Floodplains and Leeves (Example: Floodplain of River Wyre, England)Floodplains are found at the lower course of a river.When river overflows due to heavy rain, flooding occurs and water spreads over a larger area, losing speed.When water recedes, river deposits material carrying on the land, leaving behind sediments on river banks and beds.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.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: Valleys and gorges are usually found in the upper course where vertical erosion is prominent.In the upper course, the volume of water is small but the gradient is steep.The swift flowing water exerts a powerful force on the river bed, forming a V-shaped valley through hydraulic action, abrasion and solution.A gorge is an exceptionally deep and narrow valley formed when the river erodes vertically through resistant rocks leaving very steep valley walls.

River flows through across rocks of different resistance, eroding the less resistant rocks more rapidly, causing a change of gradient in river course. Over time, river plunges from great height to hit river bed below with tremendous force, forming a waterfall.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. Repeated pounding of river bed leaves a depression at base of waterfall. Depression is further deepened by rocks and boulders swirling around, forming a plunge pool.Over time, as the harder rock is undercut it produces an overhang which will eventually collapse.As the rock collapses the waterfall retreats upstream, leaving a gorge.

Meanders and Oxbow LakesMeanders can occur anywhere along the course of the river, however they are more prominent in the middle/ lower course.As the river travels downstream, it tends to find the easiest route, thus it will bend.Therefore, bends of the river at middle/lower course allows erosion to occur at the outer bank of a river.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.Over time, the concave bank gets undercut and a steep-sided cliff known as a river cliff is formed.As the bends become more obvious, a meander is formed.Formation of Oxbow LakesConstant 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.As deposition and erosion continues, the 2 meanders eventually meet.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.Due to deposition the old meander bend is left isolated from the main channel as an ox-bow lake.

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

Key Principles:

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).

Increase the capacity of the river. (N.B. By increasing the volume of water, more water will flow downstream, causing flooding there)

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.

Chapter 7.5: CurrentsRefers to the large-scale and persistent movements of water in the ocean.Driven mainly by winds.Longshore currents is a ocean current that flow parallel to a coast and are formed by waves that approach the coast at an oblique angle.Chapter 7.4: TidesRefers to the daily alternate rising and falling of sea level seen along coasts.Mainly caused by gravity of the Moon.The pull produces high tides on opposite sides of the Earth.Each costal area receives 2 high tides and 2 low 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.Chapter 7.2: Wave MovementWaves move in a series of circular loop-like motions. As the waves approach the shore, the water becomes shallower; the friction of the waves against the sea floor slows down wave movement. The frictional force cause the waves to rise and bend forward, and eventually collapse to foaming water.Swash is the forward movement of waves to the shore. It carries sediments to the shore.Backwash is the flow back to the sea due to gravity. It carries sediments back to the sea.Chapter 7.3: Constructive and Destructive WavesConstructive WavesDestructive WavesWave HeightLowHighWave lengthLongShortWave Frequency6-8 per minute10-14 per minuteBreakersSpillingPlungingPowerful Swash or backwashSwashBackwashPlace of occurrenceGentle costal slope, sheltered coastSteep slope, open coastProminent ProcessDepositionErosionChapter 7.1: Wave EnergyIt is the energy produced by movement of wavesFactors that can affect wave energy:Wind Energy: Wind is air moving from region of high to low pressure. The faster wind speed, the greater wave energy.Duration of wind: The longer wind blows, the larger the waves.Fetch: Distance of sea over which winds blow to generate waves. The longer the distance, the more energy the waves have.The wave energy determines what kind of coastal processes the waves possesses.

Coastal ErosionCorrasion (Abrasion): Rock fragments are hurled at cliffs by breaking waves, gradually scraping away at the cliff face.Attrition: Rock fragments carried by the waves hit each other and wear down to form sand and silt.Solution (Corrosion): Occurs when the salt water can dissolve some chemicals in the rocks. Hydraulic Action: Waves break against the cliff face, the pressure of the breaking wave compresses air in the cracks, which gradually forces open the crack in the rock. It becomes weakened as the process continues.Scouring: This occurs at the base of the cliff as the waves break and swirl around, gradually removing loose rock.Wave Pounding: The sheer force of waves hitting against the cliff face.Coastal TransportationWaves usually approach the coast at an angle in the direction of the prevailing wind.This causes the waves to break on the beach.The swash then carries materials up the beach at an angle. The backwash then flows back to the sea in a straight line at 90o due to gravity.This movement of material is called transportation.The combined effect causes material to be transported sideways along the coast known as longshore drift.The 4 ways that waves can transport sediment (solution, suspension, saltation, traction applies here too!)

Coastal DepositionDeposition occurs when the material is too heavy to be transported is left behind, building up the beach.The largest material is deposited first.Distinctive features may form due to deposition.Factors: Deposition of sediment along the coast is dependent on:Supply of sediment: Most sediment is transported down to the coast by rivers, from coastal erosion or from coasts. When the waves cannot carry their load of sediment, deposition takes place.Gradient of slope: On gentle slopes, the wave energy is spreaded out and reduced due to the friction with the shore and gravity, resulting in constructive waves as they deposit materials more than eroding them.Position of the coast: Coasts that are sheltered from strong winds and the calm coastal condition allow deposition to take place.It also occurs when waves enter a region of shallow water.

Cliffs and Wave – cut platformsCliffs are produced by the action of waves undercutting a steep rocky coast.Hydraulic action and abrasion may erode a crack on the rock surface.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.An overhanging cliff is formed, which will eventually collapse and its sediments deposited at the foot of the cliff.Those sediments might be picked by crashing waves and thrown against the base of the cliff, causing further erosion. A cliff is formed.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 BaysA headland is made of resistant rocks which extend outwards into the sea and formed due to differential erosion of coastal rocks.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.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.BeachA 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.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.As wave energy tends to concentrate at the headlands, erosion takes place there.Along the bays, waves are diverged, thus their energy is spread out and weakened. Deposition occurs, and over time beaches are formed.

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

The rationale and principle for coastal protection usually rest on the economic values of these coastal areas.

Often, the implementation of these measures led to more problems rather than solving the threats from coastal processes.

The 2 underlying principles are to reduce the energy of waves and/or retain coastal materials.

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.

MeasureAdvantagesDisadvantagesSeawalls (e.g. Kallang River in Singapore)They are built along the coast which absorbs the energy of waves before they can erode away loose materials.However, they do not prevent the powerful backsplash of refracted waves from washing away the beach materials between the walls.The backsplashes will eventually undermine the base of the seawall and eventually it collapses.They are costly to build and maintain as repairs have to be made to prevent their collapse.BreakwatersThey help protect the coast and harbour by reducing the force of high energy waves before they reach the waves.They create a zone of calm water behind them.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.GroynesThey are built at right angles to the shore to prevent longshore drift.They absorb/reduce the energy of the waves and cause materials to be deposited on the side of the groyne facing the longshore drift.As no fresh materials are deposited on the downdrift side, that part will gradually be eroded.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.GabionsThey are wire cages filled with crushed rocks that are piled up along the shore to reduce coastal erosion by weakening wave energy.They need to be maintained as they are easily corroded.If not properly maintained, the wire baskets become unsightly and pose a threat.Beach NourishmentRefers to the constant replenishment of large quantities of sand to the beach system, which leads to the improvement of beach quality and storm protection.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.Relocation of PropertyCoastal planners are trying to protect man-made structures by relocating them and let nature reclaim the beach slowly.No building of new structures is allowed in coastal areas vulnerable to coastal erosion.This approach is likely to be opposed by people who want to invest in the coastal areas.Planting of MangrovesMangroves can help to trap sediments and reduce coastal erosion.However some areas with violent destructive waves may not support mangroves.The depth of the coast may also become shallower, affecting coastal transportation and port activities.Coastal DunesCoastal dunes can be found along the 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.However they are very fragile and thus access points to the beach are controlled and designated.Shrubs and trees are planted to stabilise the dunes to anchor the sand.Growth of Coral ReefsThey can weaken wave energy.Artificial reefs are created along the coast to help enhance fishing opportunities, serve as undersea barriers and replace damaged coral reefs.Tourists can damage these coral reefs.