research & Development Center for
Grass and Environment, Beijing Academy of Agriculture and Forestry Sciences,
Beijing, China.; 2. Center for Water System Security, Graduate
University of Chinese Academy of Sciences, Beijing, China.; 3. State Key Laboratory of Soil Erosion and
Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation,
Chinese Academy of Sciences, Yangling, Shaanxi, China.; Lakehead University, Canada, |
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Abstract: | Soil water retention parameters are critical to quantify flow and solute
transport in vadose zone, while the presence of rock fragments remarkably
increases their variability. Therefore a novel method for determining water
retention parameters of soil-gravel mixtures is required. The procedure to
generate such a model is based firstly on the determination of the quantitative
relationship between the content of rock fragments and the effective saturation
of soil-gravel mixtures, and then on the integration of this relationship with
former analytical equations of water retention curves (WRCs). In order to find
such relationships, laboratory experiments were conducted to determine WRCs of
soil-gravel mixtures obtained with a clay loam soil mixed with shale clasts or
pebbles in three size groups with various gravel contents. Data showed that the
effective saturation of the soil-gravel mixtures with the same kind of gravels
within one size group had a linear relation with gravel contents, and had a
power relation with the bulk density of samples at any pressure head. Revised
formulas for water retention properties of the soil-gravel mixtures are proposed
to establish the water retention curved surface models of the power-linear
functions and power functions. The analysis of the parameters obtained by
regression and validation of the empirical models showed that they were
acceptable by using either the measured data of separate gravel size group or
those of all the three gravel size groups having a large size range.
Furthermore, the regression parameters of the curved surfaces for the
soil-gravel mixtures with a large range of gravel content could be determined
from the water retention data of the soil-gravel mixtures with two
representative gravel contents or bulk densities. Such revised water retention
models are potentially applicable in regional or large scale field
investigations of significantly heterogeneous media, where various gravel sizes
and different gravel contents are present. |
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