This is a Profile of a River-Middle, Upper and Lower Stages:This is a Profile of a River-Middle, Upper and Lower Stages:

o In the upper course of the river, there are many features. o The river channel is narrow and fast, with interlocking interlocking

spurs spurs and v-shaped valleysv-shaped valleyso Steep drops in the river with extremely fast flows are

waterfalls,waterfalls, with retreating gorges of recessiongorges of recession, ending with a plunge poolplunge pool.

The river cuts The river cuts downwardsdownwards like a saw. like a saw.This happens in the upper part of the river and makes the This happens in the upper part of the river and makes the valley go deep.valley go deep.Rain erodes the edges to make it wider at the top.Rain erodes the edges to make it wider at the top.

Vertical Vertical erosion is erosion is dominantdominant

12/04/23By Mohammad yaseen Serry and Mohammad Osama Hassanally

Middle course of the river has more energy and a high volume of water. Middle course of the river has more energy and a high volume of water. The gradient here is gentle and The gradient here is gentle and lateral (sideways) erosionlateral (sideways) erosion has widened the has widened the river channel. The river channel has also deepened. A larger river channel river channel. The river channel has also deepened. A larger river channel means there is less friction, so the water flows faster: means there is less friction, so the water flows faster:

o As the river erodes laterally, to the right side then the left side, it forms large bends, then horseshoe-like loops called meanders.

o The formation of meandersmeanders is due to both deposition and erosion.

o The force of the water erodes and undercuts the river bank on the outside of the bend where water flow has most energy.

o On the inside of the bend, where the river flow is slower, material is deposited.

o Over time the horseshoe become tighter, until the ends become very close together. As the river breaks through and the ends join, the loop is cut-off from the main channel. The cut-off loop is called an oxbow lakeoxbow lake. The animation demonstrates how these features form.

River Landscapes and Processes By Mohammad Yaseen Serry and Mohammad Osama Hassanally

12/04/23By Mohammad yaseen Serry and Mohammad Osama Hassanally

o In the lower course, the river has a high volume and a large discharge. discharge. The river channel is now deep and wide and the landscape around it is flat. However, as a river reaches the end of its journey, energy levels are low and deposition takes place.

o The river now has a wide floodplain. A floodplain is the area around a river that is covered in times of flood. A floodplain is a very fertile area due to the rich alluviumalluvium deposited by floodwaters. This makes floodplains a good place for agriculture. A build up of alluvium on the banks of a river can create levees levees which raise the river bank.

o Deltas Deltas are found at the mouth of large rivers - for example, the Mississippi. A delta is formed when the river deposits its material faster than the sea can remove it. There are three main types of delta, named after the shape they create:

(i)(i) Fan-ShapedFan-Shaped(ii)(ii) Tooth-ShapedTooth-Shaped(iii)(iii) Birds FootBirds Foot

12/04/23By Mohammad yaseen Serry and Mohammad Osama Hassanally

Erosion: This involves the wearing away of rock and soil found along the river bed and banks, mainly in the upper course. There are four main forms of river erosion:

o Hydraulic action : river wears away the river bank from underneath.o Attrition : rocks being carried by the river collide and break into smaller

particles.o Abrasion/Corrasion : rocks carried along by the river wear down the river bed

and banks.o Solution/Corrosion : smaller particles are dissolved into the river.

Transportation: This involves transporting the eroded material downstream.

o Traction: Large boulders roll along the river bed.o Saltation: pebbles bounce along the bed.o Suspension: Sand/silt carried in the flow.o Solution: Minerals are dissolved and carried in the flow.

Large particles such as gravel and coarse sand are lifted and dropped along the river, so they bounce along the river bed in a series of bed.

Larger particles like pebbles and boulders roll and slide along the river bed.

Smaller particles such as clay, silt and fine sand are carried along without contact with the river bed. 

Dissolved materials containing minerals like calcium and sodium are carried in the water

Solution

Causes:o 50 days of raino Faulty levées

Effects:o The floods occurred in 1993o 23 people died, 1000s evacuatedo 6 million acres of farmland were submergedo Electricity cables, roads and railway lines

drownedo $10 billion was needed for repairs etc

Effects: Over 57% of land was flooded. 240 villages were submerged. Over 1000 people were killed. Shortages of drinking water. Cost the country $1 billion.

Physical causes: 70% of the land is less than 1 metre above sea level. Rivers, lakes and swaps cover 10% of the land. Tropical Cyclones, heavy monsoon rain and coastal

floods. Snow melts in the Himalayas Most of Bangladesh is the huge flood plain and delta of

the rivers Ganges and Brahmaputra.

Human causes: Deforestation (Nepal & Tibet) Construction of dams in India Global warming Flood defences such as embankments Urbanization creating obstacles to the free flow of water

River managemento Rivers can be useful, they bring fertile soil in floods-e.g. In the meander scar and

flood plain.

o However, floods can destroy people and settlements.

o By introducing plans, floods can be prevented, some of these are:

QuestionsThe point where two rivers meet and flow into the sea

     The force of the water wearing away the bed and banks of

the river

(i)Deforestation (ii) Construction of dams (iii) Global warming

(i) Raise levees (ii) Planting trees (iii) Cutting river channels (iv) Dredging

It is the zigzag flow of the river

2. What is Corrosion ?

1. What is a confluence?

4. Name at least 4 ways of preventing floods.

3. Name at least 3 human causes of floods in Bangladesh?

5. Explain what a meander is?