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lec 7, Modulus of elasticity coefficient_ Hydraulic conductivity.pptx

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lec 7, Modulus of elasticity coefficient_ Hydraulic conductivity.pptx

1. 1. Lec. # 7: Modulus of Elasticity coefficient; Hydraulic conductivity BOT-609 (Plant nutrient water relationships) Credit hrs: 3 (2-1) Dr. Noreen Zahra Assistant Professor, Department of Botany GCWUF
2. 2. An elastic modulus (also known as modulus of elasticity) • Is a quantity that measures an object or substance's resistance to being deformed elastically (i.e., non-permanently) when a stress is applied to it. • The elastic modulus of an object is defined as the slope of its stress–strain curve in the elastic deformation region:A stiffer material will have a higher elastic modulus.
3. 3. An elastic modulus has the form: where • stress is the force causing the deformation divided by the area to which the force is applied and • strain is the ratio of the change in some parameter caused by the deformation to the original value of the parameter. • If stress is measured in pascals, then since strain is a dimensionless quantity, the units of λ will be pascals as well.
4. 4.  Saturated hydraulic conductivity is a quantitative measure of a saturated soil's ability to transmit water when subjected to a hydraulic gradient. It can be thought of as the ease with which pores of a saturated soil permit water movement. • All pores are contributing to fluxes • Primarily driven by gravitational forces • Less common state of flow in soil Applications: • Runoff modeling • Groundwater flow • Green Infrastructure Assessment
5. 5.  Unsaturated hydraulic conductivity refers to a measure of soil's water-retaining ability when soil pore space is not saturated with water. • Varies depending on pore sizes, which are able to contribute to water fluxes • Primarily driven by matric forces • Most common state of flow in soil Applications: • Vadose zone hydrology • Hyporheic exchange
6. 6. Hydraulic conductivity curves for three different soils. Values to the right of the vertical axis indicate saturated conductivity values. Values to the left indicate unsaturated values. Note that the vertical axis is a logarithmic axis. Thus differences are order of magnitude differences (0=water potantail)
7. 7. There are two methods of estimation of hydraulic conductivity 1:Estimation by empirical approach 2:Determination by experimental approach 1:Estimation by empirical approach There are two types of empirical approach a) Estimation from grain size b) Pedotransfer function
8. 8. b) Pedotransfer function In soil science, pedotransfer functions (PTF) are predictive functions of certain soil properties using data from soil surveys. Allen Hazen derived an empirical formula for approximating hydraulic conductivity from grain size analyses a) Estimation from grain size
9. 9. 2. Determination by experimental approach There are relatively simple and inexpensive laboratory tests that may be run to determine the hydraulic conductivity of a soil: constant-head method falling-head method.
10. 10. FIELD TECHNIQUES: SATURATED HYDRAULIC CONDUCTIVITY 1.Ring infiltrometers (Kfs) • Single ring infiltrometer (Kfs) • Double ring infiltrometer (Kfs) 2. SATURO (Kfs) 3. Pressure infiltrometer (Kfs) 4. Borehole permeameters (Kfs)
11. 11. FIELD TECHNIQUES: UNSATURATED HYDRAULIC CONDUCTIVITY 1. Tension infiltrometers (K(Ψ))
12. 12. References: 1.Wösten, J.H.M., Pachepsky, Y.A., and Rawls, W.J. (2001). "Pedotransfer functions: bridging the gap between available basic soil data and missing soil hydraulic characteristics". Journal of Hydrology. 251 (3–4): 123– 150. Bibcode:2001JHyd..251..123W. doi:10.1016/S0022-1694(01)00464-4. 2. Controlling capillary flow an application of Darcy's law 3. Liu, Cheng "Soils and Foundations." Upper Saddle River, New Jersey: Prentice Hall, 2001ISBN 0-13-025517-3 4.S.B.Hooghoudt, 1934, in Dutch. Bijdrage tot de kennis van enige natuurkundige grootheden van de grond. Verslagen Landbouwkundig Onderzoek No. 40 B, p. 215-345. Soil hydraulic conductivity—What it is. How to measure it | METER Environment

Notas del editor

• stress is a physical quantity that expresses the internal forces that neighbouring particles of a continuous material exert on each other, while strain is the measure of the deformation of the material. For example, when a solid vertical bar is supporting an overhead weight, each particle in the bar pushes on the particles immediately below it. When a liquid is in a closed container under pressure, each particle gets pushed against by all the surrounding particles
• Biopores are voids in the soil which were formed by the activity of soil life. The first scientific studies on biopores were published in the 1870s–90s by Victor Hensen who stated that earthworms were opening channels to the subsoil and coating them with humus, thus creating a beneficial environment for root growth.
• the rate of flow of a fluid, radiant energy, or particles across a given area.
A runoff model is a mathematical model describing the rainfall–runoff relations of a rainfall catchment area, drainage basin or watershed. More precisely, it produces a surface runoff hydrograph in response to a rainfall event, represented by and input as a hyetograph
A hyetograph is a graphical representation of the distribution of rainfall intensity over time.
• Matric forces: forces acting on soil water that are independent of gravity.
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").
Hyporheic exchange is the mixing of surface and shallow subsurface water through porous sediment surrounding a river and is driven by spatial and temporal variations in channel characteristics (streambed pressure, bed mobility, alluvial volume and hydraulic conductivity).
• Figure 1 shows soil hydraulic conductivity curves for three different soils. The vertical axis is at 0 head (water potential). Values to the right indicate saturated conductivity values. Values to the left indicate unsaturated values. The poorly structured clayey soil (lower line) has a saturated conductivity much lower than the sandy soil. This is because the clayey soil consists of small pores and the flow paths are more restricted. But, if that clayey soil (dotted line) had good structure (i.e., it contained aggregates with large pores between those aggregates which created better flow paths) then its saturated hydraulic conductivity could be higher than the conductivity of the sand.
On the left side of Figure 1, where the head (water potential) is negative, the soil starts to desaturate, and the pores empty. As the pores (especially the large pores) empty, the hydraulic conductivity decreases dramatically. So, the unsaturated conductivity is always less, and in most cases, orders of magnitude less than it is when the soil is saturated.
Notice that the unsaturated hydraulic conductivity for the poorly structured clayey soil and the well structured clayey soil eventually meet. This is because at a certain point the macropores stop contributing to the flow, and then flow occurs only in the mesopores between the soil particles. Also note that the unsaturated hydraulic conductivity curve for the structureless sandy soil starts out higher than the clayey soil, but as the soil dries, the unsaturated hydraulic conductivity becomes lower than the clayey soils.
• Soil survey, soil mapping, is the process of classifying soil types and other soil properties in a given area and geo-encoding such information. It applies the principles of soil science, and draws heavily from geomorphology, theories of soil formation, physical geography, and analysis of vegetation and land use patterns.