Glossary of terms


The accumulation of sediment by the action of natural forces.
Advance the existing line
A Strategy to move the defence of an area seaward of its existing position.


The beach area landward of the foreshore above the normal reach of the tides that provides the primary protection to the hinterland.

The water that runs back down the beach following waves breaking.
The topographic relief of the seabed.
The deposit of non-cohesive material on the interface between dry land and the sea.
The value of an area being defended.


Coastal processes
Collective term covering the action of natural forces on the shoreline and adjoining seabed.
Coastal response
The movement of coastal sediments and coastline position as a result of natural forces.
Collapsing waves
A combination of plunging and surging waves.


Do nothing
Carry out no coastal defence activity except for safety measures.
Downdrift affects
Impacts occurring in the ‘shadow’ of any coastal processes, particularly sediment movements


The wearing away of material by the action of natural forces.


The distance of open water over which wind blows.
The area of the beach lying between high water and low water.


The study of land forms and land forming processes (including the mobile seabed).


Hard defences
Static shoreline structures such as those constructed from timber, steel, concrete, asphalt and rubble.
High tide
The result of the Moon’s gravitational pull on the Earth creating a bulging in the sea surface. Occurs twice daily.
The area extending landward from the upper limit of extreme wave and tidal activity.
Hold the Line
A strategy to continue to hold the line of defence to an area where it is; continuing to protect the coastline.


Line of defence
The position of the existing defended area which may be an existing defence structure or the natural coastline where no structures exist.
Longshore movement/transport
Movement of material approximately parallel to the shoreline
Low tide
The areas of water on the Earth’s surface between high tide bulges that repel water.


Managed retreat
See ‘retreat the existing line.’
Management unit
A length of coast with coherent characteristics in terms of natural coastal processes and land use that requires a specific coastal defence option for the future which is consistent with the overall strategic requirements for a management area.


Natural coastline/shoreline movement/evolution
The movement of the coastline should natural development continue without the intervention of any defences.
Neap tides
Where the Moon isn’t aligned with the Sun and Earth, and it’s gravitational pull is reduced by the Sun’s.
The area adjacent to the coast where significant seabed profile change and sediment movements occur as a consequence of storm action and the beach.


Onshore-offshore sediment movement/transport
Movement of material perpendicular to the shore.
The flow of water over the top of a defence as a result of the prevailing tidal water level exceeding the crest height of the defence.
The flow of water over the top of a defence as a result of wave run-up or surge action.


Plunge line
The point where wave steepness exceeds 1:7 and the wave breaks.
Plunging waves
Occur on medium steepness beaches, and are characterised by a steep wave face with the crest curling over the top.
Process unit
A sub-section of coastline defined for management purposes that possesses coherent characteristics, in terms of natural coastal processes, which are sufficiently independent of adjacent stretches of shoreline.


Residual life
The remaining working life of a defence structure.
Retreat of the existing line/managed retreat
A strategy to encourage the movement of the shoreline landward of its present position in a managed or controlled manner, hence the term “managed retreat”. Sometimes also referred to as “managed set-back”.


Sediment budget
A description of the movement of coastal sediments including their sources and sinks (areas of deposition).
Sediment cell
A length of coastline, and its associated nearshore area, within which the movement of sand and shingle is largely self contained
Sediment sub-cell
A division of a sediment cell based on best available knowledge of large scale processes within that cell
The interface between land and sea.
Shoreline Management Plan (SMP)
A document that sets out a strategy for coastal defence for a specified length of coast, taking account of natural coastal processes and human and environmental influences and needs.
Soft defences
Mobile/responsive defence measures which consist of sand or shingle (beaches, and dunes or banks) which may be natural or constructed, and may include control structures.
Spilling waves
These occur on gently sloping beaches, where the crest breaks and spills down the face of the wave.
Spring tides
When the Moon, Earth, and Sun are aligned to create a larger tidal bulge.
Standard of service
The overall level of protection provided by the defence against sea conditions. Usually expressed in terms of the largest storm return period for which the defence can provide adequate protection.
Strategic coastal defence options
Generic term for any coastal management strategy e.g. do nothing, advance, retreat or hold the existing coastal defence line.
Surf Zone
The area where waves break.
Surging waves
These occur on steep beaches, with smooth wave faces and little foam or bubbles.
The foaming body of water after a wave has broken


Tidal range
The difference between high and low tides.
Waves caused by submarine shockwaves generated by seismic activity.


The result of the transfer of frictional energy from wind blowing across open water.
Wave Crest
The highest point of a wave.
Wave Energy
Proportional to the square of wave height multiplied by wave length (E ∞ LH2)
Wave Length
The distance between two consecutive crests.
Wave Period
The time taken for a wave to travel one wave length.
Wave Height
The distance between each crest and trough.
Wave refraction
Where the drag of the seabed on an irregular coastline slows and bends waves at different rates so that the waves are shore parallel.
Wave Steepness
The ratio of wave height to wave length.
Wave Trough
The lowest point of a wave.
Wave Velocity/Celerity
The speed of a wave crest over a period of time.