Applied Mechanics and Materials Vols. 353-356 (2013) pp 2983-2986
© (2013) Trans Tech Publications, Switzerland
doi:10.4028/www.scientific.net/AMM.353-356.2983
Soil Water Infiltration and its Affecting Factors
Zhang Zhong.Yuan1,a, Sa Teng.Teng1, Tie Xiao.Qiang1, Lan Hong1,
Zhang Wei.Hua1,*
1
College of Resources and Environment, Southwest University
a
[email protected]; 1,*Corresponding author: [email protected]
Keywords: soil water; infiltration; research progress
Abstract: Through comparing and analyzing domestic and foreign research on soil infiltration in
recent years, this article summarizes the research progress on soil infiltration, especially the
innovation in theory, method and progress in practical use and gives the advantages and
disadvantages among various methods. It can provide reference for the researchers engaged in the
study of soil infiltration and efficient soil water utilization.
Introduction
Infiltration refers to the process of moisture which goes into the soil from the surface after a
precipitation or irrigation. It is a key component of hydrological cycle and dominates the amount of
runoff, soil moisture replenishment and ground recharge.
Soil permeability, one of the important physical properties of soil, is closely related to water
supply intensity, soil structure and soil moisture conditions. It directly affects the generation of
surface runoff and indirectly affects soil and water conservation and plant growth. Therefore, the
study of soil infiltration plays an important role in ecological and social perspective.
The main methodology in infiltration study
Infiltration, essentially, is a process where the moisture in the soil reaches the mechanical
balance under the comprehensive effects of the molecular attraction, capillary and gravitational
forces. According to the combination of changing forces and their dynamic, the physical process of
infiltration can be divided into three stages: penetrating, leakage and infiltration. The first two
stages are non-saturated water movement, while the third stage is a saturated water movement.
However, the first two stages, as some scholars regard as the early infiltration process, is a
process with decreasing infiltration rate. At this moment, infiltration rate is affected not only by the
level of soil properties, structure and profile, but also by the impact of soil moisture content. The
latter process is called the stable infiltration process. When soil moisture increasing or soil water
potential reducing, soil infiltration rate gradually reduce until to a certain extent, where the
infiltration speed is just soil infiltration rate.
The key to infiltration theory is the match between infiltration curve and formula. The infiltration
curve is obtained by three ways as follows: the unsaturated infiltration theory, saturated infiltration
theoretical and empirical infiltration theory. In 1931, Richard deduced the basic equation of
unsaturated soil water movement, which is known as Richard equation.
Unsaturated infiltration equation is the special case of Richard equation in the vertical
one-dimensional.
Green and Ampt assumed that soil is isotropic and the initial moisture content is very low but
evenly distributed. Finally, they got the famous Green-Apt formula.
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Advances in Civil and Industrial Engineering
In actual applications, empirical formulas are often used. In the empirical formulas describing
the relationship between soil infiltration rate and time, there are two most famous formulas:
Kostiakov formula (in 1931) and Horton formula (in 1940). Kang Shao.Zhong found that Kostiakov
formula is measured better with real in the instantaneous phase of infiltration (0-10min), while
Horton formula in the gradient phase (10-20min) [1].
Other empirical formulas are also used, such as Holtan formula in 1961 and Smith formula.
Experimental methods
Soil Agricultural Chemistry Analysis Handbook [2] by Lao Jiacheng described “the permeation
tube method” and “the cutting ring method”, which are widely used to determine soil permeability
coefficient. Permeation tube method is commonly called “double ring infiltration method” or
“concentric ring infiltration method”. Hu Shunjun [3] analyzed the pressure potential distribution
law in saturated soil when measuring the saturated soil permeability coefficient by “double ring
infiltration method” and “the cutting ring method” in the hydraulic energy point of view, and
according to Darcy's law, researched quantitatively the methods of calculating soil permeability
coefficient by the two methods. It came to that the formulas are different to calculate saturated
permeability coefficient by these methods.
Figure 1 The double ring infiltration diagram
Figure 2 The cutting ring method diagram
In Figure 1, according to Darcy's law, it can be obtained:
φ − φ TO
P −L−H
L + H − PB
i = q = − K s TB
= −Ks B
= Ks
ZB − ZO
ZB − 0
L
So the formula by double ring infiltration method is:
L
Ks =
i
L+H
In Figure 2, also in accordance with Darcy's law:
i = q = −K s
φ TC − φ TO
−L − H
= −K s
ZC − Z O
L−0
So the formula by cutting ring method is:
L
Ks =
i
L+H
The results showed that saturated soil permeability coefficient is greater than the steady
infiltration rate measured by the bicyclic infiltration method; the water pressure potential of a soil
profile is different when measuring saturated soil permeability coefficient by using different
methods. Therefore, the calculating formulas are also different.
Applied Mechanics and Materials Vols. 353-356
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In addition, Xu Mingxiang [4] measured the permeability of the soils under different using
patterns by “disc permeameter method”.
There are other methods of determination of soil permeability constant-head permeameter,
falling head permeameter method, simulated rainfall method, soil column, drilling method, stable
flux method and so on.
Factors affecting infiltration process
a. The physical properties of the soil:
Soil permeability is very significantly positive related to soil non-capillary porosity degree, soil
aeration degree, non-capillary water held, and a significant positive correlation with total soil
porosity, the saturated water holding capacity but a negative correlation with soil bulk density,
capillary porosity, Capillary moisture [5].
The larger the soil non-capillary porosity is, the better ventilation is; the stronger the soil
water-holding capacity is, the better the permeability of the soil is; the greater soil bulk density and
the capillary porosity are, the worse the permeability of the soil is. The soil permeability indicators
show a highly significant correlation with non-capillary porosity and a significant correlation with
capillary porosity, so non-capillary porosity makes greater impacts on soil permeability than the
capillary porosity. In addition, soil compaction and compaction will reduce its permeability.
b. The chemical properties of the soil:
Soil permeability is significantly positively correlated with soil organic matter, total N, total K,
hydrolysis of N [5].
Soil chemical properties change the soil permeability mainly by influencing the growth of trees.
Soil organic matter and N, P, K nutrient content have a significant impact on forest growth and
development and plant roots absorb nutrients in the soil to meet their own growth and development
needs. Because of the different growth conditions and soil pore situation, soil permeability in
different forest resulting varieties. In addition, if there are more organic matter, better soil
aggregates and well-structured, the infiltration capacity is stronger.
c. Plant roots:
In general, the roots of the vegetation will have a positive impact on the permeability of soil [9].
After the decay or in the growth process the soil forms hollow holes, known as biological pores or
"root holes". Connectivity between these pores decreases as the depth increases, which can speed up
the rate of penetration. At the moment, due to the growth of trees, organic matter content of the soil
in plant roots is relatively high, so the relative porosity status and structure is better [6].
Discussion
By analyzing the domestic and foreign research of soil infiltration,the author found that domestic
scholars are more concentrated in macro research of the soil permeability of different regions:Liu
Guanglu [7] studied the soil permeability in the different types of bamboo forest, Wang Jijie [8] did
the soil permeability of different generation and forest age of eucalyptus plantation and Yu Ming
Mei and Sewage [9]did the soil permeability of Baiyun Mountain in five forest types in Guangzhou
etc. Some other scholars have compared the different research methods and studied deeply the
influencing factors of soil permeability, such as Hu Shunjun [3] searched the determination and
calculation of hydraulic conductivity of soil.
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However, foreign scholars pay more attention to the microscopic study about soil infiltration
theory and optimal selection of different permeability model, Runbin Duan et al. [10] analyzed
comprehensively different permeability model, for instance, Philip model, Kostiakov’s equation,
Mezencev’s equation, NRCS equation and Horton’s equation eta. They also did a detailed
discussion on the various methods of data analysis. At the same time, some scholars have check out
the infiltrating factors, The Hakim Boulal [11] studied the impact of land use and transportation to
irrigation water infiltration.
Acknowledgements
This work was financially supported by “Fundamental Research Funds for the Central
Universities” (No. XDJK2011C015) and the 6th Undergraduate Scientific Innovation fund
(No.1224007).
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