Flowing Rivers

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A river is a natural flowing watercourse , usually freshwater , flowing towards an ocean , sea , lake 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 stream , creek, brook, rivulet, and rill. There are no official definitions for the generic term river as applied to geographic features , [1] 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, " burn " in Scotland and northeast England, and "beck" in northern England. Sometimes a river is defined as being larger than a creek, [2] but not always: Rivers are part of the hydrological cycle ; water generally collects in a river 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.

Potamology is the scientific study of rivers, while limnology is the study of inland waters in general. A river begins at a source or more often several sources , follows a path called a course, and ends at a mouth or mouths. The water in a river is usually confined to a channel , made up of a stream bed between banks.

In larger rivers there is often also a wider floodplain shaped by flood -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 valleys depressions or along plains , and can create canyons or gorges. The term upriver or upstream refers to the direction towards the source of the river, i. Likewise, the term downriver or downstream describes the direction towards the mouth of the river, in which the current flows.

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The river channel typically contains a single stream of water, but some rivers flow as several interconnecting streams of water, producing a braided river. They also occur on peneplains and some of the larger river deltas. Anastamosing rivers are similar to braided rivers and are quite rare. They have multiple sinuous channels carrying large volumes of sediment. There are rare cases of river bifurcation in which a river divides and the resultant flows ending in different seas.

Flowing Rivers

An example is the bifurcation of Nerodime River in Kosovo. A river flowing in its channel is a source of energy which acts on the river channel to change its shape and form. In , the German hydrologist Albert Brahms 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.

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 glaciated 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, 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.

Wild and free-flowing rivers

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 volume 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. 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.

Wild rivers

Because of the gradient in pressure due to the overlying weight of the glacier, such streams can even flow uphill. 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 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 Bournemouth and Eastbourne. 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 evapotranspiration.

Normally-dry rivers in arid zones are often identified as arroyos or other regional names. The meltwater from large hailstorms can create a slurry of water, hail and sand or soil, forming temporary rivers. Rivers have been classified by many criteria including their topography , their biotic status, and their relevance to white water rafting or canoeing activities. 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. At the start of the 20th century William Morris Davis devised the " cycle of erosion " method of classifying rivers based on their "age". Although Davis's system is still found in many books today, after the s and s it became increasingly criticized and rejected by geomorphologists.

His scheme did not produce testable hypotheses and was therefore deemed non-scientific. The ways in which a river's characteristics vary between its upper and lower course are summarized by the Bradshaw model.

Power-law relationships between channel slope, depth, and width are given as a function of discharge by " river regime ". There are several systems of classification based on biotic conditions typically assigning classes from the most oligotrophic or unpolluted through to the most eutrophic or polluted. 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. 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. Fast flowing rivers and waterfalls are widely used as sources of energy, via watermills and hydroelectric plants.

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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. Perhaps helped along by Barry Gibb , who wrote the former and co-wrote the latter with Andy , both tracks reached number one on the pop charts in But, strong as they are, neither gels well with the rest of the album.

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