Rivers that Flow

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Class I is the easiest and Class VI is the hardest. 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. In certain languages, distinctions are made among rivers based on their stream order.

Since many fleuves are large and prominent, receiving many tributaries, the word is sometimes used to refer to certain large rivers that flow into other fleuves ; however, even small streams that run to the sea are called fleuve e. 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 India around BC. 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.

In some heavily forested regions such as Scandinavia and Canada , 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. Most of the major cities of the world are 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 river walks. Rivers also provide an easy means of disposing of waste water and, in much of the less developed world, other wastes.

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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, for instance in Orkney at Dounby Click Mill. Prior to the invention of steam power, watermills for grinding cereals and for processing wool and other textiles were common across Europe. In the s 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. 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 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 Plecoptera larvae. The products of these shredders are used by collectors, such as Hydropsychidae , and further downstream algae that create the primary production become the main food source 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. 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 chemical composition 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 sampling and analysis.

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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 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 flood stage.

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 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 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. Studying the flows of rivers is one aspect of hydrology. Rivers 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 fractal pattern, or a pattern that is determined by weaknesses in the bedrock, such as faults , fractures , or more erodible layers.

Volumetric flow rate , 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. 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: When the river is subject to vertical erosion , deepening the valley. Hydraulic action 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 V-shaped. Waterfalls 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. Differential erosion 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. Hydraulic action and abrasion 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 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.

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.

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Rivers are often managed or controlled to make them more useful, or less disruptive, to human activity. 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. From Wikipedia, the free encyclopedia. For other uses, see River disambiguation. For other uses, see Rivers disambiguation.

Rivers portal Environment portal Ecology portal. United States Geological Survey. Retrieved 26 January The Trustees of Princeton University.

And many's the balmy summer evening -- the air over Pittsburgh heady with the smell of date palms and the sound of the muezzin calling the faithful to prayer -- that I think it's true. But what's also true, sad to say, is that northward-flowing rivers aren't that rare. According to the National Aeronautics and Space Administration, four of the world's 10 longest rivers flow generally northward: In fact, NASA says that there are rivers flowing north on every continent.

Europe, for example, has several north-flowing rivers in one country alone: While the armies of Germany always head toward France, many of its key rivers point north -- the Rhine, the Spree, the Elbe. There are also countless north-flowing rivers in South America, Asia and elsewhere, but be honest: Do you really care?

Isn't it bad enough knowing the Germans have some? Worse yet, even Cleveland can boast of a north-flowing river: The Cuyahoga flows southwest for much of its length, but turns north toward Lake Erie and ends up further north than where it starts. Heck, the Mon isn't even the only north-flowing river in western Pennsylvania: The often-overlooked Youghiogheny also flows north to McKeesport, where it joins with the Mon. If predictions about global warming are correct, one day the frozen rivers of Antarctica will all flow north. From a global standpoint, rivers don't appear to prefer one compass heading or another.

The direction a river flows varies depending on the steepness of terrain and other local factors. Even some rivers whose general flow is southward have stretches in which a bend may take it from south to north. The Missouri flows northward for miles through Montana -- it was probably looking for a Stuckey's -- before bending east and then southeast to meet up with the Mississippi.

So why do we think north-flowing rivers are so rare? NASA's theory is that "Part of the answer is probably related to our geographic chauvinism and our lack of curiosity -- we don't know much or care about distant places. Of course, that last little remark is only going to incur the wrath of local chauvinists:

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