Physical geo - coasts

what are constructive waves

beach builders - strong swash, weak backwash, long wave length, low wave height, low frequency, gently sloping beaches

what are destructive waves

weak swash, strong backwash, short wave length, high wave height, high frequency, steep beaches

what are the ways that destructive waves erode the coastline

hydraulic action - sheer force of waves hitting the coast

attrition - materials carried in waves bump against each other becoming smaller and smoother, creating sand but not eroding the coast

corrosion - seawater is slightly acidic and gradually dissolves some coastal rock

abrasion - waves pick up material and hurl it at the coast

what is longshore drift

the prevailing wind pushes the waves at an angle to the beach as they break. swash carries materials up the beach at that angle and the backwash carries the material down at a 90 degree angle. this repeats, transporting the sediment in a zigzag pattern along the beach

what is weathering

the breakdown of rock in-situ

what is mechanical weathering

physically breaks up rock. ex. freeze-thaw (water gets into the cracks and freezes —> expanding the rock) or salt weathering (water in the cracks evaporates —> salt crystals —> expand)

what is chemical weathering

broken down by chemical processes ex. rainwater is slightly acidic and reacts with minerals in the rock, creating new material

what is biological weathering

worn away by living organisms ex. burrowing animals or trees growing

what is mass movement

the downhill movement of material under gravity’s influence

four types of mass movement

flow - soil is saturated with water

slide - movement of material in a group

fall - fragments of rock break away from the slope

slump - weaker rocks, saturated soil moves down a curved surface

headland and bay (erosional)

found in areas of alternating bands of resistant (hard) and less resistant (soft) rocks running perpendicular to oncoming waves (discordant coastline). destructive waves wear down soft rocks first —> bay

cove (erosional)

bands of resistant (hard) and less resistant (soft) rock running parallel to waves (concordant). wave processes exploit faults in resistant rock and erode softer rock, leaving a circular cove with a narrow entry

cliffs and wave cut platforms (erosional)

cliffs are steep rock faces that have been eroded over time, wave cut platforms are found at the foot of a cliff. the sea attacks the base of the cliff, creating a wave cut notch. further erosion leads to the instability of the cliff and the backwash carries the eroded material, leaving a wave cut platform

cave, arch, stack, stump (erosional)

crack opened by hydraulic action, becomes a cave after further erosion. waves break through the headland, forming an arch. the arch erodes and collapses, leaving a tall rock stack, which erodes to create a stump

beaches (depositional)

formed in sheltered areas, such as bays

spit (depositional)

extended stretch of sand/shingles from shore to sea. sediment is transported by longshore drift and the coastline changes shape there is deposition of sediment, which increases due to friction and forms a spit. a change in the wind direction causes a hooked end

bar (depositional)

when a spit continues to grow across a bay, joining two headlands together

lagoon (depositional)

small body of water cutoff from the sea (short-term)

tombolo (depostional)

spit grows to join the mainland to an island

sea levels

sea levels rising —> submergent coastlines

sea levels falling —> emergent coastlines

coral reef conditions

temperature needs to be between 23-29 degrees celsius —> normally found in the tropics

light required for photosynthesis

water - less than 25m for sunlight

salinity - 32-42%

types of coral reefs

fringing reefs - formed around a landmass

barrier reefs - parallel to shore but separated by water channel

mangrove conditions

temperature of approx 27 degrees celsius required —> warm tropical waters

water - 0.5m - 2.5m for trees

high levels of humidity and rainfall

sand dunes

accumulation of sand, shaped into mounds + ridges by the wind —> located at the back of the beach above the reach of the tide

best: at wide beach with lots of sand with prevailing wind onshore

formation: wind blown sand is deposited against an obstruction —> more and more sand particles are caught and there is an increase in size

salt marshes

not temperature dependent —> found worldwide

found in well sheltered coastal areas, behind spits

causes of coastal flooding

storm surge - rapid rise in sea level caused by really low-pressure storms

storm tides - when there is a combination of high tide and low-pressure storm

tsunamis - large waves resulting from underwater earthquakes

sea levels - rise, due to global warming

how to predict coastal flooding

early warning systems, GIS, satellite monitoring, weather stations can forecast and track potential hazard events

shoreline management plans

reduce risk of erosion/flooding to people, settlements, natural environments and agricultural land

types of shoreline management plans

hold the line - long-term and costly, build + maintain coastal defences, hard/soft engineering

advance - build new defences, hard/soft engineering

managed realignment - move naturally, monitored + directed, hard/soft

do nothing - cheap, erode + move inward

hard engineering

building a form of sea defence (concrete, wood, rock), expensive and needs to be maintained, used when settlements or expensive instalments are at risk, economic benefit>cost of building defences

sea wall

hard engineering

concrete wall curved outward to deflect wave power

adv: most effective at preventing erosion + flooding

dis: very expensive and unsightly to look at, restricts beach access

groynes

hard engineering

wood, rock or steel piling built at right angles to the shore, traps beach material from longshore drift

adv: slows down beach erosion, cheap compared to other hard methods

dis: starves other beaches of sand, walking along shoreline is difficult

rip-rap

hard engineering

large boulders piled up to protect a stretch of coast

adv: cheaper, absorbs wave energy from base of cliffs/sea walls

dis: boulders could be eroded/dislodged, heavy + expensive to transport

gabions

hard engineering

wire cages filled with stone, concrete + sand

adv: cheapest form of hard, absorbs wave energy

dis: can break easily, not as efficient

revetments

hard engineering

sloping wooden or concrete fences with an open plank structure

adv: break force of waves, traps beach material behind

dis: not effective, regular maintenance, unsightly

off-shore barriers

hard engineering

large concrete blocks, rocks, boulders are sunk offshore

adv: low maintenance, effective at breaking wave energy, beach still looks good

dis: expensive, prevents surfing

soft engineering

works with natural processes, not against. cheaper and not appearance damaging, more sustainable

beach replenishment

soft engineering

pumping and dumping sand and shingle back onto a beach to replace eroded material

adv: widens beach front, absorbs wave energy

dis: repeated regularly, expensive, impacts sediment transport

fences, hedging and replacing vegetation

soft engineering

stabilise sand dunes or beaches

adv: cheap

dis: hard to protect larger areas

cliff regrading

soft engineering

the angle of the cliff is reduced, due to mass movement

adv: prevents sudden loss of large sections, slows down wave cut nothing

dis: doesn’t stop cliff erosion

managed retreat

soft engineering

existing coastal defences are abandoned allowing the sea to flood inland until it reaches higher land

adv: no construction costs, creates new habitats

dis: disruptive to people where land/homes are lost

what is intergrated coastal zone management (ICZM)

when a range of methods is used to protect from erosion. aims to meet the needs of as many stakeholders as possible