RIVERS Erosions & Sedimentation)

By Muneeba FatimaMSc,ZOW,UoK

A RIVER is a natural flowing watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In some rare cases a river could flow into the ground and dry up completely at the end of its course, without reaching another body of water. Small rivers may be called by several other names, including stream, creek, brook, rivulet, and rill. There are no official definitions for generic terms, such as river, as applied to geographic features, although in some countries or communities a stream may be 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, but not always: the language is vague.

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.g. from glaciers). Potamology is the scientific study of rivers while limnology is the study of inland waters in general.

Erosion in the context of soil and watershed conservation is the detachment and movement of soil particles by natural forces, primarily water and wind. More broadly, erosion is the process of wearing away rocks, geologic, and soil material via water, wind, or ice (e.g., glaciers). Erosion will transport materials after mechanical weathering has broken rock and geologic materials down into smaller, moveable pieces.

River Processes: Types of erosion, transportation and deposition

There are three main types of processes that occur in a river. These are erosion, transportation and deposition. All three depend on the amount of energy there is in a river. 

Types of erosion The energy in a river causes erosion. The bed and banks can be eroded

making it wider, deeper and longer. Headward erosion makes a river longer. This erosion happens near its source.

Surface run-off and and throughflow causes erosion at the point where the water enters the valley head.

Vertical erosion makes a river channel deeper. This happens more in the upper stages of a river (the V of vertical erosion should help you remember the v-shaped valleys that are created in the upper stages).

Lateral erosion makes a river wider. This occurs mostly in themiddle and lower stages of a river.

There are four main processes of erosion that occur in rivers. These are: hydraulic action  abrasion / corrasion attrition corrosion

•Attrition - rocks being carried by the river smash together and break into smaller particles. Over time, they become smaller and eventually reduced to fine particles called silt •Abrasion - stones that the river is carrying bump into the banks and wear them away •Solution - acids in the water slowly dissolve the river banks and the stones that the river is carrying (especially limestone)

Sedimentation is the process in which particulate matter carried from its point of origin by either natural or human-enhanced processes is deposited elsewhere on land surfaces or in waterbodies. Sediment is a natural product of stream erosion; however, the sediment load may be increased by human practices. Such enhanced sources of sediment in a watershed include unvegetated streambanks and uncovered soil regions, including construction sites, deforested areas, and croplands.

Sediment is eroded from the landscape, transported by river systems, and eventually deposited in a lake or the sea. For example, the Fraser River carries an average of 20 million tonnes of sediment a year into the marine environment.

Ravi

Chenab

Jhelum

Sutlej

River INDUS

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