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River, in – In the urban landscapeA river is a natural flowing, usually, flowing towards an, or another river. In some cases a river flows into the ground and becomes dry at the end of its course without reaching another body of water. Small rivers can be referred to using names such as, creek, brook, rivulet,. There are no official definitions for the generic term river as applied to, although in some countries or communities a stream is defined by its size. Many names for small rivers are specific to geographic location; examples are 'run' in some parts of the United States, ' in Scotland and northeast England, and 'beck' in northern England. Sometimes a river is defined as being larger than a creek, but not always: the language is vague.Rivers are part of the; water generally collects in a river from through a from and other sources such as, and the release of stored water in natural ice and snowpacks (e.g., from ).
Potamology is the scientific study of rivers, while is the study of inland waters in general. Most of the are situated on the banks of rivers, as they are, or were, used as a, for obtaining, for, as, as a defensive measure, as a source of to drive machinery, for, and as a means of disposing of. The Colorado River at,A river begins at a (or more often several sources), follows a path called a course, and ends at a or mouths. The water in a river is usually confined to a, made up of a between. In larger rivers there is often also a wider shaped by -waters over-topping the channel. Floodplains 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.Rivers can flow down mountains, through or along, and can create or gorges.The term upriver (or upstream) refers to the direction towards the source of the river, i.e. Against the direction of flow. Likewise, the term downriver (or downstream) describes the direction towards the mouth of the river, in which the flows.The term left bank refers to the left bank in the direction of flow, right bank to the right.The river channel typically contains a single stream of water, but some rivers flow as several interconnecting streams of water, producing a.
Extensive braided rivers are now found in only a few regions worldwidesuch as the of. They also occur on and some of the larger.
Are similar to braided rivers and are quite rare. They have multiple sinuous channels carrying large volumes of sediment. There are rare cases of in which a river divides and the resultant flows ending in different seas. An example is the in. From the Green Dragon Bridge, Cambridge A river flowing in its channel is a source of energy which acts on the river channel to change its shape and form. In 1757, the German hydrologist empirically observed that the submerged weight of objects that may be carried away by a river is proportional to the sixth power of the river flow speed. This formulation is also sometimes called Airy's law.
Thus, if the speed of flow is doubled, the flow would dislodge objects with 64 times as much submerged weight. 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.
A river valley that was created from a U-shaped valley, can often easily be identified by the V-shaped channel that it has carved. In the middle reaches where a river flows over flatter land, 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.
Rivers that carry large amounts of may develop conspicuous deltas at their mouths. Rivers whose mouths are in saline waters may form.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 volume flowing through sub-surface rocks and gravels that underlie the river and its (called the ). For many rivers in large valleys, this unseen component of flow may greatly exceed the visible flow.Subsurface streamsMost but not all rivers flow on the surface.
Flow underground in or caverns. Such rivers are frequently found in regions with. Are the braided rivers that flow at the beds of glaciers and, permitting meltwater to be discharged at the front of the glacier. Because of the gradient in due to the overlying weight of the glacier, such streams can even flow uphill.Permanence of flow. Main article:An intermittent river (or 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 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 England these rivers are called bournes and give their name to places such as. Even in humid regions, the location where flow begins in the smallest tributary streams generally moves upstream in response to precipitation and downstream in its absence or when active summer vegetation diverts water for. Normally-dry rivers in arid zones are often identified as or other regional names.The meltwater from large hailstorms can create a of water, hail and sand or soil, forming temporary rivers. Leisure activities on the at Avon Valley Country Park,. A boat giving trips to the public passes a moored private boat.Rivers have been a source of food since pre-history. They are often a rich source of fish and other edible aquatic life, and are a major source of fresh water, which can be used for drinking.
Rivers help to determine the of cities and neighbourhoods and their corridors often present opportunities for through the development of such as river walks. Rivers also provide an easy means of disposing of and, in much of the less developed world, other wastes.Rivers have been used for for thousands of years. The earliest evidence of navigation is found in the, which existed in northwestern India around 3300 BC. Riverine navigation provides a cheap means of transport, and is still used extensively on most major rivers of the world like the, the, the, the, and the.
Since river boats are often not regulated, they contribute a large amount to global, and to local cancer due to inhaling of emitted by the transports.Rivers have been important in determining political boundaries and defending countries. For example, the was a long-standing border of the, and today it forms most of the border between. The Mississippi in and the in Europe are major east-west boundaries in those continents. The and Rivers in form the boundaries between provinces and countries along their routes.In some heavily forested regions such as and, 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. Watermill in BelgiumFast flowing rivers and waterfalls are widely used as sources of energy, via.
Evidence of watermills shows them in use for many hundreds of years, for instance in at. Prior to the invention of steam power, watermills for grinding and for processing and other textiles were common across. In the 1890s the first machines to generate power from river water were established at places such as in 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.The coarse sediments, and, 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, with or even occur. Rapids are often used for recreation, such as.
Main article:The organisms in the respond to changes in river channel location and patterns of flow. The ecosystem of rivers is generally described by the, which has some additions and refinements to allow for dams and waterfalls and temporary extensive flooding. The concept describes the river as a system in which the physical parameters, the availability of food particles and the composition of the ecosystem are continuously changing along its length. The food (energy) that remains from the upstream part is used 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 larvae. The products of these shredders are used by collectors, such as, and further downstream algae that create the become the main food source of the organisms. All changes are gradual and the distribution of each species can be described as a, with the highest density where the conditions are optimal.
In rivers is virtually absent and the composition of the ecosystem stays fixed in time.Chemistry. Caused by a large amount of rain falling in a short amount of timeFlooding 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 the. In many developed areas, human activity has changed the form of river channels, altering magnitudes and frequencies of flooding. Some examples of this are the building of, the straightening of channels, and the draining of natural. In many cases human activities in rivers and floodplains have dramatically increased the risk of flooding.
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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 only protects the area behind the levees and not those further downstream. Levees and flood-banks can also increase flooding upstream because of the back-water pressure as the river flow is impeded by the narrow channel banks.
Finally also reduce the risk of flooding significantly by being able to take up some of the flood water.FlowStudying the flows of rivers is one aspect of. River meandering courseRivers flow downhill with their power derived from gravity. The direction can involve all directions of the compass and can be a complex meandering path.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 pattern, or a pattern that is determined by weaknesses in the bedrock, such as, or more erodible layers.Rate. Main article:, also known as 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 (cumec) or (cfs), where 1 m 3/s = 35.51 ft 3/s; it is sometimes also measured in or 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. In general, velocity increases with the depth (or ) 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.Fluvial erosionIn the youthful stage;When the river is subject to, deepening the valley. Loosens and dislodges the rock. The rivers load further erodes its banks and the river bed.
Over time, this will deepen the river bed and create steeper sides which are then weathered.The steepened nature of the banks causes the sides of the valley to move downslope causing the valley to become.also form in the youthful river valley.Waterfalls usually form where a band of hard rock lies next to a layer of soft rock (easier to erode). Occurs as the river can erode the soft rock easier than the hard rock, this leaves the hard rock more elevated and stands out from the river below.
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And are what erodes the soft rock and the water to fall down to the river bed. A plunge pool forms at the bottom and deepens as a result of hydraulic action and abrasion. Sediment yieldSediment yield is the total quantity of particulate matter (suspended or bedload) reaching the outlet of a drainage basin over a fixed time frame. Yield is usually expressed as kilograms per square kilometre per year. Sediment delivery processes are affected by a myriad of factors such as drainage area size, basin slope, climate, sediment type (lithology), vegetation cover, and human land use / management practices. The theoretical concept of the 'sediment delivery ratio' (ratio between yield and total amount of sediment eroded) captures the fact that not all of the sediment is eroded within a certain catchment that reaches out to the outlet (due to, for example, deposition on floodplains). Such storage opportunities are typically increased in catchments of larger size, thus leading to a lower yield and sediment delivery ratio.
Re-reversing The Chicago River
Main article:Rivers are often managed or controlled to make them more useful or less disruptive to human activity. or may be built to control the flow, store water, or extract energy., known as dikes in Europe, may be built to prevent river water from flowing on floodplains or floodways.
connect rivers to one another for or. 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, 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, as they are critical for many and plants, and, and many.See also.