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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 can reduce storm damage to coastal structures by dissipating energy across the
surf zone As ocean surface waves approach shore, they get taller and break, forming the foamy, bubbly surface called ''surf''. The region of breaking waves defines the surf zone, or breaker zone. After breaking in the surf zone, the waves (now reduced i ...
, protecting upland structures and infrastructure from storm surges, tsunamis and unusually high tides. Beach nourishment is typically part of a larger
integrated coastal zone management Integrated coastal zone management (ICZM), integrated coastal management (ICM), or integrated coastal planning is a coastal management process for the management of the coast using an integrated approach, regarding all aspects of the coastal zone ...
aimed at coastal defense. Nourishment is typically a repetitive process since it does not remove the physical forces that cause erosion but simply mitigates their effects. The first nourishment project in the United States was at
Coney Island Coney Island is a peninsular neighborhood and entertainment area in the southwestern section of the New York City borough of Brooklyn. The neighborhood is bounded by Brighton Beach and Manhattan Beach to its east, Lower New York Bay to the s ...
,
New York New York most commonly refers to: * New York City, the most populous city in the United States, located in the state of New York * New York (state), a state in the northeastern United States New York may also refer to: Film and television * ...
in 1922 and 1923. It is now a common shore protection measure used by public and private entities.


History

The first nourishment project in the U.S. was constructed at
Coney Island Coney Island is a peninsular neighborhood and entertainment area in the southwestern section of the New York City borough of Brooklyn. The neighborhood is bounded by Brighton Beach and Manhattan Beach to its east, Lower New York Bay to the s ...
, New York in 1922–1923. Before the 1970s, nourishment involved directly placing sand on the beach and
dunes A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, fl ...
. Since then more shoreface nourishments have been carried out, which rely on the forces of the wind,
waves Waves most often refers to: * Waves, oscillations accompanied by a transfer of energy that travel through space or mass. * Wind waves, surface waves that occur on the free surface of bodies of water. Waves may also refer to: Music *Waves (ban ...
and tides to further distribute the sand along the shore and onto the beaches and dunes. The number and size of nourishment projects has increased significantly due to population growth and projected relative sea-level rise.


Erosion

Beach erosion Coastal erosion is the loss or displacement of land, or the long-term removal of sediment and rocks along the coastline due to the action of waves, currents, tides, wind-driven water, waterborne ice, or other impacts of storms. The landward ...
is a specific subset of
coastal erosion Coastal erosion is the loss or displacement of land, or the long-term removal of sediment and rocks along the coastline due to the action of waves, currents, tides, wind-driven water, waterborne ice, or other impacts of storms. The landward ...
, which in turn is a type of
bioerosion Bioerosion describes the breakdown of hard ocean substrates – and less often terrestrial substrates – by living organisms. Marine bioerosion can be caused by mollusks, polychaete worms, phoronids, sponges, crustaceans, echinoids, and ...
which alters
coastal geography Coastal geography is the study of the constantly changing region between the ocean and the land, incorporating both the physical geography (i.e. coastal geomorphology, climatology and oceanography) and the human geography (sociology and history) ...
through beach morphodynamics. There are numerous incidences of
modern recession of beaches 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 d ...
, mainly due to longshore drift and
coastal development hazards A coastal development hazard is something that affects the natural environment by human activities and products. As coasts become more developed, the vulnerability component of the equation increases as there is more value at risk to the hazard. The ...
.


Causes of erosion

Beaches can erode naturally or due to human impact (
beach theft Sand theft or unauthorised or illegal sand mining leads to a widely unknown global example of natural and non-renewable resource depletion problem comparable in extent to global water scarcity. Beach theft is illegal removal of large quantities ...
/ sand mining). Erosion is a natural response to storm activity. During storms, sand from the visible beach submerges to form sand bars that protect the beach. Submersion is only part of the cycle. During calm weather smaller waves return sand from bars to the visible beach surface in a process called
accretion Accretion may refer to: Science * Accretion (astrophysics), the formation of planets and other bodies by collection of material through gravity * Accretion (meteorology), the process by which water vapor in clouds forms water droplets around nucl ...
. Some beaches do not have enough sand available to coastal processes to respond naturally to storms. When not enough sand is available, the beach cannot recover following storms. Many areas of high erosion are due to human activities. Reasons can include:
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, conservatio ...
s locking up
sand dunes A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, fl ...
, coastal structures like ports and harbors that prevent
longshore transport 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 ...
,
dam A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, a ...
s and other river management structures. Continuous, long-term renourishment efforts, especially in cuspate-cape coastlines, can play a role in longshore transport inhibition and downdrift erosion. These activities interfere with the natural sediment flows either through
dam A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, a ...
construction (thereby reducing riverine sediment sources) or construction of littoral barriers such as jetties, or by deepening of inlets; thus preventing longshore transport of sediment.


Types of shoreline protection approaches

The
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 ...
for the shoreline protection involves: *
Soft engineering Regarding the civil engineering of shorelines, soft engineering is a shoreline management practice that uses sustainable ecological principles to restore shoreline stabilization and protect riparian habitats. Soft Shoreline Engineering (SSE) uses th ...
: Beach nourishment is a type of soft approach. it gained popularity because it preserved beach resources and avoided the negative effects of hard structures. Instead, nourishment creates a “soft” (i.e., non-permanent) structure by creating a larger sand reservoir, pushing the shoreline seaward. *
Hard engineering Hard engineering involves the construction of hydraulic structures to protect coasts from erosion. Such structures include seawalls, gabions, breakwaters, groynes and tetrapods. Effects Hard engineering can cause unintended environmental conseq ...
:
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 ...
and beach accretion can be facilitated by the four main type of
hard engineering Hard engineering involves the construction of hydraulic structures to protect coasts from erosion. Such structures include seawalls, gabions, breakwaters, groynes and tetrapods. Effects Hard engineering can cause unintended environmental conseq ...
structures 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 ...
are, namely
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, conservatio ...
, revetment,
groyne A groyne (in the U.S. groin) is a rigid hydraulic structure built perpendicularly from an ocean shore (in coastal engineering) or a river bank, interrupting water flow and limiting the movement of sediment. It is usually made out of wood, concr ...
or
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, Antarctica * Breakwater Islands, Nunavut, Canada * Br ...
. Most commonly used hard structures are seawall and series of "headland breakwater" (breakwater connected to the shore with groyne). *
Managed retreat Managed retreat involves the purposeful, coordinated movement of people and buildings away from risks. This may involve the movement of a person, infrastructure (e.g., building or road), or community. It can occur in response to a variety of hazar ...
, the shoreline is left to erode, while relocating buildings and infrastructure further inland.


Beach nourishment approach


Assessment


Advantages

* Widens the beach. * Protects structures behind beach. * Storm protection. * Increases land value of nearby properties. * Economic growth through tourism and recreation. * Can serve as additional habitat for a number of species. * Beach nourishment is the only practical environmentally friendly approach to address erosional pressure. * Encourages new vegetation growth that helps stabilize tidal flats.


Disadvantages

*Added sand may erode, because of storms or lack of up-drift sand sources. *Expensive and requires repeated application. *Restricted access during nourishment. *Destroy/bury marine life. *Difficulty finding sufficiently similar materials.


Considerations


Costs

Nourishment is typically a repetitive process, since nourishment mitigates the effects of erosion, but does not remove the causes. A benign environment increases the interval between nourishment projects, reducing costs. Conversely, high erosion rates may render nourishment financially impractical. In many coastal areas, the economic impacts of a wide beach can be substantial. Since 1923, the U.S. has spent $9 billion to rebuild beaches. One of the most notable example is the –long shoreline fronting Miami Beach, Florida, which was replenished over the period 1976–1981. The project cost approximately US$ 86 million and revitalized the area's economy. Prior to nourishment, in many places the beach was too narrow to walk along, especially during
high tide Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables can ...
. In 1998 an overview has been made of all known beach nourishment projects in the USA (418 projects). The total volume of all these nourishments was 648 million cubic yards (495 m3) with a total cost of US$ 3387 million (adjusted to price level 1996). This is US$ 6.84 per m3. Between 2000 and 2020 the price per m3 has gone up considerably in the USA (see table below), while in Europe the price has gone down. Around the North Sea prices are much lower. In 2000 an inventory was made by the North Sea Coastal Management Group. From the Netherlands more detailed data are available, see below in the section on Dutch case studies. The price for nourishments in areas without an available dredging fleet is often in the order of € 20 - € 30 per cubic meter.


Storm damage reduction

A wide beach is a good energy absorber, which is significant in low-lying areas where severe storms can impact upland structures. The effectiveness of wide beaches in reducing structural damage has been proven by field studies conducted after storms and through the application of accepted coastal engineering principles.


Environmental impact

Beach nourishment has significant impacts on local ecosystems. Nourishment may cause direct mortality to
sessile Sessility, or sessile, may refer to: * Sessility (motility), organisms which are not able to move about * Sessility (botany), flowers or leaves that grow directly from the stem or peduncle of a plant * Sessility (medicine), tumors and polyps that ...
organisms in the target area by burying them under the new sand. Seafloor habitat in both source and target areas are disrupted, e.g. when sand is deposited on coral reefs or when deposited sand hardens. Imported sand may differ in character (chemical makeup, grain size, non-native species) from that of the target environment. Light availability may be reduced, affecting nearby reefs and
submerged aquatic vegetation Aquatic plants are plants that have adapted to living in aquatic environments (saltwater or freshwater). They are also referred to as hydrophytes or macrophytes to distinguish them from algae and other microphytes. A macrophyte is a plant that g ...
. Imported sand may contain material toxic to local species. Removing material from near-shore environments may destabilize the shoreline, in part by steepening its submerged slope. Related attempts to reduce future erosion may provide a false sense of security that increases development pressure.


=Sea turtles

= Newly deposited sand can harden and complicate nest-digging for turtles. However, nourishment can provide more/better habitat for them, as well as for sea birds and beach flora. Florida addressed the concern that dredge pipes would suck turtles into the pumps by adding a special grill to the dredge pipes.


Material used

The selection of suitable material for a particular project depends upon the design needs, environmental factors and transport costs, considering both short and long-term implications. The most important material characteristic is the sediment grain size, which must closely match the native material. Excess silt and clay fraction (mud) versus the natural turbidity in the nourishment area disqualifies some materials. Projects with unmatched grain sizes performed relatively poorly. Nourishment sand that is only slightly smaller than native sand can result in significantly narrower equilibrated dry beach widths compared to sand the same size as (or larger than) native sand. Evaluating material fit requires a sand survey that usually includes geophysical profiles and surface and core samples. Some beaches were nourished using a finer sand than the original.
Thermoluminescence Thermoluminescence is a form of luminescence that is exhibited by certain crystalline materials, such as some minerals, when previously absorbed energy from electromagnetic radiation or other ionizing radiation is re-emitted as light upon h ...
monitoring reveals that storms can erode such beaches far more quickly. This was observed at a
Waikiki Waikiki (; haw, Waikīkī; ; also known as Waikiki Beach) is a neighborhood of Honolulu on the south shore of the island of Oahu in the U.S. state of Hawaii. Waikiki is most famous for Waikiki Beach, which is one of six beaches in the distri ...
nourishment project in Hawaii.


Profile nourishment

''Beach Profile Nourishment'' describes programs that nourish the full beach profile. In this instance, "profile" means the slope of the uneroded beach from above the water out to sea. The Gold Coast profile nourishment program placed 75% of its total sand volume below low water level. Some coastal authorities ''overnourish'' the below water beach (aka "nearshore nourishment") so that over time the natural beach increases in size. These approaches do not permanently protect beaches eroded by human activity, which requires that activity to be mitigated.


Project impact measurements

Nourishment projects usually involve physical, environmental and economic objectives. Typical physical measures include dry beach width/height, post-storm sand volume, post-storm damage avoidance assessments and aqueous sand volume. Environmental measures include marine life distribution, habitat and population counts. Economic impacts include recreation, tourism, flood and "disaster" prevention. Many nourishment projects are advocated via economic impact studies that rely on additional tourist expenditure. This approach is however unsatisfactory. First, nothing proves that these expenditures are incremental (they could shift expenditures from other nearby areas). Second, economic impact does not account for costs and benefits for all economic agents, as
cost benefit analysis In production, research, retail, and accounting, a cost is the value of money that has been used up to produce something or deliver a service, and hence is not available for use anymore. In business, the cost may be one of acquisition, in which ...
does. Techniques for incorporating nourishment projects into
flood insurance Flood insurance is the specific insurance coverage issued against property loss from flooding. To determine risk factors for specific properties, insurers will often refer to topographical maps that denote lowlands, floodplains and other areas tha ...
costs and disaster assistance remain controversial.National Research Council, 1995. Beach Nourishment and Protection. National Academy Press, Washington, D.C., 334 p. pg. 4, 94., Figure 4-6. The performance of a beach nourishment project is most predictable for a long, straight shoreline without the complications of inlets or engineered structures. In addition, predictability is better for overall performance, e.g., average shoreline change, rather than shoreline change at a specific location. Nourishment can affect eligibility in the U.S. National Flood Insurance Program and federal disaster assistance. Nourishment may have the unintended consequence of promoting coastal development, which increases risk of other coastal hazards.


Other shoreline protection approaches

Nourishment is not the only technique used to address eroding beaches. Others can be used singly or in combination with nourishment, driven by economic, environmental and political considerations. Human activities such as dam construction can interfere with natural sediment flows (thereby reducing riverine sediment sources.) Construction of littoral barriers such as jetties and deepening of inlets can prevent longshore sediment transport.


Hard engineering or structural approach

The structural approach attempts to prevent erosion. Armoring involves building revetments,
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, conservatio ...
s, detached
breakwaters A breakwater is a permanent structure constructed at a coastal area to protect against tides, currents, waves, and storm surges. Part of a coastal management system, breakwaters are installed to minimize erosion, and to protect anchorages, h ...
, groins, etc. Structures that run parallel to the shore (seawalls or revetments) prevent erosion. While this protects structures, it doesn't protect the beach that is outside the wall. The beach generally disappears over a period that ranges from months to decades. Groynes and breakwaters that run perpendicular to the shore protect it from erosion. Filling a breakwater with imported sand can stop the breakwater from trapping sand from the littoral stream (the ocean running along the shore.) Otherwise the breakwater may deprive downstream beaches of sand and accelerate erosion there. Armoring may restrict beach/ocean access, enhance erosion of adjacent shorelines, and requires long-term maintenance.


Managed retreat

Managed retreat Managed retreat involves the purposeful, coordinated movement of people and buildings away from risks. This may involve the movement of a person, infrastructure (e.g., building or road), or community. It can occur in response to a variety of hazar ...
moves structures and other infrastructure inland as the shoreline erodes. Retreat is more often chosen in areas of rapid erosion and in the presence of little or obsolete development.


Soft engineering approaches


Beach dewatering

All beaches grow and shrink depending on tides, precipitation, wind, waves and current. Wet beaches tend to lose sand. Waves infiltrate dry beaches easily and deposit sandy sediment. Generally a beach is wet during falling tide, because the sea sinks faster than the beach drains. As a result, most erosion happens during falling tide. Beach drainage (beach dewatering) using Pressure Equalizing Modules (PEMs) allow the beach to drain more effectively during falling tide. Fewer hours of wet beach translate to less erosion.
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 ...
PEM tubes inserted vertically into the foreshore connect the different layers of groundwater. The groundwater enters the PEM tube allowing gravity to conduct it to a coarser sand layer, where it can drain more quickly. The PEM modules are placed in a row from the dune to the mean low waterline. Distance between rows is typically but this is project-specific. PEM systems come in different sizes. Modules connect layers with varying hydraulic conductivity. Air/water can enter and equalize pressure. PEMs are minimally invasive, typically covering approximately 0.00005% of the beach. The tubes are below the beach surface, with no visible presence. PEM installations have been installed on beaches in Denmark, Sweden, Malaysia and Florida. The effectiveness of beach dewatering has not been proven convincingly on life-sized beaches, in particular for the sand beach case. Dewatering systems have been shown to lower very significantly the watertable but other morphodynamical effects generally overpower any stabilizing effect of dewatering for fine sediments, although some mixed results on upper beach accretion associated to erosion in middle and lower have been reported. This is in line with the current knowledge of swash-groundwater sediment dynamics which states that the effects of in/exfiltration flows through sand beds in the swash zone associated to modification of swash boundary layer and relative weight of the sediment and overall volume loss of the swash tongue are generally lower than other drivers, at least for fine sediments such as sand


Recruitment

Appropriately constructed and sited fences can capture blowing sand, building/restoring sand dunes, and progressively protecting the beach from the wind, and the shore from blowing sand.


Projects

The setting of a beach nourishment project is key to design and potential performance. Possible settings include a long straight beach, an inlet that may be either natural or modified and a
pocket beach A pocket beach is usually a small beach that is isolated between two headlands. There is typically very little or no exchange of sediment between the pocket beach and adjacent shorelines. Pocket beaches can be natural or artificial. Many natural ...
. Rocky or
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, conservatio ...
ed shorelines, that otherwise have no sediment, present unique problems.


Cancun, Mexico

Hurricane Wilma Hurricane Wilma was an extremely intense and destructive Atlantic hurricane which was the most intense storm of its kind and the second-most intense tropical cyclone recorded in the Western Hemisphere, after Hurricane Patricia in 2015. Part o ...
hit the beaches of Cancun and the
Riviera Maya The Riviera Maya () is a tourism and resort district south of Cancun, Mexico. It straddles the coastal Federal Highway 307, along the Caribbean coastline of the state of Quintana Roo, located in the eastern portion of the Yucatán Peninsul ...
in 2005. The initial nourishment project was unsuccessful at a cost of $19 million, leading to a second round that began in September 2009 and was scheduled to complete in early 2010 with a cost of $70 million. The project designers and the government committed to invest in beach maintenance to address future erosion. Project designers considered factors such as the time of year and sand characteristics such as density. Restoration in Cancun was expected to deliver of sand to replenish of coastline.


Northern Gold Coast, Queensland, Australia

Gold Coast beaches in Queensland, Australia have experienced periods of severe erosion. In 1967 a series of 11 cyclones removed most of the sand from Gold Coast beaches. The Government of Queensland engaged engineers from Delft University in the Netherlands to advise them. The 1971 Delft Report outlined a series of works for Gold Coast Beaches, including beach nourishment and an artificial reef. By 2005 most of the recommendations had been implemented. The Northern Gold Coast Beach Protection Strategy (NGCBPS) was an A$10 million investment. NGCBPS was implemented between 1992 and 1999 and the works were completed between 1999 and 2003. The project included dredging of compatible sand from the
Gold Coast Broadwater The Gold Coast Broadwater, also known as Southport Broadwater, Gold Coast Harbour and The Broadwater, is a large shallow estuary of water located in the district of South East Queensland, Australia. The estuary reaches from the locality of i ...
and delivering it through a pipeline to nourish of beach between
Surfers Paradise Surfing is a surface water sport in which an individual, a surfer (or two in tandem surfing), uses a board to ride on the forward section, or face, of a moving wave of water, which usually carries the surfer towards the shore. Waves suitable ...
and Main Beach. The new sand was stabilized by an
artificial reef An artificial reef is a human-created underwater structure, typically built to promote marine life in areas with a generally featureless bottom, to control erosion, block ship passage, block the use of trawling nets, or improve surfing. Many re ...
constructed at Narrowneck out of huge
geotextile Geotextiles are permeable fabrics which, when used in association with soil, have the ability to separate, filter, reinforce, protect, or drain. Typically made from polypropylene or polyester, geotextile fabrics come in two basic forms: woven (r ...
sand bags. The new reef was designed to improve wave conditions for surfing. A key monitoring program for the NGCBPS is the ARGUS coastal camera system.


Netherlands


Background

More than one-quarter of the Netherlands is below sea level. The coastline along the North Sea (approx. ) is protected against flooding by natural
sand dune A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, f ...
s (only in the estuaries and behind the barrier islands there are no dunes). This coastline is eroding for centuries; in the 19th and beginning of 20th centuries it was tried to stop erosion by construction of
groyne A groyne (in the U.S. groin) is a rigid hydraulic structure built perpendicularly from an ocean shore (in coastal engineering) or a river bank, interrupting water flow and limiting the movement of sediment. It is usually made out of wood, concr ...
s, which was costly and not very successful. Beach nourishment was more successful, but there were questions on the method of funding. In the Coastal Memorandum of 1990 the government decided, after a very detailed study, that all erosion along the full Dutch coastline would be compensated by artificial beach nourishment. The shoreline is closely monitored by yearly recording of the
cross section Cross section may refer to: * Cross section (geometry) ** Cross-sectional views in architecture & engineering 3D *Cross section (geology) * Cross section (electronics) * Radar cross section, measure of detectability * Cross section (physics) **Abs ...
at points apart, to ensure adequate protection. Where long-term erosion is identified, beach nourishment using high-capacity suction dredgers is deployed. In 1990 the Dutch government has decided to compensate in principal all coastal erosion by nourishment. This policy is still ongoing and successful. All costs are covered by the National Budget. A novel beach nourishment strategy was implemented in
South Holland South Holland ( nl, Zuid-Holland ) is a province of the Netherlands with a population of over 3.7 million as of October 2021 and a population density of about , making it the country's most populous province and one of the world's most densely ...
, where a new beach form was created using vast quantities of sand with the expectation that the sand would be distributed by natural processes to nourish the beach over many years (see Sand engine).


Basic Coastline

The basic coastline in the Netherlands is a representation of the low water line of 1990. This line is used to identify coastal erosion and coastal growth and to take measures if necessary. In the Coastal Memorandum, the Dutch Government decides to maintain the 1990 coastline by beach nourishment. The coastline in question is the low-water line. For practical application, the definition of this does not appear to be unambiguous, which is why the Memorandum also defines the momentary coastline (also called instantaneous coastline) (MKL) and basic Coastline (BKL). Each year, the shoreline to be tested ( TKL) is determined on the basis of the MKL, and if it threatens to come inland from the BKL, a sand nourishment is carried out.


Definition of the instantaneous coastline

The problem with the low water line mentioned in the 1990 Coastal Memorandum is that the height of the average low tide is well defined, but the position in the horizontal direction is not. See the attached figure, here the beach profile crosses three times the low water line. In fact, it is also not important to maintain a line, but to maintain the amount of sand in the active beach profile. To determine this volume, two heights are used, the average low water level (glw) and the height of the dune foot (dv). The height of the dune foot is basically determined by finding the intersection of the steep slope of the dune front and of the dry beach. In general, this theoretical dune foot point will be slightly below the sand. It is very difficult to redefine the height of the dune foot every year. Some administrators define the dune foot line as a certain elevation line, on which the dune foot usually lies. In relatively unalterable coastal sections, this is an acceptable approach. The method of determining the MKL is such that it is not very sensitive to the precise choice of the value dv. The location of the dune foot is thus determined by the height above NAP (National Datum, approx. Mean Sea Level) and the distance from that elevation line to the administrative coastline (Xdv). This administrative line has no physical meaning, but is simply the basis for survey work. The recipe for calculating the position of the MKL is: *Determine the location of the dune foot *The height of the average low water (glw) is determined *The height h of the dune foot above average low water is calculated *The sand volume A is calculated; A is the volume of sand seaward of the dune foot and above the level (glw-h) *The position of the momentary coastline (SKL) is defined in relation to the national beach pile line as: (A/2h) - Xdv The background of this method is that the thickness of the sand layer to be taken must be a function of the measuring wave height; however, it is unknown. But because the elevation of the dune foot is also a function of the measuring wave height, the value h is a good representation of the effect of both tide and wave influences. For the determination of the beach profiles, the so-called JarKus profiles are measured along the coastline. These profiles are roughly 250 metres apart and are measured annually from around 800 meters in the sea to just behind the dunes. These measurements are available throughout the coast from 1965 onwards. From the period from about 1850 there are also profile soundings available in some places, but these are often slightly shifted compared to the jarkus rowing and are therefore more difficult to analyse. In the case of groynes, the sounding is carried out exactly in the middle between the groynes.


The Basic Coastline (BKL)

The Basic Coastline is by definition the coastline of 1 January 1990. But of course there are no measurements made on exactly that date, moreover, there are always variations in the measurements. The BKL is therefore determined by taking the beach measurements of the approximately 10 years prior to 1990 and by determining the MKL for each of those years. These values are placed in a graph, a regression line is determined. Where this regression line cuts the date 1-1-1990 lies the basic coastline BKL. In principle, the location of the BKL is immutable. In very special cases, where the coast is substantially altered by a work, it can be decided to shift the BKL. This is not based on a technical or morphological calculation, but actually a political decision. An example of this is the Hondsbossche Zeewering, as sea dike near the village of
Petten Petten is a village in the Dutch province of North Holland. It is a part of the municipality of Schagen, and lies about 15 km northwest of Alkmaar, on the North Sea. The population is ca. 1900. Petten's economy is based on agriculture (bulb ...
, where the BKL was actually on the toe of the dike. Due to the construction of a new artificial dune in front of this dike (the Hondsbossche Duinen), a piece of dune was added, of which the intention is to preserve it. So there is the BKL shifted seaward.


The coastline to be tested (TKL) 

Within the framework of the coastal policy is determined annually whether nourishment is required in a given coastal sector. This is done by determining the coastline (TKL) to be tested before the reference date. This is determined in the same way as the BKL, namely by a regression analysis of the MKL values of the previous years. See the attached graph. In this example, a supplementation was carried out in 1990, causing the MKL to shift far seawards. The number of years over which the regression analysis can be carried out is therefore somewhat limited. If there are too few years available, a regression line is usually adopted parallel to the previous regression line (so it is assumed that the erosion before and after supplementation is approximately the same). By the way, the first year after supplementation is often more than average due to adjustment effects. In this case, it appears that the TKL is still just satisfactory for 1995 and is no longer satisfactory for 1996. In principle, a supplement at this location would be required in the course of 1995. Now the decision to supplement does not depend on a single BKL exceedance, but only if multiple profiles are threatened to become negative. In order to assess this, coastal maps are issued annually by Rijkswaterstaat. These maps indicate whether the coast is growing or eroding with a dark green or light green block. A red block indicates that in that place the TKL has exceeded the BKL, and that something has to happen there. A red hatched indicator means that the TKL has exceeded the BKL, but this coastal section has an accreting tendency, so no urgent works are needed


Beach nourishment design

A beach nourishment to broaden the beach and maintain the coastline can be designed using mathematical calculation models or on the basis of beach measurements. In the Netherlands, Belgium and Germany,a nourishment design is mainly based on measurement, while mathematical models are mainly used elsewhere. A nourishment design for coastal maintenance and beach widening can be made much more reliable based on measurement data, provided that they are present. If there are no good, long-term series of measurements of the beach profile, one must make the design using calculation models. In the Netherlands, the coast has been measured annually for years (JarKus measurements) and therefore the very reliable method based on measurements is used in the Netherlands for the design of supplements to prevent erosion.


Use of measurements for nourishment design

To compensate for coastal erosion, the design of a supplementation is actually very simple, every year the same amount of sand has to be applied as erosion disappears annually. The assumption is that there is no significant change in the wave climate and the orientation of the coastline. With most nourishments, this is a correct assumption. In case of substantial changes in the coastal orientation, this method is therefore not always usable (e.g. in the design of the sand engine). In practice, the length of the nourishment must be 20-40 times the width in order to apply this method. In short, the method consists of the following steps: #Make sure there are enough measured profiles (at least 10 years). #Use these profiles to calculate the annual sand loss (in m3/year) for a coastal section. #Multiply this amount by an appropriate lifetime (e.g. 5 years). #Add a loss factor (order 40 %). #Place this amount of sand somewhere on the beach between the low water line and the dune foot. To determine the amount of sand in the profile, the same method can be used as used for the basic Coastline. Given the fact that the instantaneous coastline has been measured for the necessary years and thus the decline of this coastline, determining the loss of sand is quite simple. Suppose the decline of the MKL is 5 m/year, then the annual sand loss is 5*(2h) m3 per year per linear meter of coastline. Here is 2h the height of the active beach profile. Along the Dutch coast, h is near Hoek van Holland in the order of 4 m, so in the above example the erosion would be 40 m3 per year per linear meter of coast. For a nourishment with a length of 4 km and a lifespan of 5 years is therefore 40*4000*5 = 80 000 m3. Because there is extra sand loss immediately after construction, a good amount is 1.4 *80000 = 112 000 m3. This is a seaward shift of 1.4*5*5= 35 m. In the practice of beach nourishments (from 1990 onwards), this method appears to work very well. Analyses of nourishments in northern Germany also show that this is a reliable method. The starting point is that the grain size of the nourishment sand is equal to the original beach sand. If this is not the case, it must be corrected. In case of finer sand in the win area, the volume of the nourishment will need to increase.


Use of mathematical models for nourishment design

''Single line model'' For relatively wide and short nourishment (such as the sand motor), a single-line model can be used. In this model, the coast is represented by a single line (e.g. the instantaneous coastline) and a constant profile along the entire coastline. For each profile, the orientation of the coast is given, and in each profile the sand transport is calculated by the surf induced current. If in a profile 1 the sand transport is larger than in a profile 2, there will be between profile 1 and 2 sedimentation, for details about the model. As there is sedimentation, the coastal orientation will change, and thus also the transport of sand. This makes it possible to calculate the coastline change. A classic example is the calculation of a relatively short and wide supplementation with straight waves. The single-line model can very well predict how such supplementation can develop over time. The Unibest calculation model of Deltares is an example of a single-line model.


Field models

In highly two-dimensional situations, e.g. at a tidal inlet or the mouth of an estuary, or if the nourishment itself has a strong two-dimensional character (as with the Sand Engine), an approach with profile measurements is not possible. A single-line model is often inappropriate. In these cases, a two-dimensional sand transport model is made (usually with models such as Delft3D from Deltares in the Netherlands or Mike 21 of DHI in Denmark). In such a model, the bed of the area is introduced as a depth map. Then there is a tidal flow calculation and a wave penetration calculation. After that, the sand transport is calculated at each mesh-point and from the difference in sand transport between the different mesh-points, the sedimentation and erosion is calculated in all boxes. It can then be assessed whether a nourishment behaves as intended. The problem with this type of model is that (apart from the fairly long computation times for the computer) the results are rather sensitive to inaccuracies in the input. For example, at the edge of the model, the water levels and flow rates must be properly entered, and the wave climate must be well known. Also variations in the sand composition (grain size) have a great influence.


Channel wall nourishment

At some places along the Dutch coast tidal channels are very near to the beach. In the years from around 1990 these beaches were also nourished in the classical way, but the problem was that the width of the beach is small. So the amount of sand to be placed is limited, resulting in a short lifetime of the nourishment. It was found that in such cases it is more effective to nourish the landward wall of the channel, and in some cases uses sand from the seaward side of the channel as borrow area. This is in fact moving the tidal channel further from the coastline (chapter 4)


Foreshore nourishments

Instead of directly supplying the beach, it is also possible to supple the foreshore (underwater bank). The advantage of this is that the implementation of the nourishment is cheaper, and there is no direct effect of the work on the use of the beach. The sand is then transported over time by the waves from deeper water to the coast. A foreshore nourishment is calculated just like a beach nourishment, but the use of measurement data with beach profiles is then less easy, as a foreshore nourishment does not give a new beach line. Therefore, in those cases, a single-line model or a field model is usually used. In the period 1990-2020 in total 236 million cubic meters has been nourished, mainly as beach nourishment. However after 2004 more focus has been on foreshore nourishment. In 2006 the costs of some nourishment were analysed in detail. This resulted in: F= Foreshore, B= Beach nourishment, B+F is combination; Price level 2006, excluding VAT.


Hawaii


Waikiki

Hawaii planned to replenish
Waikiki Waikiki (; haw, Waikīkī; ; also known as Waikiki Beach) is a neighborhood of Honolulu on the south shore of the island of Oahu in the U.S. state of Hawaii. Waikiki is most famous for Waikiki Beach, which is one of six beaches in the distri ...
beach in 2010. Budgeted at $2.5 million, the project covered in an attempt to return the beach to its 1985 width. Prior opponents supported this project, because the sand was to come from nearby shoals, reopening a blocked channel and leaving the overall local sand volume unchanged, while closely matching the "new" sand to existing materials. The project planned to apply up to of sand from deposits located offshore at a depth of . The project was larger than the prior recycling effort in 2006-07, which moved .


Maui

Maui, Hawaii The island of Maui (; Hawaiian: ) is the second-largest of the islands of the state of Hawaii at 727.2 square miles (1,883 km2) and is the 17th largest island in the United States. Maui is the largest of Maui County's four islands, which ...
illustrated the complexities of even small-scale nourishment projects. A project at Sugar Cove transported upland sand to the beach. The sand allegedly was finer than the original sand and contained excess silt that enveloped coral, smothering it and killing the small animals that lived in and around it. As in other projects, on-shore sand availability was limited, forcing consideration of more expensive offshore sources. A second project, along Stable Road, that attempted to slow rather than halt erosion, was stopped halfway toward its goal of adding of sand. The beaches had been retreating at a "comparatively fast rate" for half a century. The restoration was complicated by the presence of old seawalls, groins, piles of rocks and other structures. This project used sand-filled
geotextile tube A geotextile tube (also known as a titan tube or geotube) is a large, tube-shaped bag made of porous, weather-resistant geotextile and filled with a sand slurry, to form an artificial coastal structure such as a breakwaters, dune or levee. Geo ...
groins that were originally to remain in place for up to 3 years. A pipe was to transport sand from deeper water to the beach. The pipe was anchored by concrete blocks attached by fibre straps. A video showed the blocks bouncing off the coral in the current, killing whatever they touched. In places the straps broke, allowing the pipe to move across the reef, "planing it down". Bad weather exacerbated the damaging movement and killed the project. The smooth, cylindrical geotextile tubes could be difficult to climb over before they were covered by sand. Supporters claimed that 2010's seasonal summer erosion was less than in prior years, although the beach was narrower after the restoration ended than in 2008. Authorities were studying whether to require the project to remove the groins immediately. Potential alternatives to geotextile tubes for moving sand included floating dredges and/or trucking in sand dredged offshore. A final consideration was sea level rise and that Maui was sinking under its own weight. Both Maui and
Hawaii Island Hawaii ( ; haw, Hawaii ) is the largest island in the United States, located in the state of Hawaii. It is the southeasternmost of the Hawaiian Islands, a chain of volcanic islands in the North Pacific Ocean. With an area of , it has 63% of t ...
surround massive mountains ( Haleakala, Mauna Loa, and Mauna Kea) and were expanding a giant
dimple A dimple, also called a gelasin (, ) is a small natural indentation in the flesh on a part of the human body, most notably in the cheek. Numerous cultures believe that cheek dimples are a good luck charm that entices people who perceive them as ...
in the ocean floor, some below the mountain summits.


The

Outer Banks The Outer Banks (frequently abbreviated OBX) are a string of barrier islands and spits off the coast of North Carolina and southeastern Virginia, on the east coast of the United States. They line most of the North Carolina coastline, separatin ...

The
Outer Banks The Outer Banks (frequently abbreviated OBX) are a string of barrier islands and spits off the coast of North Carolina and southeastern Virginia, on the east coast of the United States. They line most of the North Carolina coastline, separatin ...
off the coast of North Carolina and southeastern Virginia include a number of towns. Five of the six town have undergone beach nourishment since 2011. The projects were as follows:
Duck, North Carolina Duck is a town in Dare County, North Carolina, United States. As of the 2020 census, the population was 746. During the peak vacation season, starting after Memorial Day, the population increases to over 20,000. Duck is the northernmost incorpo ...
: the beach nourishment took place in 2017 and cost an estimated $14,057,929.
Southern Shores, North Carolina Southern Shores is a town in Dare County, North Carolina, United States. It is located on the Outer Banks and the population was 3,107 at the 2020 census. Geography Southern Shores is located at (36.124454, -75.732612). According to the Unite ...
- the estimated costs for the Southern Shores project was approximately $950,000 and was completed in 2017. There is a proposed additional project to widen the beaches in 2022 with an estimated cost of between $9 million and $13.5 million.
Kitty Hawk, North Carolina Kitty Hawk is a town in Dare County, North Carolina, United States, and is a part of what is known as North Carolina's Outer Banks. The population was 3,708 at the 2020 Census. It was established in the early 18th century as Chickahawk. History ...
- the beach nourishment project in Kitty Hawk was completed in 2017 and included 3.58 miles of beaches running from the Southern Shores to Kitty Hawk and cost $18.2 million.
Kill Devil Hills, North Carolina Kill Devil Hills is a town in Dare County, North Carolina, United States. The population was 7,633 at the 2020 census, up from 6,683 in 2010. It is the most populous settlement in both Dare County and on the Outer Banks of North Carolina. The ...
- the beach nourishment project was completed in 2017.
Nags Head, North Carolina Nags Head is a town in Dare County, North Carolina, United States. It is a busy vacation spot because of its beaches and sand dunes of Jockey's Ridge. The population was 3,146 at the 2020 census. History Early maps of the area show Nags Head as ...
- The town's first beach nourishment project took place in 2011 and cost between $36 million and $37 million. The renourishment project in 2019 cost an estimated $25,546,711. Upcoming Projects - the towns of Duck, Southern Shores, Kitty Hawk and Kill Devil Hills have secured a contract with Coastal Protection Engineering for tentative re-nourishment projects scheduled for 2022.


Florida

Ninety PEMs (Pressure Equalizing Modules) were installed in February 2008 at Hillsboro Beach. After 18 months the beach had expanded significantly. Most of the PEMs were removed in 2011. Beach volume expanded by 38,500 cubic yards over 3 years compared to an average annual loss of 21,000.


New Jersey, USA

More than 200 million cubic yards of sand have been pumped onto the New Jersey Coast in the least few decades with a cost running into the billions. This has resulted in the decimation of inshore marine life, extensive scarping (sand cliffs), and the creation of hazardous "shore break" wave conditions. In many cases the projects are extremely short-lived with the sand vanishing soon after completion.


Hong Kong

The beach in Gold Coast was built as an artificial beach in the 1990s with HK$60m. Sands are supplied periodically, especially after typhoons, to keep the beach viable.


See also

* Beach erosion and accretion **
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 ...
** Beach morphodynamics **
Raised beach A raised beach, coastal terrace,Pinter, N (2010): 'Coastal Terraces, Sealevel, and Active Tectonics' (educational exercise), from 2/04/2011/ref> or perched coastline is a relatively flat, horizontal or gently inclined surface of marine origin, ...
**
Modern recession of beaches 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 d ...
**
Paleoshoreline A paleoshoreline (ancient shoreline) is a shoreline which existed in the geologic past. (''Paleo'' is from an ancient Greek word meaning "old" or "ancient".) A perched coastline is an ancient (fossil) shoreline positioned above the present sho ...
*
Integrated coastal zone management Integrated coastal zone management (ICZM), integrated coastal management (ICM), or integrated coastal planning is a coastal management process for the management of the coast using an integrated approach, regarding all aspects of the coastal zone ...
**
Coastal management Coastal management is defence against flooding and erosion, and techniques that stop erosion to claim lands. Protection against rising sea levels in the 21st century is crucial, as sea level rise accelerates due to climate change. Changes ...
, to prevent coastal erosion and creation of beach ** Coastal and oceanic landforms **
Coastal development hazards A coastal development hazard is something that affects the natural environment by human activities and products. As coasts become more developed, the vulnerability component of the equation increases as there is more value at risk to the hazard. The ...
**
Coastal erosion Coastal erosion is the loss or displacement of land, or the long-term removal of sediment and rocks along the coastline due to the action of waves, currents, tides, wind-driven water, waterborne ice, or other impacts of storms. The landward ...
**
Coastal geography Coastal geography is the study of the constantly changing region between the ocean and the land, incorporating both the physical geography (i.e. coastal geomorphology, climatology and oceanography) and the human geography (sociology and history) ...
**
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 ...
**
Coastal and Estuarine Research Federation The Coastal and Estuarine Research Federation (CERF) is a private, nonprofit organization that was created in 1971. At that time, the members of two regionally based organizations, the Atlantic Estuarine Research Society (AERS) and the New England ...
(CERF) ** Sedimentation enhancing strategies * Erosion **
Bioerosion Bioerosion describes the breakdown of hard ocean substrates – and less often terrestrial substrates – by living organisms. Marine bioerosion can be caused by mollusks, polychaete worms, phoronids, sponges, crustaceans, echinoids, and ...
** Blowhole **
Natural arch A natural arch, natural bridge, or (less commonly) rock arch is a natural landform where an arch has formed with an opening underneath. Natural arches commonly form where inland cliffs, coastal cliffs, fins or stacks are subject to erosion fr ...
** Wave-cut platform * Longshore drift ** Deposition (sediment) **
Coastal sediment supply Coastal sediment supply is the transport of sediment to the beach environment by both fluvial and aeolian transport. While aeolian transport plays a role in the overall sedimentary budget for the coastal environment, it is paled in comparison to t ...
**
Sand dune stabilization Sand dune stabilization is a coastal management practice designed to prevent erosion of sand dunes. Sand dunes are common features of shoreline and desert environments. Dunes provide habitat for highly specialized plants and animals, including rar ...
** Submersion


References


External links


Beach nourishment /NOAA and NOS / Main Page
* ttps://web.archive.org/web/20130212154133/http://ci.wrl.unsw.edu.au/index.php ARGUS Beach Nourishment Monitoring Program at the University of New South Walesbr>USGS assessments and mapping of sand and gravel resources in U.S. offshore environmentsBeach nourishment
Coastal Care.org * {{DEFAULTSORT:Beach Nourishment Coastal engineering Oceans