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NSW Coastline Management Manual

New South Wales Government
September 1990

ISBN 0730575063

Glossary

Accreted Profile The profile (cross-section) of a sandy beach that develops in the "calm" periods between major storm events. During such periods, swell waves move sediment from the offshore bar back onto the beach to rebuild the beach berm.
Artificial Headlands Man- made offshore structures connected to the shoreline to provide coastal protection or to restrict longshore transport.
Barometric Setup The increase in mean sea level caused by a drop in barometric pressure.
Bathymetry The measurement of depths of water; also information derived from such measurements.
Beach Berm That area of shoreline lying between the swash zone and the dune system.
Beach Erosion The offshore movement of sand from the sub- aerial beach during storms.
Beach Nourishment The supply of sediment by mechanical means to supplement sand on an existing beach or to build up an eroded beach.
Blowout The removal of sand from a dune by wind drift after protective dune vegetation has been lost. Unless repaired promptly, the area of blowout will increase in size and could lead to the development of a migrating sand dune and its associated problems.
Bore A broken swell wave travelling shorewards across the surf zone.
Breaker Index The ratio between the height of a wave and the water depth in which the wave breaks.
Breaker Zone That area of coastal waters where shoaling effects cause swell waves to break. This typically occurs in the shallower waters over an offshore bar.
Breaking Waves As waves increase in height through the shoaling process, the crest of the wave tends to speed up relative to the rest of the wave. Waves break when the speed of the crest exceeds the speed of advance of wave as a whole. Waves can break in three modes: spilling, surging and plunging.
Breakwater Structure protecting a shoreline, harbour, anchorage or basin from ocean waves.
Buffer Zone An appropriately managed and unalienated zone of unconsolidated land between beach and development, within which coastline fluctuations and hazards can be accommodated in order to minimise damage to the development.
Coastal Structures Those structures on the coastline designed to protect and rebuild the coastline and/or enhance coastal amenity and use.
Coastline Hazards

Detrimental impacts of coastal processes on the use, capability and amenity of the coastline. This manual identifies seven coastline hazards:

- Beach erosion
- Shoreline recession
- Entrance Instability
- Sand drift
- Coastal inundation
- Slope and cliff instability
- Stormwater erosion

Damage Potential The susceptibility of coastline development to damage by coastline hazards.
Design Wave Height The wave height adopted for the purposes of designing coastal structures such as breakwaters and seawalls. It is chosen to ensure that the structures are not at undue risk of wave damage.
Diffraction The "spreading" of waves into the lee of obstacles such as breakwaters by the transfer of wave energy along wave crests. Diffracted waves are lower in height than the incident waves.
Dune Field The system of incipient dunes, foredunes and hinddunes that is formed on sandy beaches to the rear of the beach berm.
Dune Maintenance The management technique by which dunes, dune vegetation and dune protective structures are kept in good " working order " ; activities may include weed/pest/fire control, replanting, fertilising, repair of fences and accessways, and publicity.
Dune Management The general term describing all activities associated with the restoration and/or maintenance of the role and values of beach dune systems; dune management activities and techniques include planning, dune reconstruction, revegetation, dune protection, dune maintenance, and community involvement.
Dune Protection The management technique by which the dune system is protected from damage by recreational and development activities; dune protection activities generally include the use of fences, accessways and signposts to restrict and control access to dune systems.
Entrance Instability Refers to the tendency of entrances to estuaries and coastal lakes to migrate along the shore, close up, reopen, form new entrances, etc. in response to wave and current action and freshwater flows.
Ebb Tide The outflow of coastal waters from bays and estuaries caused by the falling tide.
Fetch (Fetch Length) The horizontal distance over which a wind blows in generating waves.
Flood Tide The inflow of coastal waters into bays and estuaries caused by the rising tide.
Forbland Area characterised by low, herbaceous or slightly woody plants, annual or sometimes perennial (not grasses).
Foredune The larger and more mature dune lying between the incipient dune and the hinddune area. Foredune vegetation is characterised by grasses and shrubs. Foredunes provide an essential reserve of sand to meet erosion demand during storm conditions. During storm events, the foredune can be eroded back to produce a pronounced dune scarp.
Greenhouse Effect A term used to describe the likely global warming predicted to accompany the increasing levels of carbon dioxide and other " greenhouse " gases in the atmosphere.
Groynes Low walls built perpendicular to a shoreline to trap longshore sediment. Typically, sediment buildup on the updrift side of a groyne is offset by erosion on the downdrift side.
Groyne Field A system of regularly spaced groynes along a section of shoreline.
Hinddunes Sand dunes located to the rear of the foredune. Characterised by mature vegetation including trees and shrubs.
Incipient Dune The most seaward and immature dune of the dune system. Vegetation characterised by grasses. On an accreting coastline, the incipient dune will develop into a foredune.
Littoral Zone Area of the coastline in which sediment movement by wave, current and wind action is prevalent. The littoral zone extends from the onshore dune system to the seaward limit of the offshore zone and possibly beyond.
Longshore Currents Currents flowing parallel to the shore within the inshore and nearshore zones. Longshore currents are typically caused by waves approaching the beach at an angle. The " feeder " currents to rip cells are another example of longshore currents.
Mass Transport The net shorewards current associated with the movement of waves through the nearshore and inshore zones. Sediment transport from the offshore bar by this current is responsible for the rebuilding of storm eroded beaches during inter-storm periods.
Nearshore Zone Coastal waters between the offshore bar and the 60m depth contour. Swell waves in the nearshore zone are unbroken, but their behaviour is influenced by the presence of the seabed. (This definition is adopted for simplicity in this Manual and is based on wave motion considerations rather than sedimentology).
Offshore Bar Also known as a longshore bar. Submerged sandbar formed offshore by the processes of beach erosion and accretion. Typically, swell waves break on the offshore bar.
Offshore Breakwater Offshore structure built parallel to the beach to protect the beach and/or reduce wave action in inshore waters.
Offshore Zone Coastal waters to the seaward of the nearshore zone. Swell waves in the offshore zone are unbroken and their behaviour is not influenced by the presence of the seabed. (See note to "Nearshore Zone" ).
Onshore/Offshore Transport The process whereby sediment is moved onshore and offshore by wave, current and wind action.
Plunging Waves The wave crest breaks suddenly and with tremendous force by curling over a near vertical wave face.
Pocket Beaches Small beach systems typically bounded by rocky headlands. Because of the presence of the headlands and the small size of these beaches, longshore currents are relatively insignificant in the overall sediment budget.
Reflected Wave That part of an incident wave that is returned seaward when a wave impinges on a steep beach, barrier, or other reflecting surface.
Refraction The tendency of wave crests to become parallel to bottom contours as waves move into shallower waters. This effect is caused by the shoaling process which slows down waves in shallower waters.
Revetment (Refer to Seawall)
Rip Currents Concentrated currents flowing back to sea perpendicular to the shoreline. Rip currents are caused by wave action piling up water on the beach. Feeder currents running parallel to the shore (longshore currents) deliver water to the rip current.
Sand Bypassing A procedure whereby sand deposited on the updrift side of a training wall or similar structure is mechanically delivered to the downdrift side. This facilitates the natural longshore movement of the sediment.
Sand Creep Diagram Representation in the form of a compass rose of the rate and direction of sand drift.
Sand Drift The movement of sand by wind. In the con text of coastlines, "sand drift" is generally used to describe sand movement resulting from natural or man-induced degradation of dune vegetation, resulting in either nuisance or major drift. Sand drift can damage buildings, roads, railways and adjoining natural features such as littoral rainforest or wetlands; sand drift can be a major coastline hazard.
Sand Drift Control The repair and maintenance of sand dunes to minimise sand drift. The protection and fostering of dune vegetation is an important element of such programs.
Sand Drift Vector The net direction and net volume flux of sand drift at a particular location.
Sand Dunes Mounds or hills of sand lying to landward of the beach berm. Sand dunes are usually classified as an incipient dune, a foredune or hinddunes. During storm conditions, incipient and foredunes may be severely eroded by waves. During the intervals between storms, dunes are rebuilt by wave and wind effects. Dune vegetation is essential to prevent sand drift and associated problems.
Scarp Also known as the Dune Scarp and Backbeach Erosion Escarpment. The landward limit of erosion in the dune system caused by storm waves. At the end of a storm the scarp may be nearly vertical; as it dries out, the scarp slumps to a typical slope of 1V:1.5H.
Seawalls Walls built parallel to the shoreline to limit shoreline recession.
Sea Waves Waves in coastal waters resulting from the interaction of different wave trains and locally generated wind waves. Typically, sea waves are of short wavelength and of disordered appearance.
Sediment Budget An accounting of the rate of sediment supply from all sources (credits) and the rate of sediment loss to all sinks (debits) from an area of coastline to obtain the net sediment supply/loss.
Sediment Sink A mode of sediment loss from the coastline, including longshore transport out of area, dredging, deposition in estuaries, windblown sand, etc.
Sediment Source A mode of sediment supply to the coastline, including longshore transport into the area, beach nourishment, fluvial sediments from rivers, etc.
Semi-Diurnal Tides Tides with a period, or time interval between two successive high or low waters, of about 12.5 hours. Tides along the New South Wales coast are semi-diurnal.
Shoaling The influence of the seabed on wave behaviour. Such effects only become significant in water depths of 60m or less. Manifested as a reduction in wave speed, a shortening in wave length and an increase in wave height.
Shelf Wave Long period waves of low height that travel along the continental shelf and may modify coastal water levels off New South Wales by up to 0.2m. Shelf waves are generated by the pressure gradients associated with atmospheric disturbances in Bass Strait.
Shoreline Recession A net long term landward movement of the shoreline caused by a net loss in the sediment budget.
Shadow Area Areas behind breakwaters and headlands in the lee of incident waves. Waves move into shadow areas by the process of diffraction.
Significant Wave Height The average height of the highest one third of waves recorded in a given monitoring period. Also referred to as H1/3 or Hs.
Slope Readjustment The slumping of a backbeach erosion escarpment from its near vertical post-storm profile to a slope of about 1V:3H.
Slipface Area at the rear of a blown out dune where drifting sand from the blowout is deposited. The slipface is typically at the angle of repose of the sand.
Spilling Waves The wave crest breaks gradually as the wave travels to the shore. Characterised by the appearance of white water at the crest.
Storm Profile The profile (cross-section) of a sandy beach that develops in response to storm wave attack. Considerable volumes of sediment from the beach berm, the incipient dune and the foredune can be eroded and deposited offshore. The landward limit of the storm profile is typically defined by a backbeach erosion escarpment (dune scarp).
Storm Surge The increase in coastal water level caused by the effects of storms. Storm surge consists of two components: the increase in water level caused by the reduction in barometric pressure (barometric setup) and the increase in water level caused by the action of wind blowing over the sea surface (wind setup).
Storm Bar An offshore bar formed by sediments eroded from the beach during storm conditions.
Strandline Line immediately above high water characterised by deposition of drift material.
Surf Beat Periodic rise and fall in coastal water levels caused by two or more different wave trains arriving at the shoreline.
Surf Zone Coastal waters between the breaker zone and the swash zone characterised by broken swell waves moving shorewards in the form of bores.
Surging Waves The wave does not "break" but maintains its basic shape as it moves towards the shore, where it surges up the beach. Very little white water is evident before surging waves reach the shore.
Swash Zone That area of the shoreline characterised by wave uprush and retreat.
Swell Profile Another term for accreted profile.
Swell Waves Wind waves remote from the area of generation (fetch) having a uniform and orderly appearance characterised by regularly spaced wave crests.
Swept Prism The active area of the coastal system in which sediment may be mobilized by the forces of wind and wave action. On a sandy beach, it extends into the dune system and offshore to the limit of the nearshore zone.
Tidal Prism The volume of water stored in an estuary or tidal lake between the high and low tide levels; the volume of water that moves into and out of the estuary over a tidal cycle.
Tides The regular rise and fall of sea level in response to the gravitational attraction of the sun, moon and planets. Tides along the New South Wales coastline are semi-diurnal in nature, i.e. they have a period of about 12.5 hours.
Training Walls Walls constructed at the entrances of estuaries and rivers to improve navigability.
Tsunami Long period ocean waves generated by geological and tectonic disturbances below the sea. Incorrectly referred to as " tidal waves " , Tsunami travel at speeds of up to 800 km/hr in the open ocean, where they are of low height. However, tsunami can rise to a height of 10m or more through the shoaling process as they approach land.
Vegetation Degradation The process by which coastal vegetation is "degraded" or damaged; this reduces the effectiveness of vegetation in protecting coastal landforms and increases the potential for erosion of underlying soil materials by wind (resulting in sand drift), water or waves.
Wave Energy Rose A representation in the form of a compass rose of the directions and frequency of incident wave energy arriving at the location of interest.
Wave Height The vertical distance between a wave trough and a wave crest.
Wave Hindcasting The estimation of wave climate from meteorological data (barometric pressure, wind) as opposed to wave measurement.
Wave Length The distance between consecutive wave crests or wave troughs.
Wave Period The time taken for consecutive wave crests or wave troughs to pass a given point.
Wave Rider Buoy A floating device used to measure water level variations caused by waves. It is approximately 0.9m in diameter and is moored to the sea floor.
Wave runup The vertical distance above mean water level reached by the uprush of water from waves across a beach or up a structure.
Wave Setup The increase in water level within the surf zone above mean still water level caused by the breaking action of waves.
Wave Train A series of waves originating from the same fetch with more or less the same wave characteristics.
Wind Setup The increase i n mean sea level caused by the "piling up" of water on the coastline by the wind.
Wind Waves The waves initially formed by the action of wind blowing over the sea surface. Wind waves are characterised by a range of heights, periods and wavelengths. As they leave the area of generation (fetch), wind waves develop a more ordered and uniform appearance and are referred to as swell or swell waves.
Windborne Sediment Transport Sand transported by the wind. Sand can be moved by the processes of suspension (fine grains incorporated in the atmosphere), saltation (medium grains "hopping" along the surface) and traction (large grains rolled along the surface).