Coasts Flashcards
Wave
Movement of energy through a body of water
Wave crest/peak
Highest point a wave reaches above calm sea level
Wave trough
Lowest point a wave reaches below calm sea level
Wave height
Vertical distance between a crest and a trough: determined by windspeed, area and friction with ocean floor
Wave period
Time for 2 crests to pass a point
Wave frequency
Number of crests passing a point each second
Wave steepness
Ratio of wave height to wave length
Wave energy
Amount of energy a wave has
Wave length
Distance between 2 crests
How do waves form
Friction between wind and ocean surface form capillary waves (circular) that form swells travelling long distances
How do waves break
Friction with ocean floor creates elliptical orbit until top of wave moves faster than bottom and breaks
Wave size depends on
Wind speed, fetch, bathymetry
Cornwall wave size
Large: long fetch and SW winds
Mediterranean wave size
Small: land surrounds and little fetch
Swash
Wave moving up beach
Backwash
Wave moving back down beach
Wave types
Constructive and destructive
Wave clapotis
Collision of incoming and reflected waves causing explosive wave height spikes
Wave refraction
Shallower ocean at headlands means waves bunch up and break so focus energy on headland erosion and deposit in bays
Mavericks waves
Large Pacific Ocean pressure differences means there are high winds and a long fetch to California, where a reef means waves break in a specific spot to large waves focused on a bay
Storm surge
Water pushing against a coastline to unusually high levels due to high tide and low pressure
Ocean current
Large scale water movement in oceans
Tidal range
Vertical sea level height differences between high and low tide
Spring tide
Tide occurring 2x monthly when Sun and moon align on the same side of Earth
Neap tide
Tide occurring 2x monthly when Sun and moon at right angles to Earth
Tides
Caused by gravitational pull of moon and Sun
Tidal bores
Due to large tidal range e.g. Seven Bore UK’s largest surfing hotspot
How does tidal range affect coastline development
Mediterranean sea: low so narrow wave action width. British isles: high so wide wave attack zone for short times and wide wave cut platforms
Tide significance
Movement generates ocean currents, high tides and low pressure can generate a high storm surge, regular movement generates renewable energy e.g. Swansea Bay, Wales
Ocean currents
Large scale movements of water in oceans caused by tides, winds and thermohaline circulation
Tidal currents
Strongest around coasts, regular predictable patterns
Wind currents
Near/at ocean surface, can form phenomena like coastal upwelling, can be global or local scale
Thermohaline circulation currents
Driven by salinity and temperature differences as dense, cold and salty water sinks and returns to surface (Indian and Pacific oceans) by upwelling, then travels on surface until N Atlantic where it cools. Gulf Stream of warm water why UK is warm
Current importance
Affects climate. Safe ship movement, docking, and navigation. Search and rescue.
Rip currents
Caused by topography: waves break over sandbars, forcing backwash through gaps. Affected by wave height, tidal level, and sandbar type. Danger to swimmers
Coastal sediment sources
Streams/rivers flowing into the sea, estuaries, offshore sand banks, cliff erosion, wind, glaciers, longshore drift, biological material
Sediment cells
A distinct area of coastline separated from others, can be regarded as closed systems e.g. English Flamborough Head to the Wash (sub-cell to Humber estuary)
Inputs to sediment cells
Rivers, coastal erosion, offshore sources
Flows in sediment cells
Longshore (littoral) drift, onshore and offshore processes like rip currents
Stores in sediment cells
Beaches, sand dunes, offshore deposits
Outputs in sediment cells
Material may be swept out to sea due to severe storms and sea level rise
Sediment cell energy sources
Sun (converted to wave energy by wind), tectonic (tsunami)
Coastal sediment budgets
Balance between sediment added and removed in cells. Positive added, negative removed
Geomorphological processes
Change Earth’s surface, can be marine or sub-aerial
Marine processes
Operate on a coastline and connected with the sea
Sub-aerial processes
Operate on land but affect coastline change
Coastal erosion
A manifestation of the Sun’s energy as wind converts to eroding waves and acts as an input
Coastal erosion example
2014: Devon storm severely eroded and dunes on a spit and several groynes damaged
Hydraulic action
Force of water as it crashes against a coastline
Cavitation
Trapped air compressed in joints by waves and expand on release, weakening rock so it breaks as bubbles implode to jets
Wave quarrying
Waves breaking against unconsolidated material and scooping it out
Corrasion
Waves pick up sediment and break at cliff surface so sediment erodes rock
Abrasion
Sediment dragged across shoreline
Solution (corrosion)
Weak acids in seawater dissolve alkaline rock, work with carbonation
Attrition
Gradually wearing down sediment particles from abrasion and collision
Coastal erosion factors
Coastal management, subaerial processes, beach, geological structure, lithology (past century, unconsolidated Lincolnshire eroded 120m and Land’s End granite eroded 10m), wave energy
Coastal transportation
Energy flow manifestation with energy not used in erosion or lost in seabed friction, type depends on mass and energy
Traction
Coarse sediment roling
Suspension
Lighter sediment carried
Saltation
Lighter sediment bounced
Solution (corrosion)
Alkaline CaCO3 dissolved in slightly acidic rain transported and precipitated elsewhere
Longshore drift
Swash in prevailing wind direction and backwash perpendicular
Example of effect of management on longshore drift
Benin’s coast eroded at 10m/yr due to Ghanaian SW winds and management meaning there’s no protective beach before cliffs
Coastal deposition
When wind/water velocity falls below a critical value for a particle size so can’t transport. Occurs when water pauses at top of swash, waves slow after breaking, water percolates into beach material
Aeolian processes
Entrainment, transportation and deposition of sediment by wind as air moves due to pressure difference between cold sea and warm land e.g. surface creep, saltation
Jurassic Coast
Dorset and East Devon coast with many Jurassic rocks and fossils, South concordant, East discordant
Eustatic change
Global changes in amount of water in sea e.g. rise with global warming as thermal expansion and sea ice melt
Isostatic change
Land sea level change as land moves e.g. isostatic readjustment with large ice sheet removal causing rise. Britain: North rising, East and South sinking
Ria
Submergent coastline. A drowned river valley where high land is visible, usually a dendritic drainage system
Fjords
Submergent coastline. Drowned glacial valleys/troughs, steep valley sides called hanging valleys, shallow section at mouth called a threshold from glacial deposition
Dalmatian coast
Submergent coastline. Type of drowned river valley system running parallel to coastline, leaves long thin islands
Raised beaches
Emergent coastline. Former wave cut platforms and beaches e.g. Isle of Arran
Relict cliffs
Emergent coastline. Old cliff displaying features like caves, arches and stacks
How much has the sea level risen per year
3.5mm/yr since 1990s
Cost-benefit analysis
Systematic approach to consider management strengths and weaknesses and evaluate
Shoreline management plan
Strategic document setting out policies to assist decisions on flooding and erosion management in the next 20, 50 and 100 years by considering whole cell (relate to 11 sediment cells and sub-cells as closed theoretically)
Shoreline management plan options
Hold the line, no active intervention, managed realignment, advance the line
What are shoreline management plans recommended for
All coast sections by DEFRA
Barmouth
2315 population, 35,000 tourists annually, seaside resort, hold the line
Fairbourne
1031 population, little industry, sea level rise, return to sea, 40% house price drop
Integrated Coastal Zone Management
Protects coast whilst establishing sustainable economic and social activity levels, brings together all stakeholders in cell, UK implements with SMPs
