A groyne (in the U.S. groin) is a rigid

hydraulic structure A hydraulic structure is a structure submerged or partially submerged in any body of water, which disrupts the natural flow of water. They can be used to divert, disrupt or completely stop the flow. An example of a hydraulic structure would be a da ...

built perpendicularly from an ocean shore (in

coastal engineering Coastal engineering is a branch of civil engineering concerned with the specific demands posed by constructing at or near the coast, as well as the development of the coast itself. The hydrodynamic impact of especially waves, tides, storm surges ...

) or a river bank, interrupting water flow and limiting the movement of

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...

. It is usually made out of wood, concrete, or stone. In the ocean, groynes create beaches, prevent beach erosion caused by

longshore drift Longshore drift from longshore current is a geological process that consists of the transportation of sediments (clay, silt, pebbles, sand, shingle) along a coast parallel to the shoreline, which is dependent on the angle incoming wave direction ...

where this is the dominant process and facilitate

beach nourishment Beach nourishment (also referred to as beach renourishment, beach replenishment, or sand replenishment) describes a process by which sediment, usually sand, lost through longshore drift or erosion is replaced from other sources. A wider beach ca ...

. There is also often cross-shore movement which if longer than the groyne will limit its effectiveness. In a river, groynes slow down the process of erosion and prevent ice-jamming, which in turn aids navigation. Groynes run generally perpendicular to the shore, extending from the upper

foreshore The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species of ...

beach A beach is a landform alongside a body of water which consists of loose particles. The particles composing a beach are typically made from rock, such as sand, gravel, shingle, pebbles, etc., or biological sources, such as mollusc shel ...

into the water. All of a groyne may be underwater, in which case it is a ''submerged groyne''. They are often used in tandem with

seawall A seawall (or sea wall) is a form of coastal defense constructed where the sea, and associated coastal processes, impact directly upon the landforms of the coast. The purpose of a seawall is to protect areas of human habitation, conservation ...

s and other coastal engineering features. Groynes, however, may cause a shoreline to be perceived as unnatural. Groynes are generally straight but could be of various plan view shapes, permeable or impermeable, built from various materials such as wood, sand, stone rubble, or

gabion A gabion (from Italian ''gabbione'' meaning "big cage"; from Italian ''gabbia'' and Latin ''cavea'' meaning "cage") is a cage, cylinder or box filled with rocks, concrete, or sometimes sand and soil for use in civil engineering, road building, ...

, etc.

Background

Etymology

The term ''groyne'' is derived from the

Old French Old French (, , ; Modern French: ) was the language spoken in most of the northern half of France from approximately the 8th to the 14th centuries. Rather than a unified language, Old French was a linkage of Romance dialects, mutually intelligib ...

, from

Late Latin Late Latin ( la, Latinitas serior) is the scholarly name for the form of Literary Latin of late antiquity.Roberts (1996), p. 537. English dictionary definitions of Late Latin date this period from the , and continuing into the 7th century in t ...

, "

snout A snout is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw. In many animals, the structure is called a muzzle, rostrum, or proboscis. The wet furless surface around the nostrils of the nose of many mammals is c ...

History

One of the earliest mentions of groynes is in connection with the planned improvements to the silted-up

Dover harbour The Port of Dover is a cross-channel ferry, cruise terminal, maritime cargo and marina facility situated in Dover, Kent, south-east England. It is the nearest English port to France, at just away, and is one of the world's busiest maritime pa ...

, by one Fernando Poyntz in 1582. In 1713 the first wooden groyne to protect

Brighton Brighton () is a seaside resort and one of the two main areas of the City of Brighton and Hove in the county of East Sussex, England. It is located south of London. Archaeological evidence of settlement in the area dates back to the Bronze A ...

's seafront and coastline was built, which had been heavily damaged in the

Great storm of 1703 The great storm of 1703 was a destructive extratropical cyclone that struck central and southern England on 26 November 1703. High winds caused 2,000 chimney stacks to collapse in London and damaged the New Forest, which lost 4,000 oaks. Ships wer ...

, and again in 1705. In 1867, the first concrete groyne was built near East Street, Brighton as a 60 m promenade.

Mechanics

Beach evolution and sedimentation accretion

A groyne gradually creates and maintains a wide area of beach on its updrift side by trapping the sediments suspended in the ocean current. This process is called accretion of sand and gravel or

beach evolution Beach evolution occurs at the shoreline where sea, lake or river water is eroding the land. Beaches exist where sand accumulated from centuries-old, recurrent processes that erode rocky and sedimentary material into sand deposits. River deltas dep ...

. It reduces erosion on the other, i.e. downdrift, side by reducing the speed and power of the waves striking the shore. It is a physical barrier to stop

sediment transport Sediment transport is the movement of solid particles (sediment), typically due to a combination of gravity acting on the sediment, and/or the movement of the fluid in which the sediment is entrained. Sediment transport occurs in natural system ...

in the direction of

(also called longshore transport). If a groyne is correctly designed, then the amount of material it can hold will be limited, and excess sediment will be free to move on through the system. However, if a groyne is too large it may trap too much sediment, which can cause severe beach erosion on the down-drift side.

Groyne fields

Groynes are generally placed in series, generally all perpendicular to the shore. The areas between groups of groynes are groyne fields.

Terminal groyne syndrome

A poorly designed groyne (too long and not suited to the unique features of the coast) can also accelerate the erosion of the downdrift beach, which receives little or no sand from longshore drift. This process is known as terminal groyne syndrome, because in a series of groynes it occurs after the terminal groyne (last groyne on the downdrift side of the beach or coastline).

Headland groyne / Headland breakwater

A ''

breakwater Breakwater may refer to: * Breakwater (structure), a structure for protecting a beach or harbour Places * Breakwater, Victoria, a suburb of Geelong, Victoria, Australia * Breakwater Island Breakwater Island () is a small island in the Palme ...

'' is an artificial offshore structure built parallel to the shore -- similar to naturally formed

barrier island Barrier islands are coastal landforms and a type of Dune, dune system that are exceptionally flat or lumpy areas of sand that form by wave and tidal action parallel to the mainland coast. They usually occur in chains, consisting of anything fro ...

s -- that normally remains unattached to the shore. When a groyne is built to attach the breakwater to the shore, it is called a "

headland A headland, also known as a head, is a coastal landform, a point of land usually high and often with a sheer drop, that extends into a body of water. It is a type of promontory. A headland of considerable size often is called a cape.Whittow, John ...

groyne", also known as "bulkhead groyne", "headland breakwater", "T-head groyne", or "T-shaped groyne".

Usage

Coastal management

A groyne's length and elevation, and the spacing between groynes is determined according to local wave energy and beach slope. Groynes that are too long or too high tend to accelerate downdrift erosion, and are ineffective because they trap too much sediment. Groynes that are too short, too low, or too

permeable Permeability, permeable, and semipermeable may refer to: Chemistry *Semipermeable membrane, a membrane which will allow certain molecules or ions to pass through it by diffusion *Vascular permeability, the movement of fluids and molecules betwe ...

are ineffective because they trap too little sediment. If a groyne does not extend far enough landward, water (for example at a high tide combined with a storm surge) may flow past the landward end and erode a channel bypassing the groyne, a process known as ''flanking''.

River management

River groynes (spur dykes, wing dykes, or

wing dam A wing dam or wing dike is a man made barrier that, unlike a conventional dam, only extends partway into a river. These structures force water into a fast-moving center channel which reduces the rate of sediment accumulation, while slowing water f ...

s) are often constructed nearly perpendicular to the riverbanks, beginning at a riverbank with a root and ending at the regulation line with a head. They maintain a channel to prevent ice jamming, and more generally improve navigation and control over lateral erosion, that would form from

meanders A meander is one of a series of regular sinuous curves in the channel of a river or other watercourse. It is produced as a watercourse erodes the sediments of an outer, concave bank (cut bank) and deposits sediments on an inner, convex bank w ...

. Groynes have a major impact on the

river morphology The terms river morphology and its synonym stream morphology are used to describe the shapes of river channels and how they change in shape and direction over time. The morphology of a river channel is a function of a number of processes and enviro ...

: they cause autonomous degradation of the river. They are also used around bridges to prevent

bridge scour Bridge scour is the removal of sediment such as sand and gravel from around bridge abutments or piers. Hydrodynamic scour, caused by fast flowing water, can carve out ''scour holes'', compromising the integrity of a structure. In the United States ...

. Groynes can be distinguished by how they are constructed, whether they are submerged, their effect on stream flow or by shape.Przedwojski ''et al.'' (1995)

By their planview shape

Groynes can be built with different planview shapes. Some examples include straight groynes, hockey stick or curved, inverted hockey stick groynes, tail or checkmark shaped groynes, L head, straight groynes with pier head (seaward end raised on the stilts, since the pier head is raised on the stilts it does not act as the breakwater), T-head ( headland groyne, breakwater attached to the shore with straight groyne, the head/breakwater itself could be shaped straight, Y-shaped, arrow or wing shaped head).

By cross-section based on material used

Wooden groynes, sheetpile groynes,

sandbag A sandbag or dirtbag is a bag or sack made of hessian (burlap), polypropylene or other sturdy materials that is filled with sand or soil and used for such purposes as flood control, military fortification in trenches and bunkers, shielding gl ...

groynes, rubble mound or

groynes, etc.

By permeability

Groynes can be permeable, allowing the water to flow through at reduced velocities, or impermeable, blocking and deflecting the current. * Permeable groynes are large rocks, bamboo or timber * impermeable groynes (solid groynes or rock armour groynes) are constructed using rock, gravel, gabions.

By whether they are submerged

Groynes can be submerged or not under normal conditions. Usually impermeable groynes are non-submerged, since flow over the top of solid groynes may cause severe erosion along the shanks. Submerged groynes, on the other hand, may be permeable depending on the degree of flow disturbance needed.

By their effect on stream flow

Groynes can be attracting, deflecting or repelling. * Attracting groynes point downstream, serving to attract the stream flow toward themselves and not repel the flow toward the opposite bank. They tend to maintain deep current close to the bank. * Deflecting groynes change the direction of flow without repelling it. They are generally short and used for limited, local protection. * Repelling groynes point upstream; they force the flow away from themselves. A single groyne may have one section, for example, attracting, and another section deflecting.

Gallery

File:Duisburg, Mündelheim, Rheinbogen, 2020-04 CN-02.jpg, Groynes on the Rhine, Germany File:GROYNES in the Dutch Rhine.jpg, Groynes in the

Waal WAAL (99.1 FM "The Whale") is a commercial radio station licensed to Binghamton, New York. It airs a classic rock radio format and is owned by Townsquare Media. WAAL is the oldest FM radio station in the Binghamton metropolitan area. It is an ...

, part of the

Rhine ), Surselva, Graubünden, Switzerland , source1_coordinates= , source1_elevation = , source2 = Rein Posteriur/Hinterrhein , source2_location = Paradies Glacier, Graubünden, Switzerland , source2_coordinates= , so ...

in the

Netherlands ) , anthem = ( en, "William of Nassau") , image_map = , map_caption = , subdivision_type = Sovereign state , subdivision_name = Kingdom of the Netherlands , established_title = Before independence , established_date = Spanish Netherl ...

File:Beach with groynes.JPG, Groyne on the east coast of

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

File:Cresbeach-groyne.jpg, Groyne in Crescent Beach, British Columbia, Canada File:Ennore Expressway gyrones.JPG, Groynes off the Ennore Expressway near

Chennai Chennai (, ), formerly known as Madras ( the official name until 1996), is the capital city of Tamil Nadu, the southernmost Indian state. The largest city of the state in area and population, Chennai is located on the Coromandel Coast of th ...

, India File:Ostrogi Wisła Warszawa 001.jpg, Groynes on the

Vistula The Vistula (; pl, Wisła, ) is the longest river in Poland and the ninth-longest river in Europe, at in length. The drainage basin, reaching into three other nations, covers , of which is in Poland. The Vistula rises at Barania Góra in ...

Warsaw Warsaw ( pl, Warszawa, ), officially the Capital City of Warsaw,, abbreviation: ''m.st. Warszawa'' is the capital and largest city of Poland. The metropolis stands on the River Vistula in east-central Poland, and its population is officia ...

, Poland File:Estuary in Pozhikara, Paravur.jpg, Groynes on the

Arabian Sea The Arabian Sea ( ar, اَلْبَحرْ ٱلْعَرَبِيُّ, Al-Bahr al-ˁArabī) is a region of the northern Indian Ocean bounded on the north by Pakistan, Iran and the Gulf of Oman, on the west by the Gulf of Aden, Guardafui Channel ...

Pozhikara Pozhikkara or Pozhikara is the Western border town of the Paravur municipality in the Kollam district of Kerala state in India. It is located at the South-Western tip of Kollam's coastal area. It is in the Arabian Sea coast. Pozhikara is a ...

on the

Malabar Coast The Malabar Coast is the southwestern coast of the Indian subcontinent. Geographically, it comprises the wettest regions of southern India, as the Western Ghats intercept the moisture-laden monsoon rains, especially on their westward-facing m ...

of India File:2017 Sarasota Cortez Beach Sea Wall Groyne at Sunset 1 FRD 7204.jpg, A groyne at Cortez Beach on

Anna Maria Island Anna Maria Island, is a barrier island on the coast of Manatee County, Florida, in the United States. It is bounded on the west by the Gulf of Mexico, on the south by Longboat Pass (which separates it from Longboat Key), on the east by Anna Ma ...

, Florida at sunset File:Silver_Beach_Sydney.jpg, Groyne at Silver Beach, Sydney, Australia File:Otago Harbour entrance, Otago, New Zealand, 12th. Dec. 2010 - Flickr - PhillipC.jpg, A 1200-metre-long

mole Mole (or Molé) may refer to: Animals * Mole (animal) or "true mole", mammals in the family Talpidae, found in Eurasia and North America * Golden moles, southern African mammals in the family Chrysochloridae, similar to but unrelated to Talpida ...

Aramoana Aramoana is a small coastal settlement north of Dunedin on the South Island of New Zealand. The settlement's permanent population in the 2001 Census was 261. Supplementing this are seasonal visitors from the city who occupy cribs. The name '' ...

(centre left of image), protects the mouth of New Zealand's

Otago Harbour Otago Harbour is the natural harbour of Dunedin, New Zealand, consisting of a long, much-indented stretch of generally navigable water separating the Otago Peninsula from the mainland. They join at its southwest end, from the harbour mouth. It ...

References

Notes

* Construction Industry Research and Information Association (1990) ''Groynes in coastal engineering : data on performance of existing groyne systems'', CIRIA technical note 135, London : CIRIA, * Crossman, M. and Simm, J. (2004)
Manual on the use of timber in coastal and river engineering
', HR Wallingford, London : Thomas Telford, * French, P.W. (2001) ''Coastal defences : processes, problems and solutions'', London : Routledge, * Hoyle, J.W. and King, J.T. (1971) ''The principles of coast protection'', Lyndhurst : the authors, * Przedwojski, B., Błażejewski, R and Pilarczyk, K.W. (1995) ''River training techniques : fundamentals, design and applications'', Rotterdam : Balkema, * Walker, D.J. (1987) ''Nearshore hydrodynamics and the behaviour of groynes on sandy beaches'', PhD thesis, Imperial College London, 277 p. * Also published in the ''Delft Hydraulics Select Series'' (No. 7/2005).

External links

Groynes in the Netherlands
*
Coastal Wiki portal
{{Authority control Hydraulic engineering Coastal construction Coastal erosion