3.1.1 Coastal Environments

Question 1

What affects the coastline?

Answer 1

Marine factors: Wave action, LSD, currents, tides, salinity, coastal surges and flooding, sea level changes
Erosional landscapes, retreating cliffs

Human: activity, tourism, sea defences, settlements, ports, farming, land reclamation, extraction, pollution, conservation, management - modification by humans

Atmospheric: climate, winds, temperature, rainfall, climate change, solar energy

Land: geology, sediment cells, offshore contours, ecosystems, tectonics, erosional agents
Lithology - hard rocks such as granite and basalt rugged landscape, soft rocks like sandstones and gravels produce low flat land
Geological structure - concordant/discordant

Ecosystem types: mangroves, corals, sand dunes, salt marshes, rocky shores - all variety

Question 2

What are coastal processes?

Answer 2

Subaerial action includes processes that break down and remove rock above the reach of the waves and tides

Marine action includes processes which happen due to the waves and tides at the base of cliffs, beaches, etc. (attrition, hydraulic action, cavitation, corrosion, attrition) - may also relate to 4 types of transportation as well as deposition on the coast. (solution, traction, suspension, saltation). Weathering may also lead to mass movements and the breakdown of material

Question 3

What are the coastal zones?

Answer 3

Offshore - area beyond where the waves impact the seabed

Inshore - area between low water mark and point where waves in the sea stop influencing land beneath

Foreshore - area between low and high water marks, most important for marine processes

Backshore - area between high water market and landward limit of marine activity - limit waves can reach.

Nearshore - area extending from high water mark to area where waves begin to break. Includes:

• Breaker zone - where waves break
• Surf zone - area between where waves break and form foamy bubbly surface where waves move up the beach as swash
• Swash zone - turbulent layer of water washes up the beach following the breaking of a wave.

Question 4

What are the 3 factors that affect waves?

Answer 4

• Wind speed
• Duration of Wind
• Length of fetch

Question 5

What is fetch and how does it affect waves?

Answer 5

The fetch is the distance of open sea over which wind blows over before reaching land. The bigger the fetch, the higher energy of the waves. As the wind blows over water and waves develop, there is larger surface area for the wind to act on, increasing the size of the orbit and helping them travel faster as they receive more energy from the wind. The biggest, fastest waves are in areas with the biggest fetch available for winds to build up the more energy.

Question 6

How do waves form?

Answer 6

Friction between wind and the sea surface. Waves in deep sea are different form those on shore. The friction creates circular motion due to energy passing through the water and transmits energy - water particles do not move far, it is more the energy

• Waves of oscillation formed due to drag over the sea surface causing water and floating objects to move in an orbital motion.
• The base of the orbit starts to slow down as it reaches shallow water and friction causes the wave front to crowd together, reducing wavelength and increasing height as the water crowds together
• The top of the wave continues at a faster speed as shoaling pushes the volume upwards, creating a breaking wave on the shoreline as the top falls.
• The area it breaks is the swash zone, and foaming water rushes up the beach and returns as backwash. Swash moves up, slows down and stops. In the upper reaches sediment is deposited as there is little energy.
• In shallower water, the circular motion decreases with depth, slowing it down and decreasing wavelength and increasing wave height - the wave is steeper and less stable causing it to break

Question 7

What is some wave terminology?

Answer 7

• Crest - top of the wave
• Trough - as water falls forms a trough - lowest point
• Height - difference between trough and crest
• Length - distance between two crests
• Period - time taken to travel one length
• Frequency - number of waves over a given period past a fixed point
• Steepness - height/wavelength
• Energy - proportional to wavelength x height squared - small increase in height lots of energy
• Plunge line - point it breaks
• Swash/backwash - foaming water up/down beach

Question 8

What are the 3 types of breaking wave?

Answer 8

Spilling breakers - gentle slopes where waves slowly break. They are steep, gradual peaking of the waves until it is unstable and the crest spills gently down the front of the wave

Plunging breakers are middle steepness coasts. The waves slow down faster and the crest curls way over the front and the wave plunges down towards the base. The shoreward face of the wave becomes vertical, curling over and plunging forward and downward

Surging breakers are found on steep beaches where the wave builds up very suddenly and breaks right onto the beach. The front face and crest of the wave remains smooth and the wave slides directly up the beach without breaking, only breaks right on the shoreline

Question 9

What are destructive waves?

Answer 9

Steep plunging waves with low swash strength but high backwash. They are tall with a short wavelength and break frequently.
Roughly 20m wavelength and 10-15/minute

It erodes sediment from the beach and deposits very little, scouring away from the beach creating a steep beach angle and offshore bar.
On a stone beach destructive waves may percolate into the rocks and be dragged back by the backwash.
-Due to the rapid steepening and curling of the wave breaking, the energy of the wave is transmitted down the beach, accelerated by the steeper gradient and so beach material is broken down.
-The force of the swash is reduced by the backwash from the previous wave, causing material to be washed back down the beach and making steeper beach profiles

Question 10

What are constructive waves?

Answer 10

Collapsing spilling breakers which are small in height with a long wavelength, breaking more infrequently.
Wavelength up to 100m, more infrequent 10 or less/min

The swash is stronger than the backwash and so deposits sediment onto the beach with little scouring, building the beach up and creating a gentle sloping beach angle.
This forms berms on sandy beaches, which are little ridges of sand
The constructive swash surges up the gentle gradient and deposits its sediment. The backwash soaks into the beach on return and so sediment is not pulled back

Question 11

What is wave refraction?

Answer 11

When waves approach a coast driven by prevailing winds, they are refracted and bend to fit the coastlines

• Waves slow in the shallow water in front of a headland as there is increased friction, so the deeper water beside it moves further ahead as it remains at the same speed
• This causes the front of the wave to bend as the slower waves bunch up and have lower wavelengths
• As the other side catches up, it bends around the headland and becomes parallel to the shore. The wave is then sheltered within the cove and energy is concentrated around the cove, creating irregular shaped coastlines

Question 12

What are the causes of wave refraction?

Answer 12

• Waves oblique to the coastline
• Irregular coastline shapes
• Irregular seabed causes differences in wave speed

Question 13

How do waves refracted around a headland?

Answer 13

Waves in deep water travel at speed and approach the coastline at an angle driven by prevailing winds

• Shallow waves slow and bunch up - off a headland first and remains deeper in the bays
• Wave slows down initially off a headland, continuing at speed outside the bays. The waves bend to fit the coastline, becoming parallel to the bay.
• Energy is therefore concentrated on the headlands which erode them into cliffs and related features. The remaining energy dissipates into the bays, causing deposition and the creation of beaching in bays
• Most headlands remain present as they are hard resistant rock

Question 14

What process can occur when refraction is not complete?

Answer 14

Longshore drift can occur from refraction as prevailing wind causes swash in that direction whereas backwash moves straight back down a beach

Question 15

What are the different wave environments?

Answer 15

• Storm wave environments - frequent to cyclones usually in high pressure zones
• West coast - significant fetch
• East coast - trade winds, high fetch, cyclones

Protected - no fetch

Question 16

What are the processes of marine erosion?

Answer 16

• Hydraulic action as air is trapped in cracks, joints and bedding planes under great pressure. As the wave retreats there is pressure release, known as cavitation
• Cavitation is when the parcel of air is trapped and compressed, the increase in pressure breaks down the rock.
• Stresses weaken coherence of the rock, aiding other forms of erosion
• Abrasion/corrasion occurs when waves throw sand, shingle and cobbles at the cliff to wear it away.
• Attrition occurs when rock falls and slumps provide materials which build up and swoosh around, hitting one another and breaking them down.
• Solution/corrosion also may occur as chemicals in the seawater dissolve rocks - key on limestones

Question 17

What are the sub-aerial processes?

Answer 17

• Frost shattering occurs on cool temperate coastline
• On desert coastline thermal fracture may occur, exfoliating layers of the rock
• Oxidation may occur decomposing iron on cliffs
• Salt crystallisation occurs and disintegrates weaker layers
• Rain plash erosion may occur
• Biological weathering occurs through vegetation
• Solution from chemical compounds and acid rain can erode at limestone

Question 18

What is the effect of weathering on coasts?

Answer 18

• Weakens the rocks of the cliff face, expands cracks and disrupts rock from within
• Water may add weight to the rock and marine processes undermining it reduces the support, causing falls and rotational slumps.
• On hard rock faces mass movement often occurs as falls whereas on unconsolidated material rotational slumping occurs, causing cliffs to retreat.
• Rockfalls, slides and flows may also occur from undercutting, weathering and unconsolidated material.

Question 19

How is sediment transported on the coast?

Answer 19

Sediment is transported by the swash of a wave in four ways

• Suspension
• Solution
• Traction
• Saltation

This moves in longshore drift/zigzag movement moving material along a beach

Question 20

What is a sediment cell?

Answer 20

Also known as a littoral cell, it is a section of coastline involved in the complete cycle of sediment transportation and deposition.

• Describes balance between movement of sand size particles and larger sediments into within and out of a coastal segment.
• Inputs and outputs are balanced
• Movement within the cells occur due to longshore drift and currents, making wave direction crucial for movements as well as prevailing winds. Sediment is only lost out to sea.
• Tidal currents can carry large amounts of sediment back to deeper waters by suspension.
• Destructive waves also take away large amounts of sediment from a cell

Question 21

What are the characteristics of a sediment cell?

Answer 21

• Sediment such as sand and silt move in distinct cells around coastlines, which move via longshore drift.
• Prevailing winds control this direction of movement.
• The size of cells are dependent on the topography and shape of the coastline, split up by well defined barriers e.g. estuaries and headlands.
• They vary in size and can be categorized into smaller sub cells
• The supply of sediment is from sea beds, beaches, river channels, estuaries and cliffs
• Each cell is a closed system with negligible transfer around large headlands or estuaries
• There are 11 on the coastline of the UK and are theoretically closed systems.

Question 22

What are the inputs/outputs/stores and throughputs of sediment cells?

Answer 22

Inputs: wave energy, cliff erosion, river sediment, onshore transport, LSD, beach nourishment

Throughputs: LSD, beach destruction and construction

Stores: spits, bars, estuaries, salt marshes and sand dunes

Outputs: offshore transport, LSD, landward dune erosion, dredging

Question 23

What is longshore drift?

Answer 23

The process by which material is transported along the beach or coastline. It is controlled by waves and their swash and backwash.
The angle of swash depends on the prevailing wind. If the waves approach at an angle, they trasnport sand and pebbles up with the beach at an angle
Due to gravity, backwash always pulls the sediment back to the sea in a straight line as it takes the shortest route, creating a resultant movement of sediment along the coastline.

Question 24

What is a beach?

Answer 24

An area of land between low tide and storm tide marks, made up of pebbles sand and mud and silt. They are formed by constructive ways
They may also form in bays where the waves lose energy due to gently sloping land and so the waves readily deposit material
Beaches are also found along straight coastlines where LSD occurs, especially if groynes are built to trap sediment

Question 25

What is beach morphology dependent on? What are the characteristics of sandy/shingle beaches?

Answer 25

Wave type, energy, sediment type and bed morphology

Sand forms wide, gentle gradient beaches. They have stronger swashes and longer run ups due to flatter profiles and similar strength backwash due to low percolation rates.

Shingle beaches are narrower and steeper. They have high percolation rates so have stronger swash than backwash. As a result lots of sediment is moved up however little material is removed.

Question 26

What is the tidal range?

Answer 26

Vertical distance between high and low tides coinciding the sweep zone. Twice a month, the Earth Moon and Sun align, putting an extra gravitational pull on the tidal bulge. This leads to a high tide called the spring tide and when the sun and moon are at right angles the tidal range is the lowest.

Low tidal ranges form narrower beaches, pone to higher erosion found on shores of enclosed seas rather than oceans.