I q b a l A l i . c o m

A river is a natural waterway that transports water through a landscape from higher to lower elevations. A river is a component of the water cycle. The water within a river is generally collected from precipitation through surface runoff, groundwater recharge (as seen at baseflow conditions / during periods of lack of precipitation) and release of stored water in natural reservoirs, such as a glacier.

A river may have its source in a spring, lake, from damp, boggy landscapes where the soil is waterlogged, from glacial melt, or from surface runoff of precipitation. Almost all rivers are joined by other rivers and streams termed tributaries, the highest of which are known as lang=”en”>headwaters. Water may also originate from groundwater sources.

Throughout the course of the river, the total volume 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.

From their source, rivers flow downhill, typically terminating in a sea or in a lake, through a confluence. In arid areas rivers sometimes end by losing water to evaporation. River water may also infiltrate into the soil or pervious rock, where it becomes groundwater. Excessive abstraction of water for use in industry, irrigation, etc., can also cause a river to dry before reaching its natural terminus.

The mouth, or lower end, of a river is known as its base level. The area drained by a river and its canals is called catchment, catchment basin, drainage basin or watershed. The term “watershed” is also used to mean a boundary between catchments, which is also called a water divide, or in some cases, continental divide.

Rivers have been a source of food since pre-history. Apart from being a rich source of fish, rivers indirectly aid cultivation by supplying water for the crops. Rivers sustain their own food chain. They are a major source of fresh water, hence, it is no surprise to find most of the major cities of the world situated on the banks of rivers. Rivers also provide an easy means of disposing of waste.

The rocks and gravel generated and moved by rivers are used in construction. The beauty of rivers and their surroundings contributeds to tourist income. In upland rivers, rapids with whitewater or even waterfalls occur. Rapids are often used for recreational purposes (see whitewater kayaking). Fast flowing rivers and waterfalls are harnessed as sources of energy, via watermills and hydroelectric plants.

The flora and fauna of rivers use the aquatic habitats available, from torrential waterfalls through to lowland mires. Although many organisms are restricted to the fresh-water in rivers, some, such as Salmon and Hilsa have adapted to be able to survive both in rivers and in the sea. 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. Human activity, however, has upset the natural way flooding occurs by walling off rivers, straightening their courses and by draining of natural wetlands.

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.

contaminated river

This artikle, writen by Siska NK