Content Revised? RiversThe units and links in the hydrological cycle.The storm hydrograph and how it responds to changes.The river basin as a system of inputs, flows, stores andoutputs.Physical causes of river flooding.The activities of people that can cause river flooding.Use of GIS, new technologies, satellite images, aerialphotographs and data in a variety of contexts tohighlight flood management schemes and theireffectiveness.How weathering, erosion, transport and depositionoperate in a river basin.The formation of fluvial landforms, including meanders,interlocking spurs, floodplains, river cliffs, valleys,waterfalls with appropriate examples. Case study Named example Theme 1 Rivers and CoastsA MEDC case study to illustrate the causes, effects andmanagement of river flooding.A LEDC case study to illustrate the causes, effects andmanagement of river flooding.A case study of one river valley and its landforms.
The River System/ Water CycleFill in the boxes using these words: Air Condensation Clouds Precipitation Transpiration Percolation Groundwater Ocean Run-off Evaporation Drainage Basin Terminology
EXAM PRACTICE1 Study the diagram which shows part of the hydrological cycle.(a)(i) Name the processes labelled 1 and 2 in the diagram. (2 marks) (ii) Describe the difference between processes A and B. (2 marks)(b) Describe how the water vapour shown in the diagram becomes water on theland at the point labelled 4. (3marks)(c) Describe two stores of water in the hydrological cycle that are not labelledin the diagram. (4 marks)(d)(i) Name the process labelled 6 in the diagram. (1 mark) (ii) Suggest how the water moved by process 6 could end up in the sea. (4 marks)
Match Up these Definitions (use the diagram on the previous page to help you if necessary)Drainage basin a stream or smaller river which joins a larger stream or riverCatchment area the edge of highland surrounding a drainage basin. It marks the boundary between two drainage basins Watershed the area of land drained by a river Source the point where the river comes to the end, usually when entering a sea Confluence - The beginning or start of a river Tributary the area within the drainage basin Mouth the point at which two rivers or streams join River Profiles A river changes shape as it flows from its source (where a river starts) to its mouth (where a river flows into a sea or lake). The shape of both the long profile (a slice through the river from source to mouth) and the cross profile (a slice across the river) changes.
Spot Test!A slice through a river from source to mouth is called what? Long profile Cross profile Cross section Steep profileA typical cross profile in the upper course will be: wide and deep. narrow and shallow. narrow and deep. wide and shallow. ErosionErosion involves the wearing away of rock and soil found along the river bed and banks. Erosion alsoinvolves the breaking down of the rock particles being carried downstream by the river.Match up the four main forms of river erosionHydraulic action rocks carried along by the river wear down the river bed and banksAbrasion soluble particles are dissolved into the riverAttrition rocks being carried by the river smash together and break into smaller, smoother and rounder particlesSolution 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 awayMatch up the four different river transport processes (use diagram on following pageonly if you NEED to).Solution small pebbles and stones are bounced along the river bedSuspension fine light material is carried along in the waterSaltation large boulders and rocks are rolled along the river bedTraction minerals are dissolved in the water and carried along in solution
TRANSPORTATAIONRivers need energy to transport material, and levels of energy change as the river moves from sourceto mouth.When energy levels are very high, large rocks and boulders can be transported. Energy levelsare usually higher near a rivers source, when its course is steep and its valley narrow. Energylevels rise even higher in times of flood.When energy levels are low, only small particles can be transported (if any). Energy levels arelowest when velocity drops as a river enters a lake or sea (at the mouth). River Processes Test - Underline the correct answer1. Which of the following is NOT a type of river erosion?Solution or corrosion Abrasion Percolation Hydraulic action Attrition2. When rocks and pebbles being carried by the river knock together and are brokendown to form smaller particles this is called:Corrosion Abrasion Percolation Hydraulic action Attrition3. When the force of the water being carried by the river wears away the bed and banksthis is called:solution or corrosion abrasion percolation hydraulic action attrition
4. Which of the following statements about deposition is NOT correct?Deposition is more common at the source of the river.Deposition occurs when a river loses energy.Deposition may occur when the river is shallow.Deposition may occur when the volume of water decreases.5. Erosion is vertical or downwards:at the source of a riverat the mouth of a river6. A wide river channel is formed:at the source of a riverat the mouth of a river River LandformsUpper-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. Upper Course Features As the river moves through the upper course it cuts downwards. The gradient here is steep and the river channel is narrow. Vertical erosion in this highland part of the river helps to create steep-sided V-shaped valleys, interlocking spurs, rapids, waterfalls and gorges. As the river erodes the landscape in the upper course, it winds and bends to avoid areas of hard rock. This creates interlocking 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 and waterfalls may form
Middle course featuresMeandersIn the middle course the river has more energy and a highvolume of water. The gradient here is gentle and lateral(sideways) erosion has widened the river channel. The riverchannel has also deepened. A larger river channel meansthere is less friction, so the water flows faster:As the river erodes laterally, to the right side then the leftside, it forms large bends, and then horseshoe-like loopscalled meanders.The formation of meanders is due to both deposition and erosion and meanders gradually migratedownstream.The force of the water erodes and undercuts the river bank on the outside of the bend where waterflow has most energy due to decreased friction.On the inside of the bend, where the river flow is slower, material is deposited, as there is morefriction.Over time the horseshoe become tighter, until the ends become very close together. As the riverbreaks through, eg during a flood when the river has a higher discharge and more energy, and theends join, the loop is cut-off from the main channel. The cut-off loop is called an oxbow lake. Lower course featuresIn the lower course, the river has a high volume and a large discharge. The river channel is now deepand wide and the landscape around it is flat. However, as a river reaches the end of its journey, energylevels are low and deposition takes place. Floodplains 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 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:
Case Study – MEDC Case Study to illustrate the causes, effects and management of river floodingBOSCASTLE - The Boscastle Flood (Cornwall) on 16th August 2004Why the flood risk?Human Factors A bridge caused a blocking point until it gave way.Physical Factors The cause was torrential rain, as over 1 months worth fell in just 3 hours. Warm moist air had moved in from the Atlantic and condensed into thunder clouds. The catchment area of Bodmin Moor was already saturated through earlier rainfall, so run-off was immediate. 3 tributaries all converge above the village, and the steep slopes created a raging torrent.ImpactsSocial Whilst no people died, the flood caused serious problems in the small town. Bridges were washed away and over 80 cars were swept along, many of them were tourist’s cars who were parked at the head of the village.Economic The unique witchcraft museum was totally lost. As many locals ran bed and breakfast businesses, their summer was ruined as it was over a year before they could re-open. Some had no insurance and never re-opened. The emergency services were over stretched and subsequently, the local council have had to spend huge sums of money introducing flood prevention schemes such as channel straightening and building holding dams (also called check dams). Over 20 houses were badly damage, with many being beyond repair. Managing the flood risks 1. Channel modification – River Valency – widened and deepened so it can carry higher flows of water. Lower river bed by an average 0.75m. Widen river channel next to the Riverside Hotel; move back the patio and replace and extend the footbridge. 2. Removal of large bridge that acted as a block for debris and the fast flowing water 3. Encourage landowners to maintain vegetation cover on valley sides and remove any dead trees 4. Form wide river channel upstream of the car park to create an area of slower flow where larger sediment will deposit and the river can spread out
Case Study – LEDC Case Study to illustrate the causes, effects and management of river floodingBangladesh is a low lying country most of which lies on the delta of Ganges, Brahmaputra and Meghna.Why the flood risk?Physical factors:Sources of rivers are in Himalayas so snowmelt adds to the discharge during spring.S Asia has a monsoon climate and experiences a wet season between May and September when low pressure andwinds blowing from SW across Bay of Bengal bring heavy rain to coastal regions.Bangladesh also suffers from cyclones that bring high winds, heavy rainfall and storm surges.Human Factors:Urbanisation - the capital city Dhaka now has a population of more than 1 million peopleRapid deforestation in Himalayas has had a negative effect on rates of interception and evapotranspirationresulting in more water reaching the rivers.River management is difficult to implement in LEDCs. Average GDP per capita is around $300.Population rely on subsistence agriculture to survive growing rice on rented plots of land so there is littleincome from taxation for Government and Bangladesh relies heavily on foreign aid to finance large scaledevelopment project which might help prevent floods.In 2004 the monsoon season brought more rainfall than usual.ImpactsSocial impacts:36 million people were made homelessBy mid September the death toll had risen to 800. People died as a result of disease because they had noaccess to clean water.Landless labourers and small farmers were the most severely affected in rural areas and in the urban areas itwas typically the slum dwellers squatting on poorly drained land who suffered the most.Economic impacts:Flood also caused serious damage to infrastructure – roads, bridges, embankments, railway lines, irrigationsystems
All domestic and internal flights had to be suspended during JulyRoad and rail links into Dhaka were severely affectedValue of damage was assessed as being in region of $2.2 billion of 4% of total GDP for 2004Environmental impacts:During July and August approximately 38% of the total land area was flooded including 800,000 ha ofagricultural land and DhakaFloods caused river bank erosion especially on embankment areas close to the main channels, soil erosion, water-logging, water contaminationResponsesShort term responsesThe government working with non-governmental organisations provided emergency relief: rice, clothing,medicines, blankets and towelsIn July the United Nations activated a disaster management team to coordinate the activities of the variousUN agencies. They supplied critical emergency supplies and conducted a ‘damage and needs assessment’ inaffected areas.Bilateral aid from individual countries was directed to the UN team.Self help schemes – local people worked together to rebuild their properties and communities.Long – term responsesLong term responses to major floods are largely dependent on foreign aid from both official and unofficialsources. Previous river management schemes implemented by foreigners and funded by aid have proved to beinadequate. These schemes paid little attention to knowledge of rivers and many attempts at river managementfailedRecent small scale community based projects have resulted in lives being saved. Food shelters and early warningsystems have been successfully put in place.Following the 2004 floods additional financial aid was granted for a period of 5 years. This was mainly in theform of a loan from the World Bank to pay for repairs to infrastructure, water resource management andeducation.And the future?Disaster preparedness is a key priority for the future. This includes flood management and improved waterresources. It is also planned that flood-resistant designs should be used in all social and economicinfrastructure projects
Why are the effects of river flooding usually greater in an LEDC than in an MEDC? 1. Less money to spend on tackling problems so less flood protection measures to prevent the same effects happening again. 2. Difficult to get to affected area due to lack of transport links which would require plenty of money to improve road networks and other transport links 3. People are attracted to living on fertile flood plains in LEDCs because farming is an important part of their economy and the alluvium (silt) deposited on the floodplain during floods is a very good and cheap fertiliser for crops.