river erosion and its associated fetures

R i v e r E r o s i o n & i t s

A s s o c i a t e d F e a t u r e s

Dr. V. R Ghodake

Department of Civil Engineering.

Sinhgad College Of Engineering, Vadgaon (Bk), Pune.Email Id- vyanky.g@gmail.com

Mobile- +919764484757

Longitudinal River Profile

Ele

vation (

feet)

0

3,000

Headwaters

UltimateBase level

River Length (Miles)100 0

This diagram outlines the longitudinal profile of ariver basin from the headwaters to the ultimatebase level, or sea level. A rivers gradient issteepest near the headwaters and gentlest nearthe base level. In South Carolina, the steepestsections are often found in the blue Ridge andPiedmont, while the gentler gradient occurs in theCoastal Plain. River length, or distance, ismeasured from the rivers mouth to itsheadwaters, seemingly reversed from what onemight expect.

Longitudinal Profile and WatershedsHeadwaters:

multiple low-order streams near

drainage divide

Base level: single outflow and

highest order stream

This figure is a hypothetical river basin. The black dotted linerepresents the drainage divide and the numbers refer to streamorder. Any rainfall that falls within the black dotted line willeventually flow into the main strem river and out at the mouth.Stream order increases from the headwaters to the base level.In this example, the river is a5th-order river.

Stream Order:

1st order and 1st order = 2nd order

2nd order and 2nd order = 3rd order

3rd order and 3rd order = 4th order

4th order and 4th order = 5th order

And so on, 5 and 5 =6, 6 and 6 =7th order…

5

1

1

1

2 2

11

3

4

3

4

5

3

Table of Contents

Rivers and Basins

Radial type Drainage Pattern

Radial Drainage pattern

Dendritic type Drainage Pattern

–

Trellis type Drainage Pattern

Rectangular type Drainage Pattern

Common River Features

A river can erode material from its bed and

banks in 4 main ways

Chemical Action

Abrasion

Hydraulic Action

Attrition

The Work of Rivers

The erosional work of streams/rivers and shapes

the landscape through which they flow.

functions of rivers

a. Erosion

b. Transportation

c. Deposition

The Work of Rivers

Erosion

•A river may erode in 4 ways

1.Abrasion/corrasion

Load carried by a river will grind against its

bed and sides.

This process slowly wears the bed and sides

away.

The Work of Rivers

2. Attrition

When thrown against the sides and bed of

rivers, the load gets broken into smaller

pieces.

The Work of Rivers

3. Hydraulic action

The work of turbulence in the water.

Running water causes friction in the joints of

rocks in a stream channel

Joints may be enlarged

The Work of Rivers

4. Solution/Corrosion

Certain minerals in rocks like limestone can

be dissolved in water.

Rocks are then eroded.

Methods of Transportation

Rivers transport material in 3 main ways

Solutio- Some minerals (particularly in limestone areas) dissolve easily in

water and are not visible to the naked eye

Suspension- As the speed or velocity of a river increases, it is able to pick up

and carry larger and larger particles in its flow. Where particles are carried

along in the flow and are not in contact with the river bed, they are said to be

travelling in suspension.

Bed load- heavy bigger rock fragments moves along with the flow of water is

known as bed load.

Methods of Transportation

Siltation - Heavier particles may not be held in the flow all the

time but may be bounced along the bed

Traction - The heaviest particles are rolled along the bed. Such

particles may only be moved when the river has a large volume of

water in it

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Boulders are large and semi-rounded, due to attrition within the load and abrasion with the stream bed and banks

Why are they rounded?

River load in upper course

River Transportation

BouncingRolling

SuspensionSolution

• A kettle-like small depressions in the rocky beds of the river valleys are called pot holes which are usually cylindrical in shape.

• Pot holes are generally formed in coarse-grained rocks e.g. sandstone and granites.

• The diameter of pot holes ranges from a few centimeters to several meters.

• They are found in the upper course of a river where it has enough potential energy to erode vertically.

• The pot holes go on increasing in both diameter and depth.

Pot Hole

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Pot holes,human scale!!

Waterfalls• Waterfalls occur where there is resistant bedrock, abrupt changes in bedrock resistance, or

along fractures or faults in the bedrock.

• Less resistant materials are weathered more quickly than resistant rocks, creating stair-

stepped ledges or drop offs where waterfalls occur. Less resistant rocks may also form pools

between resistant rocks that form waterfalls.

• Faults and fractures often provide natural pathways for the downslope movement of water.

• The location of the waterfalls origin may be referred to as a “knick-point”, continued

weathering by the stream flow causes the knick-point to slowly migrate upstream.

• Most waterfalls in South Carolina occur along streams in the Blue Ridge, Piedmont, and the

along the Regional Fall Line where there are rock layers of varying resistance.

This waterfall was formed by differential weathering

between the softer shale and harder more resistant

limestone.

Photo: SCGS

Lower White Water

Falls in the Jocassee

Gorges area of South

Carolina drops nearly

200 ft. Here, the

Toxaway Gneiss forms

a resistant bedrock that

the Lower White Water

River flows over before

draining into Lake

Jocasse.

Waterfalls

• Erosion:

• In this picture, which layers are being eroded to cause undermining?

• Kaaterskill Falls…

What is a meander?

38

Floodplain

Pebble deposits on the inner meander bend where there is low energy

River CliffSlip-Off Slope

39

Meandering Rivers

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Lower Severn Valley

Well developed meanders with barsin the channel indicating high sediment load

Very gentle valley side gradients

Very wide

floodplain

Formation of Oxbow lake

Ox Bow lake on Mississippi

Can you annotate this photo graph ?

A flood occurs whenever a river overflows its banks (over ‘bank full discharge’). However, a flood becomes a problem when the water rises to a level where it Destructs property and life.

bank full

dischargeMeander cross

section

What is a Flood?

Flood plains• Flood plains are

constructive, depositional landforms created by stream flow and sediment deposition.

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This aerial view of the Mississippi RiverValley contains many typical floodplainfeatures. The darker, green areas arefloodplain forest and they likely flood themost frequently and thus are notdeveloped with agriculture or housing.The surrounding patchwork representsagricultural fields and other developedlands that are probably at a higherelevation formed by natural or artificiallevees.

Pointbar

Cutbank

Oxbow

Lakes

Infilled

Channel

• The narrow flat surface on either side of the valley floor are called river terrace.

• Some times, the river valleys are frequented by several terraces on either side wherein they are arranged in step-like forms.

• River terraces are generally formed due to dissection of fluvial sediments of flood plains deposited along a valley floor.

• Terrace represents the level of former valley floors and the remnants of former flood plain.

River Terrace

Floods and Flood Control

Floods

A flood occurs when the discharge of a

stream becomes so great that it exceeds

the capacity of its channel and overflows its

banks.

Measures to control flooding include

artificial levees, flood control dams, and

placing limits on floodplain development.

NaturalLevees

River

Stages in the Development of a

River Valley

The River’s Journey

Rivers usually begin in the mountains. They flow downhill onto flat land and into the sea

Characteristics of Streams

• Water always flows downhill, even on theslightest of slopes.

• The speed of water flow depends upon theslope. As slope increases, the velocity of thewater increases.

Running Water is the Predominant Agent of Erosion on the Earth

• Every stream and its branches make up asingle system that collects all the runoffwithin a definite area called the drainagebasin of the system.

• A stream consists of running water, the landsurface it drains, the sediment it transports,and the potential energy used to drive it.

What determines a streams characteristics

• Stream Discharge: the volume of water that passes a point in the stream during a given amount of time.

• The average velocity of a stream increases as its discharge increases.

Life History of a Stream

• YOUTHFUL STREAM

• Steep gradients

• V-shaped cross sections

• Rough sediments flowing rapidly down stream.

• Due to greater water velocity larger sediment can be moved.

• Sediments cut through bedrock as they are moved along

• Common to find rapids and waterfalls due to differences in resistance of the bedrock to weathering.

V- Shape Valley

Mature Streams

• Potential energy for cutting and removing rock becomes less.

• The average gradient is decreased.

• Velocity near the bed becomes less.

• The size of sediment that can be moved decreases.

• Bed becomes covered with loose material, thus protecting it from further erosion.

• Cutting action of the stream becomes very slow.

• The base of the V has been widened due to weathering and the action of tributaries the valley now has gentle slopes.

• Meanders begin to form

• There is an increase in the volume of water that is carried.

• A greater mass of sediment can be carried, but most of it is silt and clay.

Old Streams

• Gradient becomes extremely small and onlythe finest of sediments can be moved.

• During times of peak flow the banks willoverflow and flood the nearby portions of itsvalley.

• When the flow subsides a layer of silt and clayis left behind on the valley surface, this is theflood plain.

• Meanders are strongly looped and from time to time they become cut off to form oxbow lakes.

Locations of Stages

• It is unlikely that any stream is at the same stage of development throughout it entire length.

• Most streams tend to have the characteristics of youth near their source and of old age near their mouths and to be in the mature stage somewhere in-between.

• A stream can be rejuvenated through crustal uplift.

The river cuts downward to

form a ‘V’shaped

valley. The river starts

to meander

River uses its meanders to cut from side

to side eating into

the valley

Floodplain

starts to

form1

2

1

2

Formatioin of Valleys

Alluvium = silt deposited by a river

Alluvial fan Caused when a stream falling from a side valley reaches flatter ground on the valley floor.

Material is dropped at the ‘break of slope’ to form this fan shape.

(This is really a depositional feature.)

Erosion/Deposition

Alluvial fan

Deltas

Deltas form where the mouth of a river meets its ultimate base level at the ocean or

sea. As the river’s velocity decreases, it looses the capacity to carry its sediment load

and the resulting deposits form a delta. Delta shapes and forms vary depending on

tidal influences, waves, currents, sediment type and quantity, river discharge, and the

stream gradient near the outlet. The most common types of deltas include bird-foot,

estuarine, and arcuate.

Not all rivers form deltas, for example the Amazon deposits its sediment load directly

into the ocean onto an underwater seaward sloping continental shelf. The Columbia

River in the northwest United States, lacks a delta altogether, because the currents

are too strong and erosive for the sediments to deposit.

Mississippi River Delta: Bird-Foot Delta

A bird-foot delta contains a large channel with multiplesmaller distributary channels draining off from the mainchannel and depositing sediments. They generally formwith rivers that have a high sediment load and flowinto an area with minimal tidal influences. This false-color infrared image provides a satellite view of theMississippi River delta. This delta has shifted positionsseveral times over the last 5000 years in relation tochanges in the Mississippi River. Scientist recognizeatleast 7 distinct deltas. The most recent beganforming 500 years ago and forms a classic bird-footdelta.

Deltas

Nile River and Arcuate Delta ACE Basin: Estuarine Delta

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River Nile

The Nile Delta, satellite view

Formation of Delta

That’s all aboutRiver & Its Associated Landforms