Rivers

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Keywords

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Confluence - the point at where two rivers join

Tributary - a smaller river witch joins a larger river

Drainage basin - the area of land drained bed by a river

Source - the start of the river

Watershed - the boundary between one drainage basin and another

Mouth - where the river meets the sea

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Processes of river erosion

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Hydraulic action - the force of the water breaks rock particles away from the river channel

Abrasion - eroded rocks picked up by the river scrape and rub against the channel wearing it away

Attrition - eroded rocks picked up by the river smash into each other and break into small fragments

Solution - river water dissolves some types of rock e.g chalk

Front 3

Process sediments

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Traction - large boulders and rocks are pushed along the river bed by the force of water

Saltation - small pebbles and stones are bounced along the river bed by the force of water

Suspension - small particles like salt and clay are carried along by the water

Solution - minerals are dissolved in the water and carried away

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Interlocking Spurs

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1. The river at its source is small and aren't powerful enough to erode side laterally

2. It flows naturally from side to side around ridges in the valley sides called Spurs. The Spurs become interlocking with those on the other side of the valley

3. The hillside that interlock with each other as the river winds around them are called interlocking spurs

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V shaped valley

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1. Abrasion and hydraulic action cut into the land scape ( vertical erosion )

2. Over time the sides of the valley are weakened by weathering

3. Mass movement causes materials from the valley sides to fall into the river

4. This material is transported downstream by the river. This results in the distinctive v shape

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V shaped valley

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1. Forms where a river slows over an area of hard rock followed by an area of softer rock

2. The softer rock is eroded more than the hard rock creating a step in the river

3. As water goes over the step it erodes more and more of the softer rock

4. A steep drops is eventually created which is called a waterfall

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1. The hard rock is eventually undercut by erosion it becomes unsupported collapses

2. The collapsed rock are swirled around at the foot of the waterfall where they erode the softer rock by abrasion. This creates a deep plunge pool

3. Over time more undercutting causes more collapses. The waterfall will retreat ( move back up the channel) leaving behind a steep sided

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Back (Definition)

Front 8

1. Flow of the water is faster on the outside of the bend because the river channel is deeper

2. So more erosion takes place on the outside of the bend forming river cliffs

3. The flow of the water is slower on the outside of the bend because the river channel is shallower

4. So eroded material is deposited on the inside of the bed forming slip of slope

Back 8

Back (Definition)

Front 9

Ox bow lake

Back 9

1. Erosion causes the outside bends to get closer until there's only a small bit of land left between the bend (neck)

2. The river breaks through the land, and the river flows along the shortest cause

3. Deposition eventually cuts off the meander forming an ox bow lake

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Human causes of flooding

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Back (Definition)

Front 11

Physical causes of flooding

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Back (Definition)

Front 12

Flood management hard engineering

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Back (Definition)

Front 13

Flood management soft engineering

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Back (Definition)

Front 14

Ganges

Back 14

Bangladesh is a very low lying country, with 70% of its
land area being less than 1m above sea level and 80%
of it being floodplain.
2. Bangladesh receives large amounts of water passing
through it with two major rivers (the Ganges and
Brahmaputra)
3. Bangladesh has a monsoon climate and the annual rains
which result often result in the rivers exceeding their capacity and flooding;
4. In the spring, melting snow from the Himalayas further increases the flood
risks as torrents of melt water enter the rivers at their source.

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Human causes

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. Increasing population pressure in the foothills has resulted in intense
deforestation.
2. Deforestation is also believed to be responsible for the increased soil erosion
which has led to large amount of silt being washed into the rivers, reducing its
channel capacity and increasing the likelihood of flooding.
3. Increasing population pressure in Bangladesh itself has resulted in the sinking of
many new wells resulting in the lowering of the water table
4. Bangladesh is an LEDC and its lack of money and heavy national debt means that
little money is available to spend on flood protection methods / defences and
many existing defences lack upkeep and are of questionable use.

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Flooding in bangladesh - Ganges

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-1998- the river Ganges passes through the lower stage of the river - very mainly tributary - the soil in the country is mostly clay which makes puddles hard to soak in - The low-lying land means it is easily flooded.

Causes of the flooding was flat land, monsoon rain

Causes of flooding human - building in flood plain and deforestation. -

Secondary effects - diseases , 3000 people died

Primary effects - homeless ,

Solution - having a better warning system - building food shelters - vegetation along the banks of the river - removing any material along the beach / channelisation - straightening the river

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NEGATIVE EFFECTS OF FLOODING

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Over two thirds of the land area was covered by water and the capital, Dhaka,
was 2m underwater.
 30 million people were made homeless in the floods with many losing all their
belongings.
 1,070 people died – due to drowning in the flood waters, contamination of water
by waste and dead bodies / animals, and the lack of a clean water supply
resulted in the spread of disease such as cholera and typhoid. 74 | Page
 Food supplies were severely affected as flooding destroyed the rice stocks with
a total of 668,529ha of crops being destroyed;
 Communications became difficult, with shopping impossible in the main port, as
well as roads and railways having been swept away making the distribution of aid
and the rescue operation very difficult

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FLOOD RELIEF / MANAGEMENT IN BANGLADESH

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Following the 1998 floods a number of short term flood relief measures were put in
place to try minimise loss of life - these included:
• international food aid programmes
• the distribution of free seed to farmers by the Bangladesh government to try
and reduce the impact of food shortages
• volunteers / aid workers worked to try and repair flood damage

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long term a number of flood prevention measure are possible:

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the creation of embankments (artificial levees) along the river to increase
channel capacity and restrict flood waters - however since 1957, 7,500km of
flood embankments have been constructed and yet many were breached in the
1998 floods;
• constructing flood protection shelters (large buildings raised above the ground)
to shelter both people and animals
• emergency flood warning systems and plans made for organising rescue and
relief services;
• providing emergency medical stores in villages
• building flood proof storage sheds for grain and other food supplies
• Dam construction upstream and major embankments around Dhaka have been
suggested however lack of money has meant that these suggestions have not
been taken furthe