Study Area

The Fog Point Living Shoreline Restoration Project, funded by the U.S. Congress under the Hurricane Sandy Disaster Relief Supplemental Appropriation Act of 2013, Public Law 113-12, is located at the northern shore of Glenn Martin National Wildlife Refuge (Martin NWR), on the northern end of Smith Island, Somerset County, Md. (fig. 1). Martin NWR covers 18.41 square kilometers (km²) of coastal wetlands composed of tidal marsh, embayments, creeks, and vegetated ridges that form an important stopover and wintering area for thousands of migratory waterfowl, as well as nesting habitats for various wildlife species (https://www.fws.gov/refuge/martin). The tidal range is approximately 0.56 m, estimated from the nearby National Oceanic and Atmospheric Administration (NOAA) station (8571421). Salinity in this region ranges from 11 to 19 parts per thousand (Perini Management Services and others, 2014).

The shorelines in the Martin NWR are exposed to prevailing wind and wave energy of the open Chesapeake Bay and are highly vulnerable to storms. Therefore, shoreline erosion (fig. 2) is an imminent risk to the refuge and the human and wildlife benefits that the refuge provides. The shorelines along the northern and western shores of the refuge have retreated at a rate of 0.61 to 5.5 m per year (2 to 18 feet per year) from 2001 to 2013, resulting in the loss of nearly 3.3 acres of prime fish and wildlife habitat annually (Perini Management Services and others, 2014; USFWS, 2015).

In 2016, rock breakwaters, approximately 76 m (250 ft) in length, were constructed in front of existing headlands adjacent to pocket beaches. Enough sand was then added to connect the marsh and breakwater to accommodate plantings of S. alterniflora (figs. 3, 4). Within the study area, sandy storm deposits are ubiquitous, and they typically extend from the low marshland inward, spanning approximately 3 to 25 m (fig. 5).

The area and shape of the sandy berm were dictated by mean high tide, storm surge high water levels, and aggressive waves (Hardaway and Byrne, 1999) when debris of plants were brought to the upper berm line (fig. 5). The Fog Point Living Shoreline Restoration Project construction was completed in fall 2016.

Field Deployment of Monitoring Equipment

For this study, we chose a specific headland with a breakwater and an adjacent embayment to monitor waves, currents, and sediment deposition with and without breakwater protection. Multiple locations within the headland were selected to assess the spatial variations in wave, current and sediment dynamics. Sensors and equipment were installed at low tide from February 10 to February 14, 2020.

To collect wave data, six pressure transducers (wave gages [WGs]) from Ocean Sensor Systems, Inc. (OSSI-010-003C) were installed at a water depth in the range of 0 (behind breakwater) to 2 m (offshore location) to measure water levels in 20-minute bursts every 30 minutes using a sampling rate of 10 hertz (Hz) (fig. 6A).

For measuring flow velocity and direction from offshore to nearshore, 11 tilt current meters (TCMs) were installed at a water depth in the range of 0.1 (behind breakwater) to 2 m (offshore location). These TCMs, from Lowell Instruments LLC, consisted of six long TCMs with a velocity range of 0–80 centimeters per second (cm/s) and five short TCMs with a velocity range of 0–60 cm/s. Each TCM was equipped with a tilt-corrected compass housed in a buoyant casing; the casing was then attached to a concrete paver block measuring 1 square foot on the sediment surface (see fig. 7B).

Additionally, an acoustic Doppler current meter (ADV) (Argonaut-ADV from SonTek) was deployed near the boundary between the breakwater and the embayment at a water depth of approximately 0.8 m to measure changes in circulation patterns for verification of the suitability of TCMs for measuring current velocity in shallow embayments (fig. 6A). The TCMs and ADV operated continuously at a rate of 16 Hz in bursts lasting 20 seconds. Sediment dynamics were quantified by following the specific methods from a previous NFWF-funded living shoreline restoration project (Wang and others, 2021). For this study, ceramic sediment tiles were used to quantify the sediment mass accumulation on the marsh surface, while pin/trap sets were used to quantify the mass flux of sediment located approximately 1.0 ft (0.3 m) above the marsh or sediment bed.

To measure sediment accumulation, six sites were selected in the study area: three behind the breakwater and three in the embayment (fig. 6B). At each site, three replicates of ceramic tiles (15.24 centimeters [cm] x 15.24 cm) were placed. Additionally, eight sediment pin/trap sets were installed, with four located behind the breakwater and four in the embayment (fig. 6B). To quantify lateral marsh erosion, 10 marsh edge erosion pins (1.25-inch PVC pipes) were placed vertically behind the shoreline along the study area to measure any horizontal movement of the marsh edge during the monitoring period. Among these pins, five were placed behind the breakwater and five along the embayment (fig. 6B). Examples of equipment installation are shown in figure 7.

The coordinates and elevations of WGs, TCMs, ADV, sediment trap/pin sets, sediment tiles, and marsh erosion pins were measured by using a survey-grade Global Positioning System during the deployment (fig. 8). An elevation survey was conducted by using a static Global Navigation Satellite System with a horizontal accuracy of ±0.015 m (0.05 ft) and a vertical accuracy of ±0.03 m (0.10 ft).

Retrieval of Equipment

A site visit to retrieve instruments and conduct additional measurements was originally scheduled for May 2020. However, travel was restricted owing to the COVID-19 pandemic. Local fishermen were asked to help with the sensor retrievals. Only two wave gages were retrieved in the summer of 2020. During August 2021, the remaining sensors were retrieved, and onsite measurements were made. On August 25, 2021, other WGs and current meters, including the ADV, were retrieved, and onsite measurements were made. One additional WG and one TCM were found and retrieved, but other WGs and current meters were lost. The ADV was completely damaged by storms and other disturbances over this 18-month period in the water. The locations where the WGs and the current meter were retrieved are shown in figure 9.

During August 2021, sediment tiles behind the breakwater were retrieved, but sediment tiles in the embayment area were lost. Of the eight sediment traps, only the four behind the breakwater and one in the embayment (TPc2 on fig. 6B) were found. The vertical movement of the traps was measured onsite, and water and sediment inside the traps were transferred to 500-milliliter (mL) bottles and shipped to Louisiana State University for laboratory analysis of sediment mass and grain size distribution. The erosion pins along the marsh edge in the embayment area were all lost, but all erosion pins protected by the breakwater survived; the distances from marsh edge to the pins were measured to determine marsh horizontal accretion or deposition at these pin locations from deployment (February 12, 2020) to retrieval (August 25, 2021).

During the retrieval phase in the summer of 2021, we also measured plant biophysical parameters, including total plant height, stem height, stem diameter, and stem density at two randomly selected 0.5-m x 0.5-m square plots. The plot behind the breakwater was dominated by S. alterniflora, and the plot in the control area was dominated by S. patens. According to Zhu and Chen (2019), total plant height is the length between the plant base and the tip of the plant with all blades aligned along the stem; stem height is the length between the plant base and the location of the topmost blade along the stem or the point at which the last leaf branches from the plant; stem diameter is the diameter measured at one-fourth of the distance of the stem from the ground; and stem density is the number of stems in an area (for example, 1 square meter).

Data Processing and Analysis

The WG-recorded raw gage pressure data were converted to desired wave parameters (water depth, wave heights, and periods) following the protocols described in Zhu and others (2020) and Wang and others (2021). The instrument measures a different atmospheric pressure from the reference pressure on calm days (in this study, it is the atmospheric pressure recorded at the nearby NOAA station 8571421 Bishops Head, which is 21.3 kilometers north of the study site). The difference in pressures was considered to be the instrument offset. The gage pressure (p) was calculated by subtracting the atmospheric pressure (p_atm) from the corrected water pressure data (ṕ) as p = ṕ−p_atm. The gage pressure was then converted to the water depth (h) as h = p/ρg, where ρ (=1,014 kilograms per cubic meter [kg/m³]) is the seawater density and g (=9.81 meters per second squared [m/s²]) is the gravitational acceleration. Then, each burst of water depth was converted to free surface elevation based on linear wave theory and was transformed to a wave energy spectrum by using the Ocean Wave Analyzing Toolbox (OCEANLYZ, version 2.0) (Karimpour and Chen, 2017). From the wave energy spectrum (S_ηη), bulk wave characteristics such as zero-moment wave height (H_m0) and peak wave period (T_p) were extracted by using the following equations:

where We set f_max-cutoff to 0.55 Hz and f_min-cutoff to 0.005 Hz so that we could discard the capillary and swell waves while focusing on the typical wind waves. The accuracy of wave height measurements is ±0.05 percent. Therefore, wave heights smaller than 0.01 m were removed from further analysis.

The raw current data collected from the TCMs underwent two processing steps:

In this study, the flood and ebb tides were determined from the water level measurements at WG3 (fig. 6A). This procedure follows the methodology outlined in Wang and others (2021). The bearing angle (θ) of the mean current is defined as the angle relative to the northward velocity component. Mean current speeds and directions during flood and ebb tides were calculated for the location of the TCM. Monitoring data on wave height, peak period, water depth and current velocity are available in Wang and others (2023a).

Wave Dynamics

WG3 was installed in front of the rock breakwater, WG4 was installed behind the breakwater, and WG5 was installed as a control location in the embayment without the protection of the headland breakwaters. The measured zero-moment wave heights (H_m0) and peak wave periods (T_p) at Fog Point from February to June 2020 ranged between 0 and 1.26 m and between 1 and 7 seconds (s), respectively (figs. 10–12). The time series of water depth, H_m0, and T_p at WG3, WG4, and WG5 during the monitoring period are shown in figures 10–12.

The wave height at WG3 was higher than at the other two gages. The wave height at WG4 behind the breakwater was lowest, ranging from 0 to 0.25 m. Note that the wave data collected at WG5 after May 11 were inaccurate; the measured water depth at WG5 deviated substantially from the tide after May 11, possibly due to the gage being disturbed by an unknown force. The cumulative distribution of wave height at the three gages is shown in figure 13. The wave height was highest at WG3 and lowest at WG4.

To better compare the wave parameters at the three gages, we generated scatter plots (fig. 14). As expected, the H_m0 at WG3 (offshore location) was the highest. The H_m0 at WG4, which was protected by structures, was the lowest among the three gages. The T_p values at WG3 and WG5 (embayment location) were similar and generally smaller than those observed at WG4, indicating that short waves were dissipated more by the low-crested breakwater. Throughout the deployment period, the average H_m0 values measured at WG3, WG4, and WG5 were 0.28 m, 0.04 m, and 0.25 m, respectively. The average T_p values were 2.77 seconds, 3.85 seconds, and 2.78 seconds at WG3, WG4, and WG5, respectively (Wang and others, 2023a). The decrease in wave height observed from WG3 to WG4 may be attributed to a combination of factors, including bathymetry (waves breaking because of varying depths), bottom friction, and the presence of breakwaters.

Current Dynamics

The temporal variations of current vector, current speed, and water depth during flood and ebb tides were recorded at STCM3 (for current parameters) and WG4 (for water depth) (fig. 9) behind the structure (fig. 15). The flood and ebb tides were defined based on the water level changes at WG4. The current vector data indicate a circulation pattern of currents. The average speed was about 10 cm/s, and the maximum average current speed recorded was 35 cm/s for a water depth greater than 30 cm.

Sediment Dynamics

Sediment tiles behind the breakwater were clean except for the one at location TLs2 toward the breakwater in the lower elevation (fig. 6B). TLs2 had a large mud deposit about 3 cm tall on the tile after the 18 months of monitoring (fig. 16B). The mud deposit indicates that fine sediment could be delivered and deposited onto salt marshes behind the breakwater; however, for most of the salt marsh areas, very little sediment accumulated during the 18-month period on the marsh surface, even with the breakwater protection in the large wave energy environment at the Fog Point project area (fig. 17).

Sediment traps measured sediment mass accumulation in the water column and the grain size distribution of sediment at the Fog Point Living Shoreline Restoration Project site (table 1). All four sediment traps behind the breakwater and one trap (TPc2; fig. 6B) in the embayment (control) area were retrieved. During the monitoring period, total sediment mass behind the breakwater ranged from 8.05 to 121.17 grams (g), with a mean value of 48.57 ± 44 g. The median sediment particle size (D50) behind the breakwater ranged from 9.56 to 17.35 micrometers (µm), with a mean D50 of 14.38 ± 3.11 µm. In comparison, the mass of trapped sediment in the embayment area tended to be larger (83.21 g) than the trapped sediment behind the breakwater (48.57 g), and the D50 value of the trapped sediment in the control area tended to be less (9.45 µm) than that behind the breakwater (14.38 µm). Because only one sediment trap in the embayment was retrieved, large uncertainty in the total mass and grain size distribution exists. Further studies are needed to evaluate the total mass of sediment and grain size distribution in the embayment area.

Based on the composition of clay, silt, and sand, trapped sediments in the embayment area were silty loam, and sediments behind the breakwater were silty clay loam. Fewer but relatively larger sized sediments were trapped in locations behind the breakwater than in the embayment area, indicating that the living shoreline structure (breakwater and salt marsh planting) indeed affected sediment transport and deposition along the shoreline. The data from WG4 indicated reduced wave heights behind the breakwater, which could lead to reduced shoreline erosion; however, fewer sediments could be transported and deposited in the area behind the structure, resulting in less sediment available to deposit to maintain shoreline morphology.

The vertical accretion during the monitoring period (February 2020–August 2021) was determined by using data from the sediment traps (table 2). Behind the breakwater, vertical sediment deposition was 1.71–2.32 cm in the high elevation vegetated locations, whereas sediment erosion was 2.56–9.57 cm in the low elevation nonvegetated tidal flat locations (table 2; fig. 18). In contrast, a large amount of sediment erosion (28.77 cm) was measured at the control site in the embayment (table 2). These measurements indicate that the living shoreline structure (“breakwater + marsh planting”) could substantially reduce sediment erosion and that vegetation plays a function in trapping sediment and protecting the shoreline from erosion.

Lateral edge erosion measurements were also made during retrieval by using the erosion pins as shown in figure 19. Marsh edge lateral accretion and erosion were observed at locations behind the breakwater during the monitoring period from February 2020 to August 2021. At EPs1 and EPs3 (fig. 6B), lateral erosion was measured as 7.42 cm, accretions ranged from 14.09 to 39.85 cm at EPs2, EPs4, and EPs5 (table 3).

Marsh edges that expanded into previously open water area (fig. 19B) and eroded (fig. 19D) are clearly seen in the photographs taken during retrieval. Erosion pins along the shoreline in the embayment area were all lost during the monitoring period; therefore, quantification of marsh edge lateral erosion in the embayment area was not possible. By comparing photographs taken on July 11, 2017, and August 25, 2021, we did observe increased marsh edge lateral erosion near wave-cut gullies in the embayment area (fig. 20).

Vegetation Survey

Total plant height, stem height, diameter, and density of S. alterniflora and S. patens were measured at the Fog Point living shoreline sites (table 4). By using the mean ± standard deviation of total plant height (44.14 ± 3.51 cm), S. alterniflora (was slightly shorter than S. patens (50.11 ± 10.17 cm). In comparison, the stem height of S. alterniflora (11.89 ± 4.73 cm) was 55 percent smaller than that of S. patens (26.21 ± 5.49 cm). The mean stem diameter of S. alterniflora was 3.29 mm, larger than that of S. patens (1.52 mm). The stem density of S. alterniflora was 128 stems per square meter, 80 percent less than that of S. patens (648 stems per square meter).

Effects of Wave Energy on Sediment Dynamics Along Fog Point Shoreline

The low sediment accumulation in the headland behind the breakwater during the 18-month study period can be explained by the block of sediment transported from the bay sediment source northwest of the breakwater (crest height of 0.76 m relative to the North American Vertical Datum of 1988; USFWS, 2016) under wind-induced wave height (0.3–0.61 m) experienced between March and May 2020 (fig. 10) (Perini Management Services and others, 2014). Perini Management Services and others (2014) found that marsh edge sediments were transported southward in the project area (in other words, along the west of the coast) most of the time. Nevertheless, during storm conditions when wave heights range from 0.91 to 1.52 m, waves can overtop the breakwater, bringing sediments to the headland behind the breakwater (fig. 17). This occasional overtopping (less than 10 percent of the time) during storm periods could be responsible for the large amount of mud deposition measured on one tile in the middle of the marsh edge behind the breakwater. Maximum wave height in our study area (WG3, offshore) during the monitoring period was 1.35 m, which is just 0.23 m less than the estimated maximum wave height (1.58 m) along the Martin NWR coast, driven by an approximate 45-mile-per-hour northwest wind with a storm surge greater than (>) 1.37 m and determined by using a wind/wave model developed by the U.S. Army Corps of Engineers (Perini Management Services and others, 2014).

The small amount of sediment that was transported and deposited on tidal flat and salt marsh areas behind the breakwater is opposite the expectation that more sediment (mud accumulation) would have been trapped in areas protected by living shoreline structures. At the Gandys Beach, N.J., living shoreline and the Chincoteague, Va., living shoreline constructed oyster reefs (oyster castles) are used as living shoreline structures; more sediments were trapped and accumulated in areas behind the living shoreline structures than sites without structures (Wang and others, 2021, 2023b32). Coarser sediments were trapped at the Gandys Beach site (Wang and others, 2021), and finer sediments were trapped at the Chincoteague site (Wang and others, 2023b). Sediment size depended on the characteristics and availability of sediments and hydrodynamic forces including wave, current, and vegetation effects that drive sediment transport, deposition, and erosion. Additionally, sediments were composed of mostly silts or clays regardless of location behind the structure and in the embayment, reflecting the fine sandy silts and clay sediments of late Pleistocene age in this region (Perini Management Services and others, 2014; USFWS, 2015).

At Martin NWR, marsh edge lateral accretion and erosion were observed in the area behind the breakwater, indicating a large variation in erosive forces (for example, wave energy) and processes that transport sediments after the construction of the breakwater and marsh planting. This finding is consistent with our studies at Gandys Beach, N.J., and Chincoteague, Va., where constructed oyster reefs (or oyster castles) were used as living shoreline structures (Wang and others, 2021, 2023b). Under higher wind wave energy and storm surge conditions, erosion was measured at seaward and leeward sides of constructed oyster reefs, despite reduced erosion compared to sites in the control area without oyster reefs (Chowdhury and others, 2019; Wang and others, 2021, 2023b). By using wave flume and field experiments, Feagin and others (2009) found that salt marsh provided no significant direct protection from wave-induced erosion at marsh edges. In this study, our limited monitoring data demonstrated that salt marsh vegetation along the Fog Point shoreline provided limited direct erosion protection under the prevailing energy environment. This limited protection could be attributed to the low stem height and density in marsh areas along the Fog Point shoreline (refer to the “Limited Role of Vegetation in Wave Energy Reduction Along Fog Point Shoreline” section of this report) capturing less mineral sediment, especially fine-grained sediment, and binding the sediment to the soils with plant roots.

Long-Term Erosion in the Embayment of Fog Point Shoreline

SLR and sustained or repetitive wave action are two long-term processes that cause shorelines to recede (Hardaway and Byrne, 1999; McLoughlin and others, 2015). The effects of SLR and wave action are noticeable in the Fog Point project area. A preliminary analysis of imagery from 1998 to 2015 showed that sand beach bands and high marsh lines had receded by approximately 43 m, with an annual shoreline retreat rate of 2.53 m/yr. Multiple wave-cut gullies (V-shaped notches) with varying lengths and widths were observed along the low marsh in the embayment area (figs. 21, 22). Wave-cut gullies are sub-triangular incisions that are common along deteriorating marsh scarps (Schwimmer and Pizzuto, 2000; Priestas and Fagherazzi, 2011; Priestas and others, 2015). At the study site, gullies tended to form along the shoreline with dead vegetation. During normal and stormy conditions, waves incised the marsh platform, causing erosions at gully heads and ends and marsh collapse at gully ends (Fagherazzi and others, 2013). Wave shoaling by wave crest compression is hypothesized to concentrate wave energy at gully heads, leading to accelerated marsh incision (Priestas and Fagherazzi, 2011; Leonardi and others, 2016). Jagged marsh boundaries may be indicative of relatively low wave energy and high marsh strength, whereas the converse can result in a more uniform morphology (Leonardi and Fagherazzi, 2015). The occurrence of wave gullies is a sign of accelerated marsh deterioration (Priestas and Fagherazzi, 2011). Furthermore, once gullies are formed, shoreline erosion tends to increase, because erosion rates increase with boundary sinuosity at a small spatial scale (tens of meters) (Priestas and others, 2015).

Priestas and Fagherazzi (2011) reported that the formation of wave gullies requires areas of cohesive mud substrate along the scarped edges and waves with heights greater than 20–30 cm to impact the scarp with enough force to remove material. Wave gullies do not form in marsh shorelines with very shallow offshore slopes because of wave energy dissipation by depth-limited wave breaking, even with large offshore waves, nor do they form in scarped edges without sufficient wave power (Priestas and Fagherazzi, 2011; Priestas and others, 2015). Furthermore, Priestas and Fagherazzi (2011) reported that the size and spacing of wave gullies could be related to the strength of the eroding material relative to the wave power. Waves exert significant force on the scarp and can cause marsh erosion when the water elevation equals the marsh platform elevation, a condition conducive to increased dynamic wave pressure (Tonelli and others, 2010). However, it is important to also consider the findings of Priestas and others (2023), which demonstrate that maximum impact pressures can occur under optimal (plunging) wave-breaking conditions, emphasizing the significance of wave shoaling, breaking dynamics, and water depth in the erosion process. One of the consequences of salt marsh erosion is the loss of sediment-trapping capacity by vegetation. The sediment-trapping capacity of salt marsh platforms could decrease exponentially with salt marsh erosion (for example, up to 50 percent of the sediment mass trapped by vegetation is lost once 25 percent of the marsh area is eroded) (Donatelli and others, 2018). Therefore, maintaining the physical conditions (for example, tolerant inundation duration at marsh surface elevation) for optimal vegetation growth and trapping inorganic sediments is an important component for the success of living shoreline restoration.

Limited Role of Vegetation in Wave Energy Reduction Along Fog Point Shoreline

In salt marshes of Chesapeake Bay, the stem density of S. alterniflora averaged 344 stems per square meter with a range of 270–425 stems per square meter and a standard deviation of 80 stems per square meter (Garzon and others, 2019). Garzon and others (2019) found that the average and the standard deviation of stem height were 71 and 22 cm, respectively, and stem diameters varied between 4 and 7 mm, with an average of 5 mm and a standard deviation of 1.5 mm. Marsooli and others (2017) found that the density of S. alterniflora varied between 20 and 390 stems/m², and stem height ranged between 26 and 58 cm in salt marshes in Jamaica Bay, N.Y., along the North Atlantic coast. Zhu and Chen (2019) found that the representative total plant height and stem density of S. alterniflora in Terrebonne Bay along the Louisiana coast were 63 cm and 422 stems/m², respectively. Few studies have measured S. patens plant attributes for the purpose of detecting the effects of this species on wave attenuation in vegetated shorelines along the Atlantic and Gulf coasts. Hu and others (2015) found that in brackish marshes dominated by S. patens along the Louisiana coast, the average stem height, stem diameter, and stem density were 50 cm, 1.50 mm, and 740 stems/m², respectively. A 3-year study of living shoreline using sill and salt marsh along the North Carolina coast showed that S. alterniflora stem height, stem density, and percentage of cover were lower in the restoration sites than in the natural marsh sites (Currin and others, 2008).

The stem height and density of S. alterniflora and S. patens measured at the Fog Point living shoreline sites (table 4) tended to be smaller or in the lower range measured along the Atlantic and Gulf coasts in the limited studies. The short stem height and relatively low stem density of these two species in the Fog Point living shoreline area reflected the harsh environmental conditions such as large wind-driven and storm-induced waves from the west or southwest that can cause high wave energy to pass the breakwater, which is oriented southwest to northeast. Because tall stem height is more effective in mitigating wave energy than short stems (Zhu and others, 2023), salt marshes along the Fog Point living shoreline were expected to have a limited role in attenuating wave energy, even with the breakwaters constructed. It should be noted that while the S. alterniflora community behind the breakwater was planted after the construction in late 2016, the S. patens community in the control area had grown under natural conditions. Therefore, the S. alterniflora community at the Fog Point shoreline area is expected to take longer than 5 years to develop into a stage with tall stems and high stem densities such as those reported to be capable of playing an effective role in wave energy attenuation and sediment trapping.

Further Research Opportunities

The Fog Point shoreline with the “headland - breakwater - embayment” pattern is representative of one major type of shoreline along the Chesapeake Bay coast. Integration of rock breakwaters, sand nourishment, and salt marsh plant species is a popular living shoreline restoration technique that has been used to restore and protect the shorelines with salt marshes, beaches, and dunes. These shorelines provide ecosystem services, including wave attenuation, surge reduction, and enhancement of habitat for fish and wildlife species. Although living shoreline restoration projects, such as the Fog Point Living Shoreline Restoration Project, have been constructed along these shorelines, very few field studies have been conducted to simultaneously monitor wave, current, and sediment dynamics as well as vegetation characteristics, with and without the living shoreline structures, especially during storms when large wave energy is generated (Wang and others, 2021).

In this study, we collected wave, current, sediment, and vegetation data along the Fog Point living shoreline in Martin NWR in early 2020, during the occurrence of large wind- and storm-induced waves were the major drivers of shoreline erosion and retreat. Our study represents a critical step to understanding the mechanisms of shoreline erosion, including the hydrodynamic forces (wave and current) on sediment transport, deposition, and erosion, and the role of vegetation in sediment trapping and accumulation. Because of COVID-19 pandemic travel restrictions, we were unable to collect wave, current, and sediment measurements at all deployed locations, especially in the control (embayment) area. The loss of data made it difficult to quantify the spatial patterns in wave, current, and sediment dynamics, especially in the control area. Therefore, uncertainties remain in assessing the variability in wave height, peak period, current velocity, circulation pattern, and sediment transport, deposition, and erosion with and without the breakwaters along the Fog Point living shoreline. Thus, long-term monitoring (decadal scale) of spatial wave, current, sediment, and vegetation dynamics, including shoreline morphological changes (both lateral and vertical) along the living shoreline, could help to assess the effectiveness of these types of living shoreline structures under future climate change and SLR conditions.

Because of a limited sediment supply behind the breakwater and continued marsh edge erosion along the embayment, use of external sources of sediments (for example, dredging materials) could help to supplement sediments for marsh accretion both laterally and vertically. Marsh planting is a crucial component of this type of living shoreline structure; maintenance of physical conditions (for example, tolerant inundation duration at marsh surface elevation) for optimal vegetation growth and trapping inorganic sediments is important for sustainable living shoreline development. Furthermore, process-driven models of wave, hydrodynamic, sediment transport, and shoreline morphology could be coupled to examine the effects of the “breakwater + marsh planting” structure on wave attenuation, circulation patterns, sediment deposition, erosion, and shoreline change, and to develop the optimal design of living shoreline structures.