Cascadilla Creek, near Ithaca, New York in the United States, an example of an upland river habitat. Upland and lowland (freshwater ecology) From Wikipedia, the free encyclopedia In studies of the ecology of freshwater rivers, habitats are classified as upland and lowland. Contents 1 Definitions 2 Upland 3 Lowland 4 See also Definitions Upland habitats are cold, clear, rocky, fast flowing rivers in mountainous areas; lowland habitats are warm, slow flowing rivers found in relatively flat lowland areas, with water that is frequently coloured by sediment and organic matter. These classifications overlap with the geological definitions of "upland" and "lowland". In geology an "upland" is generally considered to be land that is at a higher elevation than the alluvial plain or stream terrace, which are considered to be "lowlands". The term "bottomland" refers to low-lying alluvial land near a river. Many freshwater fish and invertebrate communities around the world show a pattern of specialisation into upland or lowland river habitats. Classifying rivers and streams as upland or lowland is important in freshwater ecology as the two types of river habitat are very different, and usually support very different populations of fish and invertebrate species. Upland In freshwater ecology, upland rivers and streams are the fast flowing rivers and streams that drain elevated or mountainous country, often onto broad alluvial plains (where they become lowland rivers). However, altitude is not the sole determinant of whether a river is upland or lowland. Arguably the most important determinants are that of stream power and course gradient. Rivers with a course that drops in altitude rapidly will have faster water flow and higher stream power or "force of water". This in turn produces the other characteristics of an upland river - an incised course, a river bed dominated by bedrock and coarse sediments, a riffle and pool structure and cooler water temperatures. Rivers with a course that drops in altitude very slowly will have slower water flow and lower force. This in turn produces the other characteristics of a lowland river - a meandering course lacking rapids, a river bed dominated by fine sediments and higher water temperatures. Lowland rivers tend to carry more suspended sediment and organic matter as well, but some lowland rivers have periods of high water clarity in seasonal low flow periods. The generally clear, cool, fast-flowing waters and bedrock and coarse sediment beds of upland rivers encourage fish species with limited temperature tolerances, high oxygen needs, strong swimming ability and specialised Amazon River near Manaus, Brazil, an example of a lowland river habitat. reproductive strategies to prevent eggs or larvae being swept away. These characteristics also encourage invertebrate species with limited temperature tolerances, high oxygen needs and ecologies revolving around coarse sediments and interstices or "gaps" between those coarse sediments. Lowland The generally more turbid, warm, slow-flowing waters and fine sediment beds of lowland rivers encourage fish species with broad temperature tolerances and greater tolerances to low oxygen levels, and life history and breeding strategies adapted to these and other traits of lowland rivers. These characteristics also encourage invertebrate species with broad temperature tolerances and greater tolerances to low oxygen levels and ecologies revolving around fine sediments or alternative habitats such as submerged woody debris ("snags") or submergent macrophytes ("water weed"). See also Freshwater biology River reclamation Riparian zone Retrieved from "http://en.wikipedia.org/wiki/Upland_and_lowland_(freshwater_ecology)" Categories: Freshwater ecology | Water and the environment | Riparian | Rivers This page was last modified on 25 April 2011 at 22:39. Text is available under the Creative Commons Attribution-ShareAlike License; additional terms may apply. See Terms of use for details. Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. Deep, eroding glaciofluvial deposits alongside the Matanuska River, Alaska Fluvial From Wikipedia, the free encyclopedia Fluvial is used in geography and Earth science to refer to the processes associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluvioglacial is used.[1][2] Contents 1 Fluvial processes 2 See also 2.1 Fluvial processes 2.2 Fluvial channel patterns 2.3 Fluvial landforms 2.4 Related terms 3 References Fluvial processes Fluvial processes comprise the motion of sediment and erosion or deposition (geology) on the river bed. Erosion by moving water can happen in two ways. Firstly, the movement of water across the bed exerts a shear stress directly onto the bed. If the cohesive strength of the substrate is lower than the shear exerted, or the bed is composed of loose sediment which can be mobilized by such stresses, then the bed will be lowered purely by clearwater flow. However, if the river carries significant quantities of sediment, this material can act as tools to enhance wear of the bed (abrasion). At the same time the fragments themselves are ground down, becoming smaller and more rounded (attrition). Sediment in rivers is transported as either bedload (the coarser fragments which move close to the bed) or suspended load (finer fragments carried in the water). There is also a component carried as dissolved material. For each grain size there is a specific velocity at which the grains start to move, called entrainment velocity. However the grains will continue to be transported even if the velocity falls below the entrainment velocity due to the reduced (or removed) friction between the grains and the river bed. Eventually the velocity will fall low enough for the grains to be deposited. This is shown by the Hjulstrøm curve. A river is continually picking up and dropping solid particles of rock and soil from its bed throughout its length. Where the river flow is fast, more particles are picked up than dropped. Where the river flow is slow, more particles are dropped than picked up. Areas where more particles are dropped are called alluvial or flood plains, and the dropped particles are called alluvium. Even small streams make alluvial deposits, but it is in the flood plains and deltas of large rivers that large, geologically-significant alluvial deposits are found. The amount of matter carried by a large river is enormous. The names of many rivers derive from the color that the transported matter gives the water. For example, the Huang He in China is literally translated "Yellow River", and the Mississippi River in the United States is also called "the Big Muddy." It has been estimated that the Mississippi River annually carries 406 million tons of sediment to the sea,[3] the Huang He 796 million tons, and the Po River in Italy 67 million tons.[4] See also Fluvial processes Bradshaw model Erosion Downcutting Saltation Solution Suspension This is also related to multistory deposits Fluvial channel patterns Straight Braided Meandering Anastomosed Fluvial landforms Bar Basin Confluence Cutbank Crevasse splay Delta Esker Flood plain Fluvial terrace Gorge and Canyon Gully Island Levee Meander Ox-bow lake Point bar Plunge pool Riffle River Spring Stream Stream pool Towhead Valley (also vale) Waterfall Watershed Related terms Lacustrine - of or relating to a lake Maritime - of or relating the sea Oceanic - of or relating to an ocean Palustrine - of or relating to a marsh References 1. ^ K.K.E. Neuendorf, J.P. Mehl, Jr., and J.A. Jackson, eds., 2005, Glossary of Geology. (http://www.agiweb.org/pubs/pubdetail.html?item=300154) American Geological Institute, Alexandria, Virginia. 800 pp. 2. ^ Wilson, W.E. & Moore, J.E. 2003. Glossary of Hydrology, (http://books.google.co.uk/books?id=if- PaNVS7cAC&pg=PA84&dq=fluvioglacial+definition&lr=&ei=KaQrSpnHMIncygTF_fScBw) American Geological Institute, Springer, 248pp. 3. ^ Mathur, Anuradha; Dilip da Cunha (2001). Mississippi Floods: Designing a Shifting Landscape. New Haven, CT: Yale University Press. ISBN 0-300-08430-7 4. ^ Dill, William A. (1990). Inland fisheries of Europe. Rome, Italy: UN Food and Agriculture Organization. ISBN 92-5-102999-7. http://www.fao.org/docrep/009/t0377e/t0377e00.htm Retrieved from "http://en.wikipedia.org/wiki/Fluvial" Categories: Hydrology | Fluvial landforms | Geomorphology | Sedimentology This page was last modified on 10 June 2011 at 10:45. Text is available under the Creative Commons Attribution-ShareAlike License; additional terms may apply. See Terms of use for details. Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. Melting toe of Athabasca Glacier, Jasper National Park, Alberta, Canada. A false-color satellite photograph of the Amazon River in Brazil. River From Wikipedia, the free encyclopedia A river is a natural watercourse,[1] usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including stream, creek, brook, rivulet, tributary and rill; there is no general rule that defines what can be called a river, although in some countries or communities a stream may be defined by its size. Many names for small rivers are specific to geographic location; one example is "burn" in Scotland and northeast England. Sometimes a river is said to be larger than a creek,[2] but this is not always the case, because of vagueness in the language.[3] A river is part of the hydrological cycle. Water within a river is generally collected from precipitation through a drainage basin from surface runoff and other sources such as groundwater recharge, springs, and the release of stored water in natural ice and snowpacks (e.g., from glaciers). Potamology is the scientific study of rivers. Contents 1 Topography 1.1 Subsurface streams 1.2 Permanence of flow 2 Classification 2.1 Topographical classification 2.2 Biotic classification 2.3 Whitewater classification 2.4 Stream order classification 3 Uses 4 Ecosystem 5 Chemistry 6 Brackish water 7 Flooding 8 Flow 8.1 Direction 8.2 Rate 9 Management 10 See also 10.1 Crossings 10.2 Transport Nile River delta, as seen from Earth orbit. The Nile is an example of a wave-dominated delta that has the classic Greek delta (.) shape after which River deltas were named. 11 References 12 Further reading Topography The water in a river is usually confined to a channel, made up of a stream bed between banks. In larger rivers there is also a wider floodplain shaped by flood-waters over-topping the channel. Flood plains may be very wide in relation to the size of the river channel. This distinction between river channel and floodplain can be blurred especially in urban areas where the floodplain of a river channel can become greatly developed by housing and industry. The term upriver refers to the direction leading to the source of the river, which is against the direction of flow. Likewise, the term downriver describes the direction towards the mouth of the river, in which the current flows. The river channel typically contains a single stream of water, but some rivers flow as several interconnecting streams of water, producing a braided river. Extensive braided rivers are now found in only a few regions worldwide, such as the South Island of New Zealand. They also occur on peneplains and some of the larger river deltas. Anastamosing rivers are similar to braided rivers and are also quite rare. They have multiple sinuous channels carrying large volumes of sediment. A river flowing in its channel is a source of energy which acts on the river channel to change its shape and form. According to Brahm's law (sometimes called Airy's law), the mass of objects that may be carried away by a river is proportional to the sixth power of the river flow speed. Thus, when the speed of flow increases two times, it can transport 64 times larger (i.e., more massive) objects.[4] In mountainous torrential zones this can be seen as erosion channels through hard rocks and the creation of sands and gravels from the destruction of larger rocks. In Ushaped glaciated valleys, the subsequent river valley can often easily be identified by the V-shaped channel that it has carved. In the middle reaches where the river may flow over flatter land, meanders may form through erosion of the river banks and deposition on the inside of bends. Sometimes the river will cut off a loop, shortening the channel and forming an oxbow lake or billabong. Rivers that carry large amounts of sediment may develop conspicuous deltas at their mouths, if conditions permit. Rivers whose mouths are in saline tidal waters may form estuaries. Throughout the course of the river, the total volume of water transported downstream will often be a combination of the free water flow together with a substantial contribution flowing through sub-surface rocks and gravels that underlie the river and its floodplain (called the hyporheic zone). For many rivers in large valleys, this unseen component of flow may greatly exceed the visible flow. Subsurface streams Most but not all rivers flow on the surface. Subterranean rivers flow underground in caves or caverns. Such rivers are frequently found in regions with limestone geologic formations. Subglacial streams are the braided rivers that flow at the beds of glaciers and ice sheets, permitting meltwater to be discharged at the front of the glacier. Because of the gradient in pressure due to the overlying weight of the glacier, such streams can even flow uphill. Permanence of flow An intermittent river (or ephemeral river) only flows occasionally and can be dry for several years at a time. These rivers are found in regions with limited or highly variable rainfall, or can occur because of geologic conditions such as having a highly permeable river bed. Some ephemeral rivers flow during the summer months but not in the winter. Such rivers are typically fed from chalk aquifers which recharge from winter rainfall. In the UK these rivers are called Bournes and give their name to place such as Bournemouth and Eastbourne Classification River have been classified by many criteria including their topography, their biotic status, their relevance to white water or canoeing activities. Topographical classification Rivers can generally be classified as either alluvial, bedrock, or some mix of the two. Alluvial rivers have channels and floodplains that are self-formed in unconsolidated or weakly-consolidated sediments. They erode their banks and deposit material on bars and their floodplains. Bedrock rivers form when the river downcuts through the modern sediments and into the underlying bedrock. This occurs in regions that have experienced some kind of uplift (thereby steepening river gradients) or in which a particular hard lithology causes a river to have a steepened reach that has not been covered in modern alluvium. Bedrock rivers very often contain alluvium on their beds; this material is important in eroding and sculpting the channel. Rivers that go through patches of bedrock and patches of deep alluvial cover are classified as mixed bedrock-alluvial. Alluvial rivers can be further classified by their channel pattern as meandering, braided, wandering, anastomose, or straight. The morphology of an alluvial river reach is controlled by a combination of sediment supply, substrate composition, discharge, vegetation, and bed aggradation. The work of William Morris Davis at the turn of the 20th century used a classification based of river “age” as a way to characterise rivers. Youthful river: A river with a steep gradient that has very few tributaries and flows quickly. Its channels erode deeper rather than wider. Examples include the Brazos, Trinity and Ebro rivers. Mature river: A river with a gradient that is less steep than those of youthful rivers and flows more slowly. A mature river is fed by many tributaries and has more discharge than a youthful river. Its channels erode wider rather than deeper. Examples include the Mississippi, Saint Lawrence, Danube, Ohio, Thames and Paraná rivers. Old river: A river with a low gradient and low erosive energy. Old rivers are characterized by flood plains. Examples include the Yellow, Ganges, Tigris, Euphrates, Indus and Nile rivers. Rejuvenated river: A river with a gradient that is raised by tectonic uplift. The way in which a river's characteristics vary between the upper course and lower course of a river are Leisure activities on the River Avon at Avon Valley Country Park, Keynsham, United Kingdom. A boat giving trips to the public passes a summarized by the Bradshaw model. Power-law relationships between channel slope, depth, and width are given as a function of discharge by "river regime". Biotic classification There are very many systems of classification based on biotic conditions typically assigning classes from the most oligotrophic or unpolluted through to the most eutrophic or polluted.[5] Other systems are based on a whole ecosystem approach such as developed by the New Zealand Ministry for the Environment.[6] In Europe, the requirements of the Water Framework Directive has led to the development of a wide range of classification methods including classifications based on fishery status [7] A system of river zonation used in francophone communities [8][9] divides rivers into three primary zones: The crenon is the uppermost zone at the source of the river. It is further divided into the eucrenon (spring or boil zone) and the hypocrenon (brook or headstream zone). These areas are characterized by low temperatures, reduced oxygen content and slow moving water. The rhithron is the upstream portion of the river that follows the crenon. It is characterized by relatively cool temperatures, high oxygen levels, and fast, turbulent flow. The potamon is the remaining downstream stretch of river. It is characterized by warmer temperatures, lower oxygen levels, slow flow and sandier bottoms. Whitewater classification The International Scale of River Difficulty is used to rate the challenges of navigation—particularly those with rapids. Class I is the easiest and Class VI is the hardest. Stream order classification The Strahler Stream Order ranks rivers based on the connectivity and hierarchy of contributing tributaries. Headwaters are first order while the Amazon River is twelfth order. Approximately 80% of the rivers and streams in the world are of the first and second order. Uses Rivers have been used as a source of water, for obtaining food, for transport, as a defensive measure, as a source of hydropower to drive machinery, for bathing, and as a means of disposing of waste. Rivers have been used for navigation for thousands of years. The earliest evidence of navigation is found in the Indus Valley Civilization, which existed in northwestern Pakistan around 3300 BC.[10] Riverine navigation provides a cheap means of transport, and is still used extensively on most major rivers of the world like the Amazon, the Ganges, the Nile, the Mississippi, and the Indus. Since river boats are often not regulated, they contribute a large amount to global greenhouse gas emissions, and to local cancer due to inhaling of particulates emitted by the transports.[11][12] In some heavily forested regions such as Scandinavia and Canada, moored private boat. lumberjacks use the river to float felled trees downstream to lumber camps for further processing, saving much effort and cost by transporting the huge heavy logs by natural means. Rivers have been a source of food since pre-history.[13] They can provide a rich source of fish and other edible aquatic life, and are a major source of fresh water, which can be used for drinking and irrigation. It is therefore no surprise to find most of the major cities of the world situated on the banks of rivers. Rivers help to determine the urban form of cities and neighbourhoods and their corridors often present opportunities for urban renewal through the development of foreshoreways such as riverwalks. Rivers also provide an easy means of disposing of wastewater and, in much of the less developed world, other wastes. Fast flowing rivers and waterfalls are widely used as sources of energy, via watermills and hydroelectric plants. Evidence of watermills shows them in use for many hundreds of years such as in Orkney at Dounby click mill. Prior to the invention of steam power, water-mills for grinding cereals and for processing wool and other textiles were common across Europe. In the 1890s the first machines to generate power from river water were established at places such as Cragside in Northumberland and in recent decades there has been a significant increase in the development of large scale power generation from water, especially in wet mountainous regions such as Norway The coarse sediments, gravel and sand, generated and moved by rivers are extensively used in construction. In parts of the world this can generate extensive new lake habitats as gravel pits re-fill with water. In other circumstances it can destabilise the river bed and the course of the river and cause severe damage to spawning fish populations which rely on stable gravel formations for egg laying. In upland rivers, rapids with whitewater or even waterfalls occur. Rapids are often used for recreation, such as whitewater kayaking. Rivers have been important in determining political boundaries and defending countries. For example, the Danube was a long-standing border of the Roman Empire, and today it forms most of the border between Bulgaria and Romania. The Mississippi in North America and the Rhine in Europe are major east-west boundaries in those continents. The Orange and Limpopo Rivers in southern Africa form the boundaries between provinces and countries along their routes. Ecosystem Main article: River ecosystem The organisms in the riparian zone respond to changes in river channel location and patterns of flow. The ecosystem of rivers is generally described by the River continuum concept, which has some additions and refinements to allow for spatial (dams, waterfalls) and temporal (extensive flooding). The basic idea is that the river can be described as a system that is continuously changing along its length in the physical parameters, the availability of food particles and the composition of the ecosystem. The food (energy) that is the leftover of the upstream part is being utilized downstream. The general pattern is that the first order streams contain particulate matter (decaying leaves from the surrounding forests), which is processed there by shredders like Plecoptera larvae. The leftovers of the shredders are utilized by collectors, such as Hydropsyche, and further downstream algae that create the primary production become the main foodsource of the organisms. All changes are gradual and the distribution of each species can be described as a normal curve with the highest density where the conditions are optimal. In rivers succession is virtually absent and the composition of the ecosystem stays fixed in time. Chemistry Main article: River chemistry The chemistry of rivers is complex and depends on inputs from the atmosphere, the geology through which it travels and the inputs from man's activities. The chemistry of the water has a large impact on the ecology of that water for both plants and animals and it also affects the uses that may be made of the river water. Understanding and characterising river water chemistry requires a well designed and managed programme of sampling and analysis Like many other Aquatic ecosystems, rivers too are under increasing threat of pollution. According to a study of the WWF's Global Freshwater Programme, the 10 most polluted rivers are: Ganges, Indus, Yangtze, Salween-Nu, Mekong-Lancang, Rio Grande/Rio Bravo, La Plata, Danube, Nile-Lake Victoria, and the Murray-Darling.[14] Brackish water Further information: Brackish water Some rivers generate brackish water by having their river mouth in the ocean. This, in effect creates a unique environment in which certain species are found. Flooding Flooding is a natural part of a river's cycle. The majority of the erosion of river channels and the erosion and deposition on the associated floodplains occur during flood stage. In many developed areas, human activity has changed river channel form, altering different magnitudes and frequencies of flooding. Some examples of this are the building of levees, the straightening of channels, and the draining of natural wetlands. In many cases human activities in rivers and floodplains have dramatically increased the risk of flooding. Straightening rivers allows water to flow more rapidly downstream increasing the risk of flooding places further downstream. Building on flood plains removes flood storage which again exacerbates downstream flooding. The building of levees may only protect the area behind the levees and not those further downstream. Levees and flood-banks can also increase flooding upstream because of back-water pressure as the upstream water has to squeeze between the levees. Flow Studying the flows of rivers is one aspect of hydrology.[15] Direction A common misconception is that most, or even all, rivers flow from north to south.[16][17][18] Rivers in fact flow downhill regardless of compass direction. Sometimes downhill is from north to south, but equally it can be from south to north, and usually is a complex meandering path involving all directions of the compass.[19][20][21] Three of the ten longest rivers in the world - the Nile, Yenisei, and Ob - flow north, as do other major rivers such as the Rhine, Mackenzie, and Nelson. River meandering course River bank repair Rivers flowing downhill, from river source to river mouth, do not necessarily take the shortest path. For alluvial streams, straight and braided rivers have very low sinuosity and flow directly down hill, while meandering rivers flow from side to side across a valley. Bedrock rivers typically flow in either a fractal pattern, or a pattern that is determined by weaknesses in the bedrock, such as faults, fractures, or more erodible layers. Rate Volumetric flow rate, also called discharge, volume flow rate, and rate of water flow, is the volume of water which passes through a given cross-section of the river channel per unit time. It is typically measured in cubic meters per second (cumec) or cubic feet per second (cfs), where 1 m³/s = 35.51 ft³/s; it is sometimes also measured in litres or gallons per second. Volumetric flow rate can be thought of as the mean velocity of the flow through a given cross-section, times that cross-sectional area. Mean velocity can be approximated through the use of the Law of the Wall. In general, velocity increases with the depth (or hydraulic radius) and slope of the river channel, while the cross-sectional area scales with the depth and the width: the double-counting of depth shows the importance of this variable in determining the discharge through the channel. Management Main article: River engineering Rivers are often managed or controlled to make them more useful, or less disruptive, to human activity. Dams or weirs may be built to control the flow, store water, or extract energy. Levees, known as dikes in Europe, may be built to prevent river water from flowing on floodplains or floodways. Canals connect rivers to one another for water transfer or navigation. River courses may be modified to improve navigation, or straightened to increase the flow rate. River management is a continuous activity as rivers tend to 'undo' the modifications made by people. Dredged channels silt up, sluice mechanisms deteriorate with age, levees and dams may suffer seepage or catastrophic failure. The benefits sought through managing rivers may often be offset by the social and economic costs of mitigating the bad effects of such management. As an example, in parts of the developed world, rivers have been confined within channels to free up flat flood-plain land for development. Floods can inundate such development at high financial cost and often with loss of life. Rivers are increasingly managed for habitat conservation, as they are critical for many aquatic and riparian plants, resident and migratory fishes, waterfowl, birds of prey, migrating birds, and many mammals. See also See also: geography, water cycle, and drainage basin Aqueduct Baer's law Blackwater river Canal Drought Estuary Hack's law Hydrology List of international border rivers List of rivers by discharge List of rivers by length List of rivers of Africa List of rivers of Asia List of rivers of Europe List of rivers of Oceania List of rivers of the Americas List of river name etymologies List of waterways Mainstem (hydrology) Playfair's Law River civilization River continuum concept River cruise The Riverkeepers (book) Rock-cut basin Salt tide Sediment transport Water dispute World Rivers Day Crossings Bridges Ferries Fords Tunnels Transport Barge Riverboat Sailing Tow-path References 1. ^ River {definition} (http://www.merriam-webster.com/dictionary/river) from Merriam-Webster. Accessed February 2010. 2. ^ "WordNet Search: River" (http://wordnetweb.princeton.edu/perl/webwn? s=river&sub=Search+WordNet&o2=&o0=1&o7=&o5=&o1=1&o6=&o4=&o3=&h=) . The Trustees of Princeton University. http://wordnetweb.princeton.edu/perl/webwn? s=river&sub=Search+WordNet&o2=&o0=1&o7=&o5=&o1=1&o6=&o4=&o3=&h=. Retrieved 2009-10-02. 3. ^ "Domestic Names: Frequently Asked Question (FAQs), #17" (http://geonames.usgs.gov/domestic/faqs.htm) . United States Geological Survey. http://geonames.usgs.gov/domestic/faqs.htm. Retrieved 2009-10-02. 4. ^ Garde, R. J. (1995). History of fluvial hydraulics. New Age Publishers. pp. 19. ISBN 812240815X. OCLC 34628134 (http://www.worldcat.org/oclc/34628134) . 5. ^ SEPA – River Classification scheme (http://www.sepa.org.uk/science_and_research/classification_schemes/river_classifications_scheme.aspx) 6. ^ NZ’s River Environment Classification system (REC) (http://www.maf.govt.nz/mafnet/publications/rmupdate/rm14/rm14-04.htm) 7. ^ Compilation and harmonisation of fish species classification (http://fame.boku.ac.at/downloads/D1_2_typology_and%20species_classification.pdf) 8. ^ J. Illies & L. Botosaneanu (1963). "Problémes et méthodes de la classification et de la zonation éologique des eaux courantes, considerées surtout du point de vue faunistique.". Mitt. int. Ver. theor. angew. Limnol. 12: 1–57. 9. ^ Hawkes, H.A. (1975). River zonation and classification. Blackwell. pp. 312–374. 10. ^ Panda.org (http://www.panda.org/about_our_earth/about_freshwater/rivers/) 11. ^ Michel Meybeck (1993). "Riverine transport of atmospheric carbon: Sources, global typology and budget". Water, Air, & Soil Pollution 70 (1–4): 443–463. doi:10.1007/BF01105015 (http://dx.doi.org/10.1007%2FBF01105015) . 12. ^ Achim Albrecht (2003). "Validating riverine transport and speciation models using nuclear reactor-derived radiocobalt". Journal of Environmental Radioactivity (Elsevier Science Ltd) 66 (3): 295–307. doi:10.1016/S0265- 931X(02)00133-9 (http://dx.doi.org/10.1016%2FS0265-931X%2802%2900133-9) . PMID 12600761 (http://www.ncbi.nlm.nih.gov/pubmed/12600761) . 13. ^ NMP.org (http://en.nmp.gov.tw/park01-2.html) 14. ^ Top 10 most polluted rivers (http://www.financialexpress.com/news/ganges-is-one-of-worlds-10-most-pollutedrivers/ 194554/) 15. ^ Cristi Cave. "How a River Flows" (http://chamisa.freeshell.org/flow.htm) . Stream Biology and Ecology. http://chamisa.freeshell.org/flow.htm. 16. ^ "Children's Misconceptions about Science" (http://amasci.com/miscon/opphys.html) . Operation Physics, American Institute of Physics. September 1998. http://amasci.com/miscon/opphys.html. 17. ^ William C. Philips (February 1991). "Earth Science Misconceptions" (http://k12s.phast.umass.edu/~nasa/misconceptions.html) . http://k12s.phast.umass.edu/~nasa/misconceptions.html. 18. ^ Gregory Vogt (2007). The Lithosphere: Earth's Crust. Twenty-First Century Books. pp. 61. ISBN 9780761328384. 19. ^ Matt Rosenberg (2006-06-08). "Do All Rivers Flow South?" (http://geography.about.com/b/a/257582.htm) . About.com. http://geography.about.com/b/a/257582.htm. 20. ^ Matt Rosenberg. "Rivers Flowing North: Rivers Only Flow Downhill; Rivers Do Not Prefer to Flow South" (http://geography.about.com/od/learnabouttheearth/a/northrivers.htm) . About.com. http://geography.about.com/od/learnabouttheearth/a/northrivers.htm. 21. ^ Nezette Rydell (1997-03-16). "Re: What determines the direction of river flow? Elevation, Topography,Gravity??" (http://www.madsci.org/posts/archives/mar97/858609276.Es.r.html) . Earth Sciences. Topography,Gravity??" (http://www.madsci.org/posts/archives/mar97/858609276.Es.r.html) . Earth Sciences. http://www.madsci.org/posts/archives/mar97/858609276.Es.r.html. Further reading Jeffrey W. Jacobs. "Rivers, Major World" (http://www.waterencyclopedia.com/Re-St/Rivers-Major- World.html) . Water Encyclopaedia. http://www.waterencyclopedia.com/Re-St/Rivers-Major-World.html. Luna B. Leopold (1994). A View of the River. Harvard University Press. ISBN 0674937325. OCLC 28889034 (http://www.worldcat.org/oclc/28889034) . ISBN. — a non-technical primer on the geomorphology and hydraulics of water. Retrieved from "http://en.wikipedia.org/wiki/River" Categories: Rivers | Fluvial landforms | Geomorphology | Sedimentology | Water streams This page was last modified on 23 June 2011 at 00:07. Text is available under the Creative Commons Attribution-ShareAlike License; additional terms may apply. See Terms of use for details. Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. Definitions Upland habitats are cold, clear, rocky, fast flowing rivers in mountainous areas; lowland habitats are warm, slow flowing rivers found in relatively flat lowland areas, with water that is frequently coloured by sediment and organic matter. These classifications overlap with the geological definitions of "upland" and "lowland". In geology an "upland" is generally considered to be land that is at a higher elevation than the alluvial plain or stream terrace, which are considered to be "lowlands". The term "bottomland" refers to low-lying alluvial land near a river. Many freshwater fish and invertebrate communities around the world show a pattern of specialisation into upland or lowland river habitats. Classifying rivers and streams as upland or lowland is important in freshwater ecology as the two types of river habitat are very different, and usually support very different populations of fish and invertebrate species. Upland In freshwater ecology, upland rivers and streams are the fast flowing rivers and streams that drain elevated or mountainous country, often onto broad alluvial plains (where they become lowland rivers). However, altitude is not the sole determinant of whether a river is upland or lowland. Arguably the most important determinants are that of stream power and course gradient. Rivers with a course that drops in altitude rapidly will have faster water flow and higher stream power or "force of water". This in turn produces the other characteristics of an upland river - an incised course, a river bed dominated by bedrock and coarse sediments, a riffle and pool structure and cooler water temperatures. Rivers with a course that drops in altitude very slowly will have slower water flow and lower force. This in turn produces the other characteristics of a lowland river - a meandering course lacking rapids, a river bed dominated by fine sediments and higher water temperatures. Lowland rivers tend to carry more suspended sediment and organic matter as well, but some lowland rivers have periods of high water clarity in seasonal low flow periods. The generally clear, cool, fast-flowing waters and bedrock and coarse sediment beds of upland rivers encourage fish species with limited temperature tolerances, high oxygen needs, strong swimming ability and specialised Amazon River near Manaus, Brazil, an example of a lowland river habitat. reproductive strategies to prevent eggs or larvae being swept away. These characteristics also encourage invertebrate species with limited temperature tolerances, high oxygen needs and ecologies revolving around coarse sediments and interstices or "gaps" between those coarse sediments. Lowland The generally more turbid, warm, slow-flowing waters and fine sediment beds of lowland rivers encourage fish species with broad temperature tolerances and greater tolerances to low oxygen levels, and life history and breeding strategies adapted to these and other traits of lowland rivers. These characteristics also encourage invertebrate species with broad temperature tolerances and greater tolerances to low oxygen levels and ecologies revolving around fine sediments or alternative habitats such as submerged woody debris ("snags") or submergent macrophytes Fluvial is used in geography and Earth science to refer to the processes associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluvioglacial is used.[1][2] Contents 1 Fluvial processes 2 See also 2.1 Fluvial processes 2.2 Fluvial channel patterns 2.3 Fluvial landforms 2.4 Related terms 3 References Fluvial processes Fluvial processes comprise the motion of sediment and erosion or deposition (geology) on the river bed. Erosion by moving water can happen in two ways. Firstly, the movement of water across the bed exerts a shear stress directly onto the bed. If the cohesive strength of the substrate is lower than the shear exerted, or the bed is composed of loose sediment which can be mobilized by such stresses, then the bed will be lowered purely by clearwater flow. However, if the river carries significant quantities of sediment, this material can act as tools to enhance wear of the bed (abrasion). At the same time the fragments themselves are ground down, becoming smaller and more rounded (attrition). Sediment in rivers is transported as either bedload (the coarser fragments which move close to the bed) or suspended load (finer fragments carried in the water). There is also a component carried as dissolved material. For each grain size there is a specific velocity at which the grains start to move, called entrainment velocity. However the grains will continue to be transported even if the velocity falls below the entrainment velocity due to the reduced (or removed) friction between the grains and the river bed. Eventually the velocity will fall low enough for the grains to be deposited. This is shown by the Hjulstrøm curve. A river is continually picking up and dropping solid particles of rock and soil from its bed throughout its length. Where the river flow is fast, more particles are picked up than dropped. Where the river flow is slow, more particles are dropped than picked up. Areas where more particles are dropped are called alluvial or flood plains, and the dropped particles are called alluvium. Even small streams make alluvial deposits, but it is in the flood plains and deltas of large rivers that large, geologically-significant alluvial deposits are found. The amount of matter carried by a large river is enormous. The names of many rivers derive from the color that the transported matter gives the water. For example, the Huang He in China is literally translated "Yellow River", and the Mississippi River in the United States is also called "the Big Muddy." It has been estimated that the Mississippi River annually carries 406 million tons of sediment to the sea,[3] the Huang He 796 million tons, and the Po River in Italy 67 million tons.[4] Limnology "lake"; and logos, "knowledge"), also called freshwater science, is the study of inland waters. It is often regarded as a division of ecology or environmental science. It covers the biological, chemical, physical, geological, and other attributes of all inland waters (running and standing waters, both fresh and saline, natural or man-made). This includes the study of lakes and ponds, rivers, springs, streams and wetlands.[1] A more recent subdiscipline of limnology, termed landscape limnology, studies, manages, and conserves these aquatic ecosystems using a landscape perspective. Limnology is closely related to aquatic ecology and hydrobiology, which study aquatic organisms in particular regard to their hydrological environment. Contents 1 History 2 Lake Classification 3 Organizations 4 Journals 5 See also 6 Notes 7 References 8 External links History The term limnology was coined by François-Alphonse Forel (1841–1912) who established the field with his studies of Lake Geneva. Interest in the discipline rapidly expanded, and in 1922 August Thienemann (a German zoologist) and Einar Naumann (a Swedish botanist) co-founded the International Society of Limnology (SIL, for originally Societas Internationalis Limnologiae). Forel's original definition of limnology, "the oceanography of lakes", was expanded to encompass the study of all inland waters.[1] Prominent early American limnologists included G. Evelyn Hutchinson, Ed Deevey, E. A. Birge, and C. Juday.[2] Lake Classification Limnology classifies lakes according to the trophic state index.[1] An oligotrophic lake is characterised by relatively low levels of primary production and low levels of nutrients. A eutrophic lake has high levels of primary productivity due to very high nutrient levels. Eutrophication of a lake can lead to algal blooms. Dystrophic lakes have high levels of humic matter and typically has yellow-brown tea coloured waters.[1] This classification system is not very clear cut and can be seen as more of a spectrum encompassing the various levels of productivity. Organizations American Society of Limnology and Oceanography Asociación Ibérica de Limnología Australian Society for Limnology (http://www.asl.org.au/) European Society of Limnology and Oceanography Society of Limnology (http://www.dgl-ev.de) Italian Association for Oceanology and Limnology (AIOL) (http://www.aiol.info) The Japanese Society of Limnology International Society of Limnology Brazilian Society of Limnology (http://www.sblimno.org.br/) New Zealand freshwater Sciences society (http://freshwater.rsnz.org/) Southern African Society of Aquatic Scientists (http://www.dwaf.gov.za/iwqs/sasaqs/index.htm) Balaton Limnological Research Institute (http://www.blki.hu/BLRI/index.htm) Polish Limnological Society Society for Freshwater Science (formerly North American Benthological Society) (http://www.benthos.org) Journals Advances in Limnology Annales de Limnologie - International Journal of Limnology (http://journals.cambridge.org/action/displayJournal?jid=anl) Aquatic Conservation (http://www.interscience.wiley.com/journal/aqc) Aquatic Ecology (http://www.springer.com/life+sciences/ecology/journal/10452) Canadian Journal of Fisheries and Aquatic Sciences (http://pubs.nrc-cnrc.gc.ca/rp-ps/journalDetail.jsp? jcode=cjfas) Chinese Journal of Oceanology and Limnology Freshwater Biology (http://www.blackwellpublishing.com/fwb) Hydrobiologia (http://www.springerlink.com/content/100271/) Journal of Ecology and Fisheries Journal of Limnology (http://www.iii.to.cnr.it/pubblicaz/jour_lim.htm) Limnetica (http://www.limnetica.org) Limnologica Limnological Review (http://ptlim.pl/wydawnictwa.html) Journal of the North American Benthological Society (http://www.benthos.org/Journal-(JNABS).aspx) Limnology and Oceanography (http://www.aslo.org/) Marine and Freshwater Research (http://www.publish.csiro.au/nid/126.htm) New Zealand Journal of Marine and Freshwater Research (http://www.informaworld.com/smpp/title~content=t918959567~db=all) Review of Hydrobiology (http://www.reviewofhydrobiology.com/) River Research and Applications (http://www.interscience.wiley.com/journal/rra) See also Limnology publications G. Evelyn Hutchinson Freshwater biology Hydrology Lake aeration Lake ecosystem Landscape limnology Lentic ecosystems Limnic eruption Lotic ecosystems Marine biology Oceanography Paleolimnology Levee From Wikipedia, the free encyclopedia A levee, levée, dike (or dyke), embankment, floodbank or stopbank is an elongate naturally occurring ridge or artificially constructed fill or wall, which regulate water levels. It is usually earthen and often parallel to the course of a river in its floodplain or along low-lying coastlines.[1] Contents 1 Etymology 1.1 Levee 1.2 Dike 2 Artificial levees 2.1 River flood prevention 2.2 Coastal flood prevention 2.3 Spur dykes 3 Natural levees 3.1 Levees in tidal waters 4 Levee failures and breaches 5 See also 6 References 6.1 Notes 6.2 General references 7 External links Etymology Levee The word levee, from the French word levée (from the feminine past participle of the French verb lever, "to raise"), is used in American English (notably in the Midwest and Deep South); it came into English use in New Orleans circa 1720.[2] The French pronunciation is [l?'ve], English /'l?vi?/. Dike The modern word dike is most probably derived from the Dutch word "dijk", with the construction of dikes in the Netherlands well attested since the 12th century. The 126 kilometres (78 mi) long Westfriese Omringdijk, for instance, was completed by 1250, and was formed by connecting existing older dikes. The Roman chronicler Tacitus however mentions the fact that the rebellious Batavi pierced dikes to flood their land and to protect their retreat (AD 70).[3] The Dutch word dijk originally indicated both the trench and the bank. The word is closely related to the English verb to dig (EWN). According to the 1911 Encyclopedia Britannica: “ Holland's chief protection against inundation is its long line of sand dunes, in which only two real breaches have been effected during the centuries of erosion. These are represented by the famous sea dikes called the Westkapelle dike and the nl:Hondsbossche Zeewering, or sea-defence, which were begun respectively in the first and second halves of the 15th century. The first extends for a distance of over 4000 yds. between the villages of Westkapelle and Domburg in the island of Walcheren; the second is about 4900 yds. long, and extends from Kamperduin to near Petten, whence it is continued for another 1100 yds. by the Pettemer dike. These two sea dikes were reconstructed by the state at great expense between the year 1860 and 1884, having consisted before that time of little more than a protected sand dike. The earthen dikes are protected by stone-slopes and by piles, and at the more dangerous points also by nl:zinkstukken (sinking pieces), artificial structures of brushwood laden with stones, and measuring some 400 yds. in circuit, by means of which the current is to some extent turned aside. The Westkapelle dike, 12,468 ft. long, has a seaward slope of 300 ft., and is protected by rows of piles and basalt blocks. On its ridge, 39 ft. broad, there is not only a roadway but a service railway. The cost of its upkeep is more than 6000 a year, and of the Hondsbossche Zeewering 2000 a year. When it is remembered that the woodwork is infested by the pile worm (Teredo navalis), the ravages of which were discovered in 1731, the labour and expense incurred in the construction and maintenance of the sea dikes now existing may be imagined. In other parts of the coast the dunes, though not pierced through, have become so wasted by erosion as to require artificial strengthening. This is afforded, either by means of a so-called sleeping dike (nl:slaperdijk) behind the weak spot, as, for instance, between Kadzand and Breskens in Zeeland-Flanders, and again between 's-Gravenzande and Loosduinen; or by means of piers or breakwaters (hoofden, heads) projecting at intervals into the sea and composed of piles, or brushwood and stones. The first of such breakwaters was that constructed in 1857 at the north end of the island of Goeree, and extends over 100 yds. into the sea at low water. ” —Encyclopedia Brittanica article on Holland, 1911, [4] In Anglo-Saxon, the word dic already existed and was pronounced with a hard c in northern England and as ditch in the south. Similar to Dutch, the English origins of the word lie in digging a trench and forming the upcast soil into a bank alongside it. This practice has meant that the name may be given to either the excavation or the bank. Thus Offa's Dyke is a combined structure and Car Dyke is a trench though it once had raised banks as well. In the midlands and north of England, and in the United States, a dike is what a ditch is in the south, a property boundary marker or small drainage channel. Where it carries a stream, it may be called a running dike as in Rippingale Running Dike, which leads water from the catchwater drain, Car Dyke, to the South Forty Foot Drain in Lincolnshire (TF1427). The Weir Dike is a soak dike in Bourne North Fen, near Twenty and alongside the River Glen, Lincolnshire. In the Norfolk and Suffolk Broads, a dyke may be a drainage ditch or a narrow artificial channel off a river or broad for access or mooring, some longer dykes being named, e.g. Candle Dyke[5]. Artificial levees The main purpose of an artificial levee is to prevent flooding of the adjoining countryside; however, they also confine the flow of the river, resulting in higher and faster water flow. Levees A levee keeps high water on the Mississippi River from flooding Gretna, Louisiana, in March 2005. can be mainly found along the sea, where dunes are not strong enough, along rivers for protection against high-floods, along lakes or along polders. Furthermore, levees have been built for the purpose of empoldering, or as a boundary for an inundation area. The latter can be a controlled inundation by the military or a measure to prevent inundation of a larger area surrounded by levees. Levees have also been built as field boundaries and as military defences. More on this type of levee can be found in the article on dry-stone walls. Levees can be permanent earthworks or emergency constructions (often of sandbags) built hastily in a flood emergency. When such an emergency bank is added on top of an existing levee it is known as a cradge. Some of the earliest levees were constructed by the Indus Valley Civilization (in Pakistan and North India from circa 2600 BC) on which the agrarian life of the Harappan peoples depended.[6] Also levees were constructed over 3,000 years ago in ancient Egypt, where a system of levees was built along the left bank of the River Nile for more than 600 miles (970 km), stretching from modern Aswan to the Nile Delta on the shores of the Mediterranean. The Mesopotamian civilizations and ancient China also built large levee systems. Because a levee is only as strong as its weakest point, the height and standards of construction have to be consistent along its length. Some authorities have argued that this requires a strong governing authority to guide the work, and may have been a catalyst for the development of systems of governance in early civilizations. However others point to evidence of large scale water-control earthen works such as canals and/or levees dating from before King Scorpion in Predynastic Egypt during which governance was far less centralized. Levees are usually built by piling earth on a cleared, level surface. Broad at the base, they taper to a level top, where temporary embankments or sandbags can be placed. Because flood discharge intensity increases in levees on both river banks, and because silt deposits raise the level of riverbeds, planning and auxiliary measures are vital. Sections are often set back from the river to form a wider channel, and flood valley basins are divided by multiple levees to prevent a single breach from flooding a large area. A levee made from stones laid in horizontal rows with a bed of thin turf between each of them is known as a spetchel. Artificial levees require substantial engineering. Their surface must be protected from erosion, so they are planted with vegetation such as Bermuda grass in order to bind the earth together. On the land side of high levees, a low terrace of earth known as a banquette is usually added as another anti-erosion measure. On the river side, erosion from strong waves or currents presents an even greater threat to the integrity of the levee. The effects of erosion are countered by planting with willows, weighted matting or concrete revetments. Separate ditches or drainage tiles are constructed to ensure that the foundation does not become waterlogged. River flood prevention Prominent levee systems exist along the Mississippi River and Sacramento River in the United States, and the Po, Rhine, Meuse River, Loire, Vistula, the delta formed by the Rhine, Maas/Meuse and Scheldt in the Netherlands and the Danube in Europe. The Mississippi levee system represents one of the largest such systems found anywhere in the world. It comprises over 3,500 miles (5,600 km) of levees extending some 1,000 kilometres (620 mi) along the Mississippi, stretching from Cape Girardeau, Missouri to the Mississippi Delta. They were begun by French settlers in Louisiana in the 18th century to protect the city of New Orleans. The first Louisianan levees were about 3 feet (0.91 m) high and covered a distance of about 50 miles (80 km) along the riverside. By the mid-1980s, they had reached their present extent and averaged 24 feet (7.3 m) in height; some Mississippi levees are as much as 50 feet (15 m) high. The Mississippi levees also include some of the longest continuous individual levees in the world. One such levee extends southwards from Pine Bluff, Arkansas for a distance of some 380 miles (610 km). Coastal flood prevention Levees are very common on the flatlands bordering the Bay of Fundy in New Brunswick and Nova Scotia Canada. The Acadians who settled the area can be credited with construction of most of the levees in the area, created for the purpose of farming the fertile tidal flatlands. These levees are referred to as "aboiteau". In the Lower Mainland around the city of Vancouver, British Columbia, there are levees to protect low-lying land in the Fraser River delta, particularly the city of Richmond on Lulu Island. There are also levees to protect other locations which have flooded in the past, such as land adjacent to the Pitt River and other tributary rivers. Spur dykes See also: Jetty and Breakwater (structure) These typically man-made hydraulic structures are situated to protect against erosion. They are typically placed in alluvial rivers perpendicular, or at an angle, to the bank of the channel or the revetment,[7] and are used widely along coastlines. Spur dykes are generally divided into two types: permeable and impermeable, depending on the materials used.[8] Natural levees Levees are commonly thought of as man-made, but they can also be natural. The ability of a river to carry sediments varies very strongly with its speed. When a river floods over its banks, the water spreads out, slows down, and deposits its load of sediment. Over time, the river's banks are built up above the level of the rest of the floodplain. The resulting ridges are called natural levees. When the river is not in flood state it may deposit material within its channel, raising its level. The combination can raise not just the surface, but even the bottom of the river above the surrounding country. Natural levees are especially noted on the Yellow River in China near the sea where oceangoing ships appear to sail high above the plain on the elevated river. Natural levees are a common feature of all meandering rivers in the world. Levees in tidal waters Natural levees may be formed along creek banks that are subject to periodic flooding due to oceanic tides. Levee formation occurs as the incoming tide carries suspended sediment of all grades upstream to the limit imposed by the energy of the tidal flow. As the tidal waters overflow the creek banks, the water flow spreads out to cover a wider area than it did when confined to the stream's main channel. As the water spreads into the flood zone, its flow rate at the brink rapidly slows and much of the sediment that had been carried upstream by the tidal current is deposited along the bank. Over time, during the course of repeated tidal flooding, this sedimentation process forms a levee. At the height of the tide, the water flow in flooded salt-marsh or flats is the most still and the finer particles slowly settle, forming clay. In the early ebb, the water level in the creek falls leaving the broad expanse of water standing on the marsh at a higher level. In an active system, the levee is always higher than the marsh. That is how it came to be called "une rive levée", or raised shore. Levee failures and breaches Main article: Levee breach Man-made levees can fail in a number of ways. The most frequent (and dangerous) form of levee failure is a levee breach. A levee breach is when part of the levee actually breaks away, leaving a large opening for water to flood the land protected by the levee. A breach can be a sudden or gradual failure that is caused either by surface erosion or by a subsurface failure of the levee. Sometimes levees are said to fail when water overtops the crest of the levee. See also Breakwater (structure) Bridge scour Bunding Dam Floodway Jetty Sleeper dike Subsidence Embankment dam From Wikipedia, the free encyclopedia An embankment dam is a massive artificial water barrier. It is typically created by the emplacement and compaction of a complex semi-plastic mound of various compositions of soil, sand, clay and/or rock. It has a semi-permanent waterproof natural covering for its surface, and a dense, waterproof core. This makes such a dam impervious to surface or seepage erosion.[1] The force of the impoundment creates a downward thrust upon the mass of the dam, greatly increasing the weight of the dam on its foundation. This added force effectively seals and makes waterproof the underlying foundation of the dam, at the interface between the dam and its stream bed.[2] Such a dam is composed of fragmented independent material particles. The friction and interaction of particles binds the particles together into a stable mass rather than the use of a cementing substance.[3] Contents 1 Types 2 Safety 3 See also 4 Notes 5 External links Types Embankment dams come in two types: the earth-filled dam (also called an earthen dam or terrain dam) made of compacted earth, and the rock-filled dam. A crosssection of an embankment dam shows a shape like a bank, or hill. Most have a central section or core composed of an impermeable material to stop water from seeping through the dam. The core can be of clay, concrete or asphalt concrete. This dam type is a good choice for sites with wide valleys. Since they exert little pressure on their foundations, they can be built on hard rock or softer soils. For a rock-fill dam, rock-fill is blasted using explosives to break the rock. Additionally, the rock pieces may need to be crushed into smaller chunks to get the right range of size for use in an embankment dam.[4] Safety The building of a dam and the filling of the reservoir behind it places a new weight on the floor and sides of a valley. The stress of the water increases linearly with its depth. Water also pushes against the upstream face of the dam, a nonrigid structure that under stress behaves semiplastically, and causes greater need for adjustment (flexibility) near Pothundi Dam, India the base of the dam than at shallower water levels. Thus the stress level of the dam must be calculated in advance of building to ensure that its break level threshold is not exceeded.[5] Overtopping or overflow of an embankment dam outside of its spillways will cause disastrous flooding through the eventual failure of the dam. In the failure process the sustained hydraulic force and pressure caused by an overtopping surface runoff; immediately erodes the dam's material structure as it flows over the top of the dam. Even a small sustained overtopping surface flow can remove thousands of tons of overburden soil from the mass of the dam within hours. The removal of this mass unbalances the forces that stabilize the dam against its impoundment. The mass of water still impounded behind the dam presses against the lighter mass of the embankment, (made lighter by surface erosion). As the mass of the dam gets lighter, the impoundment begins to move the whole structure. The embankment, having almost no elastic strength, begins to break into separate pieces, naturally allowing the impounded water to flow between them eroding and removing more material as it goes. In the final stages of failure the remaining pieces of the embankment offer almost no resistance to the flow of the water; as they continue to fracture into smaller and smaller sections of earth and/or rock. The overtopped earth embankment dam disintegrates into a thick mud soup of earth, rocks and water. Therefore safety requirements for the spillway are high, requiring the spillway to be capable of containing a maximum flood stage. Specifying a spillway able to contain a five hundred year flood is common.[6] Recently a number of embankment dam overtopping protection systems were developed.[7] These techniques include the concrete overtopping protection systems, timber cribs, sheet-piles, riprap and gabions, reinforced earth, minimum energy loss weirs, embankment overflow stepped spillways and the precast concrete block protection systems developed in Russia.