GCSE Geography. Unit One: Water on the Land. Question 5.

Transcription

1 GCSE Geography Unit One: Water on the Land. Question 5.

2 Water on the Land Revision Checklist: 1. Read through your notes and tick off whether you have notes on the topics that have been covered. If not, you must copy up ASAP. 2. For each topic you must provide a score to reflect how well you think you understand what you ve covered. This will help you focus your revision. Provide a score of Identify the topics you most need to revise and do this as a priority! 1 = Don t understand 3 = Understand some 5 = Understand all RIVER PROCESSES: Section of Topic Pages: Notes? Understanding? Erosional processes: hydraulic action, abrasion, attrition, solution, vertical & lateral erosion. 42/43 Transportational processes: traction, saltation, suspension & solution. Depositional processes: The reasons for deposition, the long profile, and the changing cross profile. RIVER LANDFORMS: Erosional landforms: waterfalls & gorges. 44/45 Erosional & depositional landforms: meanders and ox-bow lakes. Depositional landforms: levees and floodplains. DISCHARGE: Factors affecting discharge: amount & type of rainfall, temperature, previous (antecedent) weather conditions, relief, rock type (i.e. permeable, impermeable, porous, pervious) and land use. 47 FLOODING: Physical causes: prolonged rain, heavy rain, snowmelt, relief. 48/49 Human causes: deforestation, building construction.. Frequency: the frequency and location of flood events in the UK over the past 20 years. FLOODING CASE STUDIES: Case study: of flooding in a rich part of the world. 49 Case study: of flooding in a poor part of the world. NB: With a focus on the different effects and responses. THE COSTS & BENEFITS OF DIFFERENT TYPES OF MANAGEMENT: Hard engineering: dams & reservoirs and river straightening. 50 Soft engineering: flood warnings, preparation, flood plain zoning, do nothing. WATER AS A RESOURCE: The UK: The increasing demand for water, areas of deficit & areas of surplus, the need to transfer water. 51/52 Case study: A dam/reservoir to consider the resulting economic, social, and environmental issues and the need for sustainable water supplies.

3 Rivers Revision Checklist and Guide Weathering 4 types mechanical/physical/biological weathering freeze thaw, chemical ( solution, carbonation), exfoliation Erosion Hydraulic Action, Abrasion, Attrition, Solution Transportation Traction, Saltation, Suspension, Solution How a river changes from source to mouth long profile and cross profile Formation of waterfalls + gorges Formation of meanders and ox-bow lakes Formation of flood plains and deltas Hydrological cycle Storm hydrographs Factors that affect discharge (river flow) soil type, land-use etc Causes of flooding physical and human Differences between floods in richer and poorer countries Solutions to flooding soft and hard engineering Water supply where is there stress and surplus Ways of managing water supply reservoirs, water transfer, sustainable approaches Rivers

4 What are the key features of a Drainage Basin? Factors affecting drainage basins: Relief the steeper the relief, the faster surface run-off of the rain Rock type - Impermeable rock will cause more surface run-off whereas permeable (porous) rock will allow through flow and ground water flow. This slows the water down, increasing the lag time and reducing the peak discharge of the river. Soil the deeper the soil, the greater the infiltration Vegetation - trees & shrubs provide interception & reduce surface run off Land use - Urbanisation of an area means an increased amount of tarmac and drains therefore surface runoff will be increased. Use of rivers by man - If water is extracted for industry, domestic use, or irrigation, this will reduce the amount of water flowing down the river all at once. Building a dam means that water can be stored and the river's water level can be regulated. Drainage density - A large network of smaller streams to collect water more quickly will mean that the water will flow very quickly to the bottom of the river which could cause a dramatic increase in the water level over a short period of time.

5 Long and Cross Profiles of a text book river Long Profile Cross Profile The different types of 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

6 The different types of erosion 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. Deposition Deposition is when a river loses its 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 - for example, the Nile Delta.

7 A Feature of the Upper Stage The formation of a Waterfall and Gorge 1. A waterfall is most commonly found in the upper stage of a river 2. A layer of resistant rock crosses the river channel and stops vertical (downward) erosion 3. The river cuts down when it meets less resistant rock 4. Hydraulic action and abrasion wear away a plunge pool at the foot of the falls and undercut the resistant rock above 5. In time, gravity causes the overhanging resistant rock to collapse & the waterfall retreats upstream leaving a gorge 6. An example of a waterfall is Niagara Falls - USA

8 A Feature of the Middle Stage The formation of a meander The Long profile of a meander

9 Cross-section 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 (sideways) erosion has widened the river channel. The river channel has also deepened. A larger 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 flow 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 more friction to form a slip-off slope.

10 The formation of an Oxbow Lake 1. Over time the meander becomes tighter with its neck narrowing. 2. Eventually the neck of the meander becomes very narrow. 3. The river eventually breaks through, often during a period of flood when the river has a higher discharge and more energy. 4. The meander loop is cut-off from the main channel. The cut-off loop is called an oxbow lake. In time deposition occurs and dams up the oxbow lake, which becomes colonised with plants and eventually dries up leaving a meander scar

11 Features of the Lower Stage The lower stage of the river is characterised by; The river has a high volume and a large discharge The channel is now deep and wide and the landscape around it is flat. Energy levels are low and deposition takes place. The river now has a wide floodplain. Floodplains a good place for agriculture. A build-up of sediment on the banks of a river can create levees which raise the river bank and the level of the water in the channel above the floodplain The formation of Levees Levees are depositional features and are formed when rivers 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 levees 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

12 The formation of a Delta A Fan-Shaped Delta - the land around the river mouth arches out into the sea and the river splits many times on the way to the sea, creating a fan effect. The Niger Delta For a delta to form: The river needs to have travelled a considerable distance in order to collect sufficient sediment The river needs to join a shallow sea with weak currents and small tides As the River currents meet the gentle currents of the sea, the currents cancel each other out, causing the flow of the water to come to a standstill and for material to be deposited causing deltas to form. The small channels which take water to the sea through the deposited material are known as distributaries E.g. River Nile Delta in Egypt The importance of Deltas Deltas are often densely populated due to fertile soil. Rising sea level is posing a problem as it causing increasing salinity and reducing fertility NB. there are no deltas in the UK as UK rivers do not meet any of the above criteria

13 The Water Cycle Water Cycle Condensation Transpiration Precipitation Evaporation 1 2 Flow (transfer) Output Input Surface Run Off Infiltration 3 Throughflow Percolation Ground Water Flow 4 Storage 1. Interception 2. Surface storage 3. Soil moisture 4. Groundwater L.O. To understand why the amount of water fluctuates in a river

14 Storm Hydrographs Interpreting Storm Hydrographs Impermeable Heavy thunderstorm Urban Area Steep river basin Bare ground Moist soil Small catchment area High drainage density Permeable Light drizzle Farmland Shallow river basin Wooded area Dry soil Large catchment area Low drainage density

15 The Causes of flooding A flood occurs when a river bursts its banks and the water spills onto the floodplain. The following factors may encourage flooding: PHYSICAL FACTORS HUMAN FACTORS Heavy or prolonged rainfall Urbanisation Snowmelt Deforestation Steep-sided drainage basin Failure to manage rivers effectively High density drainage basin e.g. lack of dredging Impermeable rock SHORT TERM EFFECTS LONG TERM EFFECTS Positive effects Damage to local economy Flooding deposits fine silt (alluvium) onto the floodplain, making it very fertile and excellent for agriculture ( Bangladesh) Construction companies derive business from flood damage Higher insurance premiums in richer countries Flood management schemes Migration from increasingly flood prone areas in poorer countries into shanty towns Spread of disease Cycle of poverty enforced Negative Effects Destruction of property Loss of crops & seed for following year (Sri Lanka 2011) Damage to infrastructure roads, bridges, rail, power etc. Loss of life Pollution of drinking water Loss of shelter

16 Increased frequency of flooding General Rules: The bigger the flood, the less frequently they occur The poorer the country, the greater the impact Flooding in countries like Bangladesh becoming more severe due to sea level rise & climate change Serious flood incidents reported worldwide with greater frequency so far in 2011 there were significant floods in Sri Lanka, Queensland, Brazil River management Steps can be taken to manage flooding. Often these steps involve trying to lengthen the amount of time it takes for water to reach the river channel, thereby increasing the lag time. Flood management techniques can be divided into hard and soft engineering options. 'Hard' options tend to be more expensive and have a greater impact on the river and the surrounding landscape. 'Soft' options are more ecologically sensitive. Hard engineering options Dam construction River engineering Levees 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. Strengthening levees along banks of rivers (Mississippi, USA) Barrage Used during periods of peak flow and high tides, barrages open and close like gates holding back flood water. (The Tees barrage)

17 Soft engineering options Afforestation Managed flooding (also called ecological flooding) Floodplain zoning / Planning Dredging 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. 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 poorer counrties The river channel may be deepened allowing it to carry more water. The sideiment can be spread on local farmalnd or used to build up Levees (Cuckmere River, East Susex) Interest Groups and their views towards River Management: 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 electric 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.

18 2004 BANGLADESH FLOODS A case study of floods & flood management in a poorer country LOCATION: CAUSES OF FLOODING IN 2004 is one of the world's most densely populated countries! has a population of 125 million inhabitants is one of the poorest countries in the world with a GNP of $330 per head has three of the world's most powerful rivers passing through its country - The Ganges, the Meghna & the Brahmaputra contains virtually no raw materials or rock experiences floods and tropical storms every year serious floods in 1998, 2004 & 2007(Cyclone Sidr) interval between severe floods getting shorter threatened by sea-level rise The Physical Causes of the Floods 70% of country is less than 1m above sea level Over 700 waterways in the country 10% of the land is fresh water It lies on the Ganges-Brahamaputra floodplain increased surface run off & silt in rivers due to farming & deforestation Rising sea levels due to global warming some areas flooded for up to 9 months a year Monsoon climate Tropical cyclones from the Bay of Bengal Cyclone Sidr 2007 Summer snow-melt in the Himalayas feeds the Ganges 2004 saw the heaviest rainfall in 50 years 35cm on 13 / 09 / 2004he main cause was the above average & long period of heavy rain which caused all 3 rivers to have their peak flow at the same time!!! Human Causes of the Floods Deforestation in Nepal and the Himalayas 50% lost since 1950 = increases run off and adds to deposition and flooding downstream Urbanisation of the floodplain has increased magnitude & frequency of floods the building of dams in India has increased the problem of sedimentation in Bangladesh Global warming is blamed for sea level rise, increased snow melt & increased rainfall in the region Poorly maintained embankments (levees) leak & collapse in times of high discharge Ineffective warning systems in rural areas SHORT TERM EFFECTS LONG TERM EFFECTS Over 60% of the land area was flooded Loss of habitable land increases population density

19 40% of Dhaka flooded Over 600 people were killed 30 million homeless out total pop. of 140 million There was a serious shortage of drinking water & dry food Diseases spread such as bronchitus and cholera/diarrhoea 100,000 diarrhoea cases in Dhaka As the waters receded - it left fields of rotting crops, wrecked roads and bridges and destroyed villages 2 million tonnes of rice was destroyed + cash crops like jute & sugar 1/2 million cattle and poultry were lost Increased rural-urban migration = growth of shanty towns Economy suffers = increasing reliance on foreign aid Cycle of poverty continues Poorest most affected IMMEDIATE RESPONSES TO 2004 FLOOD Government asked for international help UN appeal for $74 million -received only 20% by Sept Water Aid sent water purification tablets & posters showing sanitation risks LONG TERM RESPONSES - FLOOD MANAGEMENT: In 1987 the government of Bangladesh & the World Bank began working with a number of international agencies to produce a Flood Action Plan. SHORT TERM FLOOD MANAGEMENT Rescue boats Emergency supplies for food, water, tents and medicines in warehouses Fodder for livestock Repair and rebuild houses, as well as services - sewage etc LONG TERM MANAGEMENT Flood Action Plan Build 7 large dams in Bangladesh to store excess water $30-$40 Billion & 40 yrs to complete Build 5000 flood shelters to Build 3500km of embankment - 7 metres high at a cost of $6 billion to reduce flooding Create 15 flood water storage areas Reduce Deforestation in Nepal & Himalayas effective Flood Warning Scheme

20 River Flooding in Boscastle A case study of floods & flood management in a richer country Boscastle Flash Floods 2004 Where: Boscastle is a small village in Cornwall What: The village was hit by an extreme thunderstorm, which produced 200mm of rainfall in 5 hours, an amount far exceeding the monthly average of 75mm. The rainfall poured down the steep valley slopes, swelling the normally small River Valency, causing it to burst its banks. The area which the River drains is heavily tarmaced, with open countryside covered with few trees. The rock in the area is slate, which is impermeable, causing the water to runoff quickly down the steep slopes. Effects: 58 buildings were flooded 25 businesses properties were destroyed Businesses closed resulting in a loss of income 84 wrecked cars 32 cars were lost, after being washed out to sea Several roads and bridges were damaged Local people and tourists were left traumatised Trees were uplifted Five people had to be airlifted to safety Nobody was killed The cost of repair exceeded 15 million When: This all happened in the afternoon of Monday 16 August 2004 Responses: People fled the swelling river An RAF helicopter was deployed to airlift people to safety Police were deployed to direct people to safety and try to oversee a safe evacuation of the area People without homes were put up in emergency shelters away from Boscastle Eventually people were relocated to temporary housing The village was cleared up with debris removed and cars pulled from the harbour. The roads, bridges and property that was damaged needed to be restored, using traditional building techniques in many cases Flood defences were reviewed and new defences installed to avoid a repeat of the flood event.

21 UK Water Management Rainfall varies over time and place as does water stress Areas of high water stress have a deficit while those of low stress have a surplus High water stress = insufficient rainfall on a permanent basis e.g. Drought Low water stress = abundant rainfall, small population We use between 127 & 177 litres / day Demand for water Expected to rise due to: 1. UK population increase 60+million today, 66million by Increased use of dishwashers etc. 3. Demand for out of season foodstuffs

22 UK Water Stress Sustainable Water Use Conservation strategy: Houses & appliances designed to be more water efficient Use of grey water rainwater etc Smaller cisterns Water meters Showers as opposed to baths Where does our water come from? Reservoirs Arlington on the River Cuckmere, East Sussex natural lakes, rivers London gets its water from the Thames aquifers - an aquifer is an underground layer of permeable rock, gravel or sand which is soaked with water. Eg. Willingdon from Downs aquifer Water transfer - traditional solution to supply water to areas of high stress from areas of surplus eg The Kielder reservoir in Northumberland was built to supply Tyneside, Wearside & Teeside. In 2004 gov decided that such projects were too expensive & to use like Arlington Reservoirs BENEFITS Can be used as part of flood management strategy Create HEP A leisure attraction A source of drinking water / irrigation in drier climates DRAWBACKS Expensive to build Require loss of settlements & / agricultural land Affects the flow within the river & sedimentation Can raise the local water table