- Created by: Meggyboo2000
- Created on: 13-04-14 13:03
Upper-course river features include steep-sided V-shaped valleys, interlocking spurs, rapids, waterfalls and gorges.
Middle-course river features include wider, shallower valleys, meanders, and oxbow lakes.
Lower-course river features include wide flat-bottomed valleys, floodplains and deltas.
- As the river erodes the landscape in the upper course, it winds and bends to avoid areas of hard rock. This createsinterlocking spurs, which look a bit like the interlocking parts of a zip.
- When a river runs over alternating layers of hard and soft rock, rapids andwaterfalls may form.
Middle course features
In the middle course the river has more energy and water. It is also deeper.
- As the river erodes laterally, to eaither side it forms large bends, and then horseshoe-like loops called meanders.
- The formation of meanders is due to both deposition and erosion and meanders gradually migrate downstream.
- The force of the water erodes and undercuts the river bank on the outsideof the bend where water flow has most energy due to decreased friction.
- On the inside of the bend, where the river flow is slower, material isdeposited, as there is more friction.
- Over time the horseshoe become tighter, until the ends become very close together. As the river breaks through, eg during a flood when the river has a higher discharge and more energy, and the ends join, the loop is cut-off from the main channel. The cut-off loop is called an oxbow lake.
Lower course features
In the lower course, the river has a high volume and a large discharge. The river channel is now deep and wide and the landscape around it is flat.
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 alluvium 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, which raise the river bank.
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.
Erosion involves the wearing away of rock and soil found along the river bed and banks. Erosion also involves the breaking down of the rock particles being carried downstream by the river.
The four main forms of river erosion
- Hydraulic action - the force of the river against the banks can cause air to be trapped in cracks and crevices. The pressure weakens the banks and gradually wears it away.
- Abrasion - rocks carried along by the river wear down the river bed and banks.
- Attrition - rocks being carried by the river smash together and break into smaller, smoother and rounder particles.
- Solution - soluble particles are dissolved into the river.
Rivers pick up and carry material as they flow downstream.
The four different river transport processes
- Solution - minerals are dissolved in the water and carried along in solution.
- Suspension - fine light material is carried along in the water.
- Saltation - small pebbles and stones are bounced along the river bed.
- Traction - large boulders and rocks are rolled along the river bed.
Rivers need energy to transport material, and levels of energy change as the river moves from source to mouth.
- When energy levels are very high, lots of larger objects can be carried.
- When energy levels are low, only small particles can be transported (if any).
When a river loses energy, it will drop or deposit some of the material it is carrying.
- Deposition may take place when a river enters an area of shallow water or when the volume of water decreases - for example, after a flood or during times of drought.
- Deposition is common towards the end of a river's journey, at the mouth.
- Deposition at the mouth of a river can form deltas
- Dams are often built along the course of a river in order to control the amount of discharge. Water is held back by the dam and released in a controlled way. This controls flooding.
- Water is usually stored in a reservoir behind the dam. This water can then be used to generate hydroelectric power or for recreation purposes.
- Building a dam can be very expensive.
- Sediment is often trapped behind the wall of the dam, leading to erosion further downstream.
- Settlements and agricultural land may be lost when the river valley is flooded to form a reservoir.
- The river channel may be widened or deepened allowing it to carry more water. A river channel may be straightened so that water can travel faster along the course. The channel course of the river can also be altered, diverting floodwaters away from settlements.
- Altering the river channel may lead to a greater risk of flooding downstream, as the water is carried there faster.
- Trees are planted near to the river. This means greater interception of rainwater and lower river discharge. This is a relatively low cost option, which enhances the environmental quality of the drainage basin.
Managed flooding (also called ecological flooding)
- The river is allowed to flood naturally in places, to prevent flooding in other areas - for example, near settlements.
- Local authorities and the national government introduce policies to control urban development close to or on the floodplain. This reduces the chance of flooding and the risk of damage to property.
- There can be resistance to development restrictions in areas where there is a shortage of housing. Enforcing planning regulations and controls may be harder in LEDCs.
Different interest groups have different views about flood management techniques:
- Governments and developers often favour large hard engineering options, such as dam building. Building a dam and a reservoir can generate income. Profits can be made from generating electricity or leisure revenue.
- Environmental groups and local residents often prefer softer options, such as planting trees. Soft options cause little damage to the environment and do not involve the resettlement of communities.
- Effective flood management strategies should be economically, environmentally and socially sustainable. Sustainable strategies allow management without compromising the needs of future generations.
The action of waves
Coasts are shaped by the sea and the action of waves. The processes that take place are erosion, transportation and deposition.
The action of waves
The power of waves is one of the most significant forces of coastal change. Waves are created by wind blowing over the surface of the sea. As the wind blows over the sea, friction is created - producing a swell in the water. The energy of the wind causes water particles to rotate inside the swell and this moves the wave forward.
The size and energy of a wave is influenced by:
- how long the wind has been blowing
- the strength of the wind
- how far the wave has travelled (the fetch)
Waves can be destructive or constructive.
When a wave breaks, water is washed up the beach - this is called the swash. Then the water runs back down the beach - this is called the backwash. With a destructive wave, the backwash is stronger than the swash.
- Destructive waves are created in storm conditions.
- They are created from big, strong waves when the wind is powerful and has been blowing for a long time.
- They occur when wave energy is high and the wave has travelled over a long fetch.
- They tend to erode the coast.
- They have a stronger backwash than swash.
- They have a short wave length and are high and steep.
With a constructive wave, the swash is stronger than the backwash.
- They are created in calm weather and are less powerful than destructive waves.
- They break on the shore and deposit material, building up beaches.
- They have a swash that is stronger than the backwash.
- They have a long wavelength, and are low in height.
They build up beaches. But if the waves approach at a angle, material will be transported down the coast. This is when beach management programmes take it back to even it out.
The sea shapes the coastal landscape. Coastal erosion is the wearing away and breaking up of rock along the coast. Destructive waves erode the coastline in a number of ways:
- Hydraulic action. Air may become trapped in joints and cracks on a cliff face. When a wave breaks, the trapped air is compressed which weakens the cliff and causes erosion.
- Abrasion. Bits of rock and sand in waves grind down cliff surfaces like sandpaper.
- Attrition. Waves smash rocks and pebbles on the shore into each other, and they break and become smoother.
- Solution. Acids contained in sea water will dissolve some types of rock such as chalk or limestone.
There are various sources of the material in the sea. The material has been:
- eroded from cliffs
- transported by longshore drift along the coastline
- brought inland from offshore by constructive waves
- carried to the coastline by rivers
Waves can approach the coast at an angle because of the direction of the prevailing wind. The swash of the waves carries material up the beach at an angle. The backwash then flows back to the sea in a straight line at 90°. This movement of material is called transportation.
Continual swash and backwash transports material sideways along the coast. This movement of material is called longshore drift and occurs in a zigzag.
Transporting costal sediment
There are four ways that waves and tidal currents transport sediment. These can then contribute to the movement of sediment by longshore drift.
Solution : Minerals are dissolved in sea water and carried in solution. The load is not visible. Load can come from cliffs made from chalk or limestone, and calcium carbonate is carried along in solution.
Suspension : Small particles are carried in water, eg silts and clays, which can make the water look cloudy. Currents pick up large amounts of sediment in suspension during a storm, when strong winds generate high energy waves.
Saltation : Load is bounced along the sea bed, eg small pieces of shingle or large sand grains. Currents cannot keep the larger and heavier sediment afloat for long periods.
Traction : Pebbles and larger sediment are rolled along the sea bed.
When the sea loses energy, it drops the sand, rock particles and pebbles it has been carrying. This is called deposition. Deposition happens when the swash is stronger than the backwash and is associated with constructive waves.
Deposition is likely to occur when:
- waves enter an area of shallow water.
- waves enter a sheltered area, eg a cove or bay.
- there is little wind.
- there is a good supply of material.
The process of cliff erosion
- Weather weakens the top of the cliff.
- The sea attacks the base of the cliff forming a wave-cut notch.
- The notch increases in size causing the cliff to collapse.
- The backwash carries the rubble towards the sea forming a wave-cut platform.
- The process repeats and the cliff continues to retreat.
Headlands and bays
Headlands and bays
Headlands are formed when the sea attacks a section of coast with alternating bands of hard and soft rock.
The bands of soft rock, such as sand and clay, erode more quickly than those of more resistant rock, such as chalk. This leaves a section of land jutting out into the sea called a headland. The areas where the soft rock has eroded away, next to the headland, are called bays.
Geology is the study of the types of rocks that make up the Earth's crust. Coastlines where the geology alternates between strata (or bands) of hard rock and soft rock are called discordant coastlines. (These have stripes of different rocks) A concordant coastline has the same type of rock along its length. Concordant coastlines tend to have fewer bays and headlands.
Caves, arches, stacks and stumps
Weathering and erosion can create caves, arches, stacks and stumps along a headland.
Caves occur when waves force their way into cracks in the cliff face. The water contains sand and other materials that grind away at the rock until the cracks become a cave. Hydraulic action is the predominant process.
- If the cave is formed in a headland, it may eventually break through to the other side forming an arch.
- The arch will gradually become bigger until it can no longer support the top of the arch. When the arch collapses, it leaves the headland on one side and a stack (a tall column of rock) on the other.
- The stack will be attacked at the base in the same way that a wave-cut notch is formed. This weakens the structure and it will eventually collapse to form a stump.
- One of the best examples in Britain is Old Harry Rocks, a stack found off a headland in the Isle of Purbeck.
Sea wall and groynes
Protects the base of cliffs, land and buildings against erosion. Can prevent coastal flooding in some areas. Expensive to build. Curved sea walls reflect the energy of the waves back to the sea. This means that the waves remain powerful. Over time the wall may begin to erode. The cost of maintenance is high.
Prevents the movement of beach material along the coast by longshore drift.
Allows the build up of a beach. Beaches are a natural defence against erosion and an attraction for tourists. Can be seen as unattractive. Costly to build and maintain.
Climate and weather
The climate in a particular part of the world will influence its vegetation and wildlife, so is fundamental to life on Earth. Find out about factors influencing weather and climate and how to interpret climate data.
Weather and climate
Weather describes the condition of the atmosphere. It might be sunny, hot, windy or cloudy, raining or snowing. Climate means the average weather conditions in a particular location based on the average weather experienced there over 30 years or more. Global climate zones with similar flora, faunaand climate are called biomes.
Difference between weather and climate
The weather takes into account thetemperature, precipitation, humidity andatmospheric pressure of the part of atmosphere (air) closest to the surface of the earth.
The weather is constantly changing as temperature and humidity change in the atmosphere. Landmasses, such as the British Isles, experience constantly changing weather conditions.
Climate refers to what is expected to happen in the atmosphere rather than the actual conditions. It is possible for the weather to be different from that suggested by the climate.
- Climatic conditions in an area can be affected by the landscape, relief and activities taking place (both human and natural). Climate can alter over time and space.
- Within a climatic region, the climate may vary from place to place - eg the top of a hill, the sunny side of a hill, the shaded side of a hill and the bottom of a hill. These areas with their small variations are called microclimates.
Different countries face population change issues. LEDCs have to manage rapid population growth.MEDCs have to manage slow or negative growth and an ageing population.
Causes of population growth in LEDCs
- Limited access to family planning services and education about contraception. Contraception and other methods of family planning may not be culturally or religiously acceptable.
- Children are a valuable source of labour and income for a family. They can work on the land from a young age and as they get older they can earn money in other jobs - providing for the family.
- Children can help to care for younger children and elderly family members.
- High rates of infant mortality (infant deaths) mean that women need to have many children in order to ensure that some survive through to adulthood.
- It may be traditional or culturally important to have a large family.
Main resource - bbc bitesize
Time created 12-15th April 2014
To: Revise over Easter for test week
Also have 2 pages on a word document
Pretty much all of years 7 and 8, and part of year 9