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 and tsunamis and (often) the harsh environment of salt seawater are typical challenges for the coastal engineer – as are the morphodynamic changes of the coastal topography, caused both by the autonomous development of the system and man-made changes. The areas of interest in coastal engineering include the coasts of the oceans, seas, marginal seas, estuaries and big lakes.

Besides the design, building and maintenance of coastal structures, coastal engineers are often interdisciplinary involved in integrated coastal zone management, also because of their specific knowledge of the hydro- and morphodynamics of the coastal system. This may include providing input and technology for e.g. environmental impact assessment, port development, strategies for coastal defense, land reclamation, offshore wind farms and other energy-production facilities, etc.

Big wave cheney
Wave attack on Ilfracombe's sea walls during a storm.

Specific elements of coastal engineering

Sand suppletion on the Dutch coast 2
Beach nourishment at the Dutch coast.

The coastal environment produces challenges specific for this branch of engineering: waves, storm surges, tides, tsunamis, sea level changes, sea water and the marine ecosystem.

Most often, in coastal engineering projects there is a need for metocean conditions: local wind and wave climate, as well as statistics for and information on other hydrodynamic quantities of interest. Also, bathymetry and morphological changes are of direct interest. In case of studies of sediment transport and morphological changes, relevant properties of the sea bed sediments, water and ecosystem properties are needed.

Long and short waves

Munk ICCE 1950 Fig1
Classification of the spectrum of ocean waves according to wave period, by Walter Munk (1950).[1]

The occurrence of wave phenomena – like sea waves, swell, tides and tsunamis – require engineering knowledge of their physics, as well as models: both numerical models and physical models. The practices in present-day coastal engineering are more-and-more based on models verified and validated by experimental data.

Apart from the wave transformations themselves, for the waves coming from deep water into the shallow coastal waters and surf zone, the effects of the waves are important. These effects include:

Notes

  1. ^ Munk, W.H. (1950), Origin and generation of waves, Long Beach, California: ASCE, pp. 1–4

References

  • Dean, R.G.; Dalrymple, R.A. (2004), Coastal Processes with Engineering Applications, Cambridge University Press, ISBN 9780521602754
  • Hughes, S.A. (1993), Physical Models and Laboratory Techniques in Coastal Engineering, Advanced series on ocean engineering, World Scientific, ISBN 9789810215415
  • Kamphuis, J.W. (2010), Introduction to Coastal Engineering and Management, Advanced series on ocean engineering, World Scientific, ISBN 9789812834843
  • Kraus, N.C. (1996), History and Heritage of Coastal Engineering, American Society of Civil Engineers, ISBN 9780784474143
  • Sorensen, R. (2013), Basic Coastal Engineering, Springer, ISBN 9781475726657

External links

Accropode

Accropode blocks are man-made unreinforced concrete objects designed to resist the action of waves on breakwaters and coastal structures.

Breachway

A breachway is the shore along a channel, or the whole area around where a channel meets the ocean. The Rhode Island coastline has many breachways on its map. Today's permanent breachways have rock jetties that line the sides of the channel to protect against erosion or closing of the waterway. The water channels usually lead to salt water ponds.

Breakwater (structure)

Breakwaters are structures constructed near the coasts as part of coastal management or to protect an anchorage from the effects of both weather and longshore drift.

Civil engineering

Civil engineering is a professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including public works such as roads, bridges, canals, dams, airports, sewerage systems, pipelines, structural components of buildings, and railways. Civil engineering is traditionally broken into a number of sub-disciplines. It is considered the second-oldest engineering discipline after military engineering, and it is defined to distinguish non-military engineering from military engineering. Civil engineering takes place in the public sector from municipal through to national governments, and in the private sector from individual homeowners through to international companies.

Clapotis

In hydrodynamics, the clapotis (from French: "lapping of water") is a non-breaking standing wave pattern, caused for example, by the reflection of a traveling surface wave train from a near vertical shoreline like a breakwater, seawall or steep cliff.

The resulting clapotic wave does not travel horizontally, but has a fixed pattern of nodes and antinodes.

These waves promote erosion at the toe of the wall,

and can cause severe damage to shore structures.

The term was coined in 1877 by French mathematician and physicist Joseph Valentin Boussinesq who called these waves ‘le clapotis’ meaning ‘’the lapping".In the idealized case of "full clapotis" where a purely monotonic incoming wave is completely reflected normal to a solid vertical wall,

the standing wave height is twice the height of the incoming waves at a distance of one half wavelength from the wall.

In this case, the circular orbits of the water particles in the deep-water wave are converted to purely linear motion, with vertical velocities at the antinodes, and horizontal velocities at the nodes.

The standing waves alternately rise and fall in a mirror image pattern, as kinetic energy is converted to potential energy, and vice versa.

In his 1907 text, Naval Architecture, Cecil Peabody described this phenomenon:

At any instant the profile of the water surface is like that of a trochoidal wave, but the profile instead of appearing to run to the right or left, will grow from a horizontal surface, attain a maximum development, and then flatten out till the surface is again horizontal; immediately another wave profile will form with its crests where the hollows formerly were, will grow and flatten out, etc. If attention is concentrated on a certain crest, it will be seen to grow to its greatest height, die away, and be succeeded in the same place by a hollow, and the interval of time between the successive formations of crests at a given place will be the same as the time of one of the component waves.

Cliff stabilization

Cliff stabilization is a coastal management erosion control technique. This is most suitable for softer or less stable cliffs. Generally speaking, the cliffs are stabilised through dewatering (drainage of excess rainwater to reduce water-logging) or anchoring (the use of terracing, planting, wiring or concrete supports to hold cliffs in place).

Coastal erosion

There are two common definitions of coastal erosion. First, coastal erosion is often defined as the loss or displacement of land along the coastline due to the action of waves, currents, tides, wind-driven water, waterborne ice, or other impacts of storms. This landward retreat of the shoreline is measured to a given datum over a temporal scale of tides, seasons, and other short-term cyclic processes. Finally, coastal erosion is also defined as the process of long-term removal of sediment and rocks at the coastline, leading to loss of land and retreat of the coastline landward. It may be caused by hydraulic action, abrasion, impact and corrosion by wind, water, and other forces, natural or unnatural.On non-rocky coasts, coastal erosion results in rock formations in areas where the coastline contains rock layers or fracture zones with varying resistance to erosion. Softer areas become eroded much faster than harder ones, which typically result in landforms such as tunnels, bridges, columns, and pillars. Over time the coast generally evens out. The softer areas fill up with sediment eroded from hard areas, and rock formations are eroded away. Also abrasion commonly happens in areas where there are strong winds, loose sand, and soft rocks. The blowing of millions of sharp sand grains creates a sandblasting effect. This effect helps to erode, smooth and polish rocks. The definition of abrasion is grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particles.

Dredging

Dredging is the operation of removing material from one part of the water environment and relocating it to another. In all but a few situations the excavation is undertaken by a specialist floating plant, known as a dredger. Dredging is carried out in many different locations and for many different purposes, but the main objectives are usually to recover material that has some value or use, or to create a greater depth of water.

Groyne

A groyne (in the U.S. groin) is a rigid hydraulic structure built from an ocean shore (in coastal engineering) or from a bank (in rivers) that interrupts water flow and limits the movement of sediment. It is usually made out of wood, concrete or stone. In the ocean, groynes create beaches or prevent them being washed away by longshore drift. In a river, groynes slow down the process of erosion and prevent ice-jamming, which in turn aids navigation. Ocean groynes run generally perpendicular to the shore, extending from the upper foreshore or beach into the water. All of a groyne may be under water, in which case it is a submerged groyne. The areas between groups of groynes are groyne fields. Groynes are generally placed in groups. They are often used in tandem with seawalls. Groynes, however, may cause a shoreline to be perceived as unnatural.

The term is derived from the Old French groign, from Late Latin grunium, "snout".

Iribarren number

In fluid dynamics, the Iribarren number or Iribarren parameter – also known as the surf similarity parameter and breaker parameter – is a dimensionless parameter used to model several effects of (breaking) surface gravity waves on beaches and coastal structures. The parameter is named after the Spanish engineer Ramón Iribarren Cavanillas (1900–1967), who introduced it to describe the occurrence of wave breaking on sloping beaches.For instance, the Iribarren number is used to describe breaking wave types on beaches; or wave run-up on – and reflection by – beaches, breakwaters and dikes.

Land reclamation in Monaco

Land reclamation is done in Monaco because land is very scarce, as the nation is comparatively tiny, at 0.78 mi² (2.02 km²). To solve this problem and continue economic development, for years the country has been adding to its total land area by reclaiming land from the sea.

Managed retreat

In the context of coastal erosion, managed retreat (also managed realignment) allows an area that was not previously exposed to flooding by the sea to become flooded by removing coastal protection. This process is usually in low-lying estuarine areas and almost always involves flooding of land that has at some point in the past been claimed from the sea.

In the UK, managed retreat is often a response to sea level rise exacerbated by local subsidence of the land surface due to post-glacial isostatic rebound in the north.

Region of freshwater influence

Region of Freshwater Influence (ROFI), a term coined by Prof. John Simpson of the University of Wales, Bangor, and co-authors, in 1993 in Oceanologica Acta for the Rhine river plume. The term refers to regions where rivers debouch into estuaries and coastal shelf seas where the currents patterns are governed by density differences between salt sea water and fresh river water. In other words, a ROFI is the region between the shelf sea regime and the estuary where the local input of freshwater buoyancy from the coastal source is comparable with, or exceeds, the seasonal input of buoyancy as heat which occurs all over the shelf. Americans usually use the term river plume where Europeans use ROFI.

Revetment

In stream restoration, river engineering or coastal engineering, revetments are sloping structures placed on banks or cliffs in such a way as to absorb the energy of incoming water. In military engineering they are structures, again sloped, formed to secure an area from artillery, bombing, or stored explosives. River or coastal revetments are usually built to preserve the existing uses of the shoreline and to protect the slope, as defense against erosion.

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 sea wall is to protect areas of human habitation, conservation and leisure activities from the action of tides, waves, or tsunamis. As a seawall is a static feature it will conflict with the dynamic nature of the coast and impede the exchange of sediment between land and sea. The shoreline is part of the coastal interface which is exposed to a wide range of erosional processes arising from fluvial, aeolian and terrestrial sources, meaning that a combination of denudational processes will work against a seawall.The coast is generally a high-energy, dynamic environment with spatial variations over a wide range of timescales. The coast is exposed to erosion by rivers and winds as well as the sea, so that a combination of denudational processes will work against a sea wall.

Because of these persistent natural forces, sea walls need to be maintained (and eventually replaced) to maintain their effectiveness.

The many types of sea wall in use today reflect both the varying physical forces they are designed to withstand, and location specific aspects, such as local climate, coastal position, wave regime, and value of landform. Sea walls are hard engineering shore-based structures which protect the coast from erosion. But various environmental problems and issues may arise from the construction of a sea wall, including disrupting sediment movement and transport patterns. Combined with a high construction cost, this has led to an increasing use of other soft engineering coastal management options such as beach replenishment.

Sea walls may be constructed from various materials, most commonly reinforced concrete, boulders, steel, or gabions. Other possible construction materials are: vinyl, wood, aluminium, fibreglass composite, and large biodegrable sandbags made of jute and coir. In the UK, sea wall also refers to an earthen bank used to create a polder, or a dike construction.

Soft engineering

In civil engineering of shorelines, soft engineering is the use of ecological principles and practices to reduce erosion and achieve the stabilization and safety of shorelines and the area surrounding rivers, while enhancing habitat, improving aesthetics, and saving money. Soft engineering is achieved by using vegetation and other materials to soften the land and water interface, thereby improving ecological features without compromising the engineered integrity of the shoreline or river edges and the sea.

Tetrapod (structure)

Tetrapods are a type of structure in coastal engineering used to prevent erosion caused by weather and longshore drift, primarily to enforce coastal structures such as seawalls and breakwaters. Tetrapods are made of concrete, and use a tetrahedral shape to dissipate the force of incoming waves by allowing water to flow around rather than against them, and to reduce displacement by interlocking.

Undertow (water waves)

In physical oceanography, undertow is the under-current that is moving offshore when waves are approaching the shore. Undertow is a necessary and universal feature for almost any large body of water: it is a return flow compensating for the onshore-directed average transport of water by the waves in the zone above the wave troughs. The undertow's flow velocities are generally strongest in the surf zone, where the water is shallow and the waves are high due to shoaling.In popular usage, the word "undertow" is often misapplied to rip currents. An undertow occurs everywhere underneath shore-approaching waves, whereas rip currents are localized narrow offshore currents occurring at certain locations along the coast. Unlike undertow, rip currents are strong at the surface.

University of the West of England, Bristol

The University of the West of England, Bristol (UWE Bristol) is a public research university, located in and around Bristol, England, which received university status in 1992. In common with the University of Bristol and University of Bath it can trace its origins to the Merchant Venturers' Technical College, founded as a school in 1595 by the Society of Merchant Venturers.The university is made up of several campuses in Greater Bristol. Frenchay Campus is the largest campus in terms of student numbers as most of its courses are based there. City campus provides courses in the creative and cultural industries, and is made up of Bower Ashton Studios, Arnolfini, Spike Island, and Watershed. The institution is affiliated with the Bristol Old Vic Theatre School and validates its higher education courses. Frenchay Campus and Glenside Campus are home to most of the Faculty of Health and Applied Sciences, with a further Adult Nursing cohort based at Gloucester Campus. Hartpury Campus provides training in animal sciences, sport, equine, agriculture and conservation.

The university is ranked among the top 25 higher education institutions in England for its graduate employment prospects. Recent figures show 96% of recent graduates are in employment or further study, with 78% in professional roles. Last year the university celebrated its highest ever student satisfaction levels, with 87% of students indicating they were happy with the quality of their course.

In 2018 the Teaching Excellence Framework (TEF) awarded the University of the West of England with Gold rating, which is awarded for consistently outstanding and of the highest quality found in the UK Higher Education sector. It is only one of four universities in the UK to have a University Enterprise Zone providing space for over 70 businesses, and the largest UK robotics lab.

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