Miami Beach Nourishment Case Study

Beach nourishment (also referred to as beach renourishment,[2]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, protecting upland structures and infrastructure from storm surges, tsunamis and unusually high tides.[citation needed] Beach nourishment is typically part of a larger coastal defense scheme. 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.[3][4]

Shoreline protection[edit]

Nourishment is one of three commonly accepted methods for protecting shorelines. The structural alternative involves constructing a seawall, revetment, groyne or breakwater. Alternatively, with managed retreat the shoreline is left to erode, while relocating buildings and infrastructure further inland. Nourishment 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.

Causes of erosion[edit]

Beaches can erode both naturally and due to human impacts (beach theft/sand mining).[5]

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.[6] These activities interfere with the natural sediment flows either through dam 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.[7]

Visible and submerged sand[edit]

The proportion of total sand in a beach that lies below the waterline (submersion fraction) 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.[citation needed]

Requirements for effective nourishment[edit]

Sand fill must be compatible with native beach sand.

Profile Nourishment[edit]

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.[citation needed]

Replenishment material[edit]

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.[8]

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.[8]

TypeDescriptionEnvironmental issues
OffshoreExposure 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.[8]
InletSand 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.[8]
Accretionary BeachGenerally not suitable because of damage to source beach.[8]
UplandGenerally the easiest to obtain permits and assess impacts from a land source. Offers opportunities for mitigation. Limited quantity and quality of economical deposits.[8]Potential secondary impacts from mining and overland transport.
RiverinePotentially high quality and sizeable quantity. Transport distance a possible cost factor.May interrupt natural coastal sand supply.[8]
LagoonOften excessively fine grained. Often close to barrier beaches and in sheltered waters, easing construction. Principal sources are flood-tide deltas.[8]Can compromise wetlands.
Artificial or non-indigenousTypically, high transport and redistribution costs. Some laboratory experiments done on recycling broken glass. Aragonite from Bahamas a possible source.[8]
EmergencyDeposits 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.[8]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.[9]

[edit]

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.

Environmental issues[edit]

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 (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. 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.[citation needed]

Sea turtles[edit]

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.[10]

Alternatives/complements to nourishment[edit]

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.

Structural[edit]

The structural approach attempts to prevent erosion. Armoring involves building revetments, seawalls, detached breakwaters, 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.[citation needed]

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.[citation needed]

Armoring may restrict beach/ocean access, enhance erosion of adjacent shorelines, and requires long-term maintenance.[citation needed]

Managed retreat[edit]

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.

Recruitment[edit]

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.[citation needed]

Beach dewatering[edit]

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 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 300 feet (91 m) 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.[citation needed]

PEMs are minimially invasive, typically covering approximately 0.00005% of the beach.[citation needed] The tubes are below the beach surface, with no visible presence. PEM installations have been installed on beaches in Denmark, Sweden, Malaysia and Florida[citation needed]. The effectiveness of beach dewatering, however, is debatable and has not been proven convincingly on life-sized beaches.[11]

Costs[edit]

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.[12][13]

In many coastal areas, the economic impacts of a wide beach can be substantial. The 10 miles (16 km)–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.[citation needed]

History[edit]

The first nourishment project in the U.S. was constructed at Coney Island, New York in 1922–1923.[14][15]

Projects[edit]

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.[citation needed]

Cancun, Mexico[edit]

Federal and state governments in Mexico have invested about $71 million ($957 million pesos) throughout the state of Quintana Roo in restoring the beaches along Cancun, Playa del Carmen and Cozumel.

Hurricane Wilma hit the beaches of Cancun and the Riviera Maya in 2005. The initial nourishment project was unsuccessful, leading to a second round that began in September 2009 and was scheduled to complete in early 2010. 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 1.3 billion US gallons (4,900,000 m3) of sand to replenish 450 meters (1,480 ft) of coastline.

Northern Gold Coast, Queensland, Australia[edit]

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 3,500,000 cubic metres (4,600,000 cu yd) of compatible sand from the Gold Coast Broadwater and delivering it through a pipeline to nourish 5 kilometers (3.1 mi) 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.

The cost/benefit ratio for NGCBPS was conservatively estimated at 75:1 for a A$10 million investment into beach replenishment. The benefits were estimated from a model of lost visitor nights in hotels following previous erosion events. NGCBPS so improved beach health that recovery following minor and moderate storms occurred within weeks. Additional unquantified benefits included lifestyle benefits for residents, additional public open space and improved fishing, diving and surfing conditions.

Netherlands[edit]

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 250 meters (820 ft) apart, to ensure adequate protection. Where long-term erosion is identified, beach nourishment using high-capacity suction dredgers is deployed.[16][17][18]

Hawaii[edit]

Waikiki[edit]

Hawaii planned to replenish Waikiki beach in 2010. Budgeted at $2.5 million, the project covered 1,700 feet (520 m) 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 24,000 cubic yards (18,000 m3) of sand from deposits located 1,500 to 3,000 feet (460 to 910 m) offshore at a depth of 10 to 20 feet (3.0 to 6.1 m). The project was larger than the prior recycling effort in 2006-07, which moved 10,000 cubic yards (7,600 m3).[19]

Maui[edit]

Maui, Hawaii 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.[20]

A second project, along Stable Road, that attempted to slow rather than halt erosion, was stopped halfway toward its goal of adding 10,000 cubic yards (7,600 m3) 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.[20]

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.[21] The smooth, cylindrical geotextile tubes could be difficult to climb over before they were covered by sand.[20]

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.[20]

A final consideration was sea level rise and that Maui was sinking under its own weight. Both Maui and Hawaii Island surround massive mountains (Haleakala, Mauna Loa, and Mauna Kea) and were expanding a giant dimple in the ocean floor, some 30,000 feet (9,100 m) below the mountain summits.[20]

Florida[edit]

90 PEMs 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.[22]

Hong Kong[edit]

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.[23]

Measuring project impact[edit]

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 does.[24] Techniques for incorporating nourishment projects into flood insurance costs and disaster assistance remain controversial.[25]

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.[citation needed]

Nourishment can affect eligibility in the U.S. National Flood Insurance Program and federal disaster assistance.[citation needed]

Nourishment may have the unintended consequence of promoting coastal development, which increases risk of other coastal hazards.[26]

See also[edit]

References[edit]

  1. ^"Gold Coast Beach Nourishment Project". Queensland government. Retrieved 24 January 2018.
  2. ^U.S. Supreme Court Case Stop the Beach Renourishment v. Florida Department of Environmental Protection refers to the practice as beach renourishment rather than beach nourishment.
  3. ^Farley, P.P. (1923). "Coney Island public beach and boardwalk improvements. Paper 136". the Municipal Engineers Journal. The Municipal Engineers of the City of New York. 9 (4). 
  4. ^Dornhelm, Rachel (Summer 2004). "Beach Master". Invention & Technology Magazine. American Heritage Publishing. 20 (1). Retrieved 2010-07-04. [permanent dead link]
  5. ^Central and Western Planning Areas, Gulf of Mexico Sales 147 and 150 [TX, LA, MS, AL]: Environmental Impact Statement. 1993. 
  6. ^Ells, Kenneth; Murray, A. Brad (2012-10-16). "Long-term, non-local coastline responses to local shoreline stabilization". Geophysical Research Letters. 39 (19): L19401. Bibcode:2012GeoRL..3919401E. doi:10.1029/2012GL052627. ISSN 1944-8007. 
  7. ^Basco, David; Bellomo, Douglas; Hazelton, John; Jones, Bryan (1997). "The influence of seawalls on subaerial beach volumes with receding shorelines". Coastal Engineering. 30: 203–233. doi:10.1016/S0378-3839(96)00044-0. 
  8. ^ abcdefghijNational Research Council (1995). Beach Nourishment and Protection (Report). Washington, D.C.: National Academy press. pp. 97–99, Table 4–2. 
  9. ^Waikiki replenishment[permanent dead link]
  10. ^"Archived copy". Archived from the original on 2011-06-29. Retrieved 2010-12-21. 
  11. ^Pilkey, edited by J. Andrew G. Cooper, Orrin H.; Cooper, J. Andrew G. (2012). ""Alternative" Shoreline Erosion Control Devices: A Review". Pitfalls of Shoreline Stabilization Selected Case Studies. Coastal Research Library. 3. Dordrecht: Springer Verlag. pp. 187–214. doi:10.1007/978-94-007-4123-2_12. ISBN 978-94-007-4122-5. 
  12. ^Beach Nourishment and Protection
  13. ^Dean, Robert G.; Davis, Richard A. & Erickson, Karyn M. "Beach Nourishment - Coastal Geology - Beach Nourishment: A Guide for Local Government Officials - Beach Nourishment with Emphasis on Geological Characteristics Affecting Project Performance". NOAA Coastal Services Center. Archived from the original on 30 May 2010. Retrieved 2010-07-04. 
  14. ^Farley, P.P. 1923. Coney Island public beach and boardwalk improvements. Paper 136. The Municipal Engineers Journal 9(4).
  15. ^[1][dead link]
  16. ^Pilarczyk, K. W.; Zeidler, Ryszard (1996). "Dutch case studies". Offshore breakwaters and shore evolution control. London: Taylor and Francis. p. 505. ISBN 90-5410-627-1. 
  17. ^French, Peter W (2001). "The importance of dunes in the protection of the Dutch coastline". Coastal defences. London: Routledge. p. 220. ISBN 0-415-19845-3. 
  18. ^"The Netherlands". Encyclopædia Britannica. Retrieved 2009-06-09.  
  19. ^Kubota, Gary T. (June 30, 2010). "Beach to be rebuilt with recovered sand". Hawaii Star-Advertiser. 
  20. ^ abcdeEAGAR, HARRY (July 25, 2010). "Sand replenishment effort runs aground". Maui, Hi.: Maui News. 
  21. ^Mawae, Kamuela (5 June 2010). "Maui Reef Taking a Pounding From Sand Dredging Project" – via YouTube. 
  22. ^Christensen, Kenneth W.; Nettles, Sandy; Gable, Frank J. (February 6, 2015). "Passive Dewatering - A soft way to extend the life of beach nourishments"(PDF). fsbpa.com. Retrieved December 2016. 
  23. ^"Sun特搜:泳灘「愚公移沙」康文署倒錢落海 - 太陽報". 
  24. ^Massiani, Jérôme (2013). "How to Value the Benefits of a Recreational Area? A Cost-Benefit Analysis of the Conversion of a Brownfield to a Public Beach in Muggia (Italy)". Review of Economic Analysis. 5 (1): 86–102. 
  25. ^National Research Council, 1995. Beach Nourishment and Protection. National Academy Press, Washington, D.C., 334 p. pg. 4, 94., Figure 4-6.
  26. ^Armstrong, Scott B.; Lazarus, Eli D.; Limber, Patrick W.; Goldstein, Evan B.; Thorpe, Curtis; Ballinger, Rhoda C. (2016-12-01). "Indications of a positive feedback between coastal development and beach nourishment". Earth's Future: n/a–n/a. doi:10.1002/2016EF000425. ISSN 2328-4277. 

External links[edit]

Beaches along the Gold Coast of Australia have been subjected to a beach nourishment project.[1]

Before and after photos of beach restoration efforts, Florida coastline

Performance Predicability Beach Nourishment

The beach is the centerpiece of the city’s promise of escape — escape from cold winters or college classes or family, where you can drink goblets of bright green liquor and cruise down Ocean Drive in a rented tangerine Lamborghini before retiring to the warm sand. To the casual observer, the beach may look like the only natural bit of the city, a fringe of shore reaching out from under the glass and pastel skyline. But this would be false: the beach is every bit as artificial as the towers and turquoise pools. For years the sea has been eating away at the shore, and the city has spent millions of dollars pumping up sand from the seafloor to replace it, only to have it wash away again. Every handful of sand on Miami Beach was placed there by someone.

That sand is washing away ever faster. The sea around Miami is rising a third of an inch a year, and it’s accelerating. The region is far from alone in its predicament, or in its response to an eroding coast: it’s becoming hard to find a populated beach in the United States that doesn’t require regular infusions of sand, says Rob Young, director of the Program for the Study of Developed Shorelines at Western Carolina University. Virginia Beach, North Carolina’s Outer Banks, New York’s Long Island, New Jersey’s Cape May, and countless other coastal cities are trapped in the same cycle, a cycle whose pace will become harder to maintain as the ocean rises.

"There isn’t a natural grain of sand on the beach in Northern New Jersey; there is no Miami Beach unless we build it," Young says. "The real endangered species on the coast of the US isn’t the piping plover or the loggerhead sea turtle. It’s an unengineered beach."

The sea has been slowly cutting a divot into the shore in front of Miami Beach’s iconic Fontainebleau hotel, encroaching nearly to the promenade. Patching it would normally be a small job. But Miami Beach has a problem, one more cities will soon face: it has run out of sand in the ocean nearby.

The beach is the tattered edge of the land. It’s made of debris, which we call sand when it’s too small to think about discretely, though exactly what it consists of varies. It could be pulverized coral, like in the Maldives, or crushed clamshells, like Shark Bay, Australia, or discarded glass, like around Fort Bragg, California. Often it’s rock that has been crushed by glaciers or eroded off mountains and washed down rivers to the sea. Beaches made from black basalt or purple garnet have a certain novelty value, but the ideal beach, the one you see on ads for airlines and beer, is sugary and white. It’s likely calcium carbonate or quartz.

Coastal engineers talk about "beach behavior," as if dealing with an unruly animal rather than a geologic feature. Waves sort sand grains to a depth where they no longer move them, so some beaches change with the seasons, as winter storms suck sand offshore, leaving only cobblestones, and smaller waves push it back in the summer. One thing all beaches have in common is that they’re always shifting, wave by wave over years or overnight, with a storm.

For much of the 20th century, people tried to hold beaches in place by building groins — lines of rock or wood pylons protruding from the shore. But groins robbed downdrift beaches of sand that would have come their way, creating new erosion problems. (Some came to be called "spite groins.") Seawalls made things worse, further blocking the natural movement of sand and forcing waves back onto the shore, scouring away the beach. By the 1970s, there was very little beach left on Miami Beach or shore at the Jersey Shore. So a new response became popular: add sand.

That job largely fell to the US Army Corps of Engineers. Dredges floated offshore, extending scoops or hoses tipped with cutter heads into the seafloor and piping sand back onto the eroding beach. Nourishment, as the practice is called, maintained the beach, but it was also an admission that there would never be a permanent solution to fixing the shore in place. Once you start nourishing a beach, you can never stop. Its equilibrium state lies elsewhere, and wave after wave will eat away at the shore, and you’ll keep having to find new sand to replace it.

Sand seems like an infinite resource, but it isn’t. You can’t put just any kind of sand on a beach. Forget about the thousands of miles of dunes in the Sahara and Gobi — rounded by wind, those grains are too smooth. Sand made by crushing rock is too jagged. Stones worn down by rivers and waves over millennia is ideal, but even then, it has to be the right type. If the grains are too small, they wash away quickly; too large, and the beach becomes a steep bank. If they’re the wrong density or wrong shape — say, plate-like shards of broken shells — they’ll float in the water, causing clouds. If the sand is too dark it will trap heat, and can shift the gender of sea turtles born there. "You want to match the native sand as close as you can," says Kevin Bodge, a coastal engineering consultant. "That sand was there for a reason."

Tremendous amounts of ocean sand gets used for land reclamation and construction. Countries use it to extend their borders, like Singapore and China, which has built seven new islands in the South China Sea. Billions of tons of sand gets poured into concrete. A United Nations report on sand shortages found that up to 60 billion tons of sand and gravel are mined each year, more than twice the amount moved by all the rivers in the world, which the report notes makes "humankind the largest of the planet’s transforming agents with respect to aggregates."

The United States has lined its coasts with over a billion cubic yards of sand, at a cost of $8.6 billion, according to a database maintained by Andy Coburn at Western Carolina University’s Program for the Study of Developed Shorelines. All that sand inevitably washes back into the sea. Sometimes waves bring it back, but for the most part, it’s lost to us; if it’s sucked out past a certain depth, it’s scattered along the continental shelf, too dispersed to be gathered back.

With sea levels rising, demand for beach sand is only going to grow. About 57 percent of the coast in the lower 48 states is already eroding, according to the USGS. "Every single coastal erosion problem we have right now is only going to get worse, not better," Young says. "It’s only going to erode faster, not slower, require more sand, not less." Gradually now, but soon overwhelmingly, every coastline is going to want to move inland. Young foresees a future of rising costs and conflict over diminishing sand. "If you want to invest, buy a dredge."

No state requires more sand than Florida, which sits in the middle of hurricane alley and has the longest coastline after Alaska. Half of the 825 miles of beaches monitored by the state’s Department of Environmental Protection are designated as critically eroding, from Daytona Beach to the Kennedy Space Center on Cape Canaveral to the shore in front of Mar-a-Lago, the Palm Beach estate of President Donald Trump.

On July 31st, 2015, the Army Corps released a plan for patching eroding sections of Miami Beach. Miami-Dade’s sand resources had been exhausted, the Corps wrote, and some of the best alternatives lay to the north, offshore of Martin and St. Lucie counties. Though the shoals were in federal waters and the northern counties had no greater right to them than anyone else, they viewed the sand as theirs, and with the Corps’ announcement began the latest skirmish in what local officials call "the sand wars."

State Senator Joe Negron, whose district includes parts of Martin and St. Lucie, swore that Miami-Dade "wouldn’t get a single grain." Frannie Hutchinson, a St. Lucie commissioner, demanded the Corps "take its shovels and buckets and go home." She filed 15 public comments on the Corps’ proposal, saying that it failed to address sea level rise and would rob St. Lucie of needed sand. The county erosion chair for 14 years, Hutchinson says that she cringes every time she sweeps dirt out of her house. "Do you know how much sand is in there? You can’t replace sand."

There was a sense, in council meetings and public statements, that Miami Beach was reaping what it sowed, and that with the sea rising, it was every county for itself. "They’ve squandered their sand, they’ve overdeveloped, they’ve depleted their resources and now they want to come and take ours," says Sarah Heard, a Martin County Commissioner. "We need to protect that offshore site, we need to guard it very carefully. We don’t know exactly how sea level rise is going to impact us, but we know it’s accelerating rapidly, we know there’s going to be inundation."

Heard is a Republican, but laments her party’s denial of climate change. (Last year, the Florida Center for Investigative Reporting found that the state's governor, Rick Scott, forbid state officials from using the term in emails or reports.) Jacqui Thurlow-Lippisch, another Martin County commissioner who objected to the Corps plan, is also a Republican, and also clear-eyed about what rising seas will do to her community. Just as there are proverbially no atheists in foxholes, it’s increasingly difficult to be a local politician in coastal Florida and deny the sea is rising.

Yet what to do about it at a local level is a conundrum. Right now, the answer is to keep piling on more sand. Thurlow-Lippisch describes nourishment as a loop her town is trapped in: the most expensive property is on the beach, she says, and letting it fall into the sea would rob her county of 30 percent of its tax base, making it impossible to fund schools, run buses, and provide lunches for children in need. Though she wonders whether she’s doing the right thing, she continues to fight for the sand that her community will eventually have to put on its shore. "We all have to look ourselves in the mirror and ask, is this a sustainable life? What are we doing here? But right now, we’re in it, we’re doing it."

As the northern counties lobbed angry missives at the Corps, one alternative kept coming up: the Bahamas.

The nearest Bahamian islands are just 50 miles east of Miami. The sand grains there aren’t rock, but orbs of calcium carbonate called aragonite, which some scientists believe is formed by bacteria as deep ocean water moves into the warm, shallow banks of the Caribbean. The exact process that produces the sand is poorly understood, says Lisa Robbins, an oceanographer who studies it, and occurs in only a few other places in the world, such as the Arabian Gulf.

One thing is clear: it’s premium stuff. "They’re not only mysterious, they’re gorgeous, and wonderful to step on," Robbins says of the grains, which she likens to "little pearls." The sand is so white that when coastal engineer Kevin Bodge brought in a barge’s worth in the early ‘90s for Fisher Island, a wealthy community willing to pay for it, the customs official looked on incredulously.

"It was 1991," Bodge recalls, "the height of the Miami Vice thing, so we had to clear customs, and it came in on a barge and when the sun hit that thing coming over the horizon in the early morning light, it was the most incredible pile of gleaming white powder I’ve ever seen. The customs agent just looked at me and said, ‘You gotta be kidding me.’"

The Bahamian government had been ambivalent about selling sand to nourish foreign beaches, says Anthony Myers, whose company holds a lease on a shoal near Bimini — why let tourists visit Bahamian sand beaches elsewhere? But in 2010, it relented. "I’ve helped them understand the science," Myers says. "If you don’t sell this, you’re just watching your money disappear into the chasms of the ocean."

Myers sells sand for plastics, agriculture, and other purposes, but to his great frustration, he has been unable to get his sand on Florida’s beaches. The federal government often pays half the cost of beach nourishment, with states and cities splitting the rest. But an amendment to the 1986 Water Resources Development Act prohibits federal funds from going toward foreign sand if domestic sources are available, which means anyone who wants Bahamian aragonite would have to pay the tab themselves.

His consultant on the mainland, Jayson Meyers (no relation), shares his frustration. Sitting in a concrete and glass tower in downtown Miami, Meyers pulled out a plastic vial of Bahamian sand from his leather briefcase and placed it on the table. It was white as chalk. He’s shown it to mayors and councilmembers and any number of officials, and he says everyone wants some, but until they can get federal assistance, or decide to pay for it themselves, there’s nothing to be done. "It’s great that they want it," he said, laughing bitterly. "It doesn’t do shit for getting it on the beach."

That may change eventually: in September the House passed an amendment proposed by Florida Representative Lois Frankel that would allow federal funds to go toward foreign sand, and Miami Beach is planning a small test project next year. But in the meantime, spurned by its neighbors and unable to buy sand abroad, Miami Beach turned inland, to a mine a hundred miles north. The sand from the northern counties was too dark and full of shells anyway, says an official with the county.

"They’ll be back," says Heard, the Martin County commissioner. "And they’ll receive spirited opposition next time they try it."

The mine is called Witherspoon and sits amid flat fields of pasture and scrub near the southwest shore of Lake Okeechobee. The water table is so high there that you strike it as soon as you dig, so in effect the mine is a pond, with a gray dredge floating in the middle sucking up sand from the bottom. On that late September day, the pond was still, mirroring the bright blue sky and high clouds, masking its 200-foot depth. The workers call it simply "the pit."

In a shed on the pit’s shore, Jacob Dampier scooped a small mound of sand onto a metal plate. With a spackling blade, deft and intent, sweating in the staggering heat, he cut it into four equal segments, squared their sides, leveled the top, and quartered them again. One brick he slid onto a scale, weighing out 350 grams, and slipped it into a ziploc bag. He pulled out a booklet, Munsell’s Soil Color, basically the Pantone chart for dirt, and found a match: value seven, chroma one, eggshell white.

"Sometimes it’s a little gray, sometimes it has an orange tint," Dampier said. "It depends where you are in the pit. But if it’s white, they love it. And you see how white that is? It’ll blind ya."

For 27 years Dampier has tested sand of an astonishing range and specificity: chunky sand for asphalt, finer sand for concrete, finest for masonry and glass. There’s a strict standard for volleyball courts, approved by an expert in Ontario, Canada, and a whole menu for golf courses: one blend for bunkers; another for topdressing; another, dyed green, for divot repair.

Since June, the mine had been running day and night producing sand for Miami Beach. White drifts lay beneath the tower where a machine sorts slurry from the dredge to fit exacting recipes of grain size. Tall hourglass cones lined the pit, and a dune stretched along the road where trucks sat idling, waiting to be waved out by a man standing under a rainbow beach umbrella. From here, three hundred trucks would drive 7,000 tons of sand to the parking lot of the Fontainebleau that day, and do it again the next, until over 300,000 tons have been placed on the shore.

In all, it’s projected to cost just under $12 million to patch 3,000 feet of Miami Beach’s waterfront. Sand prices have risen sharply since 2006, to an average of about $20 a cubic yard, according to Coburn’s database. Mined sand, sorted to bespoke criteria and requiring convoys of trucks, is more expensive still. Laurel Reichold, the Corps engineer managing the project, says at $60 a cubic yard, it costs twice what dredged sand would have.

Yellow all-terrain trucks complete the final leg of the journey, ferrying sand from the parking lot to the beach, escorted by men on ATVs wearing goggles and bandanas pulled over their faces. They turn onto a peninsula of fresh beach jutting out from the eroded shore and dump the sand into the sea. Bulldozers follow, grading the sand down to a gentle slope. The new beach, uniform and flat, is disorienting to be on, without markers for perspective or scale. But once the trucks leave and the waves get to work, it will seem as natural as the rest of the shore, covered in sunbathers and umbrellas.

"It’s gorgeous," said Elizabeth Wheaton, the city’s environment and sustainability director, picking up a handful of sand and letting it run through her fingers. "You just want to make snow angels in it."

Miami Beach has already begun to flood at high tide, and saltwater is pushing into the region’s aquifer. The city, like all South Florida, is doomed, says Hal Wanless, chair of the geological sciences department at the University of Miami. The state’s bedrock of porous limestone means that walls won’t stop the water; it’ll just seep up from below.

Evidence of just how radically changes in sea level can reshape Florida’s coast is everywhere, written in the sand. One of the sand deposits the Corps was eyeing offshore of Martin County was a beach about 10,000 years ago, when the sea was 60 feet lower. The Witherspoon mine was a beach 130,000 years ago, when the sea was 20 feet higher. A recent study of Antarctic ice melt predicted that if carbon emissions aren’t curtailed, by the end of the century the sea could rise by just over six feet, the high end of NOAA’s forecast, and the average elevation of Miami-Dade County. In 500 years it could rise as high as 49 feet. Well before then, the Witherspoon mine would become a beach once again.

The inertia of the climate system means that even if carbon emissions were halted tomorrow, the sea would continue to rise for centuries. With a Republican Party in denial about climate change, and a president who once called it a hoax perpetrated by China, we will likely lock in higher and faster rates of rise in the years to come. For cities on the coast it will be a slow catastrophe, involving myriad difficult decisions: whether to build infrastructure in an attempt to keep the water out, or whether to retreat from the coast, and if so, how to retreat without upending lives, economies, communities. One of the first decisions cities will face, one they’re already facing, is what to do about a shore that’s falling into the sea.

It will probably always be worth it for Miami Beach to go to absurd lengths in order to maintain its shore, right up until the moment the city sinks beneath the sea. Mayor Philip Levine, one of the first Florida politicians to raise the alarm about climate change, has spent $100 million building pumps and raising roads and plans to spend hundreds of millions more. But Florida has no income tax, so if cities are going to pay for the infrastructure needed to adapt, property values need to keep rising and tourists need to keep coming. Without a beach, why come to Miami Beach?

"The irony is, in Miami Beach and South Florida, the way to deal with rising sea levels is to build more condos," says Peter Zalewski, who tracks development through his site Condo Vultures. Just under 30,000 new units are planned or currently being built in Miami-Dade County, a region that already has more assets vulnerable to rising seas than anywhere in the world after Guangzhou, China. As long as Florida is trying to build its way out of climate change, the beach will need to be maintained, as a lure and a defense.

It won’t be worth it for other cities, however, especially if the federal government stops helping cover the cost of nourishment. The Army Corps’ mandate, Reichold says, is to protect property on the coast, and while recreation revenue is factored into the Corps’ cost-benefit analysis, that wouldn’t preclude building seawalls instead of nourishment if sand gets too expensive. Cities will face a choice: retreat, or build walls to keep the water out, destroying the beach.

"You can have buildings or you can have beaches, but you can’t have both," says Orrin Pilkey, founder of the Program for the Study of Developed Shorelines. He thinks buildings will win that calculation, and there will be a rush to build seawalls. It happened on a small scale after Hurricane Sandy, as billionaires erected metal plates and piled up boulders to defend their Hamptons mansions. As the water rises, more and more of the coast will become armored, the sand will wash away, and the shoreline will resemble a fortress of concrete and rock.

The beaches that remain would be amusement parks maintained at great expense, in cities like Miami Beach, Myrtle Beach, or Virginia Beach, perpetually rebuilt with sand from farther and farther out on the continental shelf, or inland from a once and future coast.

In late October, geologists from five East Coast states gathered at a lab in Palisades, New York, on the cliffs of the Hudson River. They were there to mark the opening of what is essentially a library of sand. For the two previous summers, a ship, the MS Thunderforce, had sailed from Miami to Boston, taking samples of the ocean floor, and now those samples had arrived at Columbia’s Lamont-Doherty Earth Observatory.

The survey was commissioned by the Bureau of Ocean Energy Management, which handles resources in federal waters, farther than most states have traditionally gone for sand. But as states have begun to run low on sand nearby, they’ve started turning to BOEM for help, says Jeff Reidenauer, the bureau’s marine minerals branch chief. With rising seas and stronger storms, it’s only a matter of time before states along the Eastern Seaboard are scrambling for sand to repair their shores, and the bureau wanted to know where to go. The survey began in the aftermath of Hurricane Sandy and goes by the apt acronym of ASAP, for Atlantic Sand Assessment Project.

In the lab, long tubes of sediment taken from the ocean floor lay displayed on tables. Researchers use the cores as time capsules, testing the stripes of clay and sand laid down over thousands of years to figure out what the planet was doing at the time. The people gathered in the lab that day, however, were mostly interested in the sand itself: its grain size, mineral type, how much of it there was and where.

The cores from the Thunderforce filled rack after rack inside a refrigerated warehouse adjoining the lab. Each plastic case was labeled by state, almost a wall for each: Massachusetts, New York, New Jersey, North Carolina, Georgia, Florida — 160 cores in all, with hundreds more on the way.

The library was opening just in time. Three weeks before, a low-pressure disturbance that began off the coast of Africa reached the Caribbean, strengthened unusually rapidly, and slammed into Haiti as Hurricane Matthew, Category 4. It was headed for a direct hit on Southeast Florida but bent to the east, skimming the coast, and flooding North Carolina.

The storm sent powerful waves into the coast as it passed, washing away large sections of the shore in Georgia and South Carolina. In Florida waves washed over more than 50 miles of dunes. Beaches in St. Lucie County retreated dozens of feet, turning into cliffs. Brevard County had to rush sand onto the beach to protect homes left teetering over the sea. Jacksonville, in the middle of putting over 900,000 tons of sand on its beach, saw just as much wash away overnight. Near St. Augustine, waves punched through a dune and created a new inlet joining the Matanzas River with the Atlantic, while to the south, waves washed away dunes and concrete armor and chewed through a mile and a half of Highway A1A. Senator Bill Nelson promised the highway would be rebuilt and a new beach installed to protect it.

The damage is still being assessed, and where the sand to replace it will come from is unclear. Maybe it will be brought from a prehistoric beach by convoys of trucks, or from a Bahamian shoal, or maybe the counties will fall into another sand war. Or maybe it will come from one of the new deposits deep out on the continental shelf, mapped, catalogued, and archived in a walk-in refrigerator on the Hudson river.

Back at Miami Beach, work has paused for the winter. Sections of the new shore crumbled as Matthew passed but were soon repaired. Art Basel begins in a few weeks, and the completed beach in front of the Fontainebleau is ready to receive the dealers and collectors and partiers who will soon descend. Work will resume in the spring, with hundreds of trucks ferrying sand from the middle of the state to the shore, patching holes in a beach to postpone the day when it will inevitably vanish.

Editor: Michael Zelenko and Elizabeth Lopatto

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