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Richards' Equation
The Richards equation represents the movement of water in unsaturated soils, and is attributed to Lorenzo A. Richards who published the equation in 1931. It is a quasilinear partial differential equation; its analytical solution is often limited to specific initial and boundary conditions. Proof of the existence and uniqueness of solution was given only in 1983 by Alt and Luckhaus. The equation is based on Darcy-Buckingham law representing flow in porous media under variably saturated conditions, which is stated as :\vec=-\mathbf(\theta) (\nabla h + \nabla z), where :\vec is the volumetric flux; :\theta is the volumetric water content; :h is the liquid pressure head, which is negative for unsaturated porous media; :\mathbf(h) is the unsaturated hydraulic conductivity; :\nabla z is the geodetic head gradient, which is assumed as \nabla z = \left(\begin 0 \\ 0 \\ 1 \end \right) for three-dimensional problems. Considering the law of mass conservation for an incompressible porous ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vadose Zone
The vadose zone, also termed the unsaturated zone, is the part of Earth between the land surface and the top of the phreatic zone, the position at which the groundwater (the water in the soil's pores) is at atmospheric pressure ("vadose" is from the Latin word for "shallow"). Hence, the vadose zone extends from the top of the ground surface to the water table. Water in the vadose zone has a pressure head less than atmospheric pressure, and is retained by a combination of adhesion (''funiculary groundwater''), and capillary action (''capillary groundwater''). If the vadose zone envelops soil, the water contained therein is termed soil moisture. In fine grained soils, capillary action can cause the pores of the soil to be fully saturated above the water table at a pressure less than atmospheric. The vadose zone does not include the area that is still saturated above the water table, often referred to as the capillary fringe. Freeze, R.A. and Cherry, J.A., 1979. Groundwater. Engl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Retention Water Capacity
Retention may refer to: General * Recall (memory), in learning, the ability to recall facts and figures in memory * Memory and retention in learning * Selective retention * Cultural retention * Customer retention * University student retention * Employee retention, the ability to keep employees within an organization * Forced retention * Grade retention, in schools, keeping a student in the same grade for another year (that is, not promoting the student to the next higher grade with his/her classmates) * Retention basin, * Retention election, in the United States court system, a process whereby a judge is periodically subject to a vote in order to remain in the position of judge * Retention rate * Retention ratio, in company earnings * Retention of vision, in magic * Water retention (medicine), abnormal accumulation of fluid in the body * Urinary retention, the lack or inability to urinate * Variable retention, in land management and forestry conservation Information and record ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Soil Physics
Soil physics is the study of soil's physical properties and processes. It is applied to management and prediction under natural and managed ecosystems. Soil physics deals with the dynamics of physical soil components and their phases as solids, liquids, and gases. It draws on the principles of physics, physical chemistry, engineering, and meteorology. Soil physics applies these principles to address practical problems of agriculture, ecology, and engineering. Prominent soil physicists *Edgar Buckingham (1867–1940) :The theory of gas diffusion in soil and vadose zone water flow in soil. *Willard Gardner (1883-1964) :First to use porous cups and manometers for capillary potential measurements and accurately predicted the moisture distribution above a water table.Sterling A. Taylor: Willard Gardner, 1883-1964. Soil Science 100(2), 1965. *Lorenzo A. Richards (1904–1993) :General transport of water in unsaturated soil, measurement of soil water potential using tensiometer. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Finite Water-content Vadose Zone Flow Method
The finite water-content vadose zone flux methodTalbot, C.A., and F. L. Ogden (2008), A method for computing infiltration and redistribution in a discretized moisture content domain, ''Water Resour. Res.'', 44(8), doi: 10.1029/2008WR006815.Ogden, F. L., W. Lai, R. C. Steinke, J. Zhu, C. A. Talbot, and J. L. Wilson (2015), A new general 1-D vadose zone solution method, ''Water Resour.Res.'', 51, doi:10.1002/2015WR017126. represents a one-dimensional alternative to the numerical solution of Richards' equation for simulating the movement of water in unsaturated soils. The finite water-content method solves the advection-like term of the Soil Moisture Velocity Equation, which is an ordinary differential equation alternative to the Richards partial differential equation. The Richards equation is difficult to approximate in general because it does not have a closed-form analytical solution except in a few cases.Ross, P.J., and J.-Y. Parlange (1994). Comparing exact and numerical sol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Infiltration (hydrology)
Infiltration is the process by which water on the ground surface enters the soil. It is commonly used in both hydrology and soil sciences. The infiltration capacity is defined as the maximum rate of infiltration. It is most often measured in meters per day but can also be measured in other units of distance over time if necessary. The infiltration capacity decreases as the soil moisture content of soils surface layers increases. If the precipitation rate exceeds the infiltration rate, runoff will usually occur unless there is some physical barrier. Infiltrometers, permeameters and rainfall simulators are all devices that can be used to measure infiltration rates. Infiltration is caused by multiple factors including; gravity, capillary forces, adsorption and osmosis. Many soil characteristics can also play a role in determining the rate at which infiltration occurs. Factors that affect infiltration Precipitation Precipitation can impact infiltration in many ways. The am ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Representative Elementary Volume
In the theory of composite materials, the representative elementary volume (REV) (also called the representative volume element (RVE) or the unit cell) is the smallest volume over which a measurement can be made that will yield a value representative of the whole. In the case of periodic materials, one simply chooses a periodic unit cell (which, however, may be non-unique), but in random media, the situation is much more complicated. For volumes smaller than the RVE, a representative property cannot be defined and the continuum description of the material involves Statistical Volume Element (SVE) and random fields. The property of interest can include mechanical properties such as elastic moduli, hydrogeological properties, electromagnetic properties, thermal properties, and other averaged quantities that are used to describe physical systems. Definition Rodney Hill defined the RVE as a sample of a heterogeneous material that: # "is entirely typical of the whole mixture on avera ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tensor
In mathematics, a tensor is an algebraic object that describes a multilinear relationship between sets of algebraic objects related to a vector space. Tensors may map between different objects such as vectors, scalars, and even other tensors. There are many types of tensors, including scalars and vectors (which are the simplest tensors), dual vectors, multilinear maps between vector spaces, and even some operations such as the dot product. Tensors are defined independent of any basis, although they are often referred to by their components in a basis related to a particular coordinate system. Tensors have become important in physics because they provide a concise mathematical framework for formulating and solving physics problems in areas such as mechanics (stress, elasticity, fluid mechanics, moment of inertia, ...), electrodynamics (electromagnetic tensor, Maxwell tensor, permittivity, magnetic susceptibility, ...), general relativity ( stress–energy tensor, cur ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isotropy
Isotropy is uniformity in all orientations; it is derived . Precise definitions depend on the subject area. Exceptions, or inequalities, are frequently indicated by the prefix ' or ', hence ''anisotropy''. ''Anisotropy'' is also used to describe situations where properties vary systematically, dependent on direction. Isotropic radiation has the same intensity regardless of the direction of measurement, and an isotropic field exerts the same action regardless of how the test particle is oriented. Mathematics Within mathematics, ''isotropy'' has a few different meanings: ; Isotropic manifolds: A manifold is isotropic if the geometry on the manifold is the same regardless of direction. A similar concept is homogeneity. ; Isotropic quadratic form: A quadratic form ''q'' is said to be isotropic if there is a non-zero vector ''v'' such that ; such a ''v'' is an isotropic vector or null vector. In complex geometry, a line through the origin in the direction of an isotropic vector is a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Water Retention Curve
Water retention curve is the relationship between the water content, θ, and the soil water potential, ψ. This curve is characteristic for different types of soil, and is also called the soil moisture characteristic. It is used to predict the soil water storage, water supply to the plants (field capacity) and soil aggregate stability. Due to the hysteretic effect of water filling and draining the pores, different wetting and drying curves may be distinguished. The general features of a water retention curve can be seen in the figure, in which the volume water content, θ, is plotted against the matric potential, \Psi_m. At potentials close to zero, a soil is close to saturation, and water is held in the soil primarily by capillary forces. As θ decreases, binding of the water becomes stronger, and at small potentials (more negative, approaching wilting point) water is strongly bound in the smallest of pores, at contact points between grains and as films bound by adsorptive forc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Soil Water Diffusivity
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former term specifically to displaced soil. Soil consists of a solid phase of minerals and organic matter (the soil matrix), as well as a Porosity, porous phase that holds Soil gas, gases (the soil atmosphere) and water (the soil solution). Accordingly, soil is a three-state of matter, state system of solids, liquids, and gases. Soil is a product of several factors: the influence of climate, terrain, relief (elevation, orientation, and slope of terrain), organisms, and the soil's parent materials (original minerals) interacting over time. It continually undergoes development by way of numerous physical, chemical and biological processes, which include weathering with associated erosion. Given its complexity and strong internal connectedness, Soil eco ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
