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Tuesday, 11 February 2014

Six components of the Hydrologic Cycle ==>>

Hydrologic Cycle

  • Evapotranspiration - is water evaporating from the ground and transpiration by plants. evapotranspiration is also the way that water vapor re-enters the atmosphere.
  • Condensation - is the process of water changing from a vapor to a liquid. Water vapor in the air rises mostly by convection. This means that warm, humid air will rise, while cooler air will flow downward. As the warmer air rises, the water vapor will lose energy, causing its temperature to drop. The water vapor then has a change of state into liquid or ice.
  • Precipitation - is water being released from clouds as rain, sleet, snow or hail. Precipitation begins after water vapor, which has condensed in the atmosphere, becomes too heavy to remain in atmospheric air currents and falls.
  • Infiltration - when a portion of the precipitation that reaches the Earth's surface seeps into the ground.
  • Percolation - is the downward movement of water through soil and rock. Percolation occurs beneath the root zone.
  • Runoff - is precipitation that reaches the surface of the Earth but does not infiltrate the soil. Runoff can also come from melted snow and ice.

Detail Description of the Hydrologic Cycle==>

Detail Description of the Hydrologic Cycle 

The Hydrologic Cycle
This is an education module about the movement of water on the planet Earth. The module includes a discussion of water movement in the United States, and it also provides specific information about water movement in Oregon.
The scientific discipline in the field of physical geography that deals with the water cycle is called hydrology. It is concerned with the origin, distribution, and properties of water on the globe. Consequently, the water cycle is also called the hydrologic cycle in many scientific textbooks and educational materials. Most people have heard of the science of meteorology and many also know about the science of oceanography because of the exposure that each discipline has had on television. People watch TV weather personalities nearly every day. Celebrities such as Jacques Cousteau have helped to make oceanography a commonly recognized science. In a broad context, the sciences of meteorology and oceanography describe parts of a series of global physical processes involving water that are also major components of the science of hydrology. Geologists describe another part of the physical processes by addressing groundwater movement within the planet's subterranean features. Hydrologists are interested in obtaining measurable information and knowledge about the water cycle. Also important is the measurement of the amount of water involved in the transitional stages that occur as the water moves from one process within the cycle to other processes. Hydrology, therefore, is a broad science that utilizes information from a wide range of other sciences and integrates them to quantify the movement of water. The fundamental tools of hydrology are based in supporting scientific techniques that originated in mathematics, physics, engineering, chemistry, geology, and biology. Consequently, hydrology uses developed concepts from the sciences of meteorology, climatology, oceanography, geography, geology, glaciology, limnology (lakes), ecology, biology, agronomy, forestry, and other sciences that specialize in other aspects of the physical, chemical or biological environment. Hydrology, therefore, is one of the interdisciplinary sciences that is the basis for water resources development and water resources management.
The global water cycle can be described with nine major physical processes which form a continuum of water movement. Complex pathways include the passage of water from the gaseous envelope around the planet called the atmosphere, through the bodies of water on the surface of earth such as the oceans, glaciers and lakes, and at the same time (or more slowly) passing through the soil and rock layers underground. Later, the water is returned to the atmosphere. A fundamental characteristic of the hydrologic cycle is that it has no beginning an it has no end. It can be studied by starting at any of the following processes: evaporation, condensation, precipitation, interception, infiltration, percolation, transpiration, runoff, and storage.
The information presented below is a greatly simplified description of the major contributing physical processes. They include: 

Evaporation Icon
Evaporation occurs when the physical state of water is changed from a liquid state to a gaseous state. A considerable amount of heat, about 600 calories of energy for each gram of water, is exchanged during the change of state. Typically, solar radiation and other factors such as air temperature, vapor pressure, wind, and atmospheric pressure affect the amount of natural evaporation that takes place in any geographic area. Evaporation can occur on raindrops, and on free water surfaces such as seas and lakes. It can even occur from water settled on vegetation, soil, rocks and snow. There is also evaporation caused by human activities. Heated buildings experience evaporation of water settled on its surfaces. Evaporated moisture is lifted into the atmosphere from the ocean, land surfaces, and water bodies as water vapor. Some vapor always exists in the atmosphere. 

Condensation Icon
Condensation is the process by which water vapor changes it's physical state from a vapor, most commonly, to a liquid. Water vapor condenses onto small airborne particles to form dew, fog, or clouds. The most active particles that form clouds are sea salts, atmospheric ions caused by lightning,and combustion products containing sulfurous and nitrous acids. Condensation is brought about by cooling of the air or by increasing the amount of vapor in the air to its saturation point. When water vapor condenses back into a liquid state, the same large amount of heat ( 600 calories of energy per gram) that was needed to make it a vapor is released to the environment. 

Precipitation Icon
Precipitation is the process that occurs when any and all forms of water particles fall from the atmosphere and reach the ground. There are two sub-processes that cause clouds to release precipitation, the coalescence process and the ice-crystal process. As water drops reach a critical size, the drop is exposed to gravity and frictional drag. A falling drop leaves a turbulent wake behind which allows smaller drops to fall faster and to be overtaken to join and combine with the lead drop. The other sub-process that can occur is the ice-crystal formation process. It occurs when ice develops in cold clouds or in cloud formations high in the atmosphere where freezing temperatures occur. When nearby water droplets approach the crystals some droplets evaporate and condense on the crystals. The crystals grow to a critical size and drop as snow or ice pellets. Sometimes, as the pellets fall through lower elevation air, they melt and change into raindrops.
Precipitated water may fall into a waterbody or it may fall onto land. It is then dispersed several ways. The water can adhere to objects on or near the planet surface or it can be carried over and through the land into stream channels, or it may penetrate into the soil, or it may be intercepted by plants.
When rainfall is small and infrequent, a high percentage of precipitation is returned to the atmosphere by evaporation.
The portion of precipitation that appears in surface streams is called runoff. Runoff may consist of component contributions from such sources as surface runoff, subsurface runoff, or ground water runoff. Surface runoff travels over the ground surface and through surface channels to leave a catchment area called a drainage basin or watershed. The portion of the surface runoff that flows over the land surface towards the stream channels is called overland flow. The total runoff confined in the stream channels is called the streamflow. 

Interception Icon
Interception is the process of interrupting the movement of water in the chain of transportation events leading to streams. The interception can take place by vegetal cover or depression storage in puddles and in land formations such as rills and furrows.
When rain first begins, the water striking leaves and other organic materials spreads over the surfaces in a thin layer or it collects at points or edges. When the maximum surface storage capability on the surface of the material is exceeded, the material stores additional water in growing drops along its edges. Eventually the weight of the drops exceed the surface tension and water falls to the ground. Wind and the impact of rain drops can also release the water from the organic material. The water layer on organic surfaces and the drops of water along the edges are also freely exposed to evaporation.
Additionally, interception of water on the ground surface during freezing and sub-freezing conditions can be substantial. The interception of falling snow and ice on vegetation also occurs. The highest level of interception occurs when it snows on conifer forests and hardwood forests that have not yet lost their leaves. 

Infiltration Icon
Infiltration is the physical process involving movement of water through the boundary area where the atmosphere interfaces with the soil. The surface phenomenon is governed by soil surface conditions. Water transfer is related to the porosity of the soil and the permeability of the soil profile. Typically, the infiltration rate depends on the puddling of the water at the soil surface by the impact of raindrops, the texture and structure of the soil, the initial soil moisture content, the decreasing water concentration as the water moves deeper into the soil filling of the pores in the soil matrices, changes in the soil composition, and to the swelling of the wetted soils that in turn close cracks in the soil.
Water that is infiltrated and stored in the soil can also become the water that later is evapotranspired or becomes subsurface runoff. 

Percolation Icon
Percolation is the movement of water though the soil, and it's layers, by gravity and capillary forces. The prime moving force of groundwater is gravity. Water that is in the zone of aeration where air exists is called vadose water. Water that is in the zone of saturation is called groundwater. For all practical purposes, all groundwater originates as surface water. Once underground, the water is moved by gravity. The boundary that separates the vadose and the saturation zones is called the water table. Usually the direction of water movement is changed from downward and a horizontal component to the movement is added that is based on the geologic boundary conditions.
Geologic formations in the earth's crust serve as natural subterranean reservoirs for storing water. Others can also serve as conduits for the movement of water. Essentially, all groundwater is in motion. Some of it, however, moves extremely slowly. A geologic formation which transmits water from one location to another in sufficient quantity for economic development is called an aquifer. The movement of water is possible because of the voids or pores in the geologic formations. Some formations conduct water back to the ground surface. A spring is a place where the water table reaches the ground surface. Stream channels can be in contact with an unconfined aquifer that approach the ground surface. Water may move from the ground into the stream, or visa versa, depending on the relative water level. Groundwater discharges into a stream forms the base flow of the stream during dry periods, especially during droughts. An influent stream supplies water to an aquifer while and effluent stream receives water from the aquifer. 

Transpiration Icon
Transpiration is the biological process that occurs mostly in the day. Water inside of plants is transferred from the plant to the atmosphere as water vapor through numerous individual leave openings. Plants transpire to move nutrients to the upper portion of the plants and to cool the leaves exposed to the sun. Leaves undergoing rapid transpiration can be significantly cooler than the surrounding air. Transpiration is greatly affected by the species of plants that are in the soil and it is strongly affected by the amount of light to which the plants are exposed. Water can be transpired freely by plants until a water deficit develops in the plant and it water-releasing cells (stomata) begin to close. Transpiration then continues at a must slower rate. Only a small portion of the water that plants absorb are retained in the plants.
Vegetation generally retards evaporation from the soil. Vegetation that is shading the soil, reduces the wind velocity. Also, releasing water vapor to the atmosphere reduces the amount of direct evaporation from the soil or from snow or ice cover. The absorption of water into plant roots, along with interception that occurs on plant surfaces offsets the general effects that vegetation has in retarding evaporation from the soil. The forest vegetation tends to have more moisture than the soil beneath the trees. 

Runoff Icon
Runoff is flow from a drainage basin or watershed that appears in surface streams. It generally consists of the flow that is unaffected by artificial diversions, storages or other works that society might have on or in a stream channel. The flow is made up partly of precipitation that falls directly on the stream , surface runoff that flows over the land surface and through channels, subsurface runoff that infiltrates the surface soils and moves laterally towards the stream, and groundwater runoff from deep percolation through the soil horizons. Part of the subsurface flow enters the stream quickly, while the remaining portion may take a longer period before joining the water in the stream. When each of the component flows enter the stream, they form the total runoff. The total runoff in the stream channels is called streamflow and it is generally regarded as direct runoff or base flow. 

Storage Icon
There are three basic locations of water storage that occur in the planetary water cycle. Water is stored in the atmosphere; water is stored on the surface of the earth, and water stored in the ground.
Water stored in the atmosphere can be moved relatively quickly from one part of the planet to another part of the planet. The type of storage that occurs on the land surface and under the ground largely depend on the geologic features related to the types of soil and the types of rocks present at the storage locations. Storage occurs as surface storage in oceans, lakes, reservoirs, and glaciers; underground storage occurs in the soil, in aquifers, and in the crevices of rock formations.
The movement of water through the eight other major physical processes of the water cycle can be erratic. On average, water the atmosphere is renewed every 16 days. Soil moisture is replaced about every year. Globally, waters in wetlands are replaced about every 5 years while the residence time of lake water is about 17 years. In areas of low development by society, groundwater renewal can exceed 1,400 years. The uneven distribution and movement of water over time, and the spatial distribution of water in both geographic and geologic areas, can cause extreme phenomena such as floods and droughts to occur. 

Sunday, 9 February 2014


Vocabulary TermDefinition
Body-Centered CubicThe crystal structure that contains an atom in the center and one atom in each corner of a cube. 
Metals with a body-centered cubic crystal structure tend to be hard.
BondAn attraction that forms when electrons are shared or transferred among atoms.
 Atomic bonds become the "glue" that holds the atoms together.
Brinell TestA hardness test that measures the diameter of a circle formed by the penEetration of a 10mm 
steel ball under a fixed load pressure.
Charpy TestAn impact test that measures the amount of energy a material can absorb. The material is broken
 by a falling pendulum, and the following upswing of the pendulum is measured.
Cold WorkingThe shaping of metal at temperatures much lower than the metal's molten state. Steel is 
often cold worked at room temperature.
Compression StrengthA material's ability to resist forces that attempt to compress or squeeze the material together.
Compression StressA force that attempts to flatten or "squeeze" a material.
Crystal StructureThe formation of crystals, which consist of a repeating pattern of atoms. A crystalline structure 
develops as a liquid metal cools and changes into a solid.
Cutting ToolA device with sharp edges used to cut metal. Cutting tools are either single point or multi-point.
DrawnThe attempt to pull a metal through a die in order to stretch it.
DuctileAble to be drawn, stretched, or formed without breaking.
DuctilityA metal's ability to be drawn, stretched, or formed without breaking.
Elastic RegionThe region of the stress-strain graph in which deformation is temporary. If a material is 
forced beyond the elastic region, it experiences plastic deformation.
Face-Centered CubicThe crystal structure that contains one atom in the center of the six sides of a cube and one
 atom in each corner of the cube. Metals with a face-centered cubic crystal structure tend to 
be ductile.
GrainAn individual crystal in a metal or alloy.
HardnessA material's ability to resist penetration, indentation, or scratching. Hard materials tend to be 
very wear resistant.
Hexagonal Close-PackedThe crystal structure that contains a collection of atoms that are closely packed into the 
shape of a hexagon. Metals with a hexagonal close-packed crystal structure tend to be brittle.
Impact ToughnessThe amount of energy that a material can absorb from a sudden, sharp blow before it breaks
 or fractures.
IndenterA device used in a hardness test that is pressed into the test material.
LoadThe weight or burden that is supported by a material.
Mechanical PropertiesThe properties that describe a material's ability to compress, stretch, bend, scratch, dent, or break.
Modulus Of ElasticityA variable that describes the relationship of stress to strain within the elastic region. 
The modulus of elasticity describes a material's stiffness.
NeckingThe reduction in diameter that occurs as a sample material is subjected to tensile stresses.
Plastic DeformationDeformation that is permanent. Plastic deformation occurs after excessive elastic deformation.
Plastic RegionAn area of the stress-strain graph in which permanent changes to a metal begin to occur.
PropertiesThe characteristics of a material that distinguish it from other materials.
Rockwell TestA hardness test that measures the degree of penetration into a metal caused by a diamond
 or other hard material that is applied under a fixed load.
Safety FactorA number that describes the safe, allowable working stress of a material.
Shear StrengthA material's ability to resist forces that attempt to cause the internal structure of the material to
 slide against itself.
Shear StressA force that attempts to cause the internal structure of a material to slide against itself.
Slip BandThe appearance of fragmented crystals and spaces indicating that a metal is about to break.
Stamping DieAn assembled device with an upper and lower plate that opens and closes and contains 
special tools for cutting or shaping sheet metal.
SteelA metal consisting of iron and carbon, usually with small amounts of manganese, phosphorus, 
sulfur, and silicon.
StrainThe ratio of change in a dimension that takes place with a material under stress.
StrengthA metal's ability to resist outside forces that are trying to break or deform the metal.
StressA force that attempts to deform an object.
Stress-Strain GraphA graph that describes the relationship between stress and strain and marks the elastic 
and plastic regions for a given material.
Tensile StrengthA material's ability to resist forces that attempt to pull it apart or stretch it.
Tensile StressA force that attempts to pull apart or stretch a material.
Torsion StressA type of shear stress that attempts to twist a material against itself.
ToughnessThe amount of energy a material can absorb before it breaks.
Yield StrengthThe point on the stress-strain curve where there is a sudden increase in strain, 
but no increase in stress. It is at this point that a metal is about to permanently deform

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