Beach nourishment
Beach nourishment 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, 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 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, New York 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, New York in 1922–1923.Erosion
The beach erosion is a specific subset of the coastal erosion which in turn is a type of bioerosion which alters the coastal geography through beach morphodynamics. There are numerous incidences of modern recession of beaches, mainly due to the longshore drift and coastal development hazards.Causes of erosion
Beaches can erode both naturally and due to human impacts.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.
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: seawalls locking up sand dunes, coastal structures like ports and harbors that prevent longshore transport, dams 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 construction 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 for the shoreline protection involves:- Soft engineering: 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” structure by creating a larger sand reservoir, pushing the shoreline seaward.
- Hard engineering: Beach evolution and beach accretion can be facilitated by the four main type of hard engineering structures in coastal engineering are, namely seawall, revetment, groyne or breakwater. Most commonly used hard structures are seawall and series of "headland breakwater".
- Managed retreat, 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.
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 for beach nourishment
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. The -long shoreline fronting Miami Beach, Florida was replenished over the period 1976-1981. The project cost approximately $64,000,000 and revitalized the area's economy. Prior to nourishment, in many places the beach was too narrow to walk along, especially during high tide.
Since 1923, the U.S. has spent $9 billion to rebuild beaches.
Impact of visible and submerged sand
The proportion of total sand in a beach that lies below the waterline critically impacts beach nourishment. Two beaches with the same amount of visible sand may be much different below the surface. An eroded beach with substantial submerged sand surrounding it may recover without nourishment. Nourishing a beach that has little submerged sand requires understanding of the reason that the submerged sand is missing. The same forces that stripped the submerged sand once are likely to do so again. The amount of submerged sand eroded is typically much greater than the amount of missing sand on shore. Replacing only the visible sand is insufficient unless the submerged sand is also replaced. Otherwise, the beach is unstable and the replenished sand quickly erodes. If human activity is a major cause of the erosion, mitigating that activity may be more cost effective over both short and long term periods than direct nourishment.Environmental impact
Beach nourishment has significant impacts on local ecosystems. Nourishment may cause direct mortality to sessile 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 from that of the target environment. Light availability may be reduced, affecting nearby reefs and submerged aquatic vegetation. 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 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 native sand. Evaluating material fit requires a sand survey that usually includes geophysical profiles and surface and core samples.
| Type | Description | Environmental issues |
| Offshore | Exposure to open sea makes this the most difficult operational environment. Must consider the effects of altering depth on wave energy at the shoreline. May be combined with a navigation project. | Impacts on hard bottom and migratory species. |
| Inlet | Sand between jetties in a stabilized inlet. Often associated with dredging of navigational channels and the ebb- or flood-tide deltas of both natural and jettied inlets. | |
| Accretionary Beach | Generally not suitable because of damage to source beach. | |
| Upland | Generally the easiest to obtain permits and assess impacts from a land source. Offers opportunities for mitigation. Limited quantity and quality of economical deposits. | Potential secondary impacts from mining and overland transport. |
| Riverine | Potentially high quality and sizeable quantity. Transport distance a possible cost factor. | May interrupt natural coastal sand supply. |
| Lagoon | Often excessively fine grained. Often close to barrier beaches and in sheltered waters, easing construction. Principal sources are flood-tide deltas. | Can compromise wetlands. |
| Artificial or non-indigenous | Typically, high transport and redistribution costs. Some laboratory experiments done on recycling broken glass. Aragonite from Bahamas a possible source. | |
| Emergency | Deposits near inlets and local sinks and sand from stable beaches with adequate supply. Generally used only following a storm or given no other affordable option. May be combined with a navigation project. | Harm to source site. Poor match to target requirements. |
Some beaches were nourished using a finer sand than the original. Thermoluminescence monitoring reveals that storms can erode such beaches far more quickly. This was observed at a Waikiki 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 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. Second, economic impact does not account for costs and benefits for all economic agents, as cost benefit analysis does. Techniques for incorporating nourishment projects into flood insurance costs and disaster assistance remain controversial.
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 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, seawalls, detached breakwaters, groins, etc. Structures that run parallel to the shore 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 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
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 using Pressure Equalizing Modules allow the beach to drain more effectively during falling tide. Fewer hours of wet beach translate to less erosion. Permeable 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.Beach nourishment 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. Rocky or seawalled shorelines, that otherwise have no sediment, present unique problems.Cancun, Mexico
hit the beaches of Cancun and the Riviera Maya 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
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 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 and delivering it through a pipeline to nourish of beach between Surfers Paradise and Main Beach. The new sand was stabilized by an artificial reef constructed at Narrowneck out of huge geotextile 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
More than one-quarter of the Netherlands is below sea level and about 81% of the coast consists of sand dune or beach. The shoreline is closely monitored by yearly recording of the cross section 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.Hawaii
Waikiki
Hawaii planned to replenish Waikiki 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
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 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 surround massive mountains and were expanding a giant dimple in the ocean floor, some below the mountain summits.
Outer Banks
The Outer Banks consists of a number of towns. 5 of the 6 town have undergone beach nourishment since 2011. The projects were as follows:Duck, NC - the beach nourishment took place in 2017 and cost an estimated $14,057,929.
Southern Shores - 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 - 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 - the beach nourishment project was completed in 2017.
Nags Head - 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.