- Created by: Ragitha
- Created on: 22-03-17 13:49
RIVER PROCESSES 1
EROSION: It involves the wearing away of rock and soil found along the river bed and banks
TRANSPORTATION: The process in which the river picks up and carries material downstream.
LOAD: Material of any size carried by the river
SEDIMENT: It is a solid material that is moved and deposited in a new location.
4 TYPES OF EROSION
HYDRAULIC ACTION: Sheer force of the water hitting the bed and the banks. Most effective when the water is moving fast and there is a lot of it.
ABRASION: When the load the river is carrying repeatedly hits the river bed and the banks, causing some of the material to break off.
ATTRITION: When the stones and boulders carried by the river knock against each other and over time are weakend, causing bits to fall off and reduce in size.
SOLUTION: Occurs only when the river flows on certain types of rocks. They are soluble in rainwater and become part of the water as they dissolve.
RIVER PROCESSES 2
VERTICAL EROSION: When the ground is eroded downward and creates a valley in the earth.
- Happens as the river flows down steep slopes- upper stages of a river.
LATERAL EROSION:When the river erodes the walls of its passageway and makes itself wider.
- Happens in the middle and lower stages of a river.
4 TYPES OF TRANSPORTATION
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 in the water and carried along in solution.
RIVER PROCESSES 3
WHY DOES DEPOSITION OCCUR AND WHERE IS THIS LIKELY TO HAPPEN?
- When a river loses its energy
- It will drop or deposit some of the material it is carrying
- It may take place when a river enters an area of shallow water
- For example, after a flood or during times of drought
- Or when the volume of water decreases
- Common towards the end of a river's journey, at the mouth
- This forms a delta
CROSS AND LONG PROFILE OF RIVER
FORMATION OF A WATERFALL AND GORGE:
- A river meets a band of softer, less resistant rock.
- The underlying, softer rock is eroded away more quickly
- Processes of erosion, such as abrasion cause undercutting
- The more resistant rock is left unsupported and overhangs.
- Eventually the more resistant rock collapses onto the riverbed.
- The rock causes abrasion of the river bed.
- Hydraulic action also helps to creat a deep plunge pool.
- This process is repeated and the waterfall retreats upstream.
- A steep-sided river valley is created called a gorge.
MEANDERS AND OX BOW LAKES 1
FORMATION OF A MEANDER:
- In the middle course the river has more energy and a high volume of water.
- The gradient here is gentle and lateral erosion has widened the river channel.
- The river channel has also deepened
- A large river channel means there is less friction, so the water flows faster
- 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 outside of the bend where water low has most energy due to the decreased friction.
- On the inside of the bend, where the river flow is slower, material is deposited, as there is more friction to form a slip-off slope.
MEANDERS AND OX BOW LAKES 3
FORMATION OF AN OX BOW LAKE THROUGH A MEANDER:
- Over time the meander becomes tighter with its neck narrowing
- Eventually the neck of the meander becomes very narrow
- The river eventually breaks through, often during a period of flood when the river has a higher discharge and more energy.
- The meander loop is cut off from the main channel. The cut off loop is called an ox bow lake.
- In time deposition occurs and dams up the ox bow lake, which becomes colonised with plants and eventually dries up leaving a meander scar.
FLOODPLAINS AND LEVEES 1
FORMATION OF A FLOOD PLAIN:
- It is due to both erosion and deposition
- Erosion widens the valley, this takes away the interlocking spurs
- Lateral erosion happens
- When the river overflows, material is dropped as energy is lost.
- Sediment forms layers on the flood plain, building it up.
FORMATION OF LEVEES:
- Leeves are depositional features and are formed when river flood repeatedly.
- Larger sediments are deposited along the banks, while finer sediments are deposited along the floodplain.
- When the river is not in flood, deposition occurs along the river bed.
- Successive periods of flooding and normal flow raise the level of both the leeves and the river bed. This results in the water level of the channel being higher than the ground level of the surrounding floodplain.
- As a result, the water table on the floodplain rises and leads to marshy land.
FACTORS AFFECTING DISCHARGE 1
FACTORS AFFECTING DISCHARGE 2
EXPLANATION OF HOW THE FOLLOWING CAN INFLUENCE DISCHARGE:
RAINFALL: High amounts of rain saturate the soil and underlying rock. If there was a drizzle, there is time for water to infiltrate the soil and underlying rock, freeing up space for more rain.
TEMPERATURE: It affects the loss of water from the drainage basin and therefore the level of discharge. When temperatures are higher, there is greater water loss through evaporation and transpiration, so river levels go down.
PREVIOUS WEATHER: If it has been dry, it will take longer for the water to reach the river and the amount will be less thn if there had been a number of wet days.
FACTORS AFFECTING DISCHARGE 3
ROCK AND SOIL TYPE: Permeable rocks and soils (such as sandy soils) absorb water easily, so surface run-off is rare. Impermeable rock and soils (such as clay soils) are more closely packed. Rainwater can’t infiltrate, so water reaches the river more quickly. Pervious rocks (like limestone) allow water to pass through joints, and porous rocks (like chalk) have spaces between the rock particles.
HUMAN LAND USES: In urban areas, surfaces like roads are impermeable – water can’t soak into the ground. Instead, it runs into drains, gathers speed and joins rainwater from
other drains – eventually spilling into the river
· In rural areas, ploughing up and down (instead of across) hillsides creates channels which allow rainwater to reach rivers faster increasing discharge
· Deforestation means less interception, so rain reaches the ground faster. The ground is likely to become saturated and surface run-off will increase
FACTORS AFFECTING DISCHARGE 4
REASONS TO WHY FLOODING OCCURS NATURALLY:
- Excessive levels of precipitation occurring over a prolonged period of time. This eventually leads to saturation of the soil. When the water table reaches the ground surface, there is increased overland flow or runoff
- Intensive precipitation over a short period of time particularly when the ground surface is baked hard after a long period without rainfall. In such circumstances the infiltration capacity is such that the ground cannot soak up the rainfall quickly enough, so more water reaches the river than would normally be the case
- The melting of snow particularly when the subsoil is still frozen, so that infiltration capacity is reduced
- Climatic hazards such as cyclones in Bangladesh, hurricanes in the Gulf of Mexico or deep low-pressure weather systems in mid-latitudes bring abnormally large amounts of precipitation
HUMAN REASONS WHY FLOODING OCCURS:
- More people are living in towns and cities- population growth and urbanisation has led to demand for land to build on - floodplains are flat and are food for housing
- Concrete and tarmac, used for roads and pavements as they are impermeable, preciptation cannot infiltrate so gets into the river much more quickly
- Less interception as trees and plant matter is removed so precipitation gets into the river much more quickly
- In poor countries rapid doforestation has taken place- land is now used for framing, settlement and mining etc.
- With no trees there is a greater risk of soil erosion as the preciptation is not intercepted.
- Flood damage is greatest near the mouth of a river because wide,flat floodplains are most susceptible to damage. The volume of water is greatest here because many tributaires have joined the river.
FREQUENCY AND LOCATION OF FLOOD EVENTS IN THE UK:
- 1607- Great flood affceted Devon, Somerset and South Wales. Major floods were infrequent in the UK.
- March 1947- major flood affected southern, central and north-eastern England including York, Shrewsbury and Sheffield.
- Combination of a storm and high tides contributed to the floods of January 1953- 307 people died.
- 1968- Great flood affecting south-east England.
FLOODING EXAMPLES 1
MEDC- SOMERSET LEVELS, UK
KEY FACTS AND FIGURES:
- Was part of the wider 2013-2014 Atlantic winter storms in Europe.
- Somerset Levels and Moors is more commonly known as the coastal plain and wetland area of central Somerset, in South West England.
- Majority of this area is below sea level- it is vulnerable to tidal and land based flooding. River Tone and Parrett had burst their banks and spilled out onto the floodplain.
- Arable crops, grassy areas and ground vegetation destroyed.
- Encouraged wetland wildlife to set a new habitat around the flooded areas.
- Some villages cut off and roads blocked.
- Farmers were prevented from grazing their animals.
- Local businesses lost trade-average of £17,352 per business being lost.
- Reports of increased crime
- Some home owners were forced to evacuate from their property.
- 44% of respondents said that employees had been late or off work this year.
FLOODING EXAMPLES 1-CONTINUING
- Providing a number of local sandbag stores to areas of high risk flood
- Sourcing and testing a range of lightweight sandbags to enable less able residents to store and deploy them easily.
- Rescue boats were deployed to help stranded people.
- Extra police patrols in response to crime levels.
- Royal Marines were sent in to help with the flood relief.
- Councils Land Drainage engineer carried out a number of home visits giving practical advice of flood defence measures.
- Signing up to the Joint Met.
- The business support scheme- a £10 million fund to support businesses
- A total funding package of £270 million has been made avaiable to repair or maintain flood defences.
FLOODING EXAMPLES 2
LEDC- 2004 BANGLADESH FLOODS
CAUSES/ BASIC FACTS:
- One of the world's most densely populated areas- population of 125 million people
- GNP of $330 per head
- Contains no raw materials or rock
- 70% of country is less than 1m above sea level.
- Increased surface run off and silt in rivers due to farming and deforestation.
- Rising sea levels due to global warming- monsoon climate
- Poorly maintained embankments
- Ineffective warning systems
- Over 60% of the land area was flooded. Loss of habitable land increases population density.
- 40% of Dhaka flooded. Over 600 people killed. 30 million people homeless.
- Diseases spread such as bronchitus and cholera. 2 million tonnes of rice was destroyed.
- Cycle of poverty continues-poorest most affected.
- Economy suffers- increasing reliance on foreign aid.
FLOODING EXAMPLES 2- CONTINUING
- Government asked for international help
- Un appeal for $74 million-recieved only 20% by September.
- Water aid sent water purification tablets and posters showing sanitation risks
- Rescue boats sent out
- Emergency supplies for water, food, tents and medicines in warehouses
- Fodder for livestock
- Repair and rebuild houses, as well as services-sweage etc.
FLOOD MANAGEMENT 1
HARD ENGINEERING: This strategy involves the use of technology in order to try to control rivers.
SOFT ENGINEERING: This option tries to work within the contraints of the natural river system and involves avoiding building on areas especially likely to flood, warning people of an impending flood and planting trees to increase lag time.
DIFFERENCES BETWEEN THEM: Hard engineering uses technology but soft engineering works alongside natural processes. HE approaches tend to give immediate results and controls the river but are expensive. SE is much cheaper and offers a more sustainable option as it does not interfere directly with the river's flow.
HARD ENGINEERING EXAMPLE- THREE GORGES DAM, CHINA: (2006), $25.5 billion cost
- Constructed at Yichang on the River Yangste
- The capacity of the river should reduce the risk of flooding downstream
- Benefits 15 million people and 25,000ha of farmland protected.
- BUT.. 50% of the silt is now deposited behind the dam which reduces the storage capacity.
- The water is becoming heavily polluted from shipping and waste
- Atleast 1.4 million people were forced to move from their homes to accommodate the dam.
FLOOD MANAGEMENT 2
SOFT ENGINEERING- STRAIGHTING MEANDERS- THE MISSISSIPPI RIVER:
- The river is made to follow a new shorter, straight section and abandon is natural meandering course.
- Telling people in advance of a flood gives them time to prepare for it.
- The Environment Agency's website contains general information on how to prepare for a flood and what to do during and afterwards.
FLOODPLAIN ZONING:This occurs where the flood risk across different parts of the floodplain is assessed and resulting land use takes this into accout.
- It takes into accounting the frequency and severity of flooding.
FLOOD MANAGEMENT 3
HARD ENGINEERING OPTIONS:
- Dam construction- Controls the amount of discharge. Water is held back by the dam and released in a controlled way.
- River engineering- It may be widened or deepened allowing it to carry more water.
- Leeves- Strengthening levees along banks of rivers.
- Barrage- Used during periods of peak flow and high tides, barrages open and close like gates holding back flood water.
SOFT ENGINEERING OPTIONS:
- Aforrestation- Trees are planted nearer the river to soak up the excess water and greater interception of rainwater and lower river discharge
- Managed flooding- Flooding prevented near settlements
- Floodplain zoning/ planning- Local authorites and national government introduce policies to control urban development close to or on the floodplain.
- Dredging- The river channel may be deepened allowing it to carry more water. The sediments can be spread on local farmland or used to build up levees.
WATER MANAGEMENT 1
WHY IS THERE AN INCREASING DEMAND FOR WATER IN THE UK? tourism, urbanisation, industrilisation, agriculture, population growth, climate change, engineering
AREAS OF DEFECIT: London, Norfolk, Essex, Birmingham
AREAS OF SURPLUS: Manchester, Scotland, Wales
There is a need for transfer as the the demand outstrips supply, places face 'water stress' and you can dam the water and put it through the pipes to urban areas.
UK WATER STRESS: Conservation strategy-
- Houses and appliances designed to be more water efficient
- Use of grey water- rain water
- Smaller cisterns
- Water meters
- Showers as opposed to baths
WATER MANAGEMENT 2
WHY BUILD DAMS?
- Millions of people depend on dams to help provide the right amount of water in the right place at the right time.
- Lots of dams provide water for growing crops and for farm animals to drink. They also store water for fighting fires and can help control floods.
- Dams also give us hydroelectric power! U.S. dams provide almost 10% of the nation’s power needs.
ISSUES RESULTING FROM DAMS: KIELDER WATER, UK
- 1.5 milion trees were cut down to build the reservoir.
- Large amounts of pollution created by trucks and excavators travelling back and forth
- Famililes had to be moved and re-housed when it was built- salmon fishing has become famous-fish population decreasing
- It cost £167 million pounds to build. Forestry is decreasing the number of trees available.
- BUT...It maintains good quality water for Northumberland. Habitats have been protected.
- Schools and youth groups use the area for recreation- HEP plant generated 6MW for 4000 homes per year.
- Local shops benefit from tourism. Jobs made available through construction.