River Landscape Revision

Key words

Mouth – the point at which a river ends. This is when the river enters the sea.

Source – the point at which a river starts. It usually starts in a valley or mountain.

Tributary – a stream or river which flows into another river.

Confluence – it’s the meeting point of the tributary and the river.

Watershed – the line of high relief that separates the drainage basins.

River drainage basin

source – the point where

the river starts

watershed – the line of high relief

that separates the drainage basin.

confluence – it’s the meeting point of a

tributary and the river

mouth – the point where

the river enters the sea

river basin

tributary – a stream or river which flows into

another river. It doesn’t flow directly into the

sea.

river channel

Types of erosion

Types of erosion

Hydraulic actionWhen water causes air to be trapped in the cracks

of the river bed and banks. The trapped air

expands and causes the material to break off.

CorrasionWhen the material in the water rub together with

the river bed or bank and causes it to wear away.

It’s like a sandpaper action.

AttritionWhen the material in the

water bang into each other and causes the

material to break down into smaller particles.

CorrosionWhen soluble materials

dissolve in the water.

Types of weathering

Types of weathering

Physical weatheringWhen water in the cracks are frozen and due to the

low, freezing temperature, it will cause pressure around the rock

and may break off.

Chemical weatheringIf the rain water contains

acid (acid rain), it will break down certain rocks

such as limestone.

Biological weatheringSeeds that fall in the

cracks will grow and put force on the rock.

Animals that burrow in cracks will also put force

on the rock.

Types of mass movement

Types of mass

movement

Soil creepIt’s the slow downhill

movement of soil due to gravity. The moisture in the soil and gravity will

pull it down.

SlumpingIt’s the fast movement of

a large area of land moving down a slope. The soil gets saturated

with water and gets pulled down by gravity.

LongprofileofaRiver

Lower courseLow gradient (flat

land)

High discharge and high velocity due to the large amount of water in the river.

River channel is wide and deep as it moves towards the

sea.

Middle courseGradient decreases.

Discharge and velocity increases as the

amount of water in the river increases.

River channel gets wider and starts to

meander.

Upper courseSteep gradient as river

starts in an area of high relief.

Low discharge and velocity as there is not

much water.

River channel is narrow.

Formation of a Meander & Ox-bow Lake

All the water is directed towards the outside of the bend. This causes erosion of the outer bend and a river cliff will form. On the inside of the bend, deposition will occur and a slip-off slope will form. This happens in the middle course.

An ox-bow lake is formed when the neck of the meander grows narrower and narrower due to erosion. When the river floods, it breaks through the meander neck and takes an easier course. Deposition occurs along the edge of the new river course and the meander will cut off from the river. This happens in the middle course.

Formation of a Waterfall

The water will erode the soft

rock and leave the hard rock,

forming an overhang. As erosion

continues, it will form a plunge

pool. Eventually, the overhang

will collapse due to hydraulic

action and the water will

retreat. A gorge is formed. This

happens in the upper course of

the river.

Formation of a V-shaped valley/interlocking spurs

As the river flows, it cuts

downwards due to low river

discharge. This sis called vertical

erosion. The soil and rocks are then

attacked by weathering processes.

Eventually, it will slip down the slop

into the river. Weathering and

erosion continue to widen and

deepen the valley into the shape of

a V. As the river flows, it erodes the

soft rocks however winds its way

around the hard rocks.

Formation of a levee

When a river’s banks burst, the land besides the river will flood, this is a flood plain. The river will deposit material called alluvium. This consists of heavy material such as pebbles, medium weight material such as sand and lightweight material such as silts and clay. These materials create a levee. This happens in the lower course of the river.

Flood Risks

Human causes Physical causes

Deforestation - plants and trees lower

the amount of water that reaches the

river channel and slows down how

long it takes for the water to reach the

river channel. It increases the risk of

flooding.

Heavy rain - This means there will be

lots of water in the drainage basin and

the water table will be high. It

increases the risk of flooding.

Building a dam - This allows you to

control the amount of water entering

the river. If there is a lot of rain you

can reduce the amount of water you

let in the river channel. It decreases

the risk of flooding.

Permeable rock - If the water soaks

through the rock, it takes longer to get

to the river channel. This slow

response lowers the risk of a flood.

Urban Development - Building on the

floodplain will mean all surfaces are

impermeable. This means when it

rains, water will flow into the river

channel quickly. This increases the risk

of flooding

Hot, sunny weather - This means there

will be ore evaporation, therefore

lowering the overall water level. It

decreases the risk of flooding.

Building roads - This increases the

amount of impermeable surface and

the roads can quickly carry the water

to the river. This increases the risk of

flooding.

Lots of tributaries - This will mean the

rain water reaches the river channel

quickly. This is because the water

travels quickly to the main river

through streams and smaller rivers.

This increases the risk of a flood.

Case study: Boscastle Flood of 2004

Boscastle is located in Cornwall which is in the south west of England.

Human causes of flood Physical causes of flood

• Deforestation on drainage basin• Built buildings and roads, making

the surface impermeable

• 20mm of rain throughout the afternoon (heavy rain)

• The River Valancy and Jordan meet, doubling the volume of water

• The river bursts its banks

Effects of the flood• Many cars were washed away• Local shops and buildings were damaged• Up to 60% of income was lost because they rely on tourism

during the summer• Sections of South West Coast Path had to be closed• A car park had to be rebuilt• Trees were washed away

Responses to flood• Residents were airlifted by helicopters• Sections of South West Coast Path had

to be closed• Infrastructure had to be rebuilt

River defencesHard Engineering Technique Description Advantages Disadvantages

Embankments Raised banks along the river To make it more difficult to flood due to the high relief. It’s natural.

Unsafe for children. Takes up space. Sometimes not high enough.

Channelisation Channel may be widened, deepened or straightened to carry more water

Reduces risk of flooding. Can lead to greater flooding downstream.

Flood relief channels Channel may be altered to divert water away from settlements

Water is diverted, protecting residents. Requires large amount of land. Expensive.

Dams Controls amount of water in river Water stored in reservoir behind dam. Can generate hydroelectricity.

Expensive. Erosion downstream.

Flood walls Vertical barrier made from concrete Can be used where space is limited. Has to be assembled well.

Storage areas Will fill with water if river floods – areas next to river

Natural looking. Doesn’t damage environment.

Only comes into use when river is flooded.

Soft Engineering Technique Description Advantages Disadvantages

Floodplain zoning Controlling development next to rivers Cheap. Reduces impact of flooding. Can’t build on that land. No one is able to live there.

Washlands River allowed to flood naturally in wasteland areas

Nothing is built. Provides wetland for birds and plants. Agricultural land.

Can’t be built on. Marshlands are formed.

Warning systems Sirens which give people early warnings of flood events

Cheap. Not enough time for residents to prepare.

Afforestation Plant trees to slow down rainfall reaching river

Increases fire risk.

Case study: River Nene in Northampton, UKHeavy rain on the 9th of April, 1998, caused the river to overflow. 2 people died as a result.

Management Technique 1A clay flood embankment raised the land by 6.8m in 2002. It cost £2 million. It’s a hard engineering technique.

Management Technique 2The warning system was upgraded by the environment agency, providing 2 hours notice. It’s a soft engineering technique.

Management Technique 3A flood retention reservoir to control water. It’s a hard engineering technique.

Management Technique 4A washland was created in 2007 to divert the water and reduce flooding. It cost £8 million. It’s a soft engineering technique.

Management Technique 54m floodwalls were installed near Northampton Railway Station. Gabion boxes protect the banks from erosion. It’s a hard engineering technique.

The managements have allowed a new housing estate to be built on the flood plain.