The disc permeameter is a field instrument used for measuring water infiltration in the soil, characterized by in situ saturated and unsaturated soil hydraulic properties. It is used to provide estimates of the hydraulic conductivity of the soil near saturation. Conventional techniques for measuring in-situ infiltration include the use of a single or double ring infiltrometer. Single and double ring infiltrometer only measures flow under ponded conditions, when used in soil with distinct macropores, preferential flow will dominate the flow; this does not reflect infiltration under rainfall or sprinkler irrigation. Therefore, many authors attempted to create a negative potential on the water flow; this is to exclude macropores in the flow process, hence only measuring the soil matrix flow. Willard Gardner and Walter Gardner developed a negative head permeameter as early as 1939. Dixon developed a closed-top ring infiltrometer to quantify macropores. Water is applied to a closed-top system, which permits the imposition of negative head or pressure on the ponded water surface.
Negative tension can be considered as simulating a positive soil air pressure, created by a negative air pressure above ponded surface water. A simplification was made by Zebchuk; the limitation of this device is the infiltration has to be started by ponding the closed-top infiltrometer adjusted to a negative pressure. Little research effort was continued in this area, instead attention has been given to the sorptivity apparatus of Dirksen which used a ceramic plate as a base. Based on this design, Brent Clothier and Ian White developed the sorptivity tube which can provide a constant negative potential on the soil surface. However, the sorptivity tube had many shortcomings, hence modifications to the design led to the development of the disc permeameter by Perroux and White from CSIRO. In the US it is known as the tension infiltrometer. For more on the development of the first permeameter as told by Walter Gardner, visit The CSIRO disc permeameter of Perroux and White comprises a nylon mesh supply membrane, a water reservoir and a bubbling tower.
The bubbling tower is open to air. The bubbling tower controls the potential h0 applied to the membrane by adjusting the water height in the air-inlet tube. So the soil pores need to have energy equivalent to h0 to overcome water, held under tension in the reservoir, it can be used to supply potential ranging -200 mm to 0 mm excluding pores with diameter bigger than 0.075 mm. Many different designs have evolved, including: automated recording tension infiltrometer, patented by the Iowa State University mini-disc infiltrometer hood infiltrometer Due to the three-dimensional water flow from the disc, a special formulation is needed to take into account the lateral absorption of water; the analyses are derived from the steady-state analysis of Wooding. For steady infiltration from a circular, inundated area, Wooding found that a remarkable feature of this curve is the fact that it never departs far from the straight line: Q ∗ = 2 π a + 4 where Q* is the dimensionless flux, a = α r / 2. R is the radius of the disc and α is the sorptive number or the parameter of Gardner’s hydraulic conductivity function: K = K s e α h where K is the hydraulic conductivity, Ks is saturated conductivity and h is soil water potential.
In terms of the actual steady-state infiltration rate q¥: q ∞ = α ϕ 0 + 4 ϕ 0 π r Clothier, B. E. White, I. 1981. Measurement of sorptivity and soil water diffusivity in the field. Soil Science Society of America Journal 45, 241-245. Dirksen, C. 1975. Determination of soil water diffusivity by sorptivity measurements. Soil Science Society of America Proceedings 39, 22-27. Dixon, R. M. 1975. Design and use of closed-top infiltrometers. Soil Science Society of America Proceedings 39, 755-763. Topp, G. C. Zebchuk, W. D. 1985. A closed adjustable head infiltrometer. Canadian Agricultural Engineering 27, 99-104. Perroux, K. M. White, I. 1988. Design for disc permeameters. Soil Science Society of America Journal, 52, 1205-1215. Wooding, R. A. 1968. Steady infiltration from a shallow circular pond. Water Resources Research 4, 1259-1273
Hydraulic head or piezometric head is a specific measurement of liquid pressure above a vertical datum. It is measured as a liquid surface elevation, expressed in units of length, at the entrance of a piezometer. In an aquifer, it can be calculated from the depth to water in a piezometric well, given information of the piezometer's elevation and screen depth. Hydraulic head can be measured in a column of water using a standpipe piezometer by measuring the height of the water surface in the tube relative to a common datum; the hydraulic head can be used to determine a hydraulic gradient between two or more points. In fluid dynamics, head is a concept that relates the energy in an incompressible fluid to the height of an equivalent static column of that fluid. From Bernoulli's Principle, the total energy at a given point in a fluid is the energy associated with the movement of the fluid, plus energy from static pressure in the fluid, plus energy from the height of the fluid relative to an arbitrary datum.
Head is expressed in units of height such as feet. The static head of a pump is the maximum height; the capability of the pump at a certain RPM can be read from its Q-H curve. A common misconception is that the head equals the fluid's energy per unit weight, while, in fact, the term with pressure does not represent any type of energy. Head is useful in specifying centrifugal pumps because their pumping characteristics tend to be independent of the fluid's density. There are four types of head used to calculate the total head in and out of a pump: Velocity head is due to the bulk motion of a fluid, its pressure head correspondent is the dynamic pressure. Elevation head is due to the gravitational force acting on a column of fluid. Pressure head is due to the static pressure, the internal molecular motion of a fluid that exerts a force on its container. Resistance head is due to the frictional forces acting against a fluid's motion by the container. A mass free falling from an elevation z > 0 will reach a speed v = 2 g z, when arriving at elevation z=0, or when we rearrange it as a head: h = v 2 2 g where g is the acceleration due to gravityThe term v 2 2 g is called the velocity head, expressed as a length measurement.
In a flowing fluid, it represents the energy of the fluid due to its bulk motion. The total hydraulic head of a fluid is composed of elevation head; the pressure head is the equivalent gauge pressure of a column of water at the base of the piezometer, the elevation head is the relative potential energy in terms of an elevation. The head equation, a simplified form of the Bernoulli Principle for incompressible fluids, can be expressed as: h = ψ + z where h is the hydraulic head known as the piezometric head. Ψ is the pressure head, in terms of the elevation difference of the water column relative to the piezometer bottom, z is the elevation at the piezometer bottom In an example with a 400 m deep piezometer, with an elevation of 1000 m, a depth to water of 100 m: z = 600 m, ψ = 300 m, h = 900 m. The pressure head can be expressed as: ψ = P γ = P ρ g where P is the gauge pressure, γ is the unit weight of the liquid, ρ is the density of the liquid, g is the gravitational acceleration The pressure head is dependent on the density of water, which can vary depending on both the temperature and chemical composition.
This means that the hydraulic head calculation is dependent on the density of the water within the piezometer. If one or more hydraulic head measurements are to be compared, they need to be standardized to their fresh water head, which can be calculated as: h f w = ψ ρ ρ f w + z where h f w is the fresh water head, ρ f w is the density of fresh water The hydraulic gradient is a vector gradient between two or more hydraulic head measurements over the length of the flow path. For groundwater, it is called the'Darcy slope', since it determines the quantity of a Darcy flux or discharge, it has applications in open-channel flow
International Standard Serial Number
An International Standard Serial Number is an eight-digit serial number used to uniquely identify a serial publication, such as a magazine. The ISSN is helpful in distinguishing between serials with the same title. ISSN are used in ordering, interlibrary loans, other practices in connection with serial literature; the ISSN system was first drafted as an International Organization for Standardization international standard in 1971 and published as ISO 3297 in 1975. ISO subcommittee TC 46/SC 9 is responsible for maintaining the standard; when a serial with the same content is published in more than one media type, a different ISSN is assigned to each media type. For example, many serials are published both in electronic media; the ISSN system refers to these types as electronic ISSN, respectively. Conversely, as defined in ISO 3297:2007, every serial in the ISSN system is assigned a linking ISSN the same as the ISSN assigned to the serial in its first published medium, which links together all ISSNs assigned to the serial in every medium.
The format of the ISSN is an eight digit code, divided by a hyphen into two four-digit numbers. As an integer number, it can be represented by the first seven digits; the last code digit, which may be 0-9 or an X, is a check digit. Formally, the general form of the ISSN code can be expressed as follows: NNNN-NNNC where N is in the set, a digit character, C is in; the ISSN of the journal Hearing Research, for example, is 0378-5955, where the final 5 is the check digit, C=5. To calculate the check digit, the following algorithm may be used: Calculate the sum of the first seven digits of the ISSN multiplied by its position in the number, counting from the right—that is, 8, 7, 6, 5, 4, 3, 2, respectively: 0 ⋅ 8 + 3 ⋅ 7 + 7 ⋅ 6 + 8 ⋅ 5 + 5 ⋅ 4 + 9 ⋅ 3 + 5 ⋅ 2 = 0 + 21 + 42 + 40 + 20 + 27 + 10 = 160 The modulus 11 of this sum is calculated. For calculations, an upper case X in the check digit position indicates a check digit of 10. To confirm the check digit, calculate the sum of all eight digits of the ISSN multiplied by its position in the number, counting from the right.
The modulus 11 of the sum must be 0. There is an online ISSN checker. ISSN codes are assigned by a network of ISSN National Centres located at national libraries and coordinated by the ISSN International Centre based in Paris; the International Centre is an intergovernmental organization created in 1974 through an agreement between UNESCO and the French government. The International Centre maintains a database of all ISSNs assigned worldwide, the ISDS Register otherwise known as the ISSN Register. At the end of 2016, the ISSN Register contained records for 1,943,572 items. ISSN and ISBN codes are similar in concept. An ISBN might be assigned for particular issues of a serial, in addition to the ISSN code for the serial as a whole. An ISSN, unlike the ISBN code, is an anonymous identifier associated with a serial title, containing no information as to the publisher or its location. For this reason a new ISSN is assigned to a serial each time it undergoes a major title change. Since the ISSN applies to an entire serial a new identifier, the Serial Item and Contribution Identifier, was built on top of it to allow references to specific volumes, articles, or other identifiable components.
Separate ISSNs are needed for serials in different media. Thus, the print and electronic media versions of a serial need separate ISSNs. A CD-ROM version and a web version of a serial require different ISSNs since two different media are involved. However, the same ISSN can be used for different file formats of the same online serial; this "media-oriented identification" of serials made sense in the 1970s. In the 1990s and onward, with personal computers, better screens, the Web, it makes sense to consider only content, independent of media; this "content-oriented identification" of serials was a repressed demand during a decade, but no ISSN update or initiative occurred. A natural extension for ISSN, the unique-identification of the articles in the serials, was the main demand application. An alternative serials' contents model arrived with the indecs Content Model and its application, the digital object identifier, as ISSN-independent initiative, consolidated in the 2000s. Only in 2007, ISSN-L was defined in the
Hydraulic conductivity, symbolically represented as K, is a property of vascular plants and rocks, that describes the ease with which a fluid can move through pore spaces or fractures. It depends on the intrinsic permeability of the material, the degree of saturation, on the density and viscosity of the fluid. Saturated hydraulic conductivity, describes water movement through saturated media. By definition, hydraulic conductivity is the ratio of velocity to hydraulic gradient indicating permeability of porous media. There are two broad categories of determining hydraulic conductivity: Empirical approach by which the hydraulic conductivity is correlated to soil properties like pore size and particle size distributions, soil texture Experimental approach by which the hydraulic conductivity is determined from hydraulic experiments using Darcy's lawThe experimental approach is broadly classified into: Laboratory tests using soil samples subjected to hydraulic experiments Field tests that are differentiated into: small scale field tests, using observations of the water level in cavities in the soil large scale field tests, like pump tests in wells or by observing the functioning of existing horizontal drainage systems.
The small scale field tests are further subdivided into: infiltration tests in cavities above the water table slug tests in cavities below the water tableThe methods of determination of hydraulic conductivity and other related issues are investigated by several researchers. Allen Hazen derived an empirical formula for approximating hydraulic conductivity from grain size analyses: K = C 2 where C Hazen's empirical coefficient, which takes a value between 0.0 and 1.5, with an average value of 1.0. A. F. Salarashayeri & M. Siosemarde give C as taken between 1.0 and 1.5, with D in mm and K in cm/s. D 10 is the diameter of the 10 percentile grain size of the material A pedotransfer function is a specialized empirical estimation method, used in the soil sciences, however has increasing use in hydrogeology. There are many different PTF methods, they all attempt to determine soil properties, such as hydraulic conductivity, given several measured soil properties, such as soil particle size, bulk density.
There are simple and inexpensive laboratory tests that may be run to determine the hydraulic conductivity of a soil: constant-head method and falling-head method. The constant-head method is used on granular soil; this procedure allows water to move through the soil under a steady state head condition while the quantity of water flowing through the soil specimen is measured over a period of time. By knowing the quantity Q of water measured, length L of specimen, cross-sectional area A of the specimen, time t required for the quantity of water Q to be discharged, head h, the hydraulic conductivity can be calculated: Q t = A v where v is the flow velocity. Using Darcy's law: v = K i and expressing the hydraulic gradient i as: i = h L where h is the difference of hydraulic head over distance L, yields: Q t = A K h L Solving for K gives: K = Q L A h t In the falling-head method, the soil sample is first saturated under a specific head condition; the water is allowed to flow through the soil without adding any water, so the pressure head declines as water passes through the specimen.
The advantage to the falling-head method is that it can be used for both fine-grained and coarse-grained soils. Calculating the hydraulic conductivity is more complicated because of the changing pressure head, requires solving a differential equation. In compare to laboratory method, field methods gives the most reliable information about the permeability of soil with minimum disturbances. In laboratory methods, the degree of disturbances affect the reliability of value of permeability of the soil. Pumping test is the most reliable method to calculate the coefficient of permeability of a soil; this test is further classified into pumping out test. There are in-situ methods for measuring the hydraulic conductivity in the field; when the water table is shallow, the augerhole method, a slug test, can be used for determini
Soil is a mixture of organic matter, gases and organisms that together support life. Earth's body of soil, called the pedosphere, has four important functions: as a medium for plant growth as a means of water storage and purification as a modifier of Earth's atmosphere as a habitat for organismsAll of these functions, in their turn, modify the soil; the pedosphere interfaces with the lithosphere, the hydrosphere, the atmosphere, the biosphere. The term pedolith, used to refer to the soil, translates to ground stone in the sense "fundamental stone". Soil consists of a solid phase of minerals and organic matter, as well as a porous phase that holds gases and water. Accordingly, soil scientists can envisage soils as a three-state system of solids and gases. Soil is a product of several factors: the influence of climate, relief and the soil's parent materials interacting over time, it continually undergoes development by way of numerous physical and biological processes, which include weathering with associated erosion.
Given its complexity and strong internal connectedness, soil ecologists regard soil as an ecosystem. Most soils have a dry bulk density between 1.1 and 1.6 g/cm3, while the soil particle density is much higher, in the range of 2.6 to 2.7 g/cm3. Little of the soil of planet Earth is older than the Pleistocene and none is older than the Cenozoic, although fossilized soils are preserved from as far back as the Archean. Soil science has two basic branches of study: pedology. Edaphology studies the influence of soils on living things. Pedology focuses on the formation and classification of soils in their natural environment. In engineering terms, soil is included in the broader concept of regolith, which includes other loose material that lies above the bedrock, as can be found on the Moon and on other celestial objects as well. Soil is commonly referred to as earth or dirt. Soil is a major component of the Earth's ecosystem; the world's ecosystems are impacted in far-reaching ways by the processes carried out in the soil, from ozone depletion and global warming to rainforest destruction and water pollution.
With respect to Earth's carbon cycle, soil is an important carbon reservoir, it is one of the most reactive to human disturbance and climate change. As the planet warms, it has been predicted that soils will add carbon dioxide to the atmosphere due to increased biological activity at higher temperatures, a positive feedback; this prediction has, been questioned on consideration of more recent knowledge on soil carbon turnover. Soil acts as an engineering medium, a habitat for soil organisms, a recycling system for nutrients and organic wastes, a regulator of water quality, a modifier of atmospheric composition, a medium for plant growth, making it a critically important provider of ecosystem services. Since soil has a tremendous range of available niches and habitats, it contains most of the Earth's genetic diversity. A gram of soil can contain billions of organisms, belonging to thousands of species microbial and in the main still unexplored. Soil has a mean prokaryotic density of 108 organisms per gram, whereas the ocean has no more than 107 procaryotic organisms per milliliter of seawater.
Organic carbon held in soil is returned to the atmosphere through the process of respiration carried out by heterotrophic organisms, but a substantial part is retained in the soil in the form of soil organic matter. Since plant roots need oxygen, ventilation is an important characteristic of soil; this ventilation can be accomplished via networks of interconnected soil pores, which absorb and hold rainwater making it available for uptake by plants. Since plants require a nearly continuous supply of water, but most regions receive sporadic rainfall, the water-holding capacity of soils is vital for plant survival. Soils can remove impurities, kill disease agents, degrade contaminants, this latter property being called natural attenuation. Soils maintain a net absorption of oxygen and methane and undergo a net release of carbon dioxide and nitrous oxide. Soils offer plants physical support, water, temperature moderation and protection from toxins. Soils provide available nutrients to plants and animals by converting dead organic matter into various nutrient forms.
A typical soil is about 50% solids, 50% voids of which half is occupied by water and half by gas. The percent soil mineral and organic content can be treated as a constant, while the percent soil water and gas content is considered variable whereby a rise in one is balanced by a reduction in the other; the pore space allows for the infiltration and movement of air and water, both of which are critical for life existing in soil. Compaction, a common problem with soils, reduces this space, preventing air and water from reaching plant roots and soil organisms. Given sufficient time, an undifferentiated soil will evolve a soil profile which consists of two or more layers, referred to as soil horizons, that differ in one or more properties such as in their texture, density, consistency, temperature and reactivity; the horizons differ in thickness and gene
Mariotte’s bottle is a device that delivers a constant rate of flow from closed bottles or tanks. It is named after French physicist Edme Mariotte. A picture of a bottle with a gas inlet is shown in the works of Mariotte, but this construction was made to show the effect of outside pressure on mercury level inside the bottle, it further misses an outlet for the liquid. The design was first reported by McCarthy; as shown in the diagram, a stoppered reservoir is supplied with a siphon. The pressure at the bottom of the air inlet is always the same as the pressure outside the reservoir, i.e. the atmospheric pressure. If it were greater, air would not enter. If the entrance to the siphon is at the same depth it will always supply the water at atmospheric pressure and will deliver a flow under constant head height, regardless of the changing water level within the reservoir; this apparatus has many variations in design and has been used extensively when a constant water pressure is needed, e.g. supplying water at constant head for measuring water infiltration into soil or supplying the mobile phase in chromatography.
The drawback of the design is that it is sensitive for gas inlet leakage and that during operation liquid cannot be added, since it would change the pressure control. Accurate control is nowadays provided by electronic devices; the Guelph Permeameter, used to measure unsaturated hydraulic conductivity in the field uses this principle to create a constant head. Another application is a similar arrangement in some fuel tanks used in control line model airplanes, where it is called a "uniflow" tank, where the tank venting tubing goes to the end of the prismatic tank, close to the fuel pick-up tube that feeds the engine. Infiltrometer web.physics.ucsb.edu Media related to Mariotte bottle at Wikimedia Commons