INTRODUCTION

Sandy beaches are limited natural resources that provide valuable real estate, recreation, and billions of dollars in annual tourist revenues in the United States alone (Houston, 2018). The loss of beaches due to erosion can have significant economic impacts, and new strategies are continuously being implemented to mitigate the effects of coastal erosion (Pilkey and Cooper, 2012). Coastal erosion can be caused by many factors, including wave activity and storm events. Measures to combat erosion usually fall into one of two categories: (1) “hard” structures such as seawalls, groynes, jetties, and breakwaters, and (2) “soft” approaches such as beach nourishment, which is the placement of compatible sand on an eroded beach. The practice of beach nourishment has been used for over a century in the United States and is considered a useful approach to combating erosion; however, it is well documented that beach nourishment is only a temporary fix to a perpetual problem (Griggs, 2024). In fact, nourished beaches often erode quickly, and nourishment is rarely a one-time process (Griggs, 2024). As a result, beach nourishment projects are usually scheduled every 2–5 years as a general maintenance plan and often cost millions of dollars (Griggs, 2024; Leonard, Clayton, and Pilkey, 1990). Another difficulty in executing a successful beach nourishment project is the identification and procurement of compatible sand. In the United States, approximately 95% of beach fill sand has historically come from offshore deposits (NRC, 1995); however, offshore sand in the United States has become scarce. In fact, Miami-Dade County exhausted its offshore sand supply in 2014 (Ousley et al., 2014). Miami Beach now relies on sand trucked in from central Florida from inland sand deposits. In 2023, a nourishment project on Miami Beach placed approximately 885,000 cubic yards (676,631 m³) of sand along 11,400 linear feet (3475 m) of shoreline. With a single dump truck capable of carrying approximately 12 cubic yards (9 m³) of sand, the economic and environmental costs in fuel consumption and CO₂ emissions of 74,000 truckloads of sand for a project of this magnitude were considerable. Adding foreign sand to a beach can also have detrimental effects, including burying shallow reefs, reducing the densities of meio- and microfauna that serve as food sources to shorebirds, surf fishes, and intertidal invertebrates (e.g., crabs), and creating environments with increased sand compaction and temperatures that are no longer suitable for marine life such as nesting sea turtles (Kleppan, 2013; Peterson and Bishop, 2005). Beaches with steep escarpments or that have compacted sand that is too difficult to dig in can prevent sea turtles from effectively laying their eggs (Steinitz, Salmon, and Wyneken, 1998). Darker-colored sand can increase sand temperatures, which is significant since higher sand temperatures increase the number of turtle hatchlings that are born female (Laloë et al., 2016). In fact, a recent study reported a highly female-skewed sex ratio, with almost all turtle hatchlings being born female (Jensen et al., 2018). If this trend continues, whether a result of climate change or unnatural heat retention in beaches nourished with incompatible sand (or a combination of the two), it could catastrophically disrupt reproductive success simply because there will not be enough males to fertilize the females (Jensen et al., 2018). Another factor of concern is the potential for newly introduced foreign sand to become easily suspended in the water column and quickly erode (Griggs, 2024). For these reasons, the continuation of beach nourishment as a primary means of shoreline protection is not environmentally sustainable (Griggs, 2024). Conventional wisdom among coastal scientists and engineers has been that beach nourishment is a “sacrificial” means of preserving the coastline (Griggs, 2024). In other words, erosion is not prevented by renourishment, it is only delayed. With the understanding that offshore sand is a limited resource, this convention must be reassessed. Natural biopolymers are known to promote sand accretion by promoting the interaction of sand with water molecules (Ham et al., 2018). With this in mind, we developed ShoreLock®, a composite biopolymer that promotes sand cohesion and wettability and that may be useful for mitigating coastal erosion. ShoreLock has also shown an ability to significantly reduce erosion escarpments, which create a public safety hazard on recreational beaches and compromise sea turtle nesting activity (Fletemeyer et al., 2018; Steinitz, Salmon, and Wyneken, 1998). Research is needed to develop the means of improving the stability and retention of both nourished and unnourished beaches to preserve the sand that still remains. Without intervention, this precious resource will surely be lost to an inevitable increase in storm activity and sea-level rise.

METHODS—BENCH STUDIES

The following data describe the results of analyses of surface characteristics exhibited by ShoreLock-coated glass slides and ShoreLock-coated sand as well as toxicity testing of the product itself. The sand analyzed in shear tests was siliceous.

Composition of ShoreLock Biopolymer

ShoreLock is a composite mixture of four natural biopolymers/phycocolloids, including guar gum, Xanthan gum, alginate, and carrageenan. It is prepared in a 70% isopropyl alcohol solvent along with emulsifying agents (e.g., Tween® 80) and one or more metal oxides (e.g., ferric oxide). The biopolymer mixture is simultaneously complexed with a composite of hydrophobic, film-forming resins and plasticizers, similar to the enteric coatings used in extended-release medications (Seo et al., 2020). The resulting alcohol/polysaccharide/resin/plasticizer slurry is then dried and milled into a powder.

Preparation of ShoreLock-Treated Sand

Silicate sand samples were collected from Key Biscayne, Florida. Then, a 5 g aliquot of ShoreLock powder was mixed with 1 L of simulated seawater/saltwater (Instant Ocean®) prepared according to manufacturer’s instructions. Although the exact composition of Instant Ocean® is not disclosed by the manufacturer, this information is available in the literature (Atkinson and Bingman, 1997). The ShoreLock/Instant Ocean® solution was mixed with 1 kg of sand into a uniform slurry. Samples were rinsed once with simulated seawater (Instant Ocean®) through a sieve to remove excess ShoreLock. All additional references to “saltwater” in this report indicate the use of Instant Ocean®. References to “seawater” indicate water collected directly from the ocean at the site of reference.

Contact Angles

Contact angle measurements were conducted at the University of Florida Particle Engineering Research Center, Gainesville, Florida. Briefly, three clean glass slides were submerged in a 5% (w/v) solution of ShoreLock dissolved in saltwater. The samples were then dried in a drying oven at 90°C for 1 hour. Contact angles were measured by placing a small droplet of deionized water on the sample surface. Advancing and receding contact angles were produced by controlling the drop volume via a micrometer syringe. Images were captured on a digital camera and analyzed using an analytical software package (Clegg, 2013). A control sample (a clean, untreated glass slide) was used to measure advancing and receding contact angles for comparative purposes. Advancing and receding contact angles were measured on the treated surface, and two subsequent measurements were made on the samples after a 10 minute saltwater wash and further drying in the oven as described above. For comparative purposes, one sample was prepared by coating a glass slide with only the hydrophilic (gum/phycocolloid) constituents of ShoreLock.

Single Point Shear Strength

Shear testing of ShoreLock-treated and untreated sand was conducted at the University of Florida Particle Engineering Research Center, Gainesville, Florida. Briefly, 1 kg of ShoreLock-treated sand and 1 kg of untreated sand samples were rinsed once with saltwater. Then, 200 g subsets of saltwater-washed treated and untreated sand were set aside. The 200 g subsets of both treated and untreated sand were placed in a clean drying oven at 90°C for 30 minutes. A second subset (200 g each) was dried in the 90°C oven for 60 minutes. A third subset of 200 g treated and 200 g untreated sand samples was allowed to dry overnight (15 hours) at standard temperature and pressure (STP: 25°C, 45% relative humidity, 1 atm). A fourth subset of 200 g samples was dried overnight at 90°C. Samples from each subset (saltwater wash, 30 minutes oven-dried, 90 minutes oven-dried, overnight at 90°C and STP) were subdivided into three replicates each composed of treated and untreated sand. All replicate samples weighed between 42 g and 54 g and were carefully placed into the shear cell without compaction; the surface was leveled to achieve a flush top with the cell’s upper edge. Powder flow data were collected for each sample, and single point shear strength was measured using a Sci-Tech Shear Scan Automated Annular Shear Cell. The yield locus was determined for a normal consolidation pressure of 5 kPa. The fail loads were set at 3.8, 3.3, 2.8, 2.3, 1.8, and 1.3 kPa. Analyses were performed using Shear Scan software, which allowed for rapid exclusion of any statistically outlying data points. The software automatically calculates the relative flowability index (RFI), f_c = unconfined yield strength, σ₁ = maximum consolidation stress, φ = internal angle of friction, and C_y = value of cohesion at the consolidation pressure of 5 kPa, and a regression fit for the line of best fit through the data points. The RFI is calculated as: RFI = MCS/UYS. This is a qualitative evaluation of comparative flowability and should be used in conjunction with the unconfined yield strength and maximum consolidation stress to gain a better view of comparative powder flowability.

Cytotoxicity Testing

Cytotoxicity testing was performed by BCS Laboratories in Gainesville, Florida, as per ASTM F895-84: Standard Test Method for Agar Diffusion Cell Culture Screening for Cytotoxicity (ASTM, 2001). Briefly, an aliquot of the ShoreLock sample was diluted to a concentration of 10 ppb in reagent-grade type 1 ASTM water. Monolayers of L929 cells were grown in six-well cell culture plates (Corning, Glendale, Arizona, U.S.A.). Following 24 hours to cell passage, the flasks were overlayed with agar-supplemented media (MediaTech, Manassas, Virginia, U.S.A.) as described by the ASTM method. Sterile 13 mm cellulosic filters (Millipore, Burlington, Massachusetts, U.S.A.) were then placed onto the surface of semisolid agar. To each of six filters, 0.1 mL aliquots of the ShoreLock solution was aseptically added. Sterile uninoculated cellulosic filters were also placed onto the agar to serve as negative controls. The cells were then incubated in 5% carbon dioxide at 36.5 ± 1°C for 24 hours. At this time, the flasks and cells were evaluated macro- and microscopically for signs of malformation, degeneration, sloughing, or lysis of the cells within the zone directly beneath and surrounding the discs. Cells were then re-incubated for an additional 24 hours at the conditions described above and evaluated again. The sizes of the zone surrounding the filter disks showing signs of cell growth inhibition and/or cell lysis were then determined.

Marine Acute Toxicity Testing

Marine acute toxicity testing was performed by Coastal Bioanalysts, Inc., in Gloucester, Virginia, as per USEPA Methods for Measuring the Acute Toxicity of Effluents and Receiving Waters to Freshwater and Marine Organisms (EPA-821-R-02-012/EPA2007.0; USEPA, 2002). Briefly, samples of ShoreLock were diluted to concentrations of 100, 200, 400, 800, and 1600 ppm in artificial seawater (salinity = 20 ppt). Americamysis bahia (Mysidopsis bahia) crustaceans were then introduced into the solution and observed for a period of 48 hours to determine viability. Samples were aerated due to the high viscosity of the 1600 ppm solution of ShoreLock used in the study.

METHODS—FIELD STUDIES

In 2012, ShoreLock was included in the Climate Change Adaptation and Disaster Risk Reduction Project in Jamaica as an alternative, ecofriendly approach to coastal resilience and restoration. The project was funded by the government of Jamaica, the European Union, and the United Nations Environment Programme. ShoreLock was tested on three beaches in Jamaica: Negril, Westmoreland; Font Hill, St. Elizabeth; and the University of the West Indies Discovery Bay Marine Lab, Saint Ann. Selected results from the data collected during this project are summarized below (Hydros Coastal Solutions, Inc., 2013). The sand tested in field tests was calcareous.

Application of ShoreLock to the Beach

The powder (Figure 1) was mixed with seawater on site and deposited in holes or trenches dug at the mean high water mark to a depth where the holes or trenches filled with water (i.e. sea level). For beaches with significant erosion escarpments, the product was placed at the toe of the escarpment as well as directly landward of the escarpment face in holes, bores, or trenches (Figures 2 and 3). Alternatively, the product can be mixed and injected directly in-line with a sand/seawater slurry during a dredging operation (Scott and Ross, 2024).

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Physical Characteristics of Untreated and Treated Sand

Sand samples were collected from the mean high water mark at Norman Manley Beach, Negril, Jamaica. Samples were delivered to Ardaman and Associates, Port Saint Lucie, Florida, and analyzed for Munsell color, carbonate and organic content (ASTM, 2002), and grain size/gradation (ASTM, 2009).

Sand Temperature

Subsurface sand temperatures were measured at the mean high water mark and the toe of the dune using a Fisher Scientific Platinum Traceable® handheld digital thermometer. Temperatures were taken at a depth of approximately 15 cm (∼6 inches).

Sand Compaction

Relative sand compaction was measured at the toe of the dune using a handheld static cone penetrometer.

Sand Moisture Content

Sand samples were collected at the mean high water mark, placed into sealed plastic bags, and then placed on ice to minimize moisture loss in transit to the laboratory. Subsamples of approximately 50 g were analyzed for moisture content. Briefly, samples were weighed and then dried in a drying oven at 115°C for at least 48 hours and then weighed again. Percent moisture content is expressed as the ratio of water loss to dry mass multiplied by 100.

RESULTS

The results of bench and field tests are shown in the following subsections.

Contact Angles

The contact angles measured on the reference untreated glass slide and ShoreLock-treated slides are shown in Table 1. The native contact angle of the clean glass slide was 16° advancing and completely hydrophilic (0°) in the receding case. Literature indicates that beach sand would have a native advancing contact angle of 40° to 60° and a receding contact angle of 20° to 40°. The value of 74° indicates that ShoreLock increased the hydrophobic nature of the surface. Following subsequent saltwater washes, the hydrophobic layer washed away from the slides, and the contact angles decreased (74° → 61° → 18°). The receding contact angles were observed to be less than 10° for all samples, which reflects strong surface wetting tendencies. Low receding contact angles indicate strong capillary forces that adhere particles together. The resulting large hysteresis (ΔH = θ_A − θ_R) (θ_A – advancing contact angle minus the θ_R − receding contact angle) suggests that the ShoreLock coating is heterogeneous (not continuous). That is, some hydrophilic surface is exposed, allowing for the low receding contact angle.

Table 1. Water contact angles measured on glass slides coated with ShoreLock biopolymer.

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Single Point Shear Strength Measurements

The measured powder flow properties for the untreated and treated beach sands are shown in Table 2 and Table 3, respectively. Cohesion values for treated and untreated sand are summarized in Table 4. As shown in Table 4, ShoreLock-treated sand exhibited up to 85% greater cohesion values than untreated sand. As the moisture content returned to values <2%, the difference became negligible. Table 5 summarizes the measured unconfined yield strength for treated and untreated sand. As shown in the table, treated sand exhibited strength values up to 65% greater than untreated sand.

Table 2. Powder flow properties for untreated sand measured in a Sci-Tech Shear Scan Automated Annular Shear Cell.

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Table 3. Powder flow properties for ShoreLock-treated sand measured in a Sci-Tech Shear Scan Automated Annular Shear Cell.

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Table 4. Comparison of cohesion values (C_y) for ShoreLock-treated and untreated sand.

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Table 5. Comparison of unconfined yield strength (f_c) for ShoreLock-treated and untreated sand.

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Cytotoxicity Testing

ShoreLock was shown to exhibit no cytotoxicity at all concentrations tested using ASTM F895-84 (2001); see Table 6 for results.

Table 6. Results of ASTM cytotoxicity testing of ShoreLock. Numerical values describe zones of lysis surrounding filter disks impregnated with 10 ppb ShoreLock.

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Acute Marine Toxicity Testing

ShoreLock was shown to be nontoxic to marine organisms at all concentrations tested using U.S. EPA 2007.0 (USEPA, 2002); see Table 7 for results. The lethal concentration 50% (LC₅₀) could not be determined because the practical limitations of the method were exceeded by the high viscosity of the ShoreLock solution at the highest concentration tested (85% survival at 1600 mg/L).

Table 7. Results of USEPA (2002) marine acute toxicity test for ShoreLock. The 48 hour LC₅₀ was determined at concentrations up to 1600 mg/L.

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Physical Characteristics of Treated and Untreated Sand

The Munsell color, uniform soil classification, carbonate content, and organic content results of untreated and treated sand are shown in Table 8. Sand color and carbonate content remained consistent throughout the study. No organics were detected in any of the samples. Grain size analyses of untreated sand and ShoreLock-treated sand are shown in Tables 9 and 10. Size distribution remained in the medium to fine sand classification throughout the study.

Table 8. Physical characteristics of Norman Manley Beach sand collected before and after ShoreLock application.

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Table 9. Grain size distribution of sand collected from Norman Manley Beach, Negril, Jamaica, on 12 November 2012 (prior to ShoreLock application).

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Table 10. Grain size distribution of sand collected from Norman Manley Beach, Negril, Jamaica, on 31 October 2013 (following ShoreLock application).

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Sand Temperature

The average sand temperatures measured at the mean high water mark and dune line are shown in Table 11. Overall, the sand temperatures were consistent, and no significant differences were observed between untreated sand and ShoreLock-treated sand.

Table 11. Sand temperature measured at mean high water mark and dune line at Norman Manley Beach, Negril, Jamaica, measured in ShoreLock-treated area and in untreated area (control).

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Sand Compaction

Average sand compaction values as measured with a static cone penetrometer are shown in Table 12. Compaction values were consistent, and no significant differences were observed between untreated sand and ShoreLock-treated sand at depths of 15 cm and 30 cm. However, compaction values decreased in ShoreLock-treated sand at the 45 cm depth.

Table 12. Average sand compaction measured at the dune line of Norman Manley Beach, Negril, Jamaica, at ShoreLock-treated area and untreated area (control).

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Sand Moisture Content

Average moisture content of untreated and ShoreLock-treated sand is shown in Table 13. No differences were observed between ShoreLock-treated sand samples and untreated samples.

Table 13. Average moisture content of Norman Manley Beach sand collected from mean high water mark and dune line at ShoreLock-treated area and untreated (control) area.

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DISCUSSION

The results reported herein show that ShoreLock-treated sand exhibits greater cohesion and unconfined yield strength under high moisture conditions than untreated sand as measured in a Sci-Tech Shear Scan Automated Annular Shear Cell. Additionally, ShoreLock exhibits no cytotoxicity and is nontoxic to marine organisms and has no observable effect on the morphology or color of treated sand. ShoreLock technology has been used successfully to restore and stabilize beaches in the Caribbean, including projects in the Bahamas (Figures 4 and 5) and Jamaica (Figures 6 and 7). Comprehensive field studies on its potential effects on the marine environment were conducted under a project commissioned by the government of Jamaica, European Union, and United Nations Environment Programme (GOJ/EU/UNEP Climate Change Adaptation and Disaster Risk Reduction Project). In addition to data presented herein from Negril, Westmoreland, the University of the West Indies carried out their own pilot site at the Discovery Bay Marine Laboratory in St. Ann, where ShoreLock’s effects on water quality, marine resources, benthic organisms, sand micro-, meio-, and macrofauna, and sand composition and size distribution were evaluated. Just as in Negril, this study concluded that ShoreLock had no negative effects on water quality, benthic organisms, sand infauna, compaction, temperature, carbonate composition, moisture content, or particle size distribution (Centre for Marine Sciences, University of the West Indies, 2013, 2014; MonaInformatix, Ltd., 2014). Sand accretion was visibly evident at this site as well (Figures 8 and 9). Future studies on ShoreLock-treated sand using a wave flume are planned to better understand its effects on beach stability and morphology under varying wave conditions and environments.

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CONCLUSIONS

ShoreLock technology has shown promise for use in providing a soft approach to coastal stabilization and erosion control. The data presented here show an increase in sand cohesion in ShoreLock-treated sand when compared to untreated sand in bench studies. Field studies have resulted in an increase in accretion of sand; however, individual results are dependent on factors such as storms, wave action, availability of offshore sand, and littoral drift. Field studies have also shown a significant reduction in the presence of erosion escarpments on treated beaches. While most ShoreLock studies have been conducted on low-energy beaches with minor erosion escarpments, ShoreLock successfully reduced a significant escarpment (∼2 m) on a high-energy beach in Middle Caicos, Turks and Caicos Islands (Figures 10 and 11). While we propose that ShoreLock may be useful as an amendment to increase the life expectancy of traditional nourishment projects, it most certainly aligns with the U.S. Army Corps of Engineers’ “Engineering with Nature®” initiative, which seeks to align nature-based and engineering solutions to conserve environmental and water resources. Ultimately, ShoreLock's most immediate impact lies in its ability to quickly reduce erosion escarpments and create a more favorable environment for nesting sea turtles. This is especially crucial on recently nourished beaches, where engineered escarpments pose a significant threat to successful nesting (Peterson and Bishop, 2005).

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