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Coasts


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Abandon the line
The strategic withdrawal of human occupation in areas of high risk. Use of less expensive and sustainable methods to “abandon the line” of the coast, often unpopular with farmers and property owners. E.g. National Trust policy Studland Bay
Accretion
The accumulation of marine sediments. Where deposition exceeds erosion.
Advance the Line
This involves active intervention to produce a defence line that is seaward in some way of the existing line. This would usually involve some form of reclamation, the construction of offshore breakwaters or similar.
Arch
A raised area left when two caves erode back to back on a headland. E.g. Durdle Door
Backshore
The part of the beach lying between foreshore and the coastline. The backshore is dry under normal conditions, it is often characterised by berms and is without vegetation.
Backwash
movement of water back towards the sea after a wave has broken
Bar
Coarse grained deposit of sediment extending across the mouth of bay, sometimes reaching the other side and sealing off the entrance. E.g. Looe Bar
Benefit cost ratio
The ratio of the present value (PV) of benefits to the PV of costs. Benefits and costs are compared with the “without project” case for each option.
Berm
Low hill of sand or gravel that forms at the upper limit of the swash. They are short-term features and are removed by successive tides and storms.
Beach nourishment
Sand and shingle brought from elsewhere are added to beaches to maintain their breadth and depth to protect from erosion in a natural way. E.g. Hengistbury Head
Blow –hole
A chimney or pipe leading from a cave up through a cliff to the surface. Caused by erosion and often exploitation of joints in the geology.
Breaching
Failure of defences allowing flooding by tidal or storm action.
Cliff profile
The height and angle of a cliff which can be affected by lithology, tilting and faulting.
Constructive waves
Low frequency 6-8 per minute waves which have elliptical water motion, with powerful swash and weak backwash. They build deposition.
Concordant geology
The alignment of geological outcrops which are parallel to the coastline. E.g. Dorset coast Lulworth
Corrosion
Includes the dissolving of carbonate rocks (e.g. limestone) in sea water and the evaporation of salt crystals which expand on formation and help the rock to disintegrate.
Cusp
Crescent-shaped embayments developed on beaches of mixed sediments.
Cuspate foreland
Is a triangular accumulation of sand and or gravel located along the coastline. This feature is formed by Longshore drift from opposing directions. E.g. Dungeness.
Defence line
The crest of a sea wall/ revetment (man-made defences) or the crest of dunes or the cliff edge (natural defences).
Deltas
Form when the amount of sediment delivered at the mouth of a river exceeds the amount removed by waves and tidal currents
Destructive waves
High frequency 13-15 per minute waves which have circular water motion, with weak swash and powerful backwash. They erode.
Differential erosion
Varying rates of erosion relating to geology, and energy of coastline.
Discordant geology
Coasts which cut across the rock structure. E.g. Dorset North of Swanage Bay
Diurnal range
The difference between the lowest temperature and the highest temperature in a 24 hour period.
Do Nothing
Where no action is taken to protect the coastline.
Downdrift
In the direction of the net Longshore transport of beach material.
Dunes
Concentrations of mound like landforms composed of sand that has been blown off the beach by onshore wind. Embryo dunes first, followed by foredunes (yellow) grey dunes, then wasting dunes.
Dynamic Equilibrium
A state of balance between continuing processes.
Emergent Coasts
Where the coastline increases in height due to isostatic rebound, tectonic processes or deposition.
Eustatic
Changes in sea level caused by variations in the amount of water in the oceans due to melting glaciers or thermal expansion.
Fetch
The distance of uninterrupted water surface over which the wind has blown to form waves. Longer fetch means higher energy waves.
Fiord
Very deep U-shaped estuaries formed by the drowning of glaciated valleys on the Western side of land masses in temperate latitudes. E.g. Drygalski Fiord, South Georgia.
Flocculation
River load particles join together on contact with the salt in sea water, increasing their weight and causing them to drop/ be deposited.
Flood
A temporary excess of water that spills over onto land
Frequency
How often floods occur
Gabion
Cages enclosing rocks to defend the coast.
Geo
Steep sided narrow inlet
Geological Structure
Relates to the layering, dipping and faulting of rocks caused by different processes. Can also relate to concordant or discordant coastlines.
Groyne
Timber, sheet steel piles, rock or concrete posts and boards which run at right angles to trap sediment drifting along the shore.
Halophytes
0pioneer plants that can tolerate salty conditions which are submerged at high tide e.g. glasswort
Hard engineering
Structures developed to protect the foot of cliffs and prevent erosion. E.g. Sea walls, revetments, groynes and gabions,
High energy coast
Coasts in which wave power is strong for a significant part of the year. e.g. Alaska to Iceland and Chile
Hold the line
Taking action to maintain the current defence line. This line may or may not be artificially defended (hard structures) at the present time.
Hydraulic action
Force exerted by moving water on the bed and banks of a river.
Isostatic
Changes in sea level resulting from the rise and fall of land masses
Inshore
A sea that moves towards or closer to the shore.
Isthmus
A narrow piece of land connecting two larger pieces of land.
ICZM
An integrated approach to coastal management which considers how actions in one place can affect processes in others.
Landform
A specific coastal feature such as headland, stack, beach or spit.
Landscape
A larger area which may include many different landforms such as headlands and bays.
Lithology
The rock’s features such as its permeability, solubility, relative hardness and texture. Can relate to igneous, metamorphic, sedimentary or unconsolidated (boulder clay).
Littoral Zone
The wider coastal zone, including coastal land areas and shallow parts of the sea offshore.
Longshore drift
(LSD) Movement of sediment in a zig-zag pattern up and down the shore with swash and backwash resulting in an overall direction along the coast.
Low energy coast
Coasts in which wave power is weaker, low fetch, few gales enclosed and therefore sheltered. e.g. Mediterranean and Baltic Seas
Magnitude
The size of the flood
Managed retreat
The deliberate re-establishment of the line of defence inland from its existing position to obtain engineering and /or environmental advantages.
Marine erosion
The wearing away of land by the sea by means of hydraulic action, abrasion, attrition and solution.
Mass Movement
Non- marine processes often seen on cliffs, like slumping, land slides and soil creep. Caused by gravity and often exacerbated by rain.
Near Shore
Relating to or denoting the region of the sea or seabed relatively close to a shore.
Prevailing wind
The direction from which the wind usually blows.
Plagioclimax
Where succession is stunted by human interference e.g. cattle grazing
Psammosere
Succession of stages of plant growth forming colonisation of bare sand to climax vegetation
Recession
With coasts, it means a retreat.
Recurrence interval
The interval at which particular levels of flooding will occur
Relic Coastlines
Ancient landforms / landscapes left behind due to falling sea level such as fossil cliffs, raised beaches etc. e.g. Isle of Arran
Retreat the line
Intervention to set back the line of defences . Building an embankment inland and letting the existing defences fall into disrepair (with monitoring).
Return period
Average time between occurrences of a given event e.g. storms
Revetment
A general term for defences that are aligned parallel to the shore including posts, pillars, or walls of rocks placed on the foreshore.
Ria
Alts A river valley drowned, usually because sea level has risen but it could be because the land level has fallen e.g. Milton Haven, and Ouse Estuaries.
Runnel
Breaks in beach ridges result from rip currents which form in the strong backwash. Inland of these, runnels form, separating pools of standing water at low tide
Saltation
Sand bounces across the surface of the beach blown by wind
Saltmarsh
Often formed in the shelter of a spit as fine river sediment is deposited in layers assisted by vegetation succession.
Sediment cell
A length of coastline that is relatively self contained as far as the movement of sand or shingle is concerned. Often boundaried by major headlands or changes in direction of coast.
Sediment sink
Point or area at which beach material is irretrievably lost from a coastal cell, such as an estuary or a deep channel in the seabed.
Slumping
Slumping is triggered by undercutting at the base of cliffs with rotation in the slip plane. E.g. Barton
Soft Engineering
Protecting the foot of cliffs to prevent erosion using more natural methods. They tend to be dynamic rather than static and absorb rather than reflect wave energy. E.g. beach nourishment, planting bushes, grasses and trees to protect dunes.
Spit
Long ridges of sand and shingle attached to land at one end. E.g. Hurst Castle Spit and Spurn Head
Spring tide
These are particularly high or low tides caused when Sun, Moon and Earth all lie in a straight line. Opposite of a neap tide.
Stack
A residual post of rock resulting from the continued erosion of arches. E.g. Old Harry Rock
Shoreline Management Plan SMP
A management plan which considers all types of defence along a stretch of coastline, often as part of a sediment cell.
Do nothing / Advance / Retreat /Hold the existing coastal defence line.
Sub-aerial erosion
Mass movement on a cliff e.g. soil creep, solifluction, earthflows, mudflows, slides, slumps, rockfall plus blown (Aeolian) material and runoff.
Submerging coasts
Coastlines which are sinking due to eustatic sea level rises, subsidence or tectonic processes.
Surges
Changes in water level as a result of meteorological forcing (may be positive or negative) e.g. storm surges.
Swash
Movement of water up the beach away from the sea as a wave reaches the shore
Swell
A circular motion caused by wind in the open sea which is non-moving.
Tidal bore
In narrow estuaries the effect of tides can be more pronounced e.g. the Severn Bore a 1 metre high wave running upstream at 30 km/hr.
Tidal Range
The variation from mean water level, high ranges on the North Sea and Channel coasts cause a broad zone of wave attack on the cliffs
Tombolo
Shingle ridge linking the mainland to an island. E.g. Chesil Beach.
Updrift
The direction opposite to predominant LSD movement of beach material.
Wave cut platform
A flat rock area in the intertidal zone created by destructive waves (also often by chemical weathering if a limestone area).
Wave crest
The highest point of a wave
Wave energy
E (is proportional to) LH2 where L is wavelength and H is wave height. A small increase in wave height will result in a large increase in energy
Wavelength
The distance between two successive crests.
Wave period
The time taken for a wave to travel one wave length.
Wave steepness
The ratio of the wave height to the wave length (note that this cannot be steeper than 1:7 as this is when the wave breaks).
Wave refraction
As waves enter shallower water approaching the coast they are affected by friction. If there is a headland, then waves are caused to curve inwards and attack the headland, whereas in bays the waves continue uninterrupted and spread outwards and are dissipated.
Wave trough
The lowest point of a wave.
Weathering
The breakdown of rocks in situ (in their original location without them being moved away). Through biological, mechanical or chemical means.