Cambridge IGCSE Geography 0460: Rivers PDF

Cambridge IGCSE Geography 0460 2.2 Rivers Memon Academy High. IGCSE Geo Page 1 2.6. RIVER LAND FORMS These are various physical features of the river which are formed when erosion or deposition occur in the river. R...

Cambridge IGCSE Geography 0460 2.2 Rivers Memon Academy High. IGCSE Geo Page 1 2.6. RIVER LAND FORMS These are various physical features of the river which are formed when erosion or deposition occur in the river. River landforms can be categorized in two different ways. They can be classified either by the processes that made them (erosion, deposition, erosion and deposition) or where they are found (upper course, or lower course). A. UPLAND LANDFORMS River land forms on the upland is mainly as a result of erosional processes. The processes of weathering and mass movement have also played a part in their formation. The upland river landforms are: Waterfalls, Rapids, Gorges, V-shaped valleys, Interlocking spurs, potholes 1. V-SHAPED VALLEYS These are river valley which assumes a V shape. V-shape valley occur on the mountainous region. Formation process. River has a lot of energy and cause more vertical erosion to occur. The river puts much of the energy toward cutting down to the base. This cuts down into the river bed and deepens the river channel. Weathering and mass movement leads to material from the valley sides collapsing into the river forming a steep v-shaped valley Memon Academy High. IGCSE Geo Page 2  2. INTERLOCKING SPURS These are sharp winding curves formed by the river when it flows down a mountain. It occurs where hard and soft rocks occur alternatively down the mountain. Interlocking spurs are ridge-like features found along the sides of river valleys, formed as rivers flow around hills or mountains. Formation process. As the river cuts its deep V-shaped valley in its upper course, down a mountain which has alternating hard and soft rocks. The river erodes the soft rock part faster than the hard rock part. The river follows the path of the easier soft eroded rock or soil. The river swings from side to side flowing in a zigzag pattern forming an interlocking spurs Memon Academy High. IGCSE Geo Page 3  3. WATERFALLS Waterfalls form where there is a drop in the river bed from one level to another. This drop is often due to changes in the hardness of the rock, where hard rock overlies soft rock. Formation process Waterfalls occur where a band of hard rock is on top of a soft rock. The softer rock is eroded more quickly leaving an OVERHANG of harder rock. Gradually, the falling water erodes the bottom part of the falling water by HYDRAULIC ACTION and Abrasion to form a plunge pool. After sometime the overhang collapse by gravity and the water fall continues to retreat upstream, leaving high rocky walls on the sides called a gorge. 4. GORGE Gorges are formed when rivers erode vertically through resistant rocks.Since these rocks are not easily eroded, the sides of the valley remain steep. Gorges is a deep valley, narrow and steep sided. Gorges can also be formed when the hard rock on a water fall is slowly eroded back by the river and so the waterfall gradually retreats upstream leaving a gorge below it. The gorge is protected from being widened by its capping of hard rock. Memon Academy High. IGCSE Geo Page 4  5. RAPIDS Rapids are sections of a river where the river bed has a relatively steep gradient, causing an increase in water velocity and turbulence. Rapids are characterized by the river becoming shallower with some rocks exposed above the flow surface. As flowing water splashes over and around the rocks, air bubbles become mixed in with it and portions of the surface acquire a white colour, forming what is called "whitewater". Rapids occur where the bed material is highly resistant to the erosive power of the stream in comparison with the bed downstream of the rapids. Rapids are stretches of fast-flowing water tumbling over a rocky-shallow riverbed. Different resistance among rocks cause rapids. 6. POTHOLES Potholes are cylindrical holes drilled into the bed of a river that vary in depth & diameter from a few centimetres to several metres. They’re found in the upper course of a river where it has enough potential energy to erode vertically and its flow is turbulent. Memon Academy High. IGCSE Geo Page 5 Formation processes In the upper course of a river, its load is large and mainly transported by traction along the river bed. When flowing water encounters bedload, it is forced over it and downcuts behind the bedload in swirling eddie currents. These currents erode the river’s bed and create small depressions in it. As these depressions deepen, pebbles can become trapped in them. As a result of the eddie currents, the pebbles drill into the depressions making them more circular, wider & deeper. Pebbles will only be able to erode a river’s bed though if the rock the pebble’s made of is stronger than the rock the river bed is made of. B. LOWLAND LAND FORMS These are river landforms which are formed as a result of the river deposition. The following features are formed at the lowlands Meanders Oxbow lakes Levees Flood plains Deltas or estuaries. Alluvial fans Memon Academy High. IGCSE Geo Page 6 1. MEANDERS A meander is a winding curve or bend of a river. Formation process A meander is formed when the river starts flowing in a low land where the gradient becomes low. The reduction in the river gradient makes the Water flows fastest on the outer bend of the river and slower in the inner bank of the river. The faster flowing water makes the outer bank to erode by hydraulic action and abrasion deepening the channel and forms a steep sided river cliff. The inner bank of the river channel water flows slowly making deposition to occur. This results to the channel becoming shallow at this part and forms a slip off slope. This eventually makes a river to take a turn and form a meander. Memon Academy High. IGCSE Geo Page 7  OX-BOW LAKES This is a lake that assumes the shape of a bow found close to a river meander on the lowland. Formation process Ox bow lakes are formed as result of the outer banks of a meander continue to be eroded through processes such as hydraulic action the neck of the meander becomes narrow and narrower. Eventually due to the narrowing of the neck, the two outer bends meet and the river cuts through the neck of the meander. The water now takes its shortest route rather than flowing around the bend. Deposition gradually seals off the old meander bend forming a new straighter river channel. Due to deposition the old meander bend is left isolated from the main channel as an ox-bow lake. Over time this feature may fill up with sediment and may gradually dry up (except for periods of heavy rain). When the water dries up, the feature left behind is known as a meander scar. Memon Academy High. IGCSE Geo Page 8 LEVEES Levees are naturally formed banks along the sides of a river channel in its lower course, as it flows through the flood plain. They are formed by the river depositing material when it floods. Formation process During a flood the river deposits its heaviest, coarsest material closest to its normal course. Over years or after many floods, this deposition has built up the natural embankments, built of coarse material. Beyond them the flood plain has been built up of the finer material that was deposited further away from the normal course of the river. Memon Academy High. IGCSE Geo Page 9 Memon Academy High. IGCSE Geo Page 10 DELTAS AND ESTUARIES A delta is a landform created when a river deposits sediment where it flows into a body of water for example a lake or an ocean. Formation process Deltas occur where a river that carries a large amount of sediment meets a lake or the sea. This meeting causes the river to lose energy and drop the sediment it is carrying. Over some years these sediments continue to accumulate to form a land or island at the river mouth called a delta. Types of delta Deltas can take on many different shapes. The three primary shapes of delta are cuspate, arcuate and bird’s foot. Arcuate deltas (e.g. The Nile Delta, Egypt) are shaped like a triangle (which is where the term delta comes from, the Greek letter delta Δ) and form when a river meets a sea with alternating current directions that shape the delta so that it looks like a triangle. Cuspate deltas (e.g. Ebro Delta, Spain) are vaguely shaped like a V with curved sides. Cuspate deltas form when a river flows into a sea with waves that hit it head on, spreading the deposited sediment out. A bird's foot delta Bird’s foot deltas (e.g. The Mississippi Delta) are shaped like (as the name suggests) a bird’s foot. They extend reasonably far into a body of water and form when the river’s current is stronger than the sea’s waves. Bird’s foot deltas are uncommon because there are very few areas where a sea’s waves are weaker than a river’s current. Distributary: A distributary is a small river or stream that breaks off from the main river in deltas. Estuary – a river mouth that is kept clear of sediments by the currents of the ocean An estuary is an inlet of the sea, into which flows a river or stream. It is where the sea and river meet. Memon Academy High. IGCSE Geo Page 11 FLOOD PLAIN – Floodplains are large, flat expanses of land that form on either side of a river. The floodplain is the area that a river floods onto when it’s experiencing high discharge. The Flood Plain is the area of alluvial deposits found beside the river in its lower course. Formation process When a river floods, its efficiency decreases rapidly because of an increase in friction, reducing the river’s velocity and forcing it to deposit its load. The load is deposited across the floodplain as alluvium. The alluvium is very fertile so floodplains are often used as farmland. Memon Academy High. IGCSE Geo Page 12  1.8 RIVER HARZARDS AND OPPORTUNITIES A.RIVER HAZARDS There are two main hazards related to a river. 1. Floods 2. Erosion 1. Flooding. River flooding results to: i. Death ii. Outbreak of water borne diseases iii. Destruction of properties. iv. Destruction of houses v. Destruction of roads vi. Water pollution vii. Destruction of water and sewage pipes viii.Destruction of crops leading to food shortages ix. Destruction of power lines leading to power loss. 2. River erosion River erosion leads to damage of infrastructures eg roads, houses, bridges farm land, water pipes gardens and farms etc. Memon Academy High. IGCSE Geo Page 13  B.RIVER OPPORTUNITIES Rivers are very important as they provide the following. 1. Availability of Water for domestic, agricultural and industrial use. 2. Availability of food example fish 3. Fertile soil for farming especially flood plains. 4. Building materials e.g. sand and stones. 5. Site to conduct a variety of sports activities e.g. river rafting 6. Tourist attraction. 7. Site for water transport. 8. Natural harbor for example a river port. 9. Site for generation of hydroelectric power. 10. Habitat for a variety of plants and animals. 11. Provide fishing as an economic activity. 12. Area for waste disposal. 13. Sites for ritual and cultural practice. Living on a flood plain "Floodplains provide a wide range of benefits to the ecosystem and community that include: o Water quality maintenance – reducing sediment loads, filtering nutrients and impurities, and moderating water temperature o Groundwater recharge o providing fertile soils with high rate of plant growth and diversity, richer agricultural harvests, and healthier forests o Habitat for a variety of fish and wildlife, including rare and endangered species o Recreational opportunities – providing areas for active and passive activities, supporting the economic base o Open space" Living close to a delta "Advantages: -fertile soil for agriculture -the deltas can trap pollutants before they flow into the gulf -sediment that is deposited in the delta does not become turbidity in the gulf -they create wildlife habits" Memon Academy High. IGCSE Geo Page 14 Living close to a river "So why do people live near rivers? 1. Availability of Water for domestic, agricultural and industrial use. 2. Availability of food example fish 3. Fertile soil for farming especially flood plains. 4. Building materials e.g. sand and stones. 5. Site to conduct a variety of sports activities e.g. river rafting 6. Tourist attraction. 7. Site for water transport. 8. Natural harbor for example a river port. 9. Site for generation of hydroelectric power. 10. Habitat for a variety of plants and animals. 11. Provide fishing as an economic activity. 12. Area for waste disposal. 13. Sites for ritual and cultural practice. 1.9. RIVER FLOODING – CAUSES, EFFECTS AND CONTROL Is the rise of a river to an elevation such that the river overflows its natural banks causing or threatening damage. Flooding occurs when the amount of water moving down a river exceeds the capacity of the river’s channel. The excess water overflows the banks and spills out across the flood plain. Flooding is a hazard that can cause great damage to the environment and people. CAUSES OF RIVER FLOODING A. Physical Factors 1. Amount and intensity of rainfall. The main cause of river flooding is high amount of rainfall. 2. Size and shape of the drainage basin. A large drainage basin means that the river’s catchment area is large so it will collect a lot of water, increasing discharge. If the basin is circular in shape, the precipitation will enter the river at roughly the same time because all points in the basin are equidistant from one another. This will produce a high peak discharge and can lead to flash floods. Memon Academy High. IGCSE Geo Page 15  3. Type of soil and rock The permeability of the soil and rock in a drainage basin is a big factor in flooding. If the basin’s soil is impermeable, then any precipitation that falls won’t infiltrate and will instead run straight into the river, increasing the river’s discharge and triggering floods. 4. Amount of vegetation The vegetation cover in a basin will affect flooding. If a basin has very dense vegetation cover, the vegetation will intercept precipitation and store it, reducing the volume of water entering a river. Conversely, if a basin is sparsely vegetated then there will be no interception and so more water will enter a river. Vegetation helps bind soil too. With no vegetation, the soil is highly susceptible to mass wasting which can cause large volumes of soil to enter a river and reduce the river’s capacity. 5. Relief The relief and steepness of the basin affects how quickly water enters a river and so how likely a river is to flood. If the river’s valley has steep sides, water will quickly enter a river increasing the river’s discharge. 6. Number of tributary Rivers with many tributary floods easily than rivers with few tributary. If a river has a lot of tributaries, the river’s discharge will be much higher because lots of water will be entering it from its tributaries. After heavy precipitation, the discharge will rise even more and floods are likely, especially at confluences (where a tributary meets the river) as this is where discharge is highest. Human Factors 1. Urbanization Urban areas are more prone to flooding than rural areas. Urbanisation (generally) involves the laying down of tarmac and concrete, impermeable substances that will increase surface runoff into the river and therefore increase the river’s discharge. 2. Deforestation This (obviously) reduces vegetation cover, reducing infiltration and increasing surface runoff into a river hence the rivr easily floods. Memon Academy High. IGCSE Geo Page 16  3. Dam construction Dams hold huge amount of water from the river upstream. This reduces the amount of water flowing in the river downstream hence reduces river flooding. 4. Climate change and global warming Through burning of fossils fuel and deforestation carbon dioxide is released into the atmosphere and continues to accumulate resulting to increasing global temperature. This has increased melting of ice in the mountains resulting to flooding. Some places have experienced climate change resulting to an increase in the amount of rainfall in the area leading to flooding. EFFECTS OF RIVER FLOODING Negative effects a. To people 1. Death 2. Injuries 3. Destruction of properties 4. Destruction of houses and settlements. 5. Power loss due to destruction of power lines. 6. Destruction of infrastructures e.g Roads Bridge, power lines, waste pipe, water pipes. 7. Displace of people/ makes people become refugees. 8. Destruction of crops leading to food shortage. 9. Rise in insurance claims b. Environments 1. Water pollution. Through destruction of waste pipes and flooding of latrines and sewage pit holes. 2. Outbreak of water borne diseases e.g. malaria and cholera. 3. Destruction of wild life habitat 4. Destruction of vegetation 5. Land slides Value of flooding 1. Makes water available for various uses. 2. Makes soil water logged for better growth of rice. 3. Recharges the underground water store. 4. Make land fertile through deposition of alluvial soil. Memon Academy High. IGCSE Geo Page 17 RIVER FLOOD CONTROL AND MANAGEMENT Flood control and flood management can involve three different types of action. 1. Prediction – 2. Adjustment or mitigation – 3. Construction – A. CONSTRUCTION : This is the building of hard-engineering structures such as dams, flood embankments (raised artificial banks), sluice gates, flood wall, river dredging, and relief channels (spillways). Basically these structures either hold back or help to safely dispose of flood water. These structures are generally expensive to build. 1. Dam and reservoir construction 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. 2. Building embankments (or artificial levees) Are raised banks along the river and they effectively make the river deeper so it can hold more water. 3. Flood Walls Are concrete walls constructed around a house or a factory to keep of flooding water from a river. 4. Straightening and dredging: Straightening the river is also called channelizing a river. It allows it to carry more water, so it doesn’t build up and is less likely to flood. It alters the ecosystem and the natural look of the river, and because the water can pass through more quickly may lead to flooding further downstream 5.Diversion channels:. This involve digging up of new river channel to make river flow away from areas where people live or have invested in case of flooding. B. ADJUSTMENT AND MITIGATION it requires working with nature rather than against it. This is sometimes referred as the soft- engineering approach to flood control. 1. Afforestation 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. 2. Managed flooding (also called ecological flooding or wash lands) The river is allowed to flood naturally in places on the flood plain where development has been Memon Academy High. IGCSE Geo Page 18 restricted and its only use maybe for instance playing fields. This is to prevent flooding in other areas - for example, near settlements. 3. Planning (or land use zoning) :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. c. PREDICTION – Prediction of river floods (their extent and depth) is important to flood control. Knowing how high, or wide a river can flood, helps people to decide, for example, how high river embankments need to be built. It also helps to avoid building houses, factories and services in areas of where there is a high risk of flooding. CASE STUDY: RIVER RIVER GANGES,  Opportunities  Causes of flooding  Floods management Memon Academy High. IGCSE Geo Page 19