• Beach drainage systems have been installed in many locations around the world to halt and reverse erosion trends in sand beaches.

• Construction techniques
  Hard engineering methods
  [edit]
  Groynes
  [edit]
  Groyne at Mundesley, Norfolk, UK
  Main article: Groyne
  Groynes are ert or walls perpendicular to the coastline to trap the sedimentation of longshore drift to gradually create a beach and for it ongoing protection by eliminating coastal erosion, often made of greenharts, concrete, rock or wood.

• Costs may be lowest if existing defences are left to fail naturally, but the realignment project may be more actively managed, for example by creating an artificial breach in existing defences to allow the sea in at a particular place in a controlled fashion, or by pre-forming drainage channels for created salt-marsh.

• Planning approaches
  Five generic strategies are involved in coastal defense:[6]
  • Abandonment
  • Managed retreat or realignment, which plans for retreat and adopts engineering solutions that accommodate natural processes of adjustment
  • Armoring by constructing seawalls and other hard structures
  • Construct defenses seaward of the coast
  • Adapting vertically by elevating land and buildings
  The choice of strategy is site-specific, depending on pattern of sea-level change, geomorphological setting, sediment availability and erosion, as well as social, economic and political factors.

• The imported sand should be of a similar quality to the existing beach material so it can meld with the natural local processes and without adverse effects.

• This normally results in protecting the land behind the halosere, as wave energy dissipates throughout the accumulated sediment and additional vegetation in the new habitat.

• Alternatively, non-morphological features may be used such as water level (high water line (HWL), mean high water line) wet/dry boundary and the physical water line.

• Twentieth century
  [edit]
  Prior to the 1950s, the general practice was to use hard structures to protect against beach erosion or storm damages.

• Alternatively, integrated coastal zone management approaches may be used to prevent development in erosion- or flood-prone areas, reducing the need to address the changes.

• This uncertainty arises because at any given time the position of the shoreline is influenced by the immediate tidal effects and a variety of long-term effects such as relative sea-level rise and along shore littoral sediment movement.

• Older-style vertical seawalls reflected all the energy of the waves back out to sea, and for this purpose were often given recurved crest walls which increased local turbulence, and thus increased entrainment of sand and sediment.

• [18]
  Stabilizing sand dunes with plants is a common practice and can be implemented on private and public beaches.

• Limited knowledge of coastal sediment transport processes often resulted in inappropriate measures of coastal erosion mitigation.

• This is generally used to absorb wave energy and hold beach material as riprap does.

• [32] More specifically the position of the shoreline in the past, at present and where it is predicted to be in the future is useful for in the design of coastal protection, to calibrate and verify numerical models to assess sea level rise, map hazard zones and to regulate coastal development.

• Managed retreat is often a response to a change in sediment budget or to sea level rise.

• The technique is used when the land adjacent to the sea is low in value.

• Shoreline mapping
  [edit]
  Defining the shoreline is a difficult task due to its dynamic nature and the intended application.

• [24]
  Costs
  [edit]
  The costs of installation and operation vary due to:
  • system length (non-linear cost elements)
  • pump flow rates (sand permeability, power costs)
  • soil conditions (presence of rock or impermeable strata)
  • discharge arrangement /filtered seawater utilization
  • drainage design, materials selection & installation methods
  • geographical considerations (location logistics)
  • regional economic considerations (local capabilities /costs)
  • study requirements /consent process.

• Modern seawalls aim to re-direct most of the incident energy in the form of sloping revetments, resulting in low reflected waves and much reduced turbulence.

• They will experience a so-called “coastal squeeze” whereby ecological or geomorphological zones that would normally retreat landwards encounter solid structures and can migrate no further.

• Managed retreat has become more of a necessary strategy due to climate change, as adaptation strategies can only do so much to stop sea level rise.

• [11]
  Alternatively, soft engineering techniques supporting natural processes and relying on natural elements such as dunes and vegetation can prevent erosive forces from reaching the back-shore.

• Other harbours were lost due to natural causes such as rapid silting, shoreline advance or retreat, etc.

• [2] With three-quarters of the world population expected to reside in the coastal zone by 2025, human activities originating from this small land area will impose heavy pressure on coasts.

• Although the halosere is not strictly man-made, as many natural processes contribute to the succession, anthropogenic factors are partially responsible for the formation, since an initial factor was needed to help start the process of succession.

• [10]
  Hold the line
  [edit]
  Holding the line typically involves shoreline hardening techniques, e.g., using permanent concrete and rock constructions.

• In other words, this is one of the first accounts of the use of a sea wall to protect a coastal settlement.

• Groynes do not protect the beach against storm-driven waves and if placed too close together create currents that carry material offshore.

• However, the availability of historical data is limited at many coastal sites and so the choice of data source is largely limited to what is available for the site at a given time.

• If the sea rises, many coasts that are developed with infrastructure along or close to the shoreline will be unable to accommodate erosion.

• The location of a seawall, must consider the swept prism of the beach profile, the consequences of long-term beach recession and amenity crest level, including cost implications.

• [27] Investigators adopt the use of shoreline indicators to represent the true shoreline position.

• Soft options such as beach nourishment protect coastlines and help to restore the natural dynamism, although they require repeated applications.

• This is generally used to absorb wave energy and hold beach material.

• They may be watertight, covering the slope completely, or porous, to allow water to filter through after the wave energy has been dissipated.

• Such conditions may include ground relief, camera tilt and atmospheric refraction.

• Material builds up on the downdrift side, where littoral drift is predominantly in one direction, creating a wider and a more plentiful beach, thereby protecting the coast because the sand material filters and absorbs wave energy.

• [26]
  Importance and application
  [edit]
  The shoreline location and its changing position over time is of fundamental importance to coastal scientists, engineers and managers.

• In some cases, armouring is used to protect land beyond the area to be flooded.

• Shoreline data derived from beach profiling is often spatially and temporally limited due to the high cost associated with that labour-intensive activity.

• Aerial photographs are the most commonly used data source because many coastal areas have extensive aerial photo coverage.

• They are useful when preventing the erosion of beaches, and can catch windblown sand which over time increases the natural formation of the beach.

• The Venetian Lagoon was one of the few populated coastal areas with continuous prosperity and development where written reports document the evolution of coastal protection works.

• Conditions outside of the camera can cause objects in an image to appear displaced from their true ground position.

• Beach profiling surveys
  [edit]
  Beach profiling surveys are typically repeated at regular intervals along the coast in order to measure short-term (daily to annual) variations in shoreline position and beach volume.

• Historically coastal strategies were heavily based on static structures, while coastal areas otherwise reflect a dynamic equilibrium.

• [19] Plant life has been established as an important stabilizing factor of sand dunes and the loss of it will cause more erosion.

• Limited intervention
  [edit]
  Limited intervention is an action taken whereby the management only addresses the problem to a certain extent, usually in areas of low economic significance.

• Human coastal activities has led to the erosion and loss of plant life on sand dunes.

• [26] [30] Shoreline monitoring campaigns provide information about historic shoreline location and movement, and about predictions of future change.

• Rock armour has a limited lifespan, is not effective in storm conditions and reduces recreational values.

• The location of the shoreline also provides information regarding shoreline reorientation adjacent to structures, beach width, volume and rates of historical change.

• Limited intervention often includes the succession of haloseres, including salt marshes and sand dunes.

• Dolos has replaced the use of concrete blocks because it is more resistant to wave action and requires less concrete to produce a superior result.

• A decision is made to allow the land to erode and flood, creating new shoreline habitats.

• Groynes are cost-effective, require little maintenance and are one of the most common defences.

• Changes in sea level damage beaches and coastal systems are expected to rise at an increasing rate, causing coastal sediments to be disturbed by tidal energy.

• During the 1920s and ’30s, private or local community interests protected many coastal areas using these techniques on an ad hoc basis.

• A useful side effect of the system is that collected seawater is relatively pure because of sand’s filtration effect.

• This situation causes objects above sea level to be displaced outward from the centre of the photograph and objects below ground level to be displaced toward the centre of the image (Figure 2).

• [33]
  Historical maps
  [edit]
  In the event that a study requires the shoreline position from before aerial photographs, or if the location has poor photographic coverage, historical maps provide an alternative.

• The frequent changes in technology prevented the emergence of one standard mapping approach.

• Survey data is limited to smaller lengths of shoreline generally less than ten kilometres.

• They provide a good database for compilation of shoreline change maps.

• One solution is a sand bypassing system to pump sand under/around the training walls.

• [29][31] The HWL represents the landward extent of the most recent high tide and is characterised by a change in sand colour due to repeated, periodic inundation by high tides.

 

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Photo credit: https://www.flickr.com/photos/emerson12/1022552036/’]