Erosion, Sedimentation and River Basin

7/27/2019 Erosion, Sedimentation and River Basin

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Erosion is a natural processwhich is usually made by rockand soil being loosened fromthe earth's surface at onelocation and moved to another.

The process begins with aprocess called weathering


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Waves in oceans and other largebodies of water produce coastalerosion. The power of oceanic waves

is huge, large storm waves canproduce 2000 pounds of pressure persquare foot. The pure energy ofwaves along with the chemicalcontent of the water is what erodes

the rock of the coastline.


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The erosive power of moving ice isactually a bit greater than thepower of water but since water is

much more common, it isresponsible for a greater amount oferosion on the earth's surface.

Glaciers can perform to erosivefunctions - they pluck and abrade


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Erosion by wind is known

as aeolian (or eolian)erosion (named afterAeolus, the Greek god ofwinds) and occurs almostalways in deserts. Aeolian

erosion of sand in thedesert is partiallyresponsible for theformation of sand dunes.

The power of the winderodes rock and sand.


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Water is the most important agentin erosion. It erodes as running

water in streams. However, waterin all its forms is erosional, evenraindrops. Raindrops creates splash

erosion that moves tiny particles ofsoil, while waters in rivers cancreate a valley.


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Water erosion may be viewed as starting withthe detachment of soil particles by the impact

of raindrops. The kinetic energy of the dropscan splash soil particles into the air.


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The splash and overland-flow

processes are responsible for sheeterosion, the relatively uniformdegradation of the soil surface.

Sheet erosion is difficult to detectexcept as the soil surface islowered below old soil marks on

fence posts, tree roots are exposed,or small pillars of soil capped by

stones remain.


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Gully erosion may occur ifturbulence in the flow is strong

enough to dislodge particles fromthe bed and banks of the channel


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Mass movement of soil as eitherslow or downward creep of thesoil mass or a landslide is an

important mechanism deliveringsoil to the streams in steep

canyons with unstable sideslopes.


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RAINFALL REGIME

VEGETAL COVERSOIL TYPE

LAND SLOPELAND USE


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Sediment moves in the stream as suspendedsediment in the flowing water and as bed load,which slides or rolls along the channel bottom.

Saltation is used to describe the movement ofparticles which seem to bounce along the bed.


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The settling velocity of suspended

particles in still water is approximatedby Stokes Law:

Where and g are densities, r is theradius of the particle, and is theabsolute viscosity of water


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For many years, analysis of bed-loadtransport has been based on the classicalequation of du Boys

Where Gi is the rate of bed-load transport per unit width ofstream, Y is an empirical coefficient depending on the sizeand shape of particles,o is the shear at streambed, and c ismagnitude of shear at which transport begins


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Because of the uncertain accuracy ofinstruments for bed-load measurement; awidely-used approach made by Einstein isused; who defines the intensity of bed-loadtransport as:

And theflow intensity as


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Hydraulic action of the wateritself moves the sediments

Water acts to corrode sedimentsby removing ions and dissolving

them Particles in the water strike

bedrock and erode it


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lateral erosion erodes the sediment

on the sides of the stream channel down cutting erodes the stream bed

deeper

headward erosion erodes thechannel upslope.


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SEDIMENTATION


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Sedimentation

is the tendency for particles in suspension to settle out ofthe fluid in which they are entrained, and come to restagainst a barrier. This is due to their motion through thefluid in response to the forces acting on them: theseforces can be due to gravity, centrifugal

acceleration or electromagnetism. In geology sedimentation is often used as the polar

opposite of erosion, i.e., the terminal end ofsedimenttransport. In that sense it includes the termination oftransport bysaltation or truebedload

transport. Settling is the falling of suspended particlesthrough the liquid, whereas sedimentation is thetermination of the settling process.
http://en.wikipedia.org/wiki/Particle_(ecology)http://en.wikipedia.org/wiki/Suspension_(chemistry)http://en.wikipedia.org/wiki/Gravitationhttp://en.wikipedia.org/wiki/Centrifugal_accelerationhttp://en.wikipedia.org/wiki/Centrifugal_accelerationhttp://en.wikipedia.org/wiki/Electromagnetismhttp://en.wikipedia.org/wiki/Sediment_transporthttp://en.wikipedia.org/wiki/Sediment_transporthttp://en.wikipedia.org/wiki/Saltationhttp://en.wikipedia.org/wiki/Bedloadhttp://en.wikipedia.org/wiki/Bedloadhttp://en.wikipedia.org/wiki/Settlinghttp://en.wikipedia.org/wiki/Settlinghttp://en.wikipedia.org/wiki/Bedloadhttp://en.wikipedia.org/wiki/Bedloadhttp://en.wikipedia.org/wiki/Bedloadhttp://en.wikipedia.org/wiki/Saltationhttp://en.wikipedia.org/wiki/Sediment_transporthttp://en.wikipedia.org/wiki/Sediment_transporthttp://en.wikipedia.org/wiki/Electromagnetismhttp://en.wikipedia.org/wiki/Centrifugal_accelerationhttp://en.wikipedia.org/wiki/Centrifugal_accelerationhttp://en.wikipedia.org/wiki/Gravitationhttp://en.wikipedia.org/wiki/Suspension_(chemistry)http://en.wikipedia.org/wiki/Particle_(ecology)


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Classification of sedimentation

Type 1 sedimentation is characterized by particlesthat settle discretely at a constant settling velocity.

Type 2 sedimentation is characterized by particles

that flocculate during sedimentation Type 3 sedimentation is also known as zone

sedimentation.


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SEDIMENT MEASUREMENT

the most common test used in sedimentmeasurement is the deep integrated hand sampler,

which is commonly used in small streams.

a good sampler must cause minimum disturbance ofstream flow, avoid error from short-periodfluctuations in sediment concentration; and give

result which can be related to the velocitymeasurements.


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SEDIMENT RATING CURVE

A sediment rating curves relating suspendedsediment discharge and water discharge iscommonly used to estimate sediment load.

Numerical expression or graphical curve thatdescribes the quantitative relationship betweenstream discharge and the sediment transported by aparticular stream.


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SEDIMENT YEILD OF A CATCHMENT

The average annual sediment production from acatchment is dependent on may factors, such as theff.:

CLIMATE

SOIL TYPE

LAND USE

TOPOGRAPHY

PRESENCE OF RESERVOIRS


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RESERVOIR SEDIMENT

The rate at which the capacity of a reservoir isreduced by sedimentation depends on:

QUANTITY OF SEDIMENT INFLOW THE PERCENTAGE OF THIS INFLOW TRAPPED

IN THE RESERVOIR

THE DENSITY OF THE DEPOSITED SEDIMENT


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RESERVOIR SEDIMENT


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RIVER BASIN


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RIVER BASIN


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RIVER BASIN

The land area that is drained by a river and

its tributaries. The Mississippi River basin, for

example, is a vast area that covers much of

the central United States from the centralranges of the Appalachian Mountains in the

east to the eastern ranges of the Rocky

Mountains in the west, funneling toward itsdelta in southern Louisiana and emptying

into the Gulf of Mexico.


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PARTS OF THE RIVER BASIN

Water Shed: A piece of land where water from rain and the melting ofice drains into a larger body of water. Includes the streams, rivers andchannels.

Tributaries: A stream or river that flows into a main or parent river. Itdoes not directly flow into a large body of water like an ocean or lake,

but instead connects up to a river that does.

Distributaries:A stream or river that branches off of the main or parentriver. It then can lead to a larger body of water, or in some cases it mightsteal so much water from the parent river that it becomes the main.

Yazoo Streams:A stream that runs parallel to a river, and eventuallyjoins up to it.

Confluence: The meeting of two or more bodies of water. It usuallyrefers to the tributary of two rivers or streams meeting up but sometimesit can be two channels, or a channel and a lake.


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PARTS OF THE RIVER BASIN

Estuary: A partly enclosed coastal body of water with one ormore rivers flowing into it and an open connection to the sea. It isprone to both ocean and river influences.

Braided Stream: A stream with many small shallow channels that

divide and recombine many times creating a braided pattern.They form when a sediment load is too heavy and it has to bedeposited along the channel.

Groundwater: Water that is located beneath the surface of theEarth in pores in the soil.


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USES OF RIVER BASIN IN HYDROLOGY

Measurement of the discharge of water from

a basin may be made by a stream

gauge located at the basin's outlet.


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OTHER USES OF HYDROLOGY

Drainage basins are important elements to consideralso in ecology. As water flows over the ground andalong rivers it can pick up nutrients, sediment,and pollutants. Like the water, they get transported

towards the outlet of the basin, and can affect theecological processes along the way as well as in thereceiving water source.

Drainage basins are the principal hydrologic unit

considered in fluvial geomorphology. A drainagebasin is the source for water and sediment thatmoves through the river system and reshapes thechannel.

Erosion, Sedimentation and River Basin

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