Coastal terms and definitions

A glossary of terms relating to coastal science.

Beach hazards and rating: Refers to the scaling of a beach according to the physical hazards associated with its beach type under normal wave conditions, together with any local physical hazards. It ranges from the low, least hazardous rating of 1 to a high, most hazardous rating of 10. It does not include biological hazards, such as sharks.

Beach ridge barrier plain: A sequence of (relict) ridges separated from the shoreline by progradation representing a successive positions of an advancing shoreline (also called a strandplain).

Beach ridge barrier: A single low, essentially continuous mound or ridge of beach material predominantly built by the action of waves (swash) on the backshore of a beach, and occurring singly or as one of a series of approximately parallel deposits. Generally composed of coarse sandy, pebbly, cobble and/or shelly material.

Beach type: Refers to the prevailing morphology (modal state) of a beach, including the waves and currents, the extent of the nearshore zone, the width and shape of the surf zone, including its bars and troughs, and the dry or subaerial beach.

Beach: Consists of a narrow backshore and foreshore (the part of the beach affected/largely built by) waves abutting to a sea cliff or structure. There is no foredune or beach ridge because of the lack of accommodation space.

Chenier plain: An accretionary feature consisting of a long, low lying, narrow strip of gravely sand (typically up to 3 m high and 40 to 400 m wide), often shelly, deposited in the form of wave-built beach ridge on a swampy, deltaic, or alluvial coastal plain of fine sediment.

Cuspate foreland: An accretionary feature consisting of a triangular accumulation of sand or shingle projecting seawards from the shoreline. It can have straight or concave shores and multiple beach ridges marking stages in progradation.

Delta: An alluvial deposit, usually triangular in planform, at the mouth of a river of other stream. It is normally built up only where there is no tidal or current action capable of removing the sediment as fast as it is deposited, and hence the delta builds seaward.

Dissipative: Highest wave energy (breakers 2-3 m high) of the wave-dominated beaches. Wide surf zone (up to 300-500 m) with 2 or 3 shore-parallel (straight) bars separated by subdued troughs. Waves dissipate their energy as they break passing over bars in the surf zone. Wide, low gradient intertidal beach composed of firm fine sand.

Estuarine coast: A shoreline inside an estuary.

Exposed coast: A shoreline that faces the open sea and is subject to ocean swell.

Exposure: The degree to which a coast is exposed to wave energy and ocean swell.

Foredune barrier plains: Systematic beach progradation over time frames of 10s to 1000s of years may lead to the development of wide foredune plains. Such plains may also develop during sea level regression and during sea level transgression as long as there is a significant sediment supply.

Foredune barriers: Shore-parallel dune ridges formed on the top of the backshore by wind and sand deposition within vegetation. Actively forming foredunes occupy a foremost seaward position in a dune system. Foredunes generally fall into two main types, incipient and established foredunes, within which there can be wide morphological and ecological variations. Also known as foredunes.

Foreshore sediment type: The type of sediment that makes up the foreshore. Made up of minerals and rock and shell fragments.

Foreshore: That part of a beach that is exposed by the low tides and submerged by high tides. This area can include many different types of habitats, including steep rocky cliffs, sandy beaches or vast mudflats. Also called intertidal beach.

Gravel: Unconsolidated sediment of particle sizes that includes granule 2-4 mm, pebbles 4-64 mm and cobbles 64-256 mm, and boulders >264 mm particle sizes.

Hapua: Is an elongated lagoon separated from the sea by a narrow barrier and situated at the mouth of large rivers that are usually braided. They form on mixed sand/gravel coasts, where the hinterland is a steep alluvial fan and are indicative of a coast being continually being reshaped, by wave- and river-dominated processes (waves most important).

Headlands: Land masses having a considerable elevation that border beaches and form the boundaries to littoral cells, compartmentalising sand transport along the shore, and reducing sand exchange between adjacent beaches.

Hinterland: Land or region behind the beach and dune or ridge systems. Can be rising ground, sea cliffs, lagoon or wetlands.

Inland headland bypass: Locations where transgressive sands climb from one coastal compartment over land to an adjacent coastal compartment.

Island: An area of land, smaller than a continent that is completely surrounded by the sea.

Lagoons/estuary/river: The area behind the beach is a lagoon, estuary or river.

Longshore bar and trough: Consists of a shore parallel bar separated from the beach by a deep trough. Breakers 1.5-2.0 m high. Moderate rip currents. Straight beach composed of medium sand with moderate to steep beach face and cusps.

Low energy coast: A shoreline that is sheltered from large waves and long period waves. Occur in gulfs and behind islands and reefs on the open coast.

Low lying plain – Drained: The land backing the beach is very low lying (near or below sea level) but is drained (cut with drains).

Low lying plain – Dry: The land backing the beach is very low lying (near or below sea level) but is dry.

Low lying plain - Wetlands: Low lying land (near or below sea level) behind the beach where water saturation is the dominant factor determining the nature of soil development and the types of plant and animal communities living in the surrounding environment. Other common names for wetlands are bogs, swamps and marshes.

Low tide terrace: Moderately steep beach face joined to an attached bar or terrace exposed at low tide. The bar extends alongshore, is flat and featureless, or cut every several 10's of metres by small rips. Breakers 0.5-1.0 m high. Beach composed of fine to medium sand. Commonly occur in areas sheltered from direct wave attack.

Mixed sand/gravel: Consists of: (1) poorly sorted mixtures of sandy and gravelly sediment, or (2) alternatively there is a clear distinction between the textural type between the upper and lower foreshore.

Morphologic and hydrodynamic controls: Features that control the morphodynamic response of a coastal compartment/beach unit e.g., headlands at either end of a pocket beach, offshore island, streams over the beach.

Mud: Unconsolidated sediment of particle sizes that includes silt 0.063-0.004 mm and clay <0.063 mm.

Offshore reefs: A ridge of rock with the top just below or just above the surface which is located at some distance from the shore.

Platform beach: A small body of sand deposited by wave action on and toward the rear of a wave cut platform. Platform beaches abut the base of the backing cliff and extend out across the platform, but are rarely to the outer edge.

Reflective + bars and rips: Tide-modified system with relatively straight, moderately steep, narrow, usually coarser and cusped reflective high-tide beach, fronted by a lower gradient, relatively featureless intertidal zone and wave dominated low-tide surf zone usually characterised by bar and rip morphology. Breakers 0.5 to 1.5 m high (height increases with onshore winds). At high tide waves break across a narrow continuous surf zone. At low tide a wider surf zone has rips (spacing 100-150 m).

Reflective + low tide terrace: Tide-modified beach type. Lowest energy of the tide-modified beaches with the coarsest sand. Steep cusped high-tide beach composed of medium to coarse sand, which changes at an abrupt break in slope into a low-gradient wide (av.120 m but can range 20-1000 m) low tide terrace composed of finer sand. Breakers 0.5-1 m high. At high tide waves surge at base of steep beach and there is no surf zone. At low tide there is a flat sand bar exposed, waves of > 0.5 m height plunge on outer end of bar, and waves >1 m height may cut rip channels across the terrace.

Reflective + rock flats: Tide-dominated system with steep reflective high tide beach fronted by rock extending seaward as an intertidal rock platform and/or rock flat. Bedrock control in the form of reefs and headlands means the beaches are short and waves average only 0.5 m height.

Reflective + sand flats: Tide-dominated beach type. Small steep (3-10°), low-gradient, very low-energy high-tide beach composed of coarse sand, fronted by flat featureless sand flats up to several hundred meters wide composed of finer sand . No waves unless strong onshore winds.

Reflective + sand ridges: Tide-dominated beach type. Steep (3-10°), narrow high-tide beach composed of coarse sand, fronted by an abrupt break in slope and a wide (several hundred metres) low gradient, usually finer sand intertidal zone containing shore parallel, numerous low amplitude sand ridges and runnels. At high tide there are no waves unless strong onshore winds, and relatively deep water off high tide beach.

Reflective + tidal mud flats: Tide-dominated system with narrow reflective high-tide beach composed of coarse sediments, fronted by wide (100's to several 1000's of metres), low gradient (<1°) mud flats with tidal draining channels. Mangroves or other vegetation may grow in the higher intertidal zone. Usually calm, only low wind chop during strong onshore winds. Occur where there is a source of mud nearby and where waves are insufficient to remove muds.

Reflective + tidal sand flats: Tide-dominated beach type. Narrow reflective high-tide beach composed of coarse sediments, fronted by wide (hundreds of metres) low gradient (<1°) sand flats, that become muddy on lower intertidal with tidal draining channels. Mangroves or other vegetation may grow in the higher intertidal zone. Entire tidal flat is covered at spring high tide. Usually calm, only low wind chop during strong onshore winds.

Reflective: Lowest wave energy of the wave-dominated beaches (breakers 0-1 m high). Steep narrow beach face with cusps on upper beach and narrow and swash zone. Short beaches composed of soft coarse sediments. Occur in locations sheltered by rocks, reefs and headlands.

Rhythmic bar and beach: High energy, beach consists of rhythmic (undulating) bar, trough and beach. Distinct rip troughs separated by detached bars. Breakers 1.5-2.0 m high. Beach has cusps (in lee of bars) and typically fine-medium sand.

Rising ground: The land backing the beach is land that is rising inland. In terms of its topography it is somewhere between low lying and a cliff.

River mouths: Location where a river emerges on the coast.

Sand: Unconsolidated sediment of particle sizes 0.062-2.0 mm.

Sea cliff – Active: The area backing the beach is a sea cliff that is actively being eroded.

Sea cliff – Fossil: The area backing the beach is a sea cliff comprising hard rock that is not actively eroding.

Spit: An accretionary feature, formed by waves consisting of a long narrow accumulation of sand or shingle, lying generally in line with the coast, with one end attached to the land the other projecting into the sea or across the mouth of an estuary.

Streams: Location where a small watercourse emerges onto the coast.

Submarine canyons: Submarine valleys that run across the continental shelf and down the continental slope. They are conduits for sand transport and are a one way trip for sand which is lost from the coastal system.

Tidal entrances: All entrances to estuaries and harbours that are not tidal inlets.

Tidal inlets: The entrance to estuaries on sandy shores that have formed where sand barriers or spits enclose bays. They comprise a flood and ebb tidal deltas, and a deep narrow throat through which strong currents flow.

Tide-dominated beaches: Occur in areas of high tide range and usually lower waves. Occur when the tide range is between 10 and 15 times the wave height and the wave height is very low. Consists of 5 types Reflective + sand ridges, Reflective + sand flats, Reflective + tidal sand flats, Reflective + tidal mud flats, Reflective + rock flats.

Tide-modified beaches: Occur in areas of high tide range and usually lower waves. Occur when the tide range is between 3 and 15 times the wave height and the wave height is <0.3m. Consist of 3 types Reflective + low tide terrace, Reflective + bars and rips, Ultra dissipative.

Tombolo: An accretionary feature comprising sand or gravel beach sediment developed by refraction, diffraction and longshore drift to form a 'neck' of land connecting a coast to an offshore island or breakwater.

Transgressive dunes: The land backing the beach consists of sand dunes migrating inland in the direction of the prevailing wind and burying the topography that includes anything except sand.

Transverse bar and rip: Bars transverse (perpendicular) to and attached to the beach separated by distinct rip troughs at 150-300 m spacing. Breakers 1.0-1.5 m high. Surf zone 50 -150 m wide with cellular circulation pattern. Undulating beach, with cusps, composed of fine to medium sand.

Ultra dissipative: Tide-modified beach type. Relatively straight, steeper, cusped high tide beach, with a low gradient concave, featureless, wide (averages 400-500 m) intertidal zone. Occur on the higher energy, tide modified coasts with waves averaging 0.5 m, and favoured by higher tide ranges and fine sand. Spilling breakers of 0.5-1.5 m height (height increases with onshore wind velocity). At high tide there is a wide zone of spilling breakers. At low tide there is a very wide zone of spilling breakers.

Waituna: Similar to a hapua but has a wider brackish lagoon separated from the sea by a narrow barrier and located at the mouth of smaller rivers. They form on mixed sand/gravel coasts, where the hinterland is a steep alluvial fan and are indicative of a coast being continually being reshaped, by wave- and river-dominated processes (waves most important).

Wave-dominated beaches: Beaches exposed to persistent ocean swell and waves and low tides (range <2m). Consist of 3 types; Reflective, Intermediate (longshore bar and trough, rhythmic bar and beach, transverse bar and rip, low tide terrace) and Dissipative. 

Pohara beach, Golden Bay. [NIWA]
Research subject: Coasts