Pure Geography SA2 Overall Revision NotesChapter 4: Rivers and Coasts

The River System

1. 3 Courses: Lower, Middle, Upper. 2. Watershed: A stretch of land that surrounds drainage basin (a.k.a. boundary) 3. Drainage Basin: A river system that collects rainwater and comprises of streams and rivers 4. Tributaries: Streams that flow in the river which is mainly found in the upper course. 5. Distributaries: Branch out from the river which is mainly found in the river delta. 6. Confluence: Area where the stream meets the river 7. River Mouth: Place where the river meets the ocean 8. River Delta: Landform created at the mouth of the sea where the river flows into. It is formed by the deposition of the sediment carried by the river as it flows into the sea.

3 Courses of a River Upper Middle Lower Place where the river begins Many tributaries join up to form larger streams which in turn join to create a river River starts to meander (curve) Many tributaries join the river Meanders are common Many distributaries River flows towards the river mouth and enters the sea Delta (land formed by sediments) may form at river mouth

Pure Geography SA2 Overall Revision NotesChapter 4: Rivers and Coasts

Factors affecting River Speed and VolumeFactors affecting Speed of water in River Definition Gradient How steep a river is. High Speed / Volume River is steeper (usually at upper course) Fewer obstacles Smoother channel Faster Low Speed / Volume River is gentler (lower course)

Roughnes s of River Channel

How rough a river channel is (affected by obstacles in river)

More obstacles More friction Reduced speed

Wetted Perimeter

Area in contact with the river. Shape of river channel affects the wetted perimeter (Length and Breadth in contact with the river)

A smaller wetted perimeter Lesser friction Faster

A larger wetted perimeter More water More friction Slower

Factors affecting Volume of water in River Factor Permeabilit y of Rocks Vegetation Cover Definition Permeability is the ability of rocks being able to hold water Vegetation: Plants at the side of the river High Speed / Volume Permeable rocks (holds more water) Lesser surface runoff Sparse vegetation Less rainwater infiltrate ground More surface runoff Large volume Hot / Wet (High Evaporation) High volume of water Low Speed / Volume Less Permeable rocks More surface runoff (more volume of water) More vegetation More rainwater infiltrate ground Lesser surface run off Smaller Volume Dry Low volume of water throughout the year

Climate

How rainfall / temperature affects the river Wet/dry weather Water level fluctuates (drop/unstable)

Size of Drainage Basin

Drainage Basin: An area which collects water (comprises of rivers)

Bigger Drainage Basin Larger Surface area Higher volume of water

Smaller drainage basin Smaller surface area Smaller volume of water

High Speed + High Volume = High Energy!

Pure Geography SA2 Overall Revision NotesChapter 4: Rivers and Coasts

Erosion, Transportation and Depositional ProcessesChapter 6.4: River ProcessesErosionUsually in upper/middle course (where energy is high). Corrosion/Abrasion Rocks grind against river bed/banks and get dislodged and carried away It widens and deepens river channel Agent: Rocks Attrition Rock fragments carried away collide with one another Greatest proportion/largest part of river load They become smaller, smoother and more rounded They make river murky Agent: Rocks Solution River water dissolves soluble minerals in rocks Examples: Limestone (calcium carbonate) dissolves when water contains carbon dioxide Agent: Water Hydraulic Action Fast flowing water hit banks and bed Water forced into joints and cracks --> Strong force breaks and loosens rocks Fragments are carried away Sufficient energy to roll or slide them Agent: Water Occurs when speed is greatest Certain heavy rocks can only be rolled during heavy flooding. More destructions (rocks and boulders) which make channel rough, causing more friction Traction Larger materials on river bed (Pebbles / Boulders) There is an increase in wetted perimeter Water flowing in shallow parts of the river encountering more friction Solution Dissolved minerals are carried in water Can take place when river speed and volume are low E.g.: Readily soluble rocks found in limestone areas are dissolved into water and transported Kept from settling down on the river bed by the turbulent flow of water Little / no rain Water flows across arid area with high evaporation rate when river flows across permeable rocks (water sinks in) Speed of Water decreases due to... Sudden change of gradient. (E.g.: When leaves mountain / enter flat lowlands) River flows into another body of water (Lake / Calm Sea) Suspension Fine particles (sand/silt) Particles do not touch river bed Volume of water decreases due to...

TransportationSaltation Small materials (Gravels) / Small rough fragments

DepositionA river may deposit its load anywhere along its course when Volume of flow is reduced

A series of hops Speed of flow is decreased Energy of river increase Most common at lower course when gradient is gentle, speed of flow is slow and amount of load carried is at maximum. Happens when

Pure Geography SA2 Overall Revision NotesChapter 4: Rivers and Coasts

River Landforms

Author Comments: This is a very important and crucial part of the chapter. Remember to know how to draw the various river landforms.

Floodplains and Leeves (Example: Floodplain of River Wyre, England)

1. Floodplains are found at the lower course of a river. 2. When river overflows due to heavy rain, flooding occurs and water spreads over a larger area, losing speed. 3. When water recedes, river deposits material carrying on the land, leaving behind sediments on river banks and beds. 4. Coarser sediments are deposited closer to river edges and fine particles are deposited away from river. The deposited materials build up on both sides of river due to flooding. 5. Over time, the accumulation of sediments at the flat plains called floodplains is formed. Coarser and heavier materials accumulated nearer to the river form raised banks called levees.

Valleys and Gorges (Example:

1. Valleys and gorges are usually found in the upper course where vertical erosion is prominent. 2. In the upper course, the volume of water is small but the gradient is steep. 3. The swift flowing water exerts a powerful force on the river bed, forming a V-shaped valley through hydraulic action, abrasion and solution. 4. A gorge is an exceptionally deep and narrow valley formed when the river erodes vertically through resistant rocks leaving very steep valley walls.

Waterfalls (Example: Iguazu Falls, border of Argentina and Brazil)

1. River flows through across rocks of different resistance, 2. eroding the less resistant rocks more rapidly, 3. causing a change of gradient in river course. 4. Over time, river plunges from great height to hit river bed below with tremendous force, forming a waterfall.

5. Waterfall can also be formed by faulting, where rocks are uplifted, causing displacement of rocks where 1 layer is higher than the other. When the river flows across an area where faulting occurred, gradient drops suddenly.

6. Repeated pounding of river bed leaves a depression at base of waterfall. 7. Depression is further deepened by rocks and boulders swirling around, forming a plunge pool. 8. Over time, as the harder rock is undercut it produces an overhang which will eventually collapse. 9. As the rock collapses the waterfall retreats upstream, leaving a gorge.

Meanders and Oxbow Lakes

1. Meanders can occur anywhere along the course of the river, however they are more prominent in the middle/ lower course. 2. As the river travels downstream, it tends to find the easiest route, thus it will bend. 3. Therefore, bends of the river at middle/lower course allows erosion to occur at the outer bank of a river. 4. Eroded materials are deposited at the inner bank where water moves in a spiral fashion. Along the outer bank, speed of river is high due to less friction and greater volume. 5. Over time, the concave bank gets undercut1 and a steep-sided cliff known as a river cliff is formed. 6. As the bends become more obvious, a meander is formed.

Formation of Oxbow Lakes 7. Constant erosion at 2 consecutive concave banks will cause the 2 meanders to more closer, forming a loop. Over time, it becomes more distinct, separated by land. 8. As deposition and erosion continues, the 2 meanders eventually meet. 9. Sediments deposited at convex banks will dam up the river, forming an oxbow lake which will be separated from the main river. The main river will flow in a straight path. 10. Due to deposition the old meander bend is left isolated from the main channel as an ox-bow lake.

Formation of Deltas

1The process in which material at the bottom of the cliff or river bank is eroded away. This may cause the upper portion of the cliff river bank to collapse.

1. Deltas are found at the lower course of the river. 2. As a river approaches sea/lake, speed decreases, thus deposition occurs. 3. Although sediments can be removed by tides, if rate of deposition is faster than removal, sediments will build up at mouth. 4. Over time, more sediment is deposited and delta extends outwards into the sea. Sediments carried will block flow of main river. 5. As a result, smaller channels known as distributaries are formed to find their way out to reach the sea or lake. 6. Deltas only form under certain conditions a. The river must be transporting a large amount of sediment b. The sea must have a small tidal range and weak currents c. The sea must be shallow at the river mouth

Pure Geography SA2 Overall Revision Notes

River Management StrategiesImportant PrinciplesKey Principles: Those which are aimed to improve the flow of the river particular in flood conditions, and those aimed to hold back the flow for navigation purposes Ideal principle for river management: Lengthen the amount of time it takes for water to reach the river channel, thus increasing the lag time Used to control the amount of discharge Water is held back by the Dam and released in a controlled way. Dams It can be very expensive, and sediment is often trapped behind the dam, leading to erosion further downstream Settlements and agricultural land may be lost due to flooding at upper course Widening/Deepening of the River to let it carry more water Straightening of the River to increase speed of flow River Channelization Altering of channel course of river to divert floodwaters away from settlements. however, it increases the risk of flooding downstream.

Chapter 4: Rivers and Coasts

Hard Options

River ManagementTrees are planted near the river to allow greater interception of rainwater and lower river discharge River is allowed to flood naturally in places to prevent flooding in other areas

Afforestation

Managed Flooding

Soft options

Local authorities introduce policies to control urban development close to the floodplain This can reduce the chance of flooding and risk to damage of property Planning However, there can be resistance to development restrictions to areas where there is shortage of housing Realignment

Ways to control floods

Resectioning Bank Protection Planting of Vegetation

1. Key Principles: a. Aimed to improve the speed of flow (take note: This can increase the amount of erosion, reducing the ability of the river to hold water). b. Increase the capacity of the river. (N.B. By increasing the volume of water, more water will flow downstream, causing flooding there) River Channelization Processes such as resectioning is the widening or deepening of a river to let it carry more water, whereas Realignment deals with straightening the river channel to increase the speed of flow. Although this can solve the problem upstream, however it will increase the chances of flooding downstream. This is because when there is greater speed and volume of the water in the river, more erosion will occur and thus more sediment will be deposited at the river bed downstream, reducing the capacity of the river to hold water. When the huge volume of water reaches downstream, it will eventually cause flooding.

Pure Geography SA2 Overall Revision Notes

Chapter 4: Rivers and Coasts

Introduction

Chapter 7.1: Wave Energy

Chapter 7.3: Constructive and Destructive Waves

1. It is the energy produced by Destructive Pure Geography Constructive movement of waves Chapter 7: Coastal System and Processes Waves Waves 2. Factors that can affect wave Coastal ProcessesLow energy: Wave Height High Wind Energy: Wind is air Wave length Long Short moving from region of high to Coastal Erosion Coastal Transportation low pressure. The faster wind Wave 6-8 per minute 10-14 per 1. Corrasion the greater Rock speed, (Abrasion): wave Frequency minute fragments are hurled at cliffs energy. by Durationwaves, gradually breaking of wind: The Breakers Spilling Plunging scraping away at the cliff face. longer wind blows, the larger 2. Attrition: Rock fragments the waves. Powerful Swash Backwash carried by Distance ofhit each Fetch: the waves sea over other andwinds blow to generate which wear down to form sand and silt. longer the waves. The 3. Solution (Corrosion): Occurs distance, the more energy when the salt have. can the waves water dissolve some chemicals in the 1. Waves usually approach the coast at an angle rocks. in the direction of the prevailing wind. Chapter 7.2: Wave Movement 4. Hydraulic Action: Waves break 2. This causes the waves to break on the beach. 4. Waves move in face, theof against the cliff a series 3. The swash then carries materials up the beach circular loop-like motions. As pressure of the breaking wave at an angle. The backwash then flows back the waves approach the shore, compresses air in the cracks, to the sea in a straight line at 90o due to the water becomes shallower; which gradually forces open gravity. the friction of the waves against the crack in the rock. It 4. This movement of material is called the sea floor slows down wave becomes weakened as the transportation. movement. The frictional force process continues. 5. The combined effect causes material to be 5. cause the waves to rise and Scouring: This occurs at the transported sideways along the coast known bend forward, and eventually base of the cliff as the waves collapse to foaming water. Coastal Deposition forward Swash is the movement of waves to the 1. Deposition occurs when the material is too heavy to be transported is left behind, shore. It carries sediments to building up the beach. the shore. 2. The largest material flow back Backwash is the is deposited first. 3. Distinctive features may form due to deposition. to the sea due to gravity. It 4. Factors: Deposition of sediment along the coast is dependent on: Chapter 7.4: Tides sediment: Most sediment is transported down to the coast by rivers, Chapter 7.5: Currents Supply of from the daily alternate rising and falling Refers tocoastal erosion or from coasts. When the waves cannot carry their load and Refers to the large-scale of sediment, deposition takes of sea level seen along coasts. place. persistent movements of water in Gradient of slope: On gentle slopes, the wave energyocean. Mainly caused by gravity of the Moon. the is spreaded out and reduced due tohigh friction with the shore and gravity, resulting in by winds. the tides on opposite sides Driven mainly constructive The pull produces waves as they deposit materials more than eroding Longshore currents is a ocean them. of the Earth. Position of the coast: high tides and 2sheltered from strong winds parallel to a coast Coasts that are Each costal area receives 2 current that flow and the calm and are formed by waves that low coastal condition allow deposition to take place. tides daily. The difference in water level between the 2 tides is known as tidal range. The rise and fall of sea level affects erosion and transportation. Areas located between low and high tides will experience more weathering and erosion as it have continuous drying and wetting. approach the coast at an oblique angle.

Chapter 7: Coastal System and Processes

Pure Geography

Coastal LandformsCliffs and Wave cut platforms 1. Cliffs are produced by the action of waves undercutting a steep rocky coast. 2. Hydraulic action and abrasion may erode a crack on the rock surface. 3. The crack can enlarge to form a notch, which is further deepened to produce a cave. Further undercutting by the waves will cause the roof of the cave to collapse. 4. An overhanging cliff is formed, which will eventually collapse and its sediments deposited at the foot of the cliff. 5. Those sediments might be picked by crashing waves and thrown against the base of the cliff, causing further erosion. A cliff is formed. 6. Continuous erosion may cause the cliff to retreat further inland and over time, a wave-cut platform is formed at the foot of the cliff.

Headlands and Bays 1. A headland is made of resistant rocks which extend outwards into the sea and formed due to differential erosion of coastal rocks. 2. Coasts with alternate strips of resistant hard rock and less resistant soft rock will cause the soft rock to be eroded faster than the hard rock. 3. The result is the formation of an indented coast with the remaining hard rocks forming headlands extending into the sea and soft rocks forming bays.

Beach

1. A beach is a zone of deposition along the coast. It is formed when materials carried by waves and currents is deposited on gentle slopes and constructive waves which allows

materials to be deposited by the strong swash. 2. They are formed at protected bays along an indented coast due to wave refraction, where waves approach the shallow sea in front of the headland first. 3. As wave energy tends to concentrate at the headlands, erosion takes place there. 4. Along the bays, waves are diverged, thus their energy is spread out and weakened. Deposition occurs, and over time beaches are formed.

Spit and Tombolo

1. Spits are beaches joined to the coast at just one end. 2. Formed by longshore drift. 3. When the direction of the coastline changes, it continues to deposit materials in the original direction which accumulate in the sea forming a spit. 4. The spit continues to grow as materials are continuously deposited, joining a nearby island to the mainland, forming a tombolo.

Chapter 7: Coastal System and Processes

Pure Geography

Coastal Protection Measures1. The rationale and principle for coastal protection usually rest on the economic values of these coastal areas. 2. Often, the implementation of these measures led to more problems rather than solving the threats from coastal processes. 3. The 2 underlying principles are to reduce the energy of waves and/or retain coastal materials. 4. Types of Approaches: Hard engineering: Construction of physical structures to defend against the erosive power of waves. Soft engineering: Focuses on planning, management and changing individual attitudes towards coastal protection.

Measure Seawalls (e.g. Kallang River in Singapore)

AdvantagesThey are built along the coast which absorbs the energy of waves before they can erode away loose materials.

Disadvantages1. However, they do not prevent the powerful backsplash of refracted waves from washing away the beach materials between the walls. 2. The backsplashes will eventually undermine the base of the seawall and eventually it collapses. 3. They are costly to build and maintain as repairs have to be made to prevent their collapse. However materials deposited in the zones behind the breakwater are protected but the zones located away from the breakwater are not, and will be eroded away.

Breakwate rs

1. They help protect the coast and harbour by reducing the force of high energy waves before they reach the waves. 2. They create a zone of calm water behind them. 1.They are built at right angles to the shore to prevent longshore drift. 2.They absorb/reduce the energy of the waves and cause materials to be deposited on the side of the groyne facing the longshore drift. 1. They are wire cages filled with crushed rocks that are piled up along the shore to reduce coastal erosion by weakening wave energy. Refers to the constant replenishment of large quantities of sand to the beach system, which leads to the improvement of beach quality and storm protection. 1. Coastal planners are trying to protect man-made structures by relocating them and let nature

Groynes

3.As no fresh materials are deposited on the downdrift side, that part will gradually be eroded. 4.To prevent this, the tips of groynes are sometimes angled about 5 to 10, but if failed, erosion can still take place on unprotected areas. 2. They need to be maintained as they are easily corroded. 3. If not properly maintained, the wire baskets become unsightly and pose a threat. However it is expensive to constantly transport sand to fill up the beach as it is continuously eroded. Coral reefs may be in danger as the sand covers the corals. It can also led to muddy and polluted water. This approach is likely to be opposed by people who want to invest in the coastal areas.

Gabions

Beach Nourishme nt

Relocation of Property

reclaim the beach slowly. 2. No building of new structures is allowed in coastal areas vulnerable to coastal erosion.

Planting of Mangroves

1. Mangroves can help to trap sediments and reduce coastal erosion.

2. However some areas with violent destructive waves may not support mangroves. 3. The depth of the coast may also become shallower, affecting coastal transportation and port activities. 2. However they are very fragile and thus access points to the beach are controlled and designated. 1. Shrubs and trees are planted to stabilise the dunes to anchor the sand.

Coastal Dunes

1. Coastal dunes can be found alongthe shore where lots of sand and strong winds exist. The winds carry and deposit the land on the coast further inland, forming coastal dunes gradually which help defend the coast from the sea. 1. They can weaken wave energy. 2. Artificial reefs are created along the coast to help enhance fishing opportunities, serve as undersea barriers and replace damaged coral reefs.

Growth of Coral Reefs

1. Tourists can damage these coral reefs.