River Landforms 2012

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River landforms/ Features

Waterfalls

Valleys and Gorges

Meanders Floodplains

Levees

Deltas

Moving from Upper

course to Lower

course of the river.


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Waterfalls

When the gradient of a river is very steep,

water plunges down from great heights to

form a waterfall. Eg. Niagara Falls; Canada-USA

2 ways of forming.


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Formation of Waterfalls

More

erosion

Less

erosion

WaterfallPlunge

pool


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1st way

When a river flows across a zone of rocks with

different resistance

Less resistant rocks erode much faster

Causing sudden change in height of river bed,

causing the water to plunge.


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2nd way

Through faulting

Rocks uplifted, resulting in displacement of

rocks- one higher than the other.

When river flows over them, height changes

and waterfall is formed.

Eg. Victoria Falls, Zimbabwe River.


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Valleys and Gorges

Caused by Vertical erosion.

Simply put: Just the downward erosion of a

river course- causes the Deepening of river.


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Valleys

Long, narrow areas of land between highlands

or mountains.

Usually have V shape

Deep and narrow in upper part of river course

but become broader and wider in lower

course.


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What is a gorge?

Deep, narrow valley

Formed when a river erodes vertically through

resistant rocks.

Formed due to the retreat of the waterfall

upstream.

Walls of the valley remain steep- forming a

gorge. Steep walls


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Gorge


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Hard rock


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3 gorges dam- Yangtze River


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Depositional landforms

Meanders

Floodplains

Levees

Deltas


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Meanders

Found in middle to lower course of river.

Land over which river flows is flatter and river

moves in wide sweeping bends.


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Why are there winds?


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River cliff created

on outer bank

Concaveslope

Outer bank is

undercut by

erosion

Convex slope

Slip-off slope

created on inner

bank


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Explaining their existence

Meanders are features found usually

between the middle and lower course of a

river where the river channel is broad andgradient is gentle.

Erosion occurs along the outer (concave

bank) of the river, while sediments aredeposited along the inner (convex bank)-

due to difference in speed of flow.


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There is higher speed along the outer bankbecause of less friction, thus erosionoccurs- forming a river cliff (steep sided

bank) Deposition along the inner bank occurs

because there is greater friction betweenthe inner bank and water- reduces speed,

therefore deposition occurs. forms a slip-off slope.


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Oxbow lakes

Oxbow lakes form when the meanders

become more pronounced.

Due to constant erosion along the concave

banks of 2 consecutive meanders, the 2meanders will move close to each other.-

eventually being separated by a narrow

neck of land meander neck


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As deposition and erosion carries on at the

convex and concave banks respectively, the

meander neck is eventually cut through,

forming a cut-off.

This allows the river to flow straight through

the channel.

Sediments will continue being deposited along

the mouth of the cut off, eventually sealing off

the cut-off. Thus, forming an oxbow lake.


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Floodplains + Levees

Flat land along the river banks that is floodedwhen the river overflows.

As the floodwater from the river spreads out

over a larger area, the water loses speed. When the water recedes, material is

deposited along the river banks and beds.


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Coarse sediments are deposited closer to the

rivers edge (heavier) while finer alluvium are

deposited further away.

Over time, floodplains and levees (raised

banks) are formed.


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Levees

Width of channel

Width of floodplain

Levee made

up of coarse

sediments

Raised river bed

Alluvium

Fine sediments


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Deltas

Found at the mouth of the river where

the river enters the sea/lake.

Depositional feature formed whensediments carried by the river is deposited

faster than it is washed away by the waves.

Distributaries (smaller channels) extendoutwards into the sea.


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High resolution true color satellite image of

Nile River Delta, Egypt (Image taken by the

MODIS instrument on NASA's Terra satellite

on August 23, 2003.)


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Mississippi river delta, louisiana

River Landforms 2012

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