RIVERS REVISION

Key words and meaning:

Hydraulic Action – The force of the river against the banks. The pressure

weakens the banks and gradually wears it away.

Attrition – Rocks being carried by the river smash together and break into

smaller, smoother and rounder pieces.

Abrasion – Rocks carried along by the river wear down the river bed and

banks

Solution – Soluble particles are dissolved into the river.

Traction – Large boulders and rocks are rolled along the river bed.

Saltation – Small pebbles and stones are bounced along the river bed.

Suspension – Fine light material is carried along in the water.

Solution – Minerals are dissolved into the water and carried along in the

solution.

Features formed by river erosion and deposition

River Erosion Deposition Both

Waterfalls Flood Plains Meanders Gorges Deltas Ox-Bow Lakes

V shaped valleys Levees

EROSION

TRANSPORTATION

Action Definition Evaporation Water turning into water vapour

Transpiration The loss of water from the leaves of plants

Precipitation The deposition of water from the atmosphere in liquid or solid form

Surface Runoff All water flowing on the Earths surface

Evapotranspiration The sum of evaporation from the Earths surface together with the transpirationfrom plants

Infiltration Seeping of water into the soil

Sustainable Capable of existing in the long term Through-Flow The movement of water through the

soil Ground Water Flow The movement of water underground

through rocks

Interception Collection of water by vegetation Water Table The upper level of underground table

Confluence Where two rivers meet Drainage Basin The area drained by a river and its

tributaries Mouth Where a river flows into the sea

Source Where the river begins Tributary A smaller river which flows into a

larger river

Water Shed The imaginary line surrounding a drainage basin

Deltas

Some rivers reach the sea in deltas, which

form where river mouths become choked with sediment, causing the main river channel to split into hundreds of

smaller channels or distributaries. Deltas only form under certain conditions

The river must be transporting a large amount of sediment

The sea must have a small tidal range and weak currents

The sea must be shallow at the river mouth

The Formation of Ox Bow Lakes

In the lower course the meanders become even larger. Erosion on the outside of bends

and deposition on the slip off slopes CONTINUE to take place.

The erosion causes the meander neck to narrow until eventually it breaks through. This often takes place when the river has

more energy as in times of flood.

The river now follows a straight path. After the meander

has been cut through the river seals off the bend

by DEPOSITION and an ox-bow lake is formed. In

time, especially in dry areas the ox-bow lake may dry

up to form a meander scar.

A meander is a winding curve or bend in a river. They are typical of the middle and

lower course of a river. This is because vertical erosion is replaced by a sideways

form of erosion called LATERAL erosion, plus deposition within the floodplain.

Levees are basically caused by floods. In times

of low flow ANY DEPOSITIONtakes place on the

river bed and this raises the height of the river

bed. In times of flood the water leaves the

channel. As it does so it loses energy and the

courser and heavier material

is DEPOSITED near to the river on the banks.

Finer material is carried further onto the flood

plain. After many floods the river builds a bank

on either side of the river and this can lead to

catastrophes. As the river has been raised above

the flood plain and the banks are often higher

still, when the river floods the water can no

longer drain back into the river channel and often

has to form a new one.

The river is now nearing the sea and DEPOSITION becomes the dominant

process. The main features of the river channel and river valley are:

It is wide and deep with a moreefficient

shaped channel

It is lined with sand and mud so this results in less friction

There maybe islands of silt called eyots in the river and the river can split into a number of channels - river braiding

The river carries a large load of alluvium

There is a wide, flat flood plain either side of the river

There are features such as meanders, ox

bow lakes and deltas

The flood plain is made up of a thick layer of alluvium

A line of river cliffs are found at the edge of the flood plain called bluffs

The Flood Plain

Flooding In Poorer And Richer Area Case Study

Flooding In A Rich Area (Cumbria, November 2009)

31.4cm of rain in 24hrs

Ground already saturated

1 person killed

Many evacuated, 1300 homes flooded

4 bridges damaged and cost of repairs over £100m

200 people rescued from their homes by emergency services

UK government gave £1m for repairs and clean-up

Flooding In A Poor Country (Pakistan, July 2010)

Unusually heavy monsoon rains

Rivers burst their banks, 69000km2 affected

1600 people killed

20 million people affected

700,000 homes flooded

$4 billion cost of repair

Rescue of 350,000 people by Pakistan military

3 months later, 7 million people were still without adequate shelter

EFFECTS OF FLOODS ON:

People – Death, disease, damage to property, insurance claims and disruption to transport

The Environment – Landslides, loss of wildlife habitats, crops lost, soil erosion and

contamination of water supplies.

Managing Water Supply

The Elan Valley Reservoirs in Powys

It was built in 1893 and supplies Birmingham with clean, safe

drinking water.

Economic Issues

1. Creates jobs in Wales

2. Generates electricity but costs a

lot to build and maintain

Social Issues

1. Popular with school visits

2. Reduced spread of water-

borne diseases in Victorian

Birmingham

Environmental Issues

o Valleys were flooded to

create reservoirs, but

now many species rely

of it