Rivers (Cambridge (CIE) IGCSE Geography)

A drainage basin is an open system that drains all the water which lands on the Earth's surface. Every drainage basin is covered by a network of tributaries which connect to a main river channel.

A watershed is the boundary between two drainage basins.

A confluence is where two rivers or streams join together.

True.

Every drainage basin is unique.

A tributary is a smaller stream or river that flows into a larger stream or main river.

Drainage density refers to the number of tributaries in a drainage basin. To calculate the drainage density the area of drainage basin is divided by the number of tributaries.

False.

Drainage basins with lots of tributaries have a high drainage density.

The mouth of a river is where the river enters the sea/lake.

The four types of erosion in rivers are:

• Hydraulic action.

• Abrasion.

• Attrition.

• Corrosion (solution).

Hydraulic action is the erosion process where the force of water wears away the bed and banks of a river.

Abrasion is the erosion process where material carried by the river grinds the bed and banks.

False.

Vertical erosion is dominant in the upper course of rivers.

The four processes of transportation in rivers are:

• Traction.

• Saltation.

• Suspension.

• Solution.

Traction is the transport of large particles along the river bed.

Saltation is the form of transportation which involves material bouncing along the river bed.

False.

Deposition occurs when a river does not have enough energy to carry materials.

The Bradshaw model summarises the changes in river characteristics as it moves downstream.

Bedload is the heaviest material carried by a river, typically along the river bed.

Upland river landforms include:

• Waterfalls.

• Gorges.

• V-shaped valleys.

• Interlocking spurs.

A plunge pool is a deep pool at the base of a waterfall formed by hydraulic action and abrasion.

False.

V-shaped valleys are formed by vertical erosion.

Interlocking spurs are alternating ridges of land that project into a river valley in upland areas.

A meander is a bend in the course of a river.

False.

Waterfalls often form where hard rock overlies soft rock.

Oxbow lakes form when a meander is cut off from the main river channel during a flood.

A floodplain is a flat expanse of land on either side of a river formed by the migration of meanders and the deposition of silt during floods.

A levée is a natural embankment formed by deposition of sediment along a river's banks.

A delta is a landform formed when a river flows into a standing body of water and deposits sediment.

The two main river hazards are flooding and erosion.

Bankfull discharge is when the water in a river reaches the top of its banks.

Two main natural causes of river flooding are heavy torrential rain and prolonged steady rain.

True.

Human activities can increase the risk of flooding.

Urbanisation is the process of land becoming more urban, often resulting in increased impermeable surfaces.

There are a range of hazards related to flooding including:

• The spread of water-related diseases.

• Deaths and injuries.

• Damage to infrastructure.

• Erosion of river banks.

• Destruction of crops.

Opportunities provided by rivers include:

• Fertile soil for agriculture.

• Water for irrigation.

• Transport routes.

• Leisure and tourism.

• Electricity generation.

• Food.

• Flat land for ease of construction.

True.

Flood waters increase the risk of water related diseases. The water may act as a breeding ground for the animals that spread disease for example, the mosquito. The water may be contaminated by bacteria which can spread diseases such as cholera

False.

Flooding leads to a increase in erosion of the banks of rivers due to increased discharge and velocity.

A flood hydrograph is a graph showing changes in river discharge after a storm event.

Lag time is the time taken for precipitation to reach the river from where it falls.

False.

Rivers with a short lag time have a higher flood risk

The two main categories of flood management are hard engineering and soft engineering.

Hard engineering involves building structures or changing the river channel to manage floods.

Examples of hard engineering include:

• Dams and reservoirs.

• Embankments or levées.

• Straightened channels.

• Flood relief channels.

• Spillways or overflow channels.

River restoration is a soft engineering technique that supports the river by restoring it back to its original regime.

Flood plain zoning is a soft engineering technique that restricts certain land uses on the flood plain to reduce risk.

False.

Dredging rivers can increase flood risk by requiring concrete reinforcement of banks

The main features of the Flood Action Plan (FAP) in Bangladesh included:

• Monitoring of flood levels.

• Construction of levées/embankments.

• Building 5 000 flood shelters.

• Creating flood water storage systems.

• A more effective flood warning system.

• Building of dams to store water.

• Reducing deforestation.