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Bar (landform)

Bar (landform)

In geography, a bar is a linear shoaling landform feature within a body of water. Bars tend to be long and narrow (linear) and develop where a current (or waves) promote deposition of particles, resulting in localized shallowing (shoaling) of the water. Bars can appear in the sea, in a lake, or in a river. They are typically composed of sand, although could be of any particulate matter that the moving water has access to and is capable of shifting around (for example, soil, silt, gravel, cobble, shingle, or even boulders). The size of the particles comprising a bar is related to the size of the waves or the strength of the currents moving the material, but the availability of material to be worked by waves and currents is also important. A vessel run aground on a bar is arguable worse off than one run aground on stationary rocks, because of the destructive capacity of the shifting action. The term bar can apply to landform features over a considerable range in size, from just a few meters in a small stream to marine depositions stretching for hundreds of kilometres along a coastline, often called barrier islands. In a nautical sense, a bar is a shoal, similar to a reef: a shallow formation of (usually) sand that is a navigation or grounding hazard. It therefore applies to a silt formation that shallows the entrance to or the course of a river or creek.

Sandbars and longshore bars

Bars that occur at or off the shoreline of a sea or a lake are related to beaches and might be considered offshore features of a beach (Bascom, 1980). At times when larger waves attack the beach berm, some of the beach material is redistributed offshore to become a longshore bar or sandbar, possibly visible at low tide. This bar forms (sometimes seaward of a trough) where the waves are breaking, because the breaking waves set up a shoreward current with a compensating counter-current along the bottom. Sand carried by the offshore moving bottom current is deposited where the current reaches the wave break (Bascom, 1980). Other longshore bars may lie further offshore, representing the break point of even larger waves, or the break point at low tide.

Bars as geological units

In addition to longshore bars discussed above that are relatively small features of a beach, the term bar can be applied to larger geological units that form off a coastline as part of the process of coastal erosion. These include spits and baymouth bars that form across the front of embayments and rias. A tombolo is a bar that forms an isthmus between an island or offshore rock and a mainland shore. The largest of the geological units of this kind are the barrier islands, such as occur along the East Coast of the United States, as well as along the Gulf coast. In places of reentrants along a coastline (such as inlets, coves, rias, and bays), sediments carried by a longshore current will fall out where the current dissipates, forming a spit. An area of water isolated behind a large bar is called a lagoon. Over time, lagoons may silt up, becoming salt marshes. See also: geomorphology, earth science.

Examples

- Abidjan, Côte d'Ivoire
- Ap Lei Chau - Ap Lei Pai, Hong Kong
- Barnegat Bay, New Jersey, United States
- Cape Canaveral, Florida, United States
- Cape St. Paul, Ghana
- Cheung Chau, Hong Kong
- Galveston Island, Texas, United States
- Great Yarmouth, England
- Lung Kwu Chau, Hong Kong
- Looe Pool, Cornwall, England
- Long Island, New York, United States
- Macao Isthmus, Macao
- Miami Beach, Florida, United States
- Minnesota Point, Duluth, Minnesota, United States
- Ninety Mile Beach, Victoria, Australia
- Ocean City, Maryland, United States
- Padre Island, Texas, United States
- Pamlico Sound, North Carolina, United States
- Port Said, Egypt
- Pui O, Hong Kong
- Sha Chau, Hong Kong
- Shek O Headland - Tai Tau Chau, Hong Kong
- Sriharikota, Andhra Pradesh, India
- Stinson Beach, California, USA
- The Coorong, South Australia, Australia
- Twin Lakes, California, United States
- Wadden islands, also known as West Frisian Islands, along the Dutch, German, and Danish coasts. The largest group of barrier islands on Earth.
- Winona, Minnesota, United States
- Yim Tin Tsai - Ma Shi Chau, Hong Kong

References

- Bascom, W. 1980. Waves and Beaches. Anchor Press/Doubleday, Garden City, New York. 366 p. Category:Landforms

Geography

)]] Geography is the study of the locational and spatial variation of both natural and human phenomena on Earth. The word derives from the Greek words Ge (γη) or Gaea (γεια), both meaning "Earth", and graphein (γραφειν) meaning "to describe" and "to write". Modern geography is a diverse discipline that draws influence from almost every other arena of knowledge. Geographers engage with other disciplines according to their particular research interests and, while subjects such as biology and economics have a powerful influence, there are geographers who use concepts taken from subjects such as sociology, psychology and sports science, among many others. Within the discipline there have been many long-running tensions among those seeking to define geography - whether as a 'science' or as a 'humanity', as a 'systematic' subject or 'regional' specialism and so forth - which at various times have come close to destroying geography as an academic discipline. Whilst profound differences do exist among geographers, the dual concepts of space and place provide a commonality of interest, which gives the subject a unique identity.

Structure of geography

William Hughes - who taught the geography of the Holy Lands to divinity students at King's College London - defined geography in an address in 1863: :"Mere place names are not geography. To know by heart a whole gazeteer full of them would not, in itself, constitute anyone a geographer. Geography has higher aims than this: it seeks to classify phenomena (alike of the natural and of the political world insofar as it treats of the latter) to compare, to generalise, to ascend from effects to causes and in doing so to trace out the great laws of nature and to mark their influence upon man. In a word, geography is a science, a thing not of mere names, but of argument and reason, of cause and effect." This was a specific rejection of geography as a merely descriptive discipline and also defined it as inclusive of both the physical world and the human. Within the discipline, however, there are many areas of specialism. Modern geographers tend to specialise in one of the broad branches (or sub-branches). However, most introductory geography syllabuses seek to ensure that geographers have at least working knowledge of the main focus of each branch of the subject.

Physical geography

Physical geography (or physiogeography) focuses on geography as an Earth science. It aims to understand the physical layout of the Earth, its weather and global flora and fauna patterns. Many areas of physical geography make use of geology, particularly in the study of weathering and sediment movement. Physical Geography can be divided into the following broad categories:
- Geomorphology
- Hydrology
- Glaciology
- Biogeography
- Climatology
- Pedology (soil study)
- Coastal/Marine studies
- Geodesy
- Palaeogeography
- Environmental Geography and management
- Landscape ecology Exact lines between these different areas are often difficult to draw. Sometimes Oceanography is included as a branch within physical geography, but is now considered a separate subject in its own right. Related topics: Atmosphere - Archipelago - Continent - Desert - Island - Landform - Ocean - Sea - River - Lake - Ecology - Soil - Timeline of geography, paleontology - Geostatistics - Environmental science - Oceanography - Environmental studies

Human geography

Human geography is a branch of geography that focuses on the study of patterns and processes that shape human interaction with various environments. It encompasses human, political, cultural, social, and economic aspects. While the major focus of human geography is not the physical landscape of the Earth (see Physical geography) it is hardly possible to discuss human geography without referring to the physical landscape on which human activities are being played out, and environmental geography is emerging as a link between the two. Human geography can be divided into broad categories, such as:
- Economic geography
- Development geography
- Population geography or Demography
-
- Urban geography
- Social geography
- Behavioral geography
- Cultural geography
- Political geography, including Geopolitics
-
- Historical geography
- Regional science
- Strategic geography
- Military geography
- Feminist geography
- Distinction between these fields of study have become increasingly blurred over time and the above list should not be considered definitive. Related topics: Countries of the world - Country - Nation - State - Personal union - Province - County - City - Municipality - Central place theory - Urban morphology

Socio-environmental geography

During the time of environmental determinism, geography was defined not as the study of spatial relationships, but as the study of how humans and the natural environment interact. Though environmental determinism has died out, there remains a strong tradition of geographers addressing the relationships between people and nature. There are two main subfields of socio-environmental geography:
- cultural and political ecology (CAPE) and
- risk-hazards research.

Cultural and political ecology

Cultural ecology grew out of the work of Carl Sauer in geography and a similar school of thought in anthropology. It examined how human societies adapt themselves to the natural environment. Sustainability science has been one important outgrowth of this tradition. Political ecology arose when some geographers used aspects of critical geography to look at relations of power and how they affect people's use of the environment. For example, an influential study by Michael Watts argued that famines in the Sahel are caused by the changes in the region's political and economic system as a result of colonialism and the spread of capitalism.

Risk-hazards research

Research on hazards began with the work of geographer Gilbert F. White, who sought to understand why people live in disaster-prone floodplains. Since then, the hazards field has expanded to become a multidisciplinary field examining both natural hazards (such as earthquakes) and technological hazards (such as nuclear reactor meltdowns). Geographers studying hazards are interested in both the dynamics of the hazard event and how people and societies deal with it.

Historical geography

This branch seeks to determine how cultural features of the multifarious societies across the planet evolved and came into being. Study of the landscape is one of many key foci in this field - much can be deduced about earlier societies from their impact on their local environment and surroundings. ; What's in a name? Historical geography and the Berkeley School "Historical Geography" can indeed refer to the reciprocal effects of geography and history on each other. But in the United States, it has a more specialized meaning: This is the name given by Carl Ortwin Sauer of the University of California, Berkeley to his program of reorganizing cultural geography (some say all geography) along regional lines, beginning in the first decades of the 20th Century. To Sauer, a landscape and the cultures in it could only be understood if all of its influences through history were taken into account: Physical, cultural, economic, political, environmental. Sauer stressed regional specialization as the only means of gaining expertise on regions of the world. Sauer's philosophy was the principal shaper of American geographic thought in the mid-20th century. Regional specialists remain in academic geography departments to this day. But many geographers feel that it harmed the discipline in the long run: Too much effort was spent on data collection and classification, and too little on analysis and explanation. Studies became more and more area specific as later geographers struggled to find places to make names for themselves. This probably led in turn to the 1950s crisis in Geography which nearly destroyed it as an academic discipline.

History of geography

:See main article: History of geography History of geography The Greeks are the first known culture to actively explore geography as a science and philosophy. Mapping by the Romans as they explored new lands added new techniques. During the Middle Ages, Arabs such as Idrisi, Ibn Batutta, and Ibn Khaldun maintained the Greek and Roman techniques and developed new ones. Following the journeys of Marco Polo, interest in geography spread throughout Europe. The great voyages of exploration in 16th and 17th centuries revived a desire for both accurate geographic detail, and more solid theoretical foundations. This period is also known as Great Geographical Discoveries. By the 18th century, geography had become recognized as a discrete discipline and became part of a typical university curriculum in Europe (especially Paris and Berlin). Over the past two centuries the quantity of knowledge and the number of tools has exploded. There are strong links between geography and the sciences of geology and botany, as well as economics, sociology and demographics. In the West during the 20th century, the discipline of geography went through four major phases: environmental determinism, regional geography, the quantitative revolution, and critical geography.
Geographic techniques
As spatial interrelationships are key to this synoptic science, maps are a key tool. Classical cartography has been joined by a more modern approach to geographical analysis, computer-based geographic information systems (GIS).
- Cartography studies the representation of the Earth's surface with abstract symbols (map making). Although other subdisciplines of geography rely on maps for presenting their analyses, the actual making of maps is abstract enough to be regarded separately. Cartography has grown from a collection of drafting techniques into an actual science. Cartographers must learn cognitive psychology and ergonomics to understand which symbols convey information about the Earth most effectively, and behavioral psychology to induce the readers of their maps to act on the information. They must learn geodesy and fairly advanced mathematics to understand how the shape of the Earth affects the distortion of map symbols projected onto a flat surface for viewing. It can be said, without much controversy, that cartography is the seed from which the larger field of Geography grew. Most geographers will cite a childhood fascination with maps as an early sign they would end up in the field. mathematics
- Geographic Information Systems deals with the storage of information about the Earth for automatic retrieval by a computer, in an accurate manner appropriate to the information's purpose. In addition to all of the other subdisciplines of geography, GIS specialists must understand computer science and database systems. GIS has so revolutionized the field of cartography that nearly all mapmaking is now done with the assistance of some form of GIS software.
- Geographic quantitative methods deal with numerical methods peculiar to (or at least most commonly found in) geography. In addition to spatial analyses, you are likely to find things like cluster analysis, discriminant analysis, and non-parametric statistical tests in geographic studies.
- Geographic qualitative methods, or ethnographic research techniques, are used by human geographers. In cultural geography there is a tradition of employing qualitative research techniques also used in anthropology and sociology. Participant Observation and in-depth interviews provide human geographers with qualitative data. In their study geographers use four interrelated approaches:
- Systematic - Groups geographical knowledge into categories that can be explored globally
- Regional - Examines systematic relationships between categories for a specific region or location on the planet.
- Descriptive - Simply specifies the locations of features and populations.
- Analytical - Asks why we find features and populations in a specific geographic area.
Related fields

Urban and regional planning
Urban planning and regional planning use the science of geography to assist in determining how to develop (or not develop) the land to meet particular criteria, such as safety, beauty, economic opportunities, the preservation of the built or natural heritage, etcetera. The planning of towns, cities and rural areas may be seen as applied geography although it also draws heavily upon the arts, the sciences and lessons of history. Some of the issues facing planning are considered briefly under the headings of rural exodus, urban exodus and Smart Growth.
Regional science
In the 1950s the regional science movement arose, led by Walter Isard to provide a more quantitative and analytical base to geographical questions, in contrast to the more qualitative tendencies of traditional geography programs. Regional Science comprises the body of knowledge in which the spatial dimension plays a fundamental role, such as regional economics, resource management, location theory, urban and regional planning, transport and communication, human geography, population distribution, landscape ecology, and environmental quality.
Reference

See also

- List of geography topics
- Geographical terms
- List of countries
- Geography reference tables
- Map
- Geographical renaming
- Geographic magazines
- National Geographic Society (United States)
- National Geographic Bee (United States)
- Point of Beginning
- Royal Geographical Society (United Kingdom)
External links

- [http://www.confluence.org/ Confluence.org - A work in progress, involving travelling to every point on the globe where the lines of longitude and latitude intersect and taking a photograph in each direction.]
- [http://www.aag.org/ Association of American Geographers]
- [http://www.gisuser.com/ GISuser.com, information-rich portal about GIS]
- [http://www.populationdata.net/ PopulationData.net]
- [http://www.freemaps.de/ Free Maps Germany]
- [http://www.ericdigests.org/1996-4/high.htm Using Literature To Teach Geography in High Schools. ERIC Digest.]
- [http://ericdigests.org/1992-5/geography.htm Teaching Geography at School and Home. ERIC Digest.]
- [http://ericdigests.org/1996-1/geography.htm The National Geography Content Standards. ERIC Digest.]
- [http://www.geo-guide.de Geo-Guide] extensive list of academic resources on geography and earth science
- [http://www.geopium.org Geopium: Geopolitics of Illicit Drugs in Asia]
- [http://www.nationalgeographic.com/ National Geographic Online]
- [http://www.rgs.org Royal Geographical Society]
- [http://www.rcgs.org Royal Canadian Geographical Society]
- [http://www.canadiangeographic.ca Canadian Geographic]
- [http://hypergeo.free.fr Hypergeo : Geographical Encyclopedia]
- [http://www.rare-maps.com/links.cfm Antique and Rare Maps - Art Source International] - Links to rare and antique maps and to cartography resources.
- [http://www.mapinfo.com/ MapInfo GIS Software]
- Category:School subjects als:Geografie ko:지리학 ms:Geografi ja:地理学 simple:Geography th:ภูมิศาสตร์

Linear

:See also linearity (computer and video games) The word linear comes from the Latin word linearis, which means created by lines.

Mathematics

Linear functions

In mathematics, a linear function f(x) is one which satisfies the following two properties (but see below for a slightly different usage of the term):
- Additivity property (also called the superposition property): f(x + y) = f(x) + f(y). This says that f is a group isomorphism with respect to addition.
- Homogeneity property: f(αx) = αf(x) for all α. In this definition, x is not necessarily a real number, but can in general be a member of any vector space. The concept of linearity can be extended to linear operators. Important examples of linear operators include the derivative considered as a differential operator, and many constructed from it, such as del and the Laplacian. When a differential equation can be expressed in linear form, it is particularly easy to solve by breaking the equation up into smaller pieces, solving each of those pieces, and adding the solutions up. Nonlinear equations and functions are of interest to physicists and mathematicians because they are hard to solve and give rise to interesting phenomena such as chaos. Linear algebra is the branch of mathematics concerned with the study of vectors, vector spaces (or linear spaces), linear transformations, and systems of linear equations. See also: linear element, linear system, nonlinearity.

Linear polynomials

In a slightly different usage to the above, a polynomial of degree 1 is said to be linear, because the graph of a function of that form is a line. Over the reals, a linear function is one of the form: : f(x) = m x + c m is often called the slope or gradient; c the y-intercept, which gives the point of intersection between the graph of the function and the y-axis. Note that this usage of the term linear is not the same as the above, because linear polynomials over the real numbers do not in general satisfy either additivity or homogeneity. In fact, they do so if and only if c = 0. Hence, if c ≠ 0, the function is often called an affine function (see in greater generality affine transformation).

Physics

In physics, linearity is a property of the differential equations governing a lot of systems (like, for instance Maxwell equations or the diffusion equation). Namely, linearity of a differential equation means that if two functions f and g are solution of the equation, then their sum f+g is also a solution of the equation.

Electronics

In electronics, the linear operating region of a transistor is where the collector-emitter current is related to the base current by a simple scale factor, enabling the transistor to be use as an amplifier that preserves the fidelity of audio signals. Linear is similarly used to describe regions of any function, mathematical or physical, that follow a straight line with arbitrary slope.

Music

In music the linear aspect is succession, either intervals or melody, as opposed to simultaneity or the vertical aspect.

Landform

A landform comprises a geomorphological unit. Landforms are categorised by characteristics such as elevation, slope, orientation, stratification, rock exposure, and soil type. Landforms by name include berms, mounds, hills, cliffs, valleys, and so forth. Oceans and continents exemplify highest-order landforms. A number of factors, ranging from plate tectonics to erosion and deposition can generate and affect landforms. Biological factors can also influence landforms -- see for example the role of plants in the development of dune systems and salt marshes, and the work of corals and algae in the formation of coral reefs. coral reefs

List of landforms

- alas
- continent
- limestone pavement
- plain and plateau
- rock formations

Erosion landforms

Landforms produced by erosion and weathering usually occur in coastal or fluvial environments, and many appear above under those headings. Some other erosion landforms that do not fall into the above categories include:
- canyon
- cave
- limestone pavement
- tea table
- Deposition landform -- landforms produced by deposition of load or sediment (usually coastal or fluvial).
- Eolian landform - landforms produced by wind weathering.

External links

- [http://www.deh.gov.au/settlements/industry/minerals/booklets/landform/ Landform Design] Category:Geomorphology ja:地形

Water

:This article focuses on water as it is experienced in everyday life. See water (molecule) for information on the chemical and physical properties of pure water (H₂O, hydrogen oxide). Water (from the Old English word wæter; c.f German "Wasser", from PIE
- wod-or, "water") is a tasteless, odorless, and nearly colorless (it has a slight hint of blue) substance in its pure form that is essential to all known forms of life and is known also as the most universal solvent. Water is an abundant substance on Earth. It exists in many places and forms. It appears mostly in the oceans and polar ice caps, but also as clouds, rain water, rivers, freshwater aquifers, and sea ice. On the planet, water is continuously moving through the cycle involving evaporation, precipitation, and runoff to the sea. Water fit for human consumption is called potable water. This natural resource is becoming more scarce in certain places as human population in those places increases, and its availability is a major social and economic concern.

Molecular properties

Forms of water

potable water] Water takes many different shapes on earth: water vapor and clouds in the sky, waves and icebergs in the sea, glaciers in the mountain, aquifers in the ground, to name but a few. Through evaporation, precipitation, and runoff, water is continuously flowing from one form to another, in what is called the water cycle. Because of the importance of precipitation to agriculture, and to mankind in general, different names are given to its various forms: while rain is common in most countries, other phenomena are quite surprising when seen for the first time. Hail, snow, fog or dew are examples. When appropriately lit, water drops in the air can refract sunlight to produce rainbows. Similarly, water runoffs have played major roles in human history as rivers and irrigation brought the water needed for agriculture. Rivers and seas offered opportunity for travel and commerce. Through erosion, runoffs played a major part in shaping the environment providing river valleys and deltas which provide rich soil and level ground for the establishment of population centers. Water also infiltrates the ground and goes into aquifers. This groundwater later flows back to the surface in springs, or more spectacularly in hot springs and geysers. Groundwater is also extracted artificially in wells. Because water can contain many different substances, it can taste or smell very differently. In fact, humans and other animals have developed their senses to be able to evaluate the drinkability of water: animals generally dislike the taste of salty sea water and the putrid swamps and favor the purer water of a mountain spring or aquifer.

Water in biology

From a biological standpoint, water has many distinct properties that are critical for the proliferation of life that set it apart from other substances. Water carries out this role by allowing organic compounds to react in ways that ultimately allows replication. It is a good solvent and has a high surface tension, and thus allows organic compounds and living things to be transported in it. Fresh water has its greatest density at 4°C, then becoming less dense as it freezes or heats up from this point. As a stable, polar molecule prevalent in the atmosphere, it plays an important atmospheric role as an absorber of infrared radiation, crucial in the atmospheric greenhouse effect without of which, the average surface temperature would be −18° Celsius. Water also has an unusually high specific heat, which plays many roles in regulating global and regional climate, such as the Gulf Stream climate, allowing life to survive. Water is a very good solvent, chemically not unlike ammonia, and dissolves many types of substances, such as various salts and sugar, and facilitates their chemical interaction, which aids complex metabolisms. Some substances, however, do not mix well with water, including oils and other hydrophobic substances. Cell membranes, composed of lipids and proteins, take advantage of this property to carefully control interactions between their contents and external chemicals. This is facilitated somewhat by the surface tension of water. Water drops are stable due to the high surface tension of water caused by the strong intermolecular forces called cohesive forces. This can be seen when small quantities of water are put onto a nonsoluble surface such as polythene: the water stays together as drops. On extremely clean glass the water may form a thin film because the molecular forces between glass and water molecules (adhesive forces) are stronger than the cohesive forces. This property plays a key role in plant transpiration. A simple but environmentally important and unique property of water is that its common solid form, ice, floats on the liquid. This solid phase is less dense than liquid water, due to the geometry of the strong hydrogen bonds which are formed only at lower temperatures. For almost all other substances and for all other 11 uncommon phases of water ice except ice-XI, the solid form is more dense than the liquid form. Fresh water is most dense at 4°C, and will sink by convection as it cools to that temperature, and if it becomes colder it will rise instead. This reversal will cause deep water to remain warmer than shallower freezing water, so that ice in a body of water will form first at the surface and progress downward, while the majority of the water underneath will hold a constant 4°C. This effectively insulates a lake floor from the cold. While this behavior may seem obvious, even intuitive, it should be noted that almost all other chemicals are denser as solids than they are as liquids, and freeze from the bottom up. Life on earth has evolved with and adapted itself to the important features of water. The existence of abundant liquid, vapor and solid forms of water on Earth has been an important factor in the abundant colonization of Earth's various environments by life-forms adapted to those varying and often extreme conditions. Civilizations have historically flourished around rivers and major waterways; Mesopotamia, the so-called cradle of civilization, is situated between two major rivers. Large metropolises like London, Paris, New York, and Tokyo owe their success in part to their easy accessibility via water and the resultant expansion of trade. Islands with safe water ports, like Singapore and Hong Kong, have flourished for precisely this reason. In places such as North Africa and the Middle East, where water is scarcer, access to clean drinking water was and is a major factor in human development.

Astronomical position of Earth and impact on its water

Mesopotamia The coexistence of the solid, liquid, and gaseous phases of water on Earth is vital to the origin, evolution, and continued existence of life on Earth. However, if the Earth's location in the solar system were even marginally closer or further from the Sun (ie, a million miles or so), the conditions which allow the three forms to be present simultaneously would be far less likely to exist. Earth's mass allows gravity to hold an atmosphere. Water vapor and carbon dioxide in the atmosphere provides a greenhouse effect which helps maintain a relatively steady surface temperature. If Earth were less massive, a thinner atmosphere would cause temperature extremes preventing the accumulation of water except in polar ice caps (as on Mars). According to the solar nebula model of the solar system's formation, Earth's mass may be largely due to its distance from the Sun. The distance between Earth and the Sun and the combination of solar radiation received and the greenhouse effect of the atmosphere ensures that its surface is neither too cold nor too hot for liquid water. If Earth were more distant, most water would be frozen. If Earth were nearer to the Sun, its higher surface temperature would limit the formation of ice caps, or cause water to exist only as vapor. In the former case, the low albedo of oceans would cause Earth to absorb more solar energy. In the second case, a runaway greenhouse effect and inhospitable conditions similar to Venus would result. It has been proposed that life itself may maintain the conditions that have allowed its continued existence. The surface temperature of Earth has been relatively constant through geologic time despite varying solar flux, indicating that a dynamic process governs Earth's temperature via a combination of greenhouse gases and surface or atmospheric albedo. This proposal is known as the Gaia hypothesis.

Human uses of water

Gaia hypothesis All known forms of life depend on water. Water is a vital part of many metabolic processes within the body. Significant quantities of water are used during the digestion of food. (Note however that some bacteria and plant seeds can enter a cryptobiotic state for an indefinite period when dehydrated, and come back to life when returned to a wet environment) About 72% of the fat free mass of the human body is made of water. To function properly the body requires between one and seven litres of water per day to avoid dehydration, the precise amount depending on the level of activity, temperature, humidity, and other factors. It is not clear how much water intake is needed by healthy people. However, for those who do not have kidney problems, it is rather difficult to drink too much water, but (especially in warm humid weather and while exercising) dangerous to drink too little. People do often drink far more water than necessary while exercising, however, putting them at risk of water intoxication, which is frequently fatal. The "fact" that a person should consume eight glasses of water per day cannot be traced back to a scientific source. However, leading dieticians and nutritionists will tell you that this is the RDI (Recommended Daily Intake) of water. [http://ajpregu.physiology.org/cgi/content/full/283/5/R993]. The latest dietary reference intake report by the National Research Council recommended 2.7 liters of water total (including food sources) for women and 3.7 liters for men[http://www.iom.edu/report.asp?id=18495]. Water is lost from the body in urine and feces, through sweating, and by exhalation of water vapor in the breath. Humans require water that does not contain too much salt or other impurities. Common impurities include chemicals and/or harmful bacteria, such as crypto sporidium. Some solutes are acceptable and even desirable for perceived taste enhancement and to provide needed electrolytes.

Water as a precious resource

:See water resources for information about fresh water supplies. fresh water Because of the growth of world population and other factors, the availability of drinking water per capita is shrinking. The issue of water shortage can be solved through more production, better distribution and less waste of it. For this reason, water is a strategic resource for many countries. Many battles and wars, such as the Six-Day War in the Middle East, have been fought to gain access to it. Experts predict more trouble ahead because of the world's growing population, increasing contamination through pollution, and global warming. UNESCO's World Water Development Report (WWDR, 2003) from its World Water Assessment Program indicates that, in the next 20 years, the quantity of water available to everyone is predicted to decrease by 30%. 40% of the world's inhabitants currently have insufficient fresh water for minimal hygiene. More than 2.2 million people died in 2000 from diseases related to the consumption of contaminated water or drought. In 2004, the UK charity WaterAid reported that a child dies every 15 seconds due to easily preventable water-related diseases. Some have predicted that clean water will become the "next oil", making Canada, with this resource in abundance, possibly the richest country in the world.

Regulating water distribution

Drinking water is often collected at springs or extracted from artificial borings in the ground, or wells. Building more wells in adequate places is thus a possible way to produce more water assuming the aquifers can supply an adequate flow. Other water sources are the rainwater and river or lake water. This surface water, however, must be purified for human consumption. This may involve removal of undissolved substances, dissolved substances and harmful microbes. Popular methods are filtering with sand which only removes undissolved material while chlorination and boiling kill harmful microbes. Distillation does all three functions. More advanced techniques exist, such as reverse osmosis. Desalination of abundant ocean or seawater is a more expensive solution used in coastal arid climates. The distribution of drinking water is done through municipal water systems or as bottled water. Governments in many countries have programs to distribute water to the needy at no charge. Others argue that the market mechanism and free enterprise are best to manage this rare resource, and to finance the boring of wells or the construction of dams and reservoirs. Reducing waste, that is using drinking water only for human consumption, is another option. In some cities, such as Hong Kong, sea water is extensively used for flushing toilets citywide in order to conserve fresh water resources. Polluting water may be the biggest single misuse of water; to the extent that a pollutant limits other uses of the water, it becomes a waste of the resource, regardless of benefits to the pollutor. Pharmaceuticals consumed by humans often end up in the waterways and can have detrimental effects on aquatic life if they bioaccumulate and if they are not biodegradable.

The impact of water on human culture

Water is considered a purifier in most religions, including Christianity, Islam, Judaism, and Shinto. For instance, baptism in Christian churches is done with water. In addition, a ritual bath in pure water is performed for the dead in many religions including Judaism and Islam. In Islam, the daily Salah can only be done after ablution (Wodoo), that is, washing parts of the body in clean water. In Shinto, water is used in almost all rituals to cleanse a person or an area. Water is often believed to have spiritual powers. In Celtic mythology, Sulis is the local goddess of thermal springs; in Hinduism, the Ganga is also personified as a goddess. Alternatively, gods can be patrons of particular springs, river or lakes: for example in Greek and Roman mythology, Peneus was a river god, one of the three thousand Oceanids. The Greek philosopher Empedocles held that water is one of the four classical elements along with fire, earth and air, and was regarded as the ylem, or basic stuff of the universe. Water was considered cold and moist. In the theory of the four bodily humours, water was associated with phlegm. Water was also one of the Five Elements in traditional Chinese philosophy, along with earth, fire, wood, and metal. A common misconception about water is that it is a powerful conductor of electricity. Any electrical properties observable in water are due to the ions of mineral salts and carbon dioxide dissolved in it. Water does self-ionize (two water molecules become one hydroxide anion and one hydronium cation), but only at a very slight, almost immeasurable level. Pure water can also be electrolized into oxygen and hydrogen gases but without any dissolved ions, this is a very slow process and thus very little current is conducted. Many bottled water companies exploit another common misconception, advertising both purity and taste, even though pure water is tasteless.

External links

- [http://www.lsbu.ac.uk/water/phase.html Phase diagrams of water]
- [http://www.publicforuminstitute.org/issues/oceans/index.htm Oceans and Water Issues Page]
- [http://www.greenfacts.org/water-disinfectants/index.htm Scientific Facts on Water disinfectants] A faithful summary by GreenFacts of a leading scientific consensus report on Drinking Water Disinfectants published by the International Programme on Chemical Safety of the WHO.
- [http://www.hkc22.com/residentialwater.html Residential water problems and markets] Study paper from Helmut Kaiser Consultancy
- [http://www.hkc22.com/watermarketsworldwide.html Water markets worldwide] Study paper from Helmut Kaiser Consultancy
- [http://www.worldwaterforum.org/ World Water Forum]
- [http://www.unesco.org/water/wwap/ World Water Assessment Program]
- [http://unesdoc.unesco.org/images/0012/001295/129556e.pdf United Nations' World Water Development Report]
- [http://www.gemswater.org/ United Nations GEMS/Water Programme]
- [http://www.lsbu.ac.uk/water/ Water Structure and Behaviour]
- [http://www.wateraid.org/ WaterAid]
- [http://www.sahra.arizona.edu/newswatch/ SAHRA—Global Water Newswatch]
- [http://www.siwi.org/ Stockholm International Water Institute] (SIWI)
- [http://www.c-win.org/ California Water Impact Network (C-WIN)]
- [http://news.bbc.co.uk/2/hi/science/nature/3752590.stm BBC: The water debate]
- [http://www.geocities.com/tapvsbottled/ Tap Water Vs Bottled Water] - Interesting site providing facts about tap and bottled water.
- [http://www.emagazine.com/september-october_2003/0903feat1.html E the Environmental Magazine piece on bottled water] (Oct 2003).
- [http://www.iapws.org/ International Association for the Properties of Water and Steam]
- [http://ga.water.usgs.gov/edu/watercycle.html US Geological Survey: Comprehensive discussion of the water cycle, in many languages]
- [http://www.dartmouth.edu/~etrnsfer/water.htm Why is water blue?]
- [http://www.water.org.uk/home/resources-and-links/water-for-health/ask-about/adults Water requirements in adults]
- [http://www.hkc22.com/environmentaltechnology.html/ Climate change raises markets for environmental technology, drinking water and clean energies]

References

- OA Jones, JN Lester and N Voulvoulis, Pharmaceuticals: a threat to drinking water? TRENDS in Biotechnology 23(4): 163, 2005
- Category:Beverages Category:Hydrology Category:Materials Category:Natural resources Category:Nutrition zh-min-nan:Chúi als:Wasser ko:물 ja:水 ms:Air simple:Water th:น้ำ

Deposition (geology)

Deposition, also known as sedimentation, is the geological process whereby material is added to a landform. This is the process by which wind, water, or ice create a sediment deposit through the laying down of granular material that has been eroded and transported from another geographical location. Deposition occurs when the forces responsible for sediment transportation are no longer sufficient to overcome forces of particle weight and friction that resist motion. Deposition can also refer to the build up of a sediment from organically derived matter or chemical processes. For example, chalk is made up partly of the microscopic calcium carbonate skeletons of marine plankton, the deposition of which have induced chemical processes to deposit further calcium carbonate. Category:Geological processes

Particles

In physics, a particle is an object, or body, with only a few degrees-of-freedom, including position, and perhaps orientation in space. The homogeneity and isotropy of space, being symmetries with respect to translation and rotation, may provide for particle properties such as momentum and angular momentum. These are common to classical mechanics and quantum mechanics. Certain internal degrees-of-freedom provide fixed physical properties, such as (electric) charge, or variable ones, such as spin angular momentum, most of which can only be understood within quantum mechanics.

Lake

A Lake is a body of water surrounded by land. The majority of lakes are fresh water, and most lie in the northern hemisphere at higher latitudes. Large lakes are sometimes referred to as "inland seas" and small seas are sometimes referred to as lakes. The term lake is also used to describe a feature such as Lake Eyre, which is dry most of the time but becomes filled under seasonal conditions of heavy rainfall. Many lakes are artificial and are constructed for hydro-electric power supply, recreation (swimming, wind surfing,...), water supply, etc. Finland is known as The Land of the Thousands Lakes (actually there are 187,888 lakes in Finland, 60,000 of them are big ones) and Minnesota is known as The Land of Ten Thousand Lakes. The Great Lakes of North America originated in the ice age. Over 60% of the world's lakes are in Canada; this is because of the deranged drainage system that dominates the country.

Origin of natural lakes

Most lakes are young, as the natural results of erosion will tend to wear away one of the basin sides containing the lake. There are a number of natural processes that can form lakes. A recent tectonic uplift of a mountain range can create bowl-shaped depressions that accumulate water and form lakes. The advance and retreat of glaciers can scrape depressions in the surface where lakes accumulate. Such lakes are common in Scandinavia, Siberia and Canada. Lakes can also form by means of landslides or by glacial blockages. An example of the latter occurred during the last ice age in the state of Washington, when a huge lake formed behind a glacial flow. When the ice retreated, the result was an immense flood that created the Dry Falls Monument at Sun Lakes, Washington. Saline lakes can form where there is no natural outlet or the water evaporates rapidly, and the drainage surface of the water table has a higher than normal salt content. Examples of salt lakes include the Great Salt Lake, the Caspian Sea and the Dead Sea. Small, crescent-shaped lakes called oxbow lakes can form in river valleys as the result of meandering. The slow-moving river forms a sinuous shape as the outer side of bends is torn away more rapidly than the inner side. Eventually a horseshoe bend is formed and the river cuts through the narrow neck. This gap now forms the main passage for the river and the ends of the bend become silted up. Lake Vostok is an under-ice lake in Antarctica, possibly the largest in the world. The pressure from ice and the internal chemical composition means that if the lake were drilled into, it may result in a fissure and spraying in the same manner as a shaken can of soda. Some lakes, like Lake Baikal and Lake Tanganyika are volcanic in origin, and lie on geological fault lines. The Crater Lake in Oregon is a lake located within the caldera of an extinct volcano. Some lakes come into existence as a result of sinkhole activity.

Characteristics

The change in level of a lake is controlled by the difference between the sources of inflow and outflow, compared to the total volume of the lake. The significant input sources are precipitation onto the lake; runoff carried by streams and channels from the lake's catchment area; groundwater channels and aquifers, and man-made sources from outside the catchment area. Output sources are evaporation from the lake; surface and groundwater flows, and any extraction of lake water by humans. As climate conditions and human water requirements vary, these will create fluctuations in the lake level. Lakes can be categorized on the basis of their richness of nutrients, which typically effects plant growth. Nutrient poor lakes are said to be oligotrophic, and are generally clear, having a low concentration of plant life. Mesotropic lakes have good clarity and an average level of nutrients. Eutrophic lakes are enriched with nutrients, resulting in good plant growth and possible algal blooms. A hypertrophic lake is a water body that has been highly enriched with nutrients. These lakes typically have poor clarity and are subject to algal blooms. Lakes typically reach this condition due to human activities, such as heavy use of fertilizers in the lake catchment area. Such lakes are of little use, and have a poor ecosystem.

Types of lakes

A periglacial lake is one in which part of its margin is formed by an ice sheet, ice cap or glacier, the ice having obstructed the natural drainage of the land. A subglacial lake is one which is permanently covered by ice. They can occur under glaciers and ice caps or ice sheets. There are many such lakes, but Lake Vostok in Antarctica is by far the largest. The are kept liquid because the overlying ice acts as a thermal insulator retaining energy introduced to its underside by friction, water percolating through crevasses, by the pressure from the mass of the ice sheet above or by geothermal heating below. Because of the unusual relationship between water's temperature and its density, the water in lakes in temperate climates mixes twice a year. Fresh water is most dense at about 4 degrees Celsius. When the temperature of the water at the surface of a lake reaches the temperature at which water is most dense all the water in the lake can mix, bringing oxygen starved water up from the depths, and bringing oxygen down to decomposing sediments. When the density of surface water differs from that of the deeper water there is a marked barrier layer, the thermocline, that prevents mixing. Deep Temperate lakes can maintain a reservoir of cold water year-round. The reservoir of deep, cold water allows cities to tap that reservoir for deep lake water cooling. Since the water of deep tropical lakes never reaches the temperature where water reaches its maximum density, there is no process that makes the water mix. The deeper layer becomes oxygen starved, and can become saturated with carbon dioxide, and possibly other gases, like sulfur dioxide, if there is even a trace of volcanic activity. Exceptional events, like earthquakes or landslides, which do cause mixing, that brings up the deep layers, can release a vast cloud of toxic gas. The amount of gas that can be dissolved in water is pressure related. As the water surfaces, and the pressure drops, a vast amount of gas cab comes out of solution. Under these circumstances even carbon dioxide is toxic. Carbon dioxide is heavier than air, and the released carbon dioxide flows down the river valley.

Artificial lakes

A reservoir (French: réservoir) is an artificial lake created by flooding land behind a dam. Some of the world's largest lakes are reservoirs. Artificial lakes can also be made deliberately by digging one or by flooding an open-pit mine.

Abiotic and biotic limnology

mine Limnology divides lakes in three zones: littoral zone, which is a sloped area that is close to land; open-water zone, where sunlight is abundant; and deep-water zone, where little sunlight can reach. The depth which light can reach in lakes depends on the density and motion of particles. These particles can be sedimentary or biological in origin and are responsible for the color of the water. Decaying plant matter for instance is responsible for a yellow or brown color, while algae result in greenish water. In very shallow water bodies, iron oxides make water reddish brown. Biological particles are algae and detritus. A sediment particle is in suspension if its weight is less than the random turbidity forces acting upon it. The turbidity is a decisive factor in the transparency of the water. Bottom-dwelling detritivorous fish are responsible for turbid waters, because they stir the mud in search for food. Piscivorous fish eat plant-eating (planktonivorous) fish, thus increasing the number of algae (see aquatic trophic cascade). The light depth or transparency is measured by using a Secchi disk. This is a 20 cm disk with alternating white and black quadrants. The depth at which the disk is no longer visible, is the Secchi depth, and is a measure for transparency. It is commonly used to test eutrophication. A lake moderates the surrounding region's temperature and climate because water has a very high specific heat capacity (4186). In the daytime, the lake can cool the land beside it with local winds, resulting in a sea breeze; in the night, it can warm it, forming a land breeze.

How lakes disappear

A lake may be infilled with deposited sediment, and gradually, the lake becomes a wetland, such as a swamp or marsh. An important difference exists between lowland and highland lakes: lowland lakes are more placid, are less rocky/more sedimentary, have a less sloping bottom, and generally contain more plant life. Large water plants (typically reeds) accelerate this closing process significantly because they trap sediment. Turbid lakes, and lakes with much plant-eating fish, tend to disappear slower. A "disappearing" lake (barely noticeable on a human timescale) typically has a water's edge with extensive plant mats. They become a new habitat for other plants (like peat moss, when conditions are right) and animals, many of which are very rare. Gradually, the lake closes, and young peat may form, forming a fen. In lowland river valleys (allowing the river to meander), the presence of peat is explained by the closing of historical oxbow lakes. In the very last stages of succession, more trees would grow in, eventually turning the wetland into a forest. Some lakes can also disappear seasonally; they are called Intermittent lakes and are typical of karstic terrain. A prime example of this is Lake Cerknica in Slovenia. On June 3, 2005 in Bolotnikovo, Russia, a lake called White Lake vanished in a short period of time (minutes). News sources reported government officials theorized that this strange phenomena may have been caused by a shift on soil underneath the lake which drained water to channels leading to Oka River. Neusiedler See, located in Austria and Hungary, dried up several times for a of number years during the past centuries. As of 2005, it is again rapidly losing water, giving rise to the fear that it will be completely dried up by 2010.

Extraterrestrial lakes

At present the surface of the planet Mars is too cold to permit pooling of liquid water on the surface. However geologic evidence appears to confirm that ancient lakes once formed on the surface. It is also possible that volcanic activity on Mars will occasionally melt the subsurface ice, forming large lakes. Under current conditions this water will quickly evaporate or freeze unless insulated in some manner, such as by a coating of volcanic ash. Jupiter's small moon Io is volcanically active due to tidal stresses, and as a result sulfur deposits have accumulated on the surface. Some photographs taken during the Galileo mission appear to show lakes of liquid sulfur on the surface. There are dark basaltic plains on the Moon, similar to lunar maria but smaller, that are called lacus (singular lacus, Latin for "lake"). They were once thought by early astronomers to be literal lakes.

Notable lakes

- The largest lake in the world by surface area is the Caspian Sea. With a surface area of 394,299 sq. km., it has a surface area greater than the next six largest lakes combined.
- The largest freshwater lake, and second largest lake altogether is Lake Superior with a surface area of 82,414 sq. km. It is also the largest lake in North America and is a part of the Great Lakes.
- The deepest lake is Lake Baikal in Siberia, with a bottom at 1,741 m (5,712 ft.) and is the world's largest freshwater lake by volume.
- The highest navigable lake is lake Titicaca, at 3821 m above sea level. It is also the second largest lake in South America.
- The world's highest lake is Lhagba Pool in Tibet at 6,368 m.
- The world's lowest lake is the Dead Sea, at 396 m (1,302 ft.) below sea level. It is also the lake with the highest salt concentration.
- The largest freshwater-lake island is Manitoulin Island on Lake Huron, with a surface area of 2,766 square km.
- The largest lake located on an island is Nettilling Lake on Baffin Island.
- Lake Toba on the island of Sumatra is located in what is probably the largest resurgent caldera on Earth.
- The largest freshwater lake in Europe is Lake Balaton, followed by Lake Geneva.
- Lake Victoria is the largest lake in Africa. It is a part of the Great Lakes of Africa.
- Lake Maracaibo is the largest lake in South America. Lake Titicaca is the largest freshwater lake in South America.
- The largest lake located completely within the boundaries of a single city is Lake Wanapitei in the city of Greater Sudbury, Ontario, Canada. Before the current city boundaries came into effect in 2001, this status was held by Lake Ramsey, also in Sudbury.
- Saimaa is the largest lake in Finland (the land of 187,888 lakes).

External links

- [http://www.highestlake.com/ Lists of the highest lakes in the US and the world]
- [http://www.mlswa.org/lkclassif1.htm Lake Classification Systems]
- [http://www.uklakes.net/ UKLakes Database]
- [http://www.midwestlakes.org/ Midwest Lakes Policy Center] Category:Bodies of water Category:Landforms ko:호수 ja:湖 simple:Lake th:ทะเลสาบ

River

:For the Second World War frigate class, see River class frigate. For the state of Nigeria, see Rivers State. MyScene.]] A river is a large natural waterway. It is a specific term in the vernacular for large streams, stream being the umbrella term used in the scientific community for all flowing natural waterways. In the vernacular, stream may be used to refer to smaller streams, as may creek, run, fork, etc. Passage via a river or stream is the usual way rainfall on land finds its way to the ocean or other large body of water such as a lake. A river consists of several basic parts, originating from headwaters or a spring at the source, that flow into the main stream. Smaller side streams that join the river are tributaries. Water flow is normally confined to a channel, with a bottom or bed between banks. The lower end of a river is its base level, commonly called its mouth, a river typically widens at its end and forms what is known as a river delta or estuary.

Topography

estuary.]]A river conducts water by constantly flowing perpendicular to the elevation curve of its bed, thereby converting the positional energy of the water into kinetic energy. Where a river flows over relatively flat areas, the river will meander: start to form loops and snake through the plain by eroding the river banks. Loops that are formed are sometimes cut off, forming a shorter river channel and leaving a remnant, oxbow lake. Rivers that carry large amounts of sediment develop conspicuous deltas at their mouths. Rivers whose mouths are in saline tidal waters may form estuaries. There are 4 main types of rivers. These types are:
- Youthful river - a river with a steep gradient that has very few tributaries and flows quickly. Its channels erode deeper rather than wider.
- Mature river - a river with a gradient that is less steep than those of youthful rivers and flows more slowly than youthful rivers. A mature river is fed by many tributaries and has more discharge than a youthful river. Its channels erode wider rather than deeper.
- Old river - a river with a low gradient and low erosive energy. Old rivers are characterized by flood plains.
- Rejuvenated river - a river with a gradient that is raised by the earth's movement. Where a river descends quickly over sloped topography, rapids with whitewater or even waterfalls occur. Rapids are often used for recreational purposes (see Whitewater kayaking). Waterfalls are sometimes used as sources of energy, via watermills and hydroelectric plants. Rivers begin at their source in higher ground, either rising from a spring, forming from glacial meltwater, flowing from a body of water such as a lake, or simply from damp, boggy places where the soil is waterlogged. They end at their base level where they flow into a larger body of water, the sea, a lake, or as a tributary to another (usually larger) river. In arid areas rivers sometimes end by losing water to evaporation and percolation into dry, porous material such as sand, soil, or pervious rock. The area drained by a river and its tributaries is called its watershed or catchment basin. (Watershed is also used however to mean a boundary between catchment basins.) Starting at the mouth of the river and following it upstream as it branches again and again the resulting river network forms a dendritic (tree-like) structure that is an example of a natural random fractal.

Biology

The flora and fauna of rivers are much different from those of the ocean because the water is fresh (non-salty). Living things in a river must be adapted to the current of the moving water.

Pollution

Human pollution of rivers is common, and very few rivers in the world today are clean of man-made substances. The most common pollutant is sewage piped into rivers, but chemical pollution is also common, and industrial accidents (and/or negligence) account for much of the destruction of riparian biomes. Heated water dumped into rivers by power plants and factories also affects river life.

Navigation

The Rhine is the busiest river in the world for transport ships. Inland vessels use the river to reach the major cities in Germany, Eastern France and Switzerland to transport bulk goods, liquids, containers AND passengers into the hinterland of the Port of Rotterdam and the ports of Amsterdam and Antwerp. Many millions of tons of goods are transported upstream yearly from these three sea ports to the industries near Nijmegen, Duisburg, Düsseldorf, Neuss, Köln, Koblenz, Mainz, Mannheim, Karlsruhe, Strasbourg, Colmar, Mulhouse and Basel. The lower part of the river is navigable for the largest inland vessels (up to 135 meters long and 17 meters wide) with an available depth of more than 2,50 even at the lower water levels. The further upstream, the more depth restrictions: at low water periods draught of ships is often limited to 1,90 m. for the stretch around Bingen (between the mouths of the Mosel and the Main). Upstream from Karlsruhe the Rhine is the border between France and Germany. The French have canalized the river by means of a series of hydropower dams and double ship locks, thus ensuring a year round navigable depth of 3.50 meters. (Source: NoorderSoft Waterways Database)

Dams

In places where the elevation changes of a river are great, dams for hydroelectric plants and other purposes are often built. This disrupts the natural flow of the river, and creates a lake behind the dam. Often the building of dams affects the whole of the river, even the part above the dam, as migrating fish are hindered (see fish ladder), waterflow is no longer bounded by seasonal changes and sediment flow is blocked. Dams are useful in many ways, such as providing HEP, acting as regulator of river flow so as to regulate the occurrence of flooding, which is especially important to wet-rice agriculture, and also to improve navigation and transport on the river. Often, dams such as Hoover Dam along Colorado River become famous tourist attractions. However, critics of dams, especially 'Green' advocates, argue that dams remove upper-river biodiversity such as through deforestation and forced migration of rural villages and indigenous tribes. Furthermore, trapping of river sediments behind the dams lead to salination and loss of nutrients for down-water fish. It also raises concern of eathquakes due to instablity of incompetent dams which have to support thousands of tonnes of sediments behind them. One very famous, and problematic, dam is the Aswan High Dam in the Nile.

Flooding

Flooding is a natural part of a river's cycles. Human activity, however, has upset the natural way flooding occurs by walling off rivers and straightening their courses. Removal of bogs, swamps and other wetlands in order to produce farmland has reduced the absorption zones for excess water and made floods into sudden disasters rather than gradual increases in water flow. In ancient Egypt, life was made possible through the floods of the Nile and the accompanying silt and sediment which enriched the fields with fresh nutrients. Nowadays, since people have built on these floodplains, floods are disasters, causing untold property loss each year. Human interference in the form of deforestation can also worsen conditions. The removal of vegetation leads to a reduction in Interception (vegetation stopping precipitation) and the 'weakening' of soil since plant roots no longer hold it together. As a result there is a reduced Infiltration capacity (how much water the soil can hold) and greater infiltration (precipitation going into the ground). This leads to faster soil saturation and therefore greater overland flow (also known as surface run off) and therefore, there are flash floods as the lag time decrease.

Logjams

Logjams are barriers within rivers, created by dead and uprooted trees. Over time, the obstruction prevents further logs to bypass, resulting in the creation of new network channels. According to author David R. Montgomery in his book, King of Fish, a logjam also causes water to buildup within a small space, forming peaceful pools within the main channel for young salmon to live within. The existence of these deep pools along with the complex web of channels creates an ideal salmon habitat. Today, many believe that the rebuilding of salmon runs is contingent upon reproducing the same environment shaped by logjams. As a result, many scientists have attempted to recreate artificial logjams. Marc Duboiski and Mike Ramsey of the Salmon Recovery Funding board staff, George Pess of the National Marine Fisheries Service, and Kevin Bauersfeld of Washington Department of Fish and Wildlife have prepared the Report to the Salmon Recovery Funding Board On the Engineered Log Jam (ELJ) Workshop ([http://iac.wa.gov/Documents/SRFB/Log_Jam_Report.pdf#search='log%20jams%20and%20salmon']), with the hope of mimicking natural logjams. Report to the Salmon Recovery Funding Board On the Engineered Log Jam (ELJ) Workshop."]]

Management

In its natural state a river may be inconvenient to man in a variety of ways. Rivers in inhabited areas have therefore been managed or controlled to make them more useful and less disrup

Bar (landform)

Sandbars and longshore bars

Bars as geological units

Examples

References

Geography

Structure of geography

Physical geography

Human geography

Socio-environmental geography

Cultural and political ecology

Risk-hazards research

Historical geography

History of geography

Geographic techniques

Related fields

Urban and regional planning

Regional science

Reference

See also

External links

Linear

Mathematics

Linear functions

Linear polynomials

Physics

Electronics

Music

See also

Landform

See also

List of landforms

Slope landforms

Coastal and oceanic landforms

Fluvial landforms

Mountain and glacial landforms

Volcanic landforms

Erosion landforms

External links

Water

Molecular properties

Forms of water

Water in biology

Astronomical position of Earth and impact on its water

Human uses of water

Water as a precious resource

Regulating water distribution

The impact of water on human culture

See also

External links

References

Deposition (geology)

Particles

See also

Lake

Origin of natural lakes

Characteristics

Types of lakes

Artificial lakes

Abiotic and biotic limnology

How lakes disappear

Extraterrestrial lakes

Notable lakes

See also

External links

River

Topography

Biology

Pollution

Navigation

Dams

Flooding

Logjams

Management