Living Shorelines as an Erosion Mitigation Strategy
Living Shorelines as an Erosion Mitigation Strategy
Evidence from the Guana Tolomato Matanzas National Estuarine Research Reserve Monica Quintiliani
Living Shorelines as an Erosion Mitigation Strategy
Table of Contents
Tables ...... ii
Figures ...... iii
Abstract ...... 1
Introduction ...... 2
Case Studies ...... 7
Grand Isle and St. Bernard Oyster Reef, Louisiana ...... 8 Saw Grass Point Salt Marsh, Dauphin Island, Alabama ...... 10 Winyah Bay South Island Living Shoreline, Yawkey Wildlife Preserve, South Carolina ...... 12 Johns Point Landing, Virginia ...... 14 Gandy’s Beach/Money Island, Downe, New Jersey ...... 16 Summary ...... 18 Study Site ...... 20
Methods ...... 23
Results ...... 25
Beach Width ...... 25 Marsh Area ...... 26 Discussion ...... 28
Conclusions ...... 33
Project Limitations ...... 33 Future Research Recommendations ...... 34 References ...... 36
Tables
Table 1. Summary of Case Study Findings ...... 18 Table 2. Beach width over time...... 25 Table 3. Marsh area over time...... 27
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Living Shorelines as an Erosion Mitigation Strategy
Figures
Figure 1. Seawall ...... 3 Figure 2. Groins ...... 3 Figure 3. Living Shoreline design ...... 5 Figure 4. Grand Isle Living Shoreline, LA ...... 8 Figure 5. Grand Isle, LA oyster substrate ...... 9 Figure 6. Saw Grass Point Living Shoreline, AL ...... 10 Figure 7. Coastal Haven System, Dauphin Island, AL ...... 11 Figure 8. Winyah Bay, SC Living Shoreline ...... 12 Figure 9. Castle Blocks, Winyah Bay, SC ...... 13 Figure 10. Johns Point Landing Living Shoreline ...... 14 Figure 11. Oyster shell bags as oyster substrate ...... 15 Figure 12. Gandy's Beach/Money Island, NJ ...... 16 Figure 13. Coir fiber logs ...... 17 Figure 14. GTMNERR and Wright's Landing ...... 21 Figure 15. Wright's Landing Living Shoreline...... 22 Figure 16. Measurement Sites, Upper Peninsula ...... 23 Figure 17. Measurement Sites, Lower Peninsula ...... 24 Figure 18. Beach width over time ...... 26 Figure 19. Marsh area over time ...... 27 Figure 20. Hurricane Mathew damage, Ponte Verde Beach, FL ...... 28 Figure 21. Hurricane Irma damage, St. Johns County ...... 29 Figure 22. Destroyed bulkhead ...... 30
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Living Shorelines as an Erosion Mitigation Strategy
Abstract
Erosion is a principal problem in coastal areas exacerbated by heavy residential and infrastructure development. Traditionally, communities have used structures such as seawalls and groins to protect their shorelines, yet new research suggests these structures increase erosion on site. Many land managers are now turning to the Living Shoreline technique which uses ecosystem engineers to create a more naturally protected shoreline. Five case studies were examined to determine whether clear trends leading to living shoreline success existed. Satellite images of the Guana Tolomato Matanzas
National Estuarine Research Reserve (GTMNERR) from 2005, 2008, 2011, 2013, 20015, and 2017 were also analyzed to determine whether the living shoreline installed in 2012 has had any large impacts on the shoreline over time.
Analysis of the GTMNERR site revealed little to no change in beach width or marsh area despite heavy hurricane activity. These findings suggest the living shoreline installation may be protecting the shoreline although no detectable accretion or erosion exists. A similar result was seen in the
Dauphin Island, AL case study. Other case studies revealed a possible benefit to marine concrete as an oyster substrate and that these projects may need more time to establish before large impacts to the shorelines will be seen. Proper planning, site selection, and monitoring are key to successful living shorelines.
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Living Shorelines as an Erosion Mitigation Strategy
Introduction
Coastal areas continue to be developed due to high economic opportunity and aesthetic value, resulting in communities facing the important problem of erosion. To combat this, communities often invest heavily in traditional forms of shoreline armoring (e.g. seawalls, groins, see Figures 1 & 2).
Conservative estimates as recent as 2015 have determined that the continental United States’ coasts are roughly 14% armored (Dethier 2016). However, these traditional armoring techniques have been found to intensify erosive forces instead of reducing them as intended (Cheong 2013) (Scyphers
2011). Furthermore, these armoring measures have been found to reduce the retention of wrack, or organic beach debris (e.g. seaweed, drift wood) usually forming a “wrack line” at the high tide extent, on the beach and the invertebrate populations residing within it. This reduces the diversity of mobile macroinvertebrates, reduces high shore habitat for beach-spawning forage fish, and increases beach temperatures resulting in increased fish egg mortality (Dethier 2016). Armored shorelines are often found to be much narrower than unarmored shorelines (Pilkey 1988), likely due to the prevention of the upper beach migrating inland as it naturally would (Dethier 2016).
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Living Shorelines as an Erosion Mitigation Strategy
Figure 1. Seawall
Source: https://www.nccoast.org/protect-the- coast/advocate/terminal-groins/ Figure 2. Groins
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Living Shorelines as an Erosion Mitigation Strategy
While negative effects of traditional armoring techniques are generally localized when a few, small installations exist on a shoreline, ecosystem scale impacts can materialize when installations become larger and more frequent. Benthic infaunal organisms, those which live burrowed into sediment, experience decreased densities, likely due to a loss of nutrients from marsh detritus that these organisms would usually consume. Reduced benthic infauna densities can affect higher levels of the food chain as less prey species will be available to the predator species (National Oceanic and
Atmospheric Administration 2015). Considering these findings, academics and public servants alike have been searching for better alternatives for shoreline protection.
Living shorelines is a new approach to shoreline protection gaining attention for its nature-based or biophilic design. Living shoreline designs (Figure 3) emphasize positive interactions that generate synergies (Cheong 2013) by using ecosystem engineers. Ecosystem engineers are species that either reduce constraining variables or provide limiting resources to other species in response to their changing environment (Crain 2006). Such species typically provide ecosystem services and influence ecosystem function greatly (Crain 2006). Research has shown that by incorporating several abiotic and biotic features into a living shoreline design (e.g. oyster reefs, saltmarsh, coir fiber logs, etc.), community recovery and stability can be increased by orders of magnitude. The living shoreline approach allows for multiple use design integrating recreation and ecosystem services, coastal defense, and climate-adaptive and disaster coastal management (Cheong 2013).
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Living Shorelines as an Erosion Mitigation Strategy
Figure 3. Living Shoreline design
Traditional armoring techniques are usually considered “easier” to implement as they are the status quo in shoreline protection and tend to have little issue gaining funding and public support. Fewer experts are needed to successfully accomplish these installations and time has allowed for refined design and installation practices. However, as discussed above, these techniques do not typically provide the desired goal of long-term shoreline protection health. While living shorelines can be more expensive and require more experts to install, monitor, and maintain, the living shoreline technique can protect shorelines from storm surges and sea level rise much more effectively than traditional armoring techniques. Improved wildlife habitat, ecosystem services, and more aesthetically pleasing shoreline protection are also benefits of this new approach (National Oceanic and Atmospheric Administration 2015).
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Living Shorelines as an Erosion Mitigation Strategy
Constructed oyster reefs, used as natural breakwaters, are a common feature among living shoreline projects and can be a self-sustaining armoring technique used to prevent erosion in estuaries as long as adequate recruitment and survival rates are maintained on the reef (Scyphers 2011). Reef success is highly dependent on proper site selection, most significantly appropriate salinity regimes, tidal exposure indices, and wave energy impacts (La Peyre 2015). While researchers are still working to understand the needs of successful oyster reefs, environmental benefits from oyster presence has been well defined. Oyster reefs have been found to have significant influence on water quality, primary production, turbidity, suspended organic material, and bacteria (Cheong 2013). Oysters participate in bioturbation and bioirrigation, processes in which sediment and water are filtered causing disturbances which affect bulk density, oxygen availability, and nutrient fluxes resulting in increased soft-sediment habitat heterogeneity. In turn, these interactions affect both ecological function and biodiversity (Norkko 2011). Examples of these impacts include improved demersal, or benthic, fish populations (Scyphers 2011) and positive effects on nutrient dynamics, commercial fisheries, and saltmarsh retreat (La Peyre 2015).
With these benefits in mind, many land managers are beginning to integrate these promising natural breakwaters into their coastal defense systems. However, there has been little research into how constructed oyster reefs impact shorelines over time. The purpose of this study was to analyze and identify the shoreline change of the Guana Tolomato Matanzas National Estuarine Research Reserve
(GTMNERR)’s western shore before and after the addition of the Wright’s Landing Living Shoreline restoration project. Case study reviews of five other living shoreline projects along the East and Gulf coasts of the United States were also included to analyze trends of successful projects. This research will contribute to the understanding of living shoreline impacts across time and at a larger scale, potentially leading to better implementation and management.
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Living Shorelines as an Erosion Mitigation Strategy
Case Studies
Five living shoreline projects were reviewed to gain insight into the factors that contribute to successful living shorelines on the East and Gulf coasts of the United States. Living shoreline projects were discovered predominantly through the Living Shorelines Academy databases (Living Shorelines
Academy n.d.) and were evaluated based on the following metrics: accretion, saltmarsh advance, oyster recruitment, oyster substrate used, land area intended to be restored, land type (urban or protected land), and reported success. Results were then compared to determine if clear trends for successful living shorelines exist.
Several different techniques were used in the following case studies to reestablish oyster reefs and saltmarsh areas. Because oyster larvae, known as spat, will only attach to and complete its life cycle on other oyster shells, each design incorporates oyster shell in some fashion.
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Living Shorelines as an Erosion Mitigation Strategy
Grand Isle and St. Bernard Oyster Reef, Louisiana
The Grand Isle and St. Bernard Oyster Reef project, located on one of Louisiana’s southwestern peninsulas (Figure 4), was constructed from 2010 to 2013 by The Nature Conservancy and partners with over $4 million of funding from National Oceanic and Atmospheric Administration (NOAA) through the Recovery Act (The Nature Conservancy 2017).
Figure 4. Grand Isle Living Shoreline, LA
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Living Shorelines as an Erosion Mitigation Strategy
The project was installed with the intention of restoring 5.47177 km of oyster reefs (The Nature
Conservancy 2017), improving habitat, and promoting the use of living shorelines as a sustainable option for storm protection and erosion prevention. This project also aimed to create both temporary and permanent jobs for local people, investing in both the local and state economies (The Nature
Conservancy n.d.). Coastal Environments, Inc., a local business, was employed to construct the triangular steal structures used to attach the oyster substrate to (Figure 5).
Figure 5. Grand Isle, LA oyster substrate
Bags of oyster shell, collected through an oyster shell recycling program in which oyster shell from local restaurants are rerouted from the landfill to restoration projects, were then attached to the steel structures and were used to recruit spat. Two years of monitoring was completed for this project by
Louisiana State University, concluding that this project was a success based on the following factors: claimed reef establishment, nondescript shoreline changes, and improved habitat (The Nature
Conservancy 2017).
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Living Shorelines as an Erosion Mitigation Strategy
Saw Grass Point Salt Marsh, Dauphin Island, Alabama
The Saw Grass Point Salt Marsh Living Shoreline, constructed in April 2005 by the Mississippi-
Alabama Sea Grant Consortium and partners, is located at the mouth of Mobile Bay (Figure 6) and is the only inhabited barrier island in Alabama.
Figure 6. Saw Grass Point Living Shoreline, AL
The goal of this project was to control erosion caused by the prevention of saltmarsh naturally migrating inland by both a major highway and residential development as well as periodic harbor and channel dredging reducing sand over-wash necessary to sustain the beach. The Coastal Haven system, pyramids of marine concrete with triangular openings in the sides to reduce pressure inside the structure (Figure 7), was used as oyster substrate for this project. Marine concrete is a 100% natural building material, the exact contents of which are protected by the manufacturing company and not shared with the public (Allied Concrete Co. 2010).
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Living Shorelines as an Erosion Mitigation Strategy
Figure 7. Coastal Haven System, Dauphin Island, AL
182 Coastal Haven units were positioned in two rows, creating 62m of structure. Despite the very active storm season of 2005, measurements in November 2006 revealed an increase in oyster density from less than one oyster/m2 before the installation to 205 oysters/m2 after installation and a 15cm accretion along the protected 14.1hc of shoreline. This project both proved and raised public awareness of the ability of living shorelines to protect private and public property from coastal storms
(Swann 2008).
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Living Shorelines as an Erosion Mitigation Strategy
Winyah Bay South Island Living Shoreline, Yawkey Wildlife Preserve, South
Carolina
The Winyah Bay South Island Living Shoreline pilot project is located in northern South Carolina
(Figure 8).
Figure 8. Winyah Bay, SC Living Shoreline
This living shoreline was constructed in September 2010 by the South Carolina Department of Natural
Resources, Horry-Georgetown Technical College, the US Fish and Wildlife Service and other partners to restore habitat, enhance environmental benefits, and improve human wellbeing and quality of life. Because there were oysters already established in other parts of Winyah Bay, the research
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Living Shorelines as an Erosion Mitigation Strategy team felt this would be an appropriate site for their living shoreline installation. Manufactured marine concrete blocks, known as castle bocks (Figure 9), were used as oyster substrate for this project.
Figure 9. Castle Blocks, Winyah Bay, SC
Approximately 1,000 castle blocks were used as oyster substrate and saltmarsh was transplanted in
October 2010 behind each castle group. This project was considered unsuccessful after the site suffered further loss of saltmarsh and slow oyster colonization. Project managers suspect that project failure was due to the high energy tidal flow washing away oyster spat and newly planted saltmarsh
(McColl 2011).
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Living Shorelines as an Erosion Mitigation Strategy
Johns Point Landing, Virginia
The Johns Point Landing Living Shoreline project was constructed in 2013 and is located on a
Virginia peninsula extending into the Chesapeake Bay (Figure 10).
Figure 10. Johns Point Landing Living Shoreline
Bagged oyster shell was used as oyster substrate in this project, a common approach to reef construction. With this approach, the natural fibers of the bags biodegrade over time, leaving nothing but the newly recruited reef (Figure 11). Saltmarsh was also transplanted on site.
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Living Shorelines as an Erosion Mitigation Strategy
Figure 11. Oyster shell bags as oyster substrate
One month after reef construction, oyster spat maturation and recruitment were observed. Saltmarsh advance and seeding was also documented within the first growing season (April to August 2014).
Mussels benefited from the installation as well, their population tripling at the site. The species diversity of benthic macroinvertebrates did not change post installation, but species composition did.
Only a select few species were present both before and after reef construction, suggesting that the introduction of constructed reefs may alter the larger habitat. This living shoreline has restored 535m2 of saltmarsh habitat and was considered a success (Bilkovic 2014).
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Living Shorelines as an Erosion Mitigation Strategy
Gandy’s Beach/Money Island, Downe, New Jersey
The Gandy’s Beach/Money Island Living Shoreline Project is located in southern New Jersey (Figure
12). Construction begun in 2014 by the US Fish and Wildlife Service, the Nature Conservancy, and partners in response to the damage seen during Hurricane Sandy in 2012. The goal of this project was to stabilize the surrounding creek banks and improve habitat and natural coastal defense and stability.
Figure 12. Gandy's Beach/Money Island, NJ
Coir fiber logs made of coconut fibers (Figure 13), castle blocks with oyster shell bags, and transplanted saltmarsh were all used in this living shoreline design.
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Living Shorelines as an Erosion Mitigation Strategy
Source: http://floridalivingshorelines.com/project/escambia-bay-2/
Figure 13. Coir fiber logs
When completed, this project will have restored 136.379 ha of coastline. The success of this project has yet to be determined as it is still considered in progress. At this time, project managers claim to have observed sediment accretion (US Fish and Wildlife Service 2016) and, as of October 2016, have reported that the structures reduced wave action on the marsh by 15% throughout a full tidal cycle.
During low and mid tides, the installation has been recorded to reduce wave action by 50% (Brunetti
2016).
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Living Shorelines as an Erosion Mitigation Strategy
Summary
Table 1 provides a summary of the case study findings.
Last Installation Saltmarsh Oyster Oyster Restored Land Project Monitoring Accretion Success Date Advance Recruitment Substrate Area Type Report
Grand Triangular 5.47177 2010-2013 2015 U U Yes Protected Yes Isle, LA frames km
Dauphin Coastal Island, 2005 2008 Yes No Yes 14.1 ha Protected Yes Haven AL
Winyah Castle 2010 2011 No No No U Protected No Bay, SC blocks
Johns 0.0535 Point, 2013 2014 U Yes Yes Shell bags Protected Yes ha VA
Gandy’s Castle 2014- 136.379 Beach, 2016 Yes U U blocks & Protected U present ha NJ Shell bags
Table 1. Summary of Case Study Findings
U = Unknown
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Living Shorelines as an Erosion Mitigation Strategy
Information on the current status of these projects proved difficult to find. Many projects are considered successful, but do not explain the metrics used to determine success. Projects are often built ambitiously, but then forgotten about once public interest subsides. Project monitoring is poorly maintained, generally due to lack of funding and labor.
However, monitoring is critical for effective adaptive management. Without data describing the conditions and health of the living shoreline, project managers do not know when intervention is needed to sustain the project and its benefits. Because living shorelines appear very natural and are intended to be self-sustaining, it may not be obvious when possible maintenance is required and failure may only be evident when it is too late to correct.
The living shorelines analyzed here have all been installed on protected lands, typical of living shorelines implemented to date. Yet project designers are beginning to explore the possibilities of implementing living shorelines on more urban coasts. Examples of this include but are not limited to
Pensacola Bay, Florida scheduled to begin construction in October of 2018 (The City of Pensacola n.d.) and Staten Island, New York City, New York in 2018 (McKee 2017). Time will tell whether the trends seen on protected lands will translate to urban shorelines.
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Living Shorelines as an Erosion Mitigation Strategy
Study Site
The Guana Tolomato Matanzas National Estuarine Research Reserve (GTMNERR) is a 74,000 acre peninsular conservation area managed collaboratively by the Florida Department of Environmental
Protection and the National Oceanic and Atmospheric Administration (NOAA) as part of the National
Estuarine Research Reserve (NERR) system (Guana Tolomato Matanzas National Estaurine Research
Reserve 2017a). NERRs are federally designated conservation areas used for estuarine protection and research. Established through the Coastal Zone Management Act, NERRs are operated as a partnership between the federal and state governments in which NOAA provides funding and guidance while a lead state agency or university manages the land with input from public partnerships.
Nationally, 1.3 million acres of estuarine land is protected through the NERR system (National
Oceanic and Atmospheric Administration 2017b).
A restoration project was undertaken in 2012 at GTMNERR’s Wright’s Landing site bordering the
Tolomato River on the western side of the peninsula (Figure 14). The restoration project was developed by the Northeast Florida Aquatic Preserves Program, part of the Florida Department of
Environmental Protection’s Florida Coastal Office, with the goal of constructing a living shoreline to reduce erosion and prevent further saltmarsh retreat at the site. Oyster reefs were constructed with bagged oyster shell from a local oyster shell recycling program placed along coir fiber logs (Figure
15) and smooth cordgrass (Spartina alterniflora) was transplanted from a GTMNERR propagation
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Living Shorelines as an Erosion Mitigation Strategy program to facilitate oyster and vegetation reestablishment (Guana Tolomato Matanzas National
Estuarine Research Reserve 2017b).
Figure 14. GTMNERR and Wright's Landing
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Living Shorelines as an Erosion Mitigation Strategy
http://www.gtmnerr.org/oceanwise-and-stewardship/
Figure 15. Wright's Landing Living Shoreline
Since installation, the Wright’s Landing living shoreline has not been consistently monitored.
GTMNERR self-reports that the living shoreline has resulted in increased biodiversity and successful oyster recruitment (Guana Tolomato Matanzas National Estuarine Research Reserve 2017b), but does not reveal the methods or metrics used to determine this.
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Living Shorelines as an Erosion Mitigation Strategy
Methods
To determine whether the living shoreline installation has had large scale impacts on the site, satellite images of the Wright’s Landing restoration site at the GTMNERR were obtained from Google Earth from the years 2005, 2008, 2011, 2013, 2015, and 2017. All images were taken in the fall and winter months (October through January), providing seasonal consistency among measurements. Beach width and saltmarsh area were then measured to capture shoreline changes over time. Beach width was measured by taking the measurement from the center of the channel to the line of established vegetation at six points along the GTMNERR peninsula: at the Wright’s Landing reef site, roughly
350m north and south of the reef site, and at three points along Guana Point. The area of coverage of three saltmarsh sections 200 m2 each were also measured. All measurements were taken using Google
Earth’s measurement tools. Measurement points are illustrated in Figures 16 and 17.
Figure 16. Measurement Sites, Upper Peninsula
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Living Shorelines as an Erosion Mitigation Strategy
Figure 17. Measurement Sites, Lower Peninsula
All beach width and saltmarsh measurements were compared to reveal shoreline changes. Major shoreline changes were compared to two extreme weather events experienced at the site to account for large shoreline changes from natural processes. Proximity, strength, and photographic evidence of severe storm damage from Hurricanes Mathew (2016) and Irma (2017) were considered.
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Living Shorelines as an Erosion Mitigation Strategy
Results
Beach Width
Beach width remained almost constant from 2005 to 2017, as illustrated in Table 2 and Figure 18.
Table 2. Beach width over time
North Wright's South Guana Guana Date Point 3 (m) Beach (m) Landing (m) Beach (m) Beach (m) Point (m)
Mar-05 298 291 201 204 243 127
Jan-08 295 287 196 203 244 126
Dec-11 294 291 200 204 244 125
Jan-13 296 284 198 204 247 128
Nov-15 299 288 200 203 248 131
Sep-17 294 288 200 205 250 133
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Living Shorelines as an Erosion Mitigation Strategy
Beach Width Change Over Time 350
300 298 295 294 296 299 294 291 287 291 284 288 288
250 243 244 244 247 248 250
204 204 204 205 200 201 196203 200 198 200203 200
150 133
127 126 125 128 131 Beach Beach Width(m) 100
50
0 Mar-05 Jan-08 Dec-11 Jan-13 Nov-15 Sep-17 Axis Title
North Beach (m) Wright's Landing (m) South Beach (m) Guana Beach (m) Point 3 (m) Guana Point (m)
Figure 18. Beach width over time
Marsh Area
Marsh area also did not experience large change. The most variable marsh area was C and Marsh A did see some decline in coverage. Marsh B reached full coverage by 2008, maintaining this level of coverage to September 2017. These results are illustrated in Table 3 and Figure 19.
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Living Shorelines as an Erosion Mitigation Strategy
Date Marsh A (m2) Marsh B (m2) Marsh C (m2)
Mar-05 124 150 30.4
Jan-08 111 200 53.4
Dec-11 101 200 33
Jan-13 97.2 200 41
Nov-15 85 200 62.4
Sep-17 68.7 194 21.78
Table 3. Marsh area over time.
Marsh Area Change Over Time 250
200 200 200 200 200 194
) 2 150 150 124 111 100 101 97.2
85 Marsh Area (m 62.4 68.7 50 53.4 41 30.4 33 21.78 0 Mar-05 Jan-08 Dec-11 Jan-13 Nov-15 Sep-17 Date
Marsh A (m2) Marsh B (m2) Marsh C (m2)
Figure 19. Marsh area over time
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Living Shorelines as an Erosion Mitigation Strategy
Discussion
Although there were no drastic changes of GTMNERR’s Wright’s Landing shoreline from 2005 to
2017 and accretion was not measured by this study, this living shoreline installation may have protected the site from the extensive damage caused by Hurricane Mathew in October 2016 and
Hurricane Irma in September of 2017. Figures 20 and 21 showcase the resulting damage from each of these storms, at Ponte Verde Beach and in St. Johns County respectively.
Source: http://abcnews.go.com/US/florida-images-show-destruction-hurricane- matthew/story?id=42664304
Figure 20. Hurricane Mathew damage, Ponte Verde Beach, FL
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Living Shorelines as an Erosion Mitigation Strategy
Source: https://www.accuweather.com/en/weather-news/reports-irma- leaves-over-6-million-without-power-across-florida/70002687
Figure 21. Hurricane Irma damage, St. Johns County, FL
Despite the damage at sites near the GTMNERR depicted above, GTMNERR’s Wright’s Landing experienced minimal damage and no detectable erosion. While estuaries naturally benefit from some inland protection and usually see less damage as the beach fronts shown in Figures 20 and 21, erosion and other damages often still occur. These results are similar to those found at the living shoreline project on Dauphin Island, AL. After being installed in April of 2005, Dauphin Island was subjected to Tropical Storm Arlene in June, Hurricanes Cindy and Denis in July, and Hurricane Katrina in
August of 2005. Minimal damage was found at the site and measurements from November 2006 revealed a 15cm accretion at 55 locations along the living shoreline installation and no erosion at three nearby reference sites. According to the research team on site, the Dauphin Island Living
Shoreline not only prevented private property damage on the island, but also raised public awareness of this possibility (Swann 2008). Page | 29
Living Shorelines as an Erosion Mitigation Strategy
Living shoreline installations along the coast of North Carolina’s outer banks also proved to provide better protection than traditional armoring techniques during storm events. After Hurricane Irene in
2011, shorelines protected by living shorelines experienced sediment accretion whereas 75% of bulkheads surveyed in the same region failed and were damaged (Figure 22). Similarly, 58% of bulkheads near Charleston, South Carolina were destroyed in 1989 during Hurricane Hugo (National
Oceanic and Atmospheric Administration 2015).
http://brick.shorebeat.com/2017/03/storm-blew-hole-in-manasquan- inlet-bulkhead-fishing-off-limits/
Figure 22. Destroyed bulkhead
Not only do living shorelines appear to protect property during heavy storm activity, they may also provide sea level rise mitigation. From 1993 to 2014 NOAA recorded a global sea level rise of 2.6 inches, with an expected 1/8th of an inch rise per year (National Oceanic and Atmospheric
Administration 2017a). Sea level rise experienced locally can be more subtle or more extreme based on factors including but not limited to: upstream flood control, erosion, land subsidence, topographical differences, and regional ocean currents (National Oceanic and Atmospheric
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Living Shorelines as an Erosion Mitigation Strategy
Administration 2017a). Healthy living shorelines maintain a wide beach front and may prevent further erosion of its protected shore, reducing the loss of available land from sea level rise.
Lack of long term monitoring appeared to be the greatest downfall of the reviewed living shoreline projects. Many projects were considered successful, but were not descriptive on what metrics were used to determine success. As with other restoration projects, living shoreline monitoring is often poorly maintained, frequently due to lack of funding and labor. However, proper monitoring is critical for effective adaptive management. If not improved, project managers will not know the status of their work or be able to intervene to sustain projects when necessary.
It is important to note that, ecologically speaking, the living shoreline projects reviewed here are still very young and may still need many years to fully establish themselves. Accretion is not always detected in these projects. However, further erosion is usually not either. This may indicate that the living shorelines may only hold the existing shoreline in place. While some would like to see accretion, preventing or ending erosion at a site can be just as beneficial. Marine concrete used to construct castle blocks and the Coastal Haven system may be the best oyster substrate, but further research is needed on the material to determine this definitively. In order to better understand the factors which make living shorelines successful, a meta-analysis of existing living shoreline projects would be beneficial. Meta-analyses involve taking data from many different projects to analyze trends in regard to factors that may determine outcomes or responses, which in this case is either project success or failure based on factors such as shoreline wave energy, slope, salinity, materials used, spatial configuration of design, and other project design factors (Biostat, Inc. 2017). Large scale experimentation may also provide valuable insights, such as using different materials and spatial designs at the same site to compare success.
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Living Shorelines as an Erosion Mitigation Strategy
Because the primary material used to construct living shorelines are living organisms, it is essential that proper planning, site selection, and monitoring are conducted throughout the entirety of the project. While many communities wish to take action immediately, project failure can be disastrous when tax payers’ money is used to fund a multimillion dollar living shoreline project such as the planned $10.8 million Pensacola Bay (The City of Pensacola n.d.) and $60 million Staten Island
(Rebuild by Design n.d.) living shorelines. Project failure may lead to miseducation or mistrust of the benefits of living shorelines as the public begins to doubt the technology’s ability to produce desired outcomes, resulting in increased difficulty gaining necessary funding for future living shoreline projects and other green infrastructure installations.
As an advocate for successful living shorelines, NOAA recommends that land managers and city planners encourage living shoreline and green infrastructure design in disaster planning. To accomplish this goal, NOAA offers partnership, along with other federal agencies and non- governmental organizations, providing technical assistance and funding for living shoreline research and design. NOAA has also provided several guiding principles to land managers considering restoration efforts. Most importantly, NOAA stresses that shorelines should be left to erode as they naturally would unless infrastructure is being threatened. Planting of Spartina spp. can reduce wave energy by 50% and planted wetland vegetation significantly reduces damages to coastal communities as well as provides fish habitat and nitrogen removal (National Oceanic and Atmospheric
Administration 2015).
NOAA also developed the Conceptual Framework for Considering Living Shorelines in 2015. The framework consists of twelve guiding questions for land managers to consider when determining the most appropriate shoreline stabilization approach for a particular site. The framework stresses proper site selection and planning for sea level rise as well as acknowledges that the best solution at a site is Page | 32
Living Shorelines as an Erosion Mitigation Strategy likely a balance between living shoreline and traditional techniques. This document also outlines the available grants and other support, including design guidance and policy considerations, NOAA and other federal agencies have available to aid in successful execution of these projects (National
Oceanic and Atmospheric Administration 2015).
Conclusions
Project Limitations
The living shoreline projects included in this study are still relatively young thus limiting the conclusions that can be drawn. Large shoreline impacts and changes may be detectable once these living shorelines further mature and stabilize. Conversely, older living shoreline projects may reveal that such installations only halt the erosive process, not cause accretion.
Case study analysis was limited by lack of public information. Information gathered by this study was obtained largely from websites explaining the plan to the public which only stated that monitoring had been or would be completed. Few monitoring reports were available to the public. Those that were available did not always incorporate sufficient data or explain their methods and metrics well.
Long term monitoring is rarely conducted at these sites resulting in large knowledge gaps as to the status and success of these living shoreline installations. Most projects complete two years of monitoring after which efforts are usually terminated due to lack of funding. It is likely that other sites are informally monitored by management staff when time allows as done by the GTMNERR, but formal reports with empirical data are lacking. Such data would give further insights into living shoreline success and impacts and should be considered highly valuable by policy and budget planners.
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The GTMNERR living shoreline is a small study site with limited available data. If monitoring records were better maintained, it is possible that more insight into the success of this installation may be discovered. Because of the landscape-level analysis of this study, accretion may not be detectable.
Satellite images used may not have been taken at a fine enough scale to reveal what may be minute accretion at this time as illustrated by the 15cm accretion recorded at the Dauphin Island living shorelines. However, there is an opportunity to increase the monitoring of this site as it continues to mature so that greater knowledge can be obtained about the viability of this type of design and ecosystem.
Future Research Recommendations
The development of a standardized assessment of living shoreline project health and success may be helpful in determining the value and effectiveness of existing and future projects. A similar approach taken to site selection could also be very beneficial. This could include more systematic identification of sites at the regional landscape scale that may be the best locations for achieving success and providing the most benefit. In addition, more research into the basic biology, habitat needs, and preferences of living shoreline species is needed to properly inform such a rubric.
Determining the best measuring technique for shoreline change would result in more accurate records of living shoreline success and impacts. On site measurements at consistent tidal phases from a fixed point may prove a much better measure of shoreline accretion or erosion than measurements made from satellite images. However, the retrospective benefit of historical satellite images is an advantage that may be better capitalized by methods different from those used in this study.
Research focusing on how long living shorelines will take to fully establish and mature may reveal a more accurate timeline for land managers to begin to expect to see shoreline impacts. With this
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Living Shorelines as an Erosion Mitigation Strategy timeline in mind, better evaluations of living shoreline status and success may be possible. Similar research may also definitively determine whether living shorelines truly are preventing erosion or causing accretion on site and/or down site from the installation.
An important issue in establishing living shorelines is the “energy level” a shoreline receives from wave action. High energy shorelines with frequent significant wave action are unlikely to harbor successful living shoreline installations due to species’ intolerance, whereas low energy shorelines provide a much greater opportunity for success. However, one of the potentially key future research findings would be to determine what techniques might work in moderate to higher energy shoreline ecosystems to provide the benefits of these projects in places that would currently be difficult or impossible to implement successfully.
As living shorelines gain more popularity and begin to be implemented in the urban setting, extensive research will be necessary to determine if the benefits of these installations do in fact extend to urban shorelines and what, if any, adaptations or special considerations need to be made to the existing technology to ensure success. Because these settings often deal with more intense ecological degradation, living shorelines may not be as easily established in these areas and may require site conditioning before installation occurs.
The living shorelines depicted here use species and designs adapted to the Gulf and East coasts of the
United States which are generally considered lower energy systems. Research focuses on determining energy thresholds for different species and techniques would be extremely valuable to the advancement of living shoreline technology. With these thresholds determined, alternative techniques for higher energy systems will soon follow, as will adaptations to different areas of the world.
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Living Shorelines as an Erosion Mitigation Strategy
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