Key+Words

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The existing coastal defence line. ||
 * **Term ** || **Definition ** ||
 * 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 ||
 * Abrasion || The wearing away of the shoreline by sediment carried by waves. Also erosion by friction scraping, scouring and rubbing of load in contact with banks and bed (Corrasion) ||
 * 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 ||
 * Attrition || The reduction and rounding of particles of sediment carried in water by repeated collision with each other and the shore. ||
 * Attrition || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Particles are reduced in size and rounded off by colliding with one another as they are washed in the waves. Erosion grinds down the cliff-fall material. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Backwash || <span style="font-family: Calibri,sans-serif; font-size: 12px;">movement of water back towards the sea after a wave has broken ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Bar || <span style="font-family: Calibri,sans-serif; font-size: 12px;">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 ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Benefit cost ratio || <span style="font-family: Calibri,sans-serif; font-size: 12px;">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. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Berm || <span style="font-family: Calibri,sans-serif; font-size: 12px;">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. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Beach nourishment || <span style="font-family: Calibri,sans-serif; font-size: 12px;">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 ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Blow –hole || <span style="font-family: Calibri,sans-serif; font-size: 12px;">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. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Breaching || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Failure of defences allowing flooding by tidal or storm action. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Char || <span style="font-family: Calibri,sans-serif; font-size: 12px;">An island formed from silt deposited in a delta. The land is about at sea level. It is very fertile and attracts settlers desperate for land. However, it can easily be washed away by monsoon floods and cyclones. Even if the cyclones do not destroy the chars, they flood them with salt water which reduces their fertility. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Constructive waves || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Low frequency 6-8 per minute waves which have elliptical water motion, with powerful swash and weak backwash. They build deposition. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Concordant geology || <span style="font-family: Calibri,sans-serif; font-size: 12px;">The alignment of geological outcrops which are parallel to the coastline. E.g. Dorset coast Lulworth ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Corrasion || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Erosion by friction of load in contact with banks and bed (abrasion) ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Corrosion || <span style="font-family: Calibri,sans-serif; font-size: 12px;">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. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Cusp || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Crescent-shaped embayments developed on beaches of mixed sediments. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Cuspate foreland || <span style="font-family: Calibri,sans-serif; font-size: 12px;">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**.** ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Defence line || <span style="font-family: Calibri,sans-serif; font-size: 12px;">The crest of a sea wall/ revetment (man-made defences) or the crest of dunes or the cliff edge (natural defences). ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Deltas || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Form when the amount of sediment delivered at the mouth of a river exceeds the amount removed by waves and tidal currents ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Destructive waves || <span style="font-family: Calibri,sans-serif; font-size: 12px;">High frequency 13-15 per minute waves which have circular water motion, with weak swash and powerful backwash. They erode. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Differential erosion || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Varying rates of erosion relating to geology, and energy of coastline. Resistant coastlines have hard rocks massive structure consolidated and not susceptible to chemical weathering. E.g. Lands End (granite). ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Discordant geology || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Coasts which cut across the rock structure. E.g. Dorset North of Swanage Bay ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Diurnal range || <span style="font-family: Calibri,sans-serif; font-size: 12px;">The difference between the lowest temperature and the highest temperature in a 24 hour period. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Do Nothing || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Where no action is taken to protect the coastline. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Downdrift || <span style="font-family: Calibri,sans-serif; font-size: 12px;">In the direction of the net Longshore transport of beach material. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Dunes || <span style="font-family: Calibri,sans-serif; font-size: 12px;">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. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Eustatic || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Changes in sea level caused by variations in the amount of water in the oceans. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Fetch || <span style="font-family: Calibri,sans-serif; font-size: 12px;">The distance of uninterrupted water surface over which the wind has blown to form waves. Longer fetch means higher energy waves. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Fiord || <span style="font-family: Calibri,sans-serif; font-size: 12px;">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. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Flocculation || <span style="font-family: Calibri,sans-serif; font-size: 12px;">River load particles join together on contact with the salt in sea water, increasing their weight and causing them to drop/ be deposited. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Flood || <span style="font-family: Calibri,sans-serif; font-size: 12px;">A temporary excess of water that spills over onto land ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Frequency || <span style="font-family: Calibri,sans-serif; font-size: 12px;">How often floods occur ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Gabion || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Cages enclosing rocks to defend the coast. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Geo || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Steep sided narrow inlet ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Groyne || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Timber, sheet steel piles, rock or concrete posts and boards which run at right angles to trap sediment drifting along the shore. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Halophytes || <span style="font-family: Calibri,sans-serif; font-size: 12px;">0pioneer plants that can tolerate salty conditions which are submerged at high tide e.g. glasswort ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Hard engineering || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Structures developed to protect the foot of cliffs and prevent erosion. E.g. Sea walls, revetments, groynes and gabions, ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">High energy coast || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Coasts in which wave power is strong for a significant part of the year. e.g. Alaska to Iceland and Chile ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Hold the line || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Taking action to maintain the current defence line. This line may or may not be artificially defended (hard structures) at the present time. In some cases “the line” might be sand dunes, mud flats or cliffs. Holding the line means that the stretch of coast in question could be the subject of works, as necessary, in the future. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Hydraulic action || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Force exerted by moving water on the bed and banks of a river. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Isostatic || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Changes in sea level resulting from the rise and fall of land masses ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Isthmus || <span style="font-family: Calibri,sans-serif; font-size: 12px;">A narrow piece of land connecting two larger pieces of land. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Longshore drift || <span style="font-family: Calibri,sans-serif; font-size: 12px;">(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. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Low energy coast || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Coasts in which wave power is weaker, low fetch, few gales enclosed and therefore sheltered. e.g. Mediterranean and Baltic Seas ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Magnitude || <span style="font-family: Calibri,sans-serif; font-size: 12px;">The size of the flood ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Managed retreat || <span style="font-family: Calibri,sans-serif; font-size: 12px;">The deliberate re-establishment of the line of defence inland from its existing position to obtain engineering and /or environmental advantages. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Mass Movement || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Non- marine processes often seen on cliffs, like slumping, land slides and soil creep. Caused by gravity and often exacerbated by rain. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Plagioclimax || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Where succession is stunted by human interference e.g. cattle grazing ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Psammosere || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Succession of stages of plant growth forming colonisation of bare sand to climax vegetation ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Recession || <span style="font-family: Calibri,sans-serif; font-size: 12px;">With coasts, it means a retreat. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Recurrence interval || <span style="font-family: Calibri,sans-serif; font-size: 12px;">The interval at which particular levels of flooding will occur ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Retreat the line || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Intervention to set back the line of defences
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Building an embankment inland and letting the existing defences fall into disrepair (with monitoring).
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Building an embankment inland and dismantling the existing defences.
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Where defences are interfering with natural processes or are exposed to unpredicted conditions they are realigned. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Return period || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Average time between occurrences of a given event e.g. storms ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Revetment || <span style="font-family: Calibri,sans-serif; font-size: 12px;">A general term for defences that are aligned parallel to the shore including posts, pillars, or walls of rocks placed on the foreshore. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Ria || <span style="font-family: Calibri,sans-serif; font-size: 12px;">A river valley drowned, usually because sea level has risen but it could be because the land level has fallen e.g. Adur and Ouse Estuaries. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Runnel || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Breaks in beach ridges result from rip currents which form in the strong backwash. Inland of these, **<span style="font-family: Calibri,sans-serif; font-size: 12px;">runnels **<span style="font-family: Calibri,sans-serif; font-size: 12px;"> form, separating pools of standing water at low tide ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Saltation || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Sand bounces across the surface of the beach blown by wind ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Sediment cell || <span style="font-family: Calibri,sans-serif; font-size: 12px;">A length of coastline that is relatively self contained as far as the movement of sand or shingle is concerned. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Sediment sink || <span style="font-family: Calibri,sans-serif; font-size: 12px;">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. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Slumping || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Slumping is triggered by undercutting at the base of cliffs with rotation in the slip plane. E.g. Barton ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Soft Engineering || <span style="font-family: Calibri,sans-serif; font-size: 12px;">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. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Spit || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Long ridges of sand and shingle attached to land at one end. E.g. Hurst Castle Spit and Spurn Head ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Spring tide || <span style="font-family: Calibri,sans-serif; font-size: 12px;">These are particularly high or low tides caused when Sun, Moon and Earth all lie in a straight line, which happens twice a month. However, when the Sun is overhead at the Equator, (21st March and 21st September) there is a boost in the gravitational pull – the Spring and Autumn Equinoxes. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Stack || <span style="font-family: Calibri,sans-serif; font-size: 12px;">A residual post of rock resulting from the continued erosion of arches. E.g. Old Harry Rock ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Strategic coastal defence option || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Term for any coastal management strategy includes
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Do nothing
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Advance
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Retreat
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Hold
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Subaerial erosion || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Mass movement on a cliff e.g. soil creep, solifluction, earthflows, mudflows, slides, slumps, rockfall plus blown (Aeolian) material and runoff. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Surges || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Changes in water level as a result of meteorological forcing (may be positive or negative) e.g. storm surges. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Swash || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Movement of water up the beach away from the sea as a wave reaches the shore ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Swell || <span style="font-family: Calibri,sans-serif; font-size: 12px;">A circular motion caused by wind in the open sea which is non-moving. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Tidal bore || <span style="font-family: Calibri,sans-serif; font-size: 12px;">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. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Tidal Range || <span style="font-family: Calibri,sans-serif; font-size: 12px;">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 ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Tombolo || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Shingle ridge linking the mainland to an island. E.g. Chesil Beach. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Updrift || <span style="font-family: Calibri,sans-serif; font-size: 12px;">The direction opposite to predominant LSD movement of beach material. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Unconsolidated material || <span style="font-family: Calibri,sans-serif; font-size: 12px;">Loose/soft soil/sediment/rock that doesn’t hold together well ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Wave cut platform || <span style="font-family: Calibri,sans-serif; font-size: 12px;">A flat rock area in the intertidal zone created by destructive waves (also often by chemical weathering if a limestone area). ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Wave crest || <span style="font-family: Calibri,sans-serif; font-size: 12px;">The highest point of a wave ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Wave energy || <span style="font-family: Calibri,sans-serif; font-size: 12px;">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 ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Wavelength || <span style="font-family: Calibri,sans-serif; font-size: 12px;">The distance between two successive crests. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Wave period || <span style="font-family: Calibri,sans-serif; font-size: 12px;">The time taken for a wave to travel one wave length. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Wave steepness || <span style="font-family: Calibri,sans-serif; font-size: 12px;">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). ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Wave refraction || <span style="font-family: Calibri,sans-serif; font-size: 12px;">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. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Wave trough || <span style="font-family: Calibri,sans-serif; font-size: 12px;">The lowest point of a wave. ||
 * <span style="font-family: Calibri,sans-serif; font-size: 12px;">Weathering || <span style="font-family: Calibri,sans-serif; font-size: 12px;">The breakdown of rocks in situ (in their original location without them being moved away). This produces finer particles that can then be removed away by agents of erosion such as wing, running water and gravity. ||