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 because it does not remove the physical forces that cause erosion; it 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.
Before the 1970s, nourishment involved directly placing sand on the beach and dunes. Since then more shoreface nourishments have been carried out, which rely on the forces of the wind, waves 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

is a specific subset of coastal erosion, which in turn is a type of bioerosion which alters coastal geography through beach morphodynamics. There are numerous incidences of the modern recession of beaches, mainly due to a gradient in longshore drift and coastal development hazards.

Causes of erosion

Beaches can erode naturally or due to human impact.
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 for coastal processes to respond naturally to storms. When not enough sand is available, the beach cannot recover after 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, and 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 which preserves beach resources and avoids 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 types 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 buildings and infrastructure are relocated further inland.
Approach

Assessment

Advantages

Widens the beach.
Protects structures behind beach.
Protects from storms.
Increases land value of nearby properties.
Grows economy through tourism and recreation.
Expands habitat.
Practical, environmentally-friendly approach to address erosional pressure.
Encourages vegetation growth to help 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.
Destroys or buries marine life.
Difficulty finding appropriate materials.
Considerations

Costs

Nourishment is typically a repetitive process, as 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.
In 1998 an overview was made of all known beach nourishment projects in the USA. The total volume of all these nourishments was 648 million cubic yards with a total cost of US$3387 million. This is US$6.84 per m³. Between 2000 and 2020 the price per m³ has gone up considerably in the USA, while in Europe the price has gone down.

location	year	quantity	cost	cost/m³	cost/m³
Miami Beach	2017	0.388	11.5	33.7	38.1
Myrtle Beach	1976	3.8	70.1	18.4	15.3
Virginia Beach	2017	1.2	21.5	17.9	20.2
Monmouth Beach	2021	0.84	26	20.1	23.7
Carolina & Kure	2022	1.4	20.3	14.5	14.5

Around the North Sea prices are much lower. In 2000 an inventory was made by the North Sea Coastal Management Group.

country	beach nourishment	foreshore nourishment
United Kingdom	10 - 18
Belgium	5-10
Netherlands	3.2 - 4.5	0.9 - 1.5
Germany	4.4
Denmark	4.2	2.6

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 organisms in the target area by burying them under the new sand. The 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 and 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.