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.

Flowing Rivers

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.

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.

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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.

Wild and free-flowing rivers

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. From Wikipedia, the free encyclopedia. Flowing Rivers Studio album by Andy Gibb. Retrieved 30 December Retrieved 20 January Australian Charts Book — Andy Gibb's Greatest Hits.

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I don't think you can pin any one thing on the way my voice and songwriting have developed. A lot of people say my album, Flowing Rivers , sounds like the Bee Gees , but if I sang or wrote any differently than I do now, it wouldn't be me at all. I was worried about my own material really, really badly. I didn't think I was a good songwriter at all.