Geography: Coastal Systems

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Geography: Coastal Systems by Mind Map: Geography: Coastal Systems

1. Coast: zone where sea/ocean meets the land

2. Coastal management

2.1. ISSUE AT HAND: Should man manage the coast?

2.2. Coastal management: defense in the coastal zone

2.2.1. management for nature conservation, recreational activity, habitat and species restoration, protection from coastal erosion and flooding & other human uses.

2.2.1.1. PPECS

2.3. Is coastal management necessary?

2.3.1. protect and conserve the coast for sustainability in this generation and the future generation

2.3.2. risks of unprotected coast

2.3.2.1. dunudation

2.3.2.2. global warming; increasing sea level; land subsidence; flooding in coastal envt

2.4. Assumptions: -We can manage the coast as long as we have the resources to manage it

2.4.1. Increasingly vulnerable; susceptible to damage & coastal degradation

2.4.2. fragile enivornment; valuable resource: protected, conserved, and restored to ensure security and economic sustainibility

2.5. What is happening? -Coasts subjected to coastal erosion

2.5.1. causes: wave action- wind speed, wind duraction & fetch

2.6. Coastal management techniques

2.6.1. hard engineering

2.6.1.1. traditional response to erosion; involves construction of structures stopping, absorbing or reflecting wave energy reaching the shore

2.6.1.1.1. mainly used in densely populated coastal areas to protect valuable resources and high-risk property

2.6.1.1.2. problems: increasing erosion elsewhere, high expenses, low sustainability

2.6.1.2. cliff-foot strategies: to protect beach from sea erosion

2.6.1.2.1. sea walls: massive, made of rocks/concrete, used to absorb waves

2.6.1.2.2. revetments: made of concrete, used to reflect waves

2.6.1.2.3. gabions: wire cages holding smaller rocks

2.6.1.2.4. groynes: rock or wooden types to hold in beach material at risk of being eroded

2.6.1.2.5. offshore bars (artificial reefs): reduce power of waves offshore

2.6.1.2.6. rip-rap: large rocks in front of sea walls/ cliffs to absorb wave impact

2.6.1.3. cliff-face strategies: to reduce damage from sub-aerial erosion

2.6.1.3.1. cliff drainage: removal of water to prevent landslide and slumping

2.6.1.3.2. cliff regrading: lowered angle of cliff to stabilise ground

2.6.2. soft engineering

2.6.2.1. more popular approach recently; promoting natural systems such as beaches and salt marshes which protect the coast

2.6.2.1.1. accommodates and works with natural processes

2.6.2.1.2. usually cheaper to construct and maintain, often more self-sustaining.

2.6.2.2. beach nourishment: sand pumped and sediments replaced

2.6.2.3. zone management: prevention of new development in coastal regions

2.6.2.4. sustainable management

2.6.2.4.1. adjusting to environment to secure future of coastline

2.6.2.4.2. coastal resilience (ecosystems): partial flooding allowing marshes and wetlands to adjust with sea water

2.6.2.4.3. corals

3. Coastal Morphological Developments (landforms)

3.1. Depositional

3.1.1. Spits, recurved spit and tombolo

3.1.1.1. spit

3.1.1.1.1. spit: narrow ridge of sand, deposited by longshore drift, with one end attached to mainland and the other protruding at a sharp/abrupt turn of the coastline or across mouth of a river

3.1.1.1.2. longshore currents reach a bay or bend, encountering shallow and shelter (slack) water, reducing wave energy, and causing the current to deposit material in the form of a ridge

3.1.1.1.3. hook/recurved spit: as a spit grows and extends into deeper water, wave action causes free end to be curved towards land

3.1.1.2. tombolo

3.1.1.2.1. tombolo: an extension of a spit joining an offshore island to the mainland/island

3.1.2. Beaches

3.1.2.1. gently sloping platform formed by accumulation of sediment material deposited by constructive waves along shore

3.1.2.1.1. bay-head beach: at head of bay between two headlands; comprises finer particles

3.1.2.1.2. bay-side beach: sides of bay, composed of coarser sand particles/ mixed with gravel & pebbles

3.1.2.1.3. bay-mouth beach (headland): at tip of headland; consisting of coarser particles, gravel and boulders

3.1.2.1.4. also classified by deposits (eg. sandy, shingle, boulder)

3.1.3. Bars: narrow ridges of sand/gravel deposited by waves across a bay, parallel to shore

3.1.3.1. may be continuous or semi-continuous with breaks in between

3.1.4. Mudflats: silty or muddy platforms deposited by waves/rivers along gently sloping shores

3.1.4.1. may be encroached by salt-tolerant vegetation (mangrove) to form a swamp or marsh

3.2. Erosional

3.2.1. Cliffs, wave-cut platforms and offshore terraces

3.2.1.1. cliff: High, steep rocks facing the coast

3.2.1.1.1. formed when weaker parts of steep coast slopes get repeatedly eroded to produce a notch

3.2.1.1.2. continued erosion and undercutting of notch forms a cliff

3.2.1.2. wave-cut platform: a gently sloping/ flat surface formed at the base of cliff

3.2.1.2.1. due to constant erosion, cliff becomes steeper and retreats inland while the wave-cut platform develops and becomes wider at the base of the cliff, exposed during low tide.

3.2.1.2.2. when wave-cut platform is buried by deposits, it causes a belt of shallow water which decreases wave energy and erosion of platform

3.2.1.3. offshore terrace: eroded materials transported away to deposit in offshore zone

3.2.2. Headlands and bays

3.2.2.1. headlands are formed when waves armed with rock debris (load) lash against shores or along coast that that have alternate bands of rocks of different resistance.

3.2.2.1.1. more resistant rocks (such as limestone and chalk) remain mostly stable, while the less resistant ones (clay, sand & gravel) are eroded and worn out more rapidly.

3.2.2.2. this results in an irregular coastline

3.2.2.2.1. headlands: protruding head-like pieces of land made of resistant rocks

3.2.2.2.2. bays: less resistant, easily eroded inward curving rocks

3.2.3. Caves, Arches, Stacks and Stumps

3.2.3.1. caves: along irregular coast of headland and bays, converging waves on headlands due to wave refraction attack and widen lines of weaknesses into hollows

3.2.3.2. arch: when two caves on opposite sides of headlands join to form a opening

3.2.3.3. stack: when arch collapses with further erosion leaving behind rock pillars

3.2.3.4. stump: when stack is reduced in size with further erosion

3.2.3.4.1. completely removed by wave erosion in time

3.2.4. Caves, blow holes and geos

3.2.4.1. blow hole: near vertical cleft/tunnel leading from rear top of sea cave upward to land surface above

3.2.4.1.1. due to presences of near vertical lines of weakness above sea cave, waves surging in during high tides force and compress air into cracks

3.2.4.1.2. when waves retreat suddenly, compressed air is set free; the air expands explosively and shatters rocks, resulting in opening and widening of lines of weakness along cave

3.2.4.1.3. part of roof of the cave collapses eventually

3.2.4.1.4. geo: continued wave erosion may widen the blow hole till the entire roof collapses to form a long, narrow, steep-sided inlet

4. Coastal development (Human)

4.1. Why are coasts important?

4.1.1. Site advantages: human

4.1.1.1. source of livelihood (fish industry, farming swamps: eg. Bangladesh- monsoon rain)

4.1.1.2. tourism industry (economic); beaches, parks

4.1.1.3. coastal flat lands for easier access & development

4.1.1.4. ports (trade and import/export, transport)

4.1.1.5. battlegrounds in time of war

4.1.2. Environmental importance

4.1.2.1. coastal ecosystems are unique and cannot be replicated

4.1.2.2. mangroves marshes, coral reefs

4.1.2.3. wide range of plant and animals species, harnessed for human needs

4.2. Centers of dense population

4.2.1. eg. the Gulf coastal plain of North America and the coastal plains of India

4.3. Sites of major global sites

4.3.1. e.g. the coastal cities of US (NY, LA), Japan (Tokyo), Africa (Cape Town) and Netherlands (Rotterdam)

4.3.2. 40 largest mega-cities; 2/3 global economic output, 9 in 10 innovations

5. Morphodynamics Behaviour

5.1. wave

5.1.1. wave: undulations (wave-like, fluid movement) of water created by wind that blows over surface of water.

5.1.2. formed as a result of the transfer of energy as wind blows over the surface if the sea and friction is created (ripples)

5.2. wave action

5.2.1. Wave Action

5.2.2. circular wave orbit: motion of waves in the open sea transmitted by circular movement of individual water molecules as there is a lack of frictional drag against ocean floor

5.2.3. elliptical motion: waves approaching land & depth of water decreased to half the wavelength; the size of circular wave orbit decreases as orbital motion of water is retarded by friction with the sea floor

5.2.4. speed of wave transmission decreases, wave length decreases, and wave height increases

5.2.5. wave heigh reaches a point of instability, wave crest is faster than trough, and breaks

5.2.5.1. EITHER collapses, at some distance from shore, to produce a spilling break if water offshore is shallow

5.2.5.2. OR topples forward and forced to break against land, forming a plunging break, if water offshore is deep

5.2.5.3. wave breaker is never 90 degrees, but at oblique angle to shore

5.2.6. water steepens, loses form and becomes a breaker

5.2.6.1. water rushes up the slope of the shore as swash, runs back down the slope as backwash

5.3. Factors affecting energy of waves:

5.3.1. duration of wind

5.3.1.1. the longer the wind blows,

5.3.2. strength of wind (velocity)

5.3.2.1. the stronger the wind,

5.3.3. fetch: distance of open sea which the wind blows over

5.3.3.1. the greater the fetch, the higher the energy/ destructive power of wave

5.3.3.2. open seas more susceptible to wave erosion as compared to sheltered locations (weak wind & short fetch, which are more prone to wave deposition)

5.4. constructive waves

5.4.1. Frequency: long, low waves long wavelength up to 100m, low frequency, wave period of <13 per minute, usually calm conditions

5.4.1.1. Breaker: SPILL waves slide forward in shallow water due to gentle offshore slope

5.4.1.1.1. Deposition: swash is more powerful than backwash, materials carried up and accumulates on shore

5.5. destructive waves

5.5.1. Frequency: long, low waves long wavelength up to 100m, high frequency, wave period of >13 per minute, usually stormy conditions

5.5.1.1. Breaker: PLUNGE waves curve downwards in deep water due to steep offshore slope

5.5.1.1.1. Erosion: backwash is more powerful than swash, materials carried down and removed from shore

5.6. Wave transport

5.6.1. wave transport: the movement of load (eg. silt, clay, mud, sand, pebbles and other sediments) along the shore and seabed

5.6.2. beach drift: when waves break obliquely at the shore, and swash moves obliquely up the shore and backwash back at right angles

5.6.2.1. eroded materials gradually carried along shore by zig-zag movement of swash & backwash

5.6.2.2. longshore drift: eroded materials moving in zig-zag movement parallel to shore

5.7. Factors governing work of waves and character of coastal landforms:

5.7.1. Wave action

5.7.1.1. waves breaking against land = wave erosion

5.7.1.1.1. destructive waves destroy coast by erosion and results in erosional coastal landforms

5.7.1.2. waves before reaching shore = wave deposition

5.7.1.2.1. constructive waves build coast by deposition and results in depositional coastal landforms

5.7.2. Geology of coastal rocks

5.7.2.1. types/composition of rocks

5.7.2.1.1. resistances of rocks to weathering & erosion

5.7.2.2. direction of dipping of rock strata

5.7.2.3. presence & arrangement of lines of weaknesses (joints, fractures)

5.7.3. Climate

5.7.4. Orientation of coast

5.7.5. Relief of coastal slope

5.7.5.1. steep slopes; plunging (destructive high energy) waves as there is little frictional drag

5.8. Work of waves and resulting coastal landforms:

5.8.1. Wave refraction: bending of wave fronts approaching a shore to break almost parallel with shore

5.8.1.1. in deep waters, water fronts are parallel to one another

5.8.1.2. when approaching shallow waters of shore, retarding influence of shallow water/ frictional drag with sea floor causes waves to slow down and to bend

5.8.1.2.1. when along an irregular coast

5.8.1.2.2. along straight line with approaching waves from oblique direction

5.8.2. Wave erosion accelerated by

5.8.2.1. Wave erosion: progression wearing away of underlying rock material from coast

5.8.2.2. high energy waves (destructive waves)

5.8.2.2.1. exposure to strong prevailing winds

5.8.2.2.2. great wind velocity

5.8.2.2.3. long fetch

5.8.2.3. steep wavefront

5.8.2.4. rapid rate of coastal rocks weathering

5.8.2.4.1. weak coastal rocks less resistant to wave attack

5.8.2.5. large wave load

5.8.2.6. WAVE ACTION

5.8.2.6.1. hydraulic action: compression of air in rock cracks, exerting pressure and expansion at retreation of wave resulting in sudden release of pressure

5.8.2.6.2. attrition: mutual wearing down of materials transported by waves; particles smoother, rounder and smaller

5.8.2.6.3. corrasion (abrasion): wearing of coastal rocks/ cliff faces by materials carried and hurled against coast by waves

5.8.2.6.4. corrosion/solution: dissolving of soluble minerals in rocks by sea water or waves, which crystalize and weaken rocks to become more susceptible to other forms of wave erosion

6. Corals