The Work of The Work of RiversRivers

The 3 Stages of The 3 Stages of RiversRivers

River StagesRiver Stages

Youthful or Upper Stage – small fast flowing rivers high up Youthful or Upper Stage – small fast flowing rivers high up in the mountains.in the mountains. Erosion Erosion takes place here.takes place here.

Mature or Middle Stage – wider but slower rivers flowing Mature or Middle Stage – wider but slower rivers flowing down gentler slopes. down gentler slopes. ErosionErosion and and DepositionDeposition take place take place herehere

Old Age or Lower Stage – Very wide rivers flowing over a Old Age or Lower Stage – Very wide rivers flowing over a plain as they near the sea. plain as they near the sea. DepositionDeposition takes place here. takes place here.

Youthful Youthful Upper StageUpper Stage

In this stage the river is flowing down steep In this stage the river is flowing down steep slopes and is eroding verticallyslopes and is eroding vertically

EROSION

V Shaped ValleyV Shaped Valley

How rivers erode (wear away How rivers erode (wear away rocks)rocks)

Hydraulic Action – the force of moving waterHydraulic Action – the force of moving water Abrasion – material carried by the river Abrasion – material carried by the river

(load) hits against the bed and walls and (load) hits against the bed and walls and wears them awaywears them away

Attrition – the load carried by the river are Attrition – the load carried by the river are worn away themselvesworn away themselves

Solution – Chemicals in the water break Solution – Chemicals in the water break down some rocksdown some rocks

Example of V shaped valley = Youthful stage of River Liffey.

Waterfall – Erosion – Youthful Stage.Waterfall – Erosion – Youthful Stage.

Water from the river flows over the hard Water from the river flows over the hard rock. Where the water flows over soft rock, it rock. Where the water flows over soft rock, it can erode or wear this softer rock away.can erode or wear this softer rock away.

Over time this soft rock is eroded more and Over time this soft rock is eroded more and

more by the water flowing over it. This more by the water flowing over it. This makes a cliff which the water topples over makes a cliff which the water topples over

At the bottom of the cliff some of the water At the bottom of the cliff some of the water splashes onto the cliff and makes a plunge splashes onto the cliff and makes a plunge pool by a process known as undercutting. A pool by a process known as undercutting. A gorge which is a steep sided river valley is gorge which is a steep sided river valley is often formed by a waterfall .often formed by a waterfall .

Example -Powerscourt Waterfall.Example -Powerscourt Waterfall.

Interlocking SpursInterlocking Spurs

Bands of harder rock which the river Bands of harder rock which the river cannot erode straight through and is cannot erode straight through and is forced to flow aroundforced to flow around

As the river is forced to “swerve” As the river is forced to “swerve” around the spurs, lateral (horizontal) around the spurs, lateral (horizontal) erosion increases due to centrifugal erosion increases due to centrifugal force – making the curves more force – making the curves more developeddeveloped

Interlocking SpursInterlocking Spurs

Mature Stage – p32Mature Stage – p32

This is the next stage of the river as it flows down from This is the next stage of the river as it flows down from mountains – Mature Stage rivers have mountains – Mature Stage rivers have Wide Floored Wide Floored Valleys Valleys with with Gently Sloping SidesGently Sloping Sides

Mature stage rivers erode horizontally and there is also some deposition of material eroded in the upper stage

Mature stage features - Valley Troughs, Meanders

MeandersMeanders

A A MeanderMeander

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The Old Age StageThe Old Age Stage

In the old age stage the river flows over flat In the old age stage the river flows over flat plains as it nears the seaplains as it nears the sea

No EROSION takes place here, only No EROSION takes place here, only DEPOSITIONDEPOSITION

Features include Flood Plains, Levees, Features include Flood Plains, Levees, Oxbow Lakes and DeltasOxbow Lakes and Deltas

The Old Age Stage The Old Age Stage

A Flood PlainA Flood Plain

Ox Bow LakesOx Bow Lakes

An Ox Bow LakeAn Ox Bow Lake

DeltasDeltas

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New Orleans – Hurricane KatrinaNew Orleans – Hurricane Katrina

Ardnacrusha DamArdnacrusha Dam

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