Coastal land

Coastal erosion

• Erosion:
• - the breaking down of materials, usually caused by wind or water
• Headland --> Bay: Stages of erosion
• Wave-cut platforms:
• - the waves attack the base of the cliff through the process of abrasion, corrosion, hydraulic action and attrition
• - over time the cliff will be undercut and a wave-cut notch is formed
• - eventually the cliff becomes unstable and collapses. Further cliff retreat will form a wave cut platform
• Types of erosion:
• 1. crack - hydraulic action creating a hole in the headland
• 2. cave - hydolic action and abrasion
• 3. arch - erosion goes through the middle part of the rock where it's soft
• 4. stack - as the arch get eroded and collapse, the reminder of the rock is a stack
• 5. stump- Stack erodes to stump

Coastal deposition : The spit

• - a spit is a long, curved landform that is built up from the mouth of a river
• - the prevailing wind comes into the river and the secondary wind comes through the other direction to create a hook as the river goes down against the waves
• - the strong current from the river helps prevent the spit to becoming a sand bar
• Longshore drift moves material along the coastline
• A spit forms when the materials is deposited
• Overtime, the spit grows and develops a hook if wind direction changes further out
• Waves cannot get past a spit, which creates a sheltered area where silt is deposited and mud flats or salt marshes form

Costal deposition

• Sand bar:
• - the sand spit extends and connects the other side of the headland or land
• - since there is no river, it can form into a sand bar
• - overtime, a marshland may form as rivers enter the lagoon a deposit sediment
• Tombolos:
• - A spit continues to extend and connects to another mainland or island
• Sand dunes:
• - Very dynamic which means they could constantly change.
• - They're found behind berms and are basically an extension of the beach
• - They are formed by dry sand being blown up by the beach.
• _ Grass stabilizes the dunes and protect the beach from erosion
• Training walls:
• - Training walls were built to stabilize the sand and to direct the river away from a landscape to clear sea way and to make the water safe for boats to come through
• - A problem with training walls is that the longshore drift started to move more north and could erode other landscape away

Coastal management

• Hard engineering:
• - man-made changes of landscape
• Groynes:
• - prevent longshore drifts
• - build up beach at small scale
• - cheaper than sea walls
• Sea walls:
• - ugly and doesn't last long and expensive
• - can be created from anything but can be eroded away quicker because the wave energy doesn't get absorbed
• Gabions:
• - ugly + hazard mesh structure that keeps the rocks in place
• - doesn't last long (5-10 years)
• - can absorb wave energy
• Soft engineering:
• - small changes to protect the environment
• Beach nourishment:
• - replace the sand back to ocean from erosion
• - prettier + safer
• - storm event may wreck the expensive sediment
• Beach reshaping:
• - natural sea defence to prevent flooding
• - stabilized by fence + cheap and effective
• - can be destroyed by people
• Managed retreat/coastal realignment:
• - Allowed to reclaim (flood) the land
• - farmland is lost
• - creates soft marshes

Extra coastal management

• Hard engineering:
• Revetments:
• - allow sediment to pass through them
• - longshore drift is not hindered
• - absorb the energy of the waves
• - also very cheap + replaced quite of ten
• Hard engineering:
• Rock amour (rip-rap):
• - large boulders = seawalls but they are permeable structures
• - dissipate wave energy by absorbing the impact
• - cheaper than sea walls + longer lasting
• - unappealing and reduce the value of the bead

Coastal management pros/cons

• Rock groynes:
• - traps sand transported by longshore drift
• - keep the beach in place
• Pro: Cheap to maintain, do not affect access to beach, simple effective
• Con: Unattractive, starve the beach on the other side of the groynes of sand
• Rock wall:
• - protect infrastructure likes home + buildings
• Pro: cheap, efficient at providing a defence against high-energy wave, wave break on rocks, not on dunes
• Con: unattractive, can block access to beach
• Sand pumping/bypass system:
• - keep placing the sand back to where it belongs so the movement is still north
• Pro: delivers large volumes of sand to replace affect area, protects river mouths, facilities navigable sea ways for commercial and recreatable vessels, natural coastal processes is maintained sand is treated
• Con: $50 million to design + construct, continued maintenance and costs, pumping needs to be suspended
• Dredging:
• -sand transported from underwater, out at sea, and is used to replenish a beach
• Pro: attractive, natural appears of beach restores, protects from damaging waves and storms
• Con: offshore dredging can increase erosion if not planned appropriately can affect and disrupt ecosystems
• Dumping and bulldozing:
• - restore the natural appearance of the beach and redistribute sand effectively
• Pro: attractive natural appears maintained, protects tourism industry
• Con: heavy machinery presented on the beach
• The construction of artificial reef:
• - split the main beach and ocean from the river
• Pro: effective, improve surfing conditions, new ecosystem, environment friendly
• Con: cost very expensive, requires ongoing maintenance + renewal to remain effective