Shoreline Modification Research Articles

Quantifying the impacts of future shoreline modification on biodiversity in a case study of coastal Georgia, United States.

People often modify the shoreline to mitigate erosion and protect property from storm impacts. The 2 main approaches to modification are gray infrastructure (e.g., bulkheads and seawalls) and natural or green infrastructure (NI) (e.g., living shorelines). Gray infrastructure is still more often used for coastal protection than NI, despite having more detrimental effects on ecosystem parameters, such as biodiversity. We assessed the impact of gray infrastructure on biodiversity and whether the adoption of NI can mitigate its loss. We examined the literature to quantify the relationship of gray infrastructure and NI to biodiversity and developed a model with temporal geospatial data on ecosystem distribution and shoreline modification to project future shoreline modification for our study location, coastal Georgia (United States). We applied the literature-derived empirical relationships of infrastructure effects on biodiversity to the shoreline modification projections to predict change in biodiversity under different NI versus gray infrastructure scenarios. For our study area, which is dominated by marshes and use of gray infrastructure, when just under half of all new coastal infrastructure was to be NI, previous losses of biodiversity from gray infrastructure could be mitigated by 2100 (net change of biodiversity of +0.14%, 95% confidence interval -0.10% to +0.39%). As biodiversity continues to decline from human impacts, it is increasingly imperative to minimize negative impacts when possible. We therefore suggest policy and the permitting process be changed to promote the adoption of NI.

Property owner shoreline modification decisions vary based on their perceptions of shoreline change and interests in ecological benefits

Even under current sea level conditions, many communities are working to protect their coastlines against flooding and shoreline erosion. Coastal communities often protect their shorelines against excessive erosion by using armoring techniques (e.g., bulkheads, riprap). Yet hardened structures reduce many of the natural adaptive mechanisms present in coastal ecosystems and reduce the sustainability of the coastal system. In contrast, natural and nature-based features (e.g., living shorelines) can better protect coastal properties from storm damage and reduce erosion while also having the potential to adapt to new conditions. Since property owners are installing armoring structures more often than living shorelines, we sought to understand the factors motivating their shoreline modification decision. We surveyed property owners in Virginia, U.S. that applied for a shoreline modification permit. Most property owners, regardless of modification sought, perceive riprap revetment to be effective, able to withstand storm damage, and able to adapt to sea level rise. Interestingly, property owners that sought out living shorelines were not highly confident in living shorelines’ protection benefits. While most property owners perceived the ecological benefits of living shorelines, these benefits did not substantially impact the decision over what type of shoreline modification to implement. Our work highlights pathways that can improve coastal resilience given the important role that shoreline property owner decisions contribute to coastal community resiliency. Our results indicate there is a need to better engage property owners about the protection and adaptation benefits of living shorelines as their perceptions were not aligned with scientific assessments of living shorelines. Concurrently, coastal policies could be strengthened to support more natural approaches to shoreline management, as the more common armoring techniques are not resilient to sea level rise or storm damage.

Improved geospatial analysis of shoreline modification using a weighted‐average‐based novel formulation

AbstractThis study presents a novel weighted‐average method (WAM) that captures the detailed nuances of shoreline change patterns over long and short periods by considering shorelines belonging to five different time frames. Using the WAM, the average shoreline modification for the longer period (136 years with intervals of ~34 years) and for the shorter period (annual changes over a period of 5 years) have been calculated for the 9 km stretch of the Kollam coast in Kerala, India. Historically, Kollam has been a prominent seaport on the Malabar Coast of India and was extensively mapped due to its importance for political, strategic, and trade reasons. The coastal information available in these older maps is unique as there are no comparable data for the coastline of that period that can be used to assess changes along the coast. The WAM demonstrated the efficacy of the historical maps as pivotal reference points. It reliably captured the different shoreline activities (i.e., growing, stable, and receding regions) of natural and anthropogenic origins within the study area, and the findings are consistent with results obtained by using the linear regression rate (LRR) and the end point rate (EPR) methods. This work presents both qualitative and quantitative analyses to evaluate shoreline change using various statistical and mathematical methods. The findings should serve as baseline information for coastal management, notably mitigating coastal hazards—whether of natural or anthropogenic origin—which could result in the enhancement of ecosystem services for coastal communities.

Quantifying the Impacts of Future Shoreline Modification on Biodiversity: An Exploration of Coastal Georgia

Quantifying the Impacts of Future Shoreline Modification on Biodiversity: An Exploration of Coastal Georgia

Responses to Lake Michigan water level rise: Trends in exposed sand cover at North Avenue Beach, Chicago

From 2013 to 2020, water levels in Lake Michigan rose from an all-time low to the highest levels observed in nearly four decades, causing shoreline changes throughout the Great Lakes. These changes are particularly noticeable at North Avenue Beach in Chicago, an artificial beach where federal, state, and city agencies have mitigated rising waters by importing sand and constructing groins. Using spring season aerial imagery from 2012 to 2020, we calculated beach area for each year and compared sand cover loss between years to water level change per the USGS station located just south of the study area. Analysis reveals year-to-year loss in sand cover since 2013, with the largest single-year change occurring between 2018 and 2019. An inverse relationship with a slight lag exists between water level and these beach area changes. We calculated sand-groin distances from 2000 to 2020 to identify north–south effects. Of the six beach cells separated by groins, the northernmost two cells failed over the study period, and experienced the largest individual sand-groin distance losses. We modeled inundation to investigate whether the sand loss was explainable by lake level change alone, with particular attention given to hardened shoreline implemented north of the beach in 2015. Observed sand cover loss markedly exceeded predictions from the inundation modeling. In addition to water level changes, a local response to shoreline modification and obstruction of sediment transport at this site may influence sand cover.

Shifting Baselines May Undermine Shoreline Management Efforts in the United States

Rising sea levels, extreme weather events, and unsustainable coastal zone development pose serious threats to growing coastal communities. Human actions, such as shoreline development and hardening in at-risk areas, can damage nearshore ecosystems and exacerbate existing risks to coastal populations. A comprehensive understanding of shoreline changes in response to development, storm events, and sea-level rise is needed to effectively mitigate coastal hazards and promote adaptive and resilient coastlines. To determine whether human modification of shorelines can be accurately quantified and assessed over time, we evaluated past and present shoreline mapping and classification efforts in the United States. We coupled a review of available US shoreline data with a survey of coastal planners and managers involved with US state shoreline mapping programs. Using these data, we estimated the current extent of shoreline modification along the Atlantic, Pacific, and Gulf US coasts. However, we found that quantifying shoreline modifications over time nationally—or even within a single state—is currently infeasible due to changes in shoreline resolution associated with advances in shoreline mapping methodologies and a lack of regularly updated shoreline maps. State-level analysis from surveys revealed that 20 US coastal states have undertaken shoreline mapping projects, with sixteen tracking shoreline type and/or condition. However, of the 36 shoreline maps and databases identified, only half (18) were updated regularly or had planned updates. Lacking shoreline change data, coastal communities risk accepting increasingly degraded coastal zones and making poor management decisions based on shifted baselines. Thus, we recommend increasing the scale and funding for several ongoing innovative shoreline mapping efforts. These efforts are particularly focused on improving and standardizing shoreline mapping techniques, as well as establishing accurate baselines for shoreline conditions in the United States. Without accurate baselines and regular, consistent updates to shoreline data, managers cannot manage shorelines in a way that effectively mitigates coastal hazards while also promoting socio-ecological resilience in a changing climate.

Effectiveness monitoring of juvenile Chinook salmon restoration projects in south Lake Washington, Washington State

Tabor RA, Liermann MC, Gearns HA, Moore ZJ, Lynch KD, Kurko K, Crittenden J, Shoemaker ME. 2022. Effectiveness monitoring of juvenile Chinook salmon restoration projects in south Lake Washington, Washington State. Lake Reserv Manage. 38:180–196. We evaluated 4 large restoration projects in south Lake Washington that were designed to improve nearshore habitat for lake-rearing juvenile Chinook salmon (Oncorhynchus tshawytscha). Restoration projects included shoreline modification, substrate enhancement, addition of engineered log jams (ELJs), and nonnatal tributary improvements. For most projects, we used a BACI (before-after-control-impact) study design. Projects were evaluated by determining the nighttime abundance of juvenile Chinook salmon through visual observations (primarily snorkeling with some surface observations in small nonnatal tributaries). Juvenile Chinook salmon are typically concentrated in the south end of the lake near their natal stream, and the project that was the farthest away from the natal stream did not appear to be beneficial, likely because few Chinook salmon were present. The highest observed abundance of juvenile Chinook salmon was associated with ELJs, where the abundance in February to April was typically 2 to 5 times higher than along adjacent, open shorelines. From January to April, juvenile Chinook salmon were usually more abundant in a daylighted nonnatal tributary (i.e., reconfigured from an unusable underground culvert to a more natural stream channel at the surface) than in 2 reference sites. Overall, all 4 project types improved juvenile use of the restored area, with substrate enhancement generally having the weakest response and ELJs the strongest response. Although most restoration projects for salmonids in the Pacific Northwest have focused on lotic systems, our results suggest projects in lentic systems may also be beneficial and should be considered by land-use managers. Supplemental data for this article is available online at https://doi.org/10.1080/10402381.2022.2027054 .

Engineering and design of the Lightning Point Shoreline Restoration Project in Bayou La Batre, Alabama

Lightning Point, located in Alabama at the confluence of the Bayou La Batre navigation channel and Mississippi Sound, is a culturally and ecologically valuable site with an extensive history of shoreline erosion. Between 1916 and 2019, the shoreline experienced approximately 750 to 1,000 ft of shoreline retreat as a result of severe weather events and anthropogenic causes such as shoreline modification and response efforts related to the Deepwater Horizon oil spill. Moffatt & Nichol worked with The Nature Conservancy to restore the lost habitat and resources through ecology-based engineering and design. The Lightning Point Shoreline Restoration Project is a 1-milelong living shoreline that includes approximately 4,700 ft of segmented, overlapping breakwaters, 40 acres of marsh and upland habitat creation, and 10,000 linear feet of tidal creeks. The project was designed to include a diversity of habitat types (subtidal, intertidal, higher scrub-shrub) and to serve as a resilient restoration solution capable of adapting in the face of sea level rise and increasing storm activity.

Evaluating the feasibility and advantage of a multi-purpose submerged breakwater for harbor protection and benthic habitat enhancement at Kahului Commercial Harbor, Hawai\u2018i: case study

Construction of breakwaters provides an engineering solution for coastal protection. However, little effort has been made toward understanding the ecological impact on local coral reef ecosystems and developing engineering structures that would enhance the coral reef environment. A submerged breakwater proposed for Kahului Commercial Harbor, Hawai‘i, provided an opportunity to design a multi-purpose ‘reef structure’ to mitigate wave impacts while providing new coral reef habitat. This design involved ecological and environmental considerations alongside engineering principles, serving as a model for environmentally sound harbor development. This field study evaluated environmental conditions and reef community composition at the proposed site in a gradient extending outward from the harbor, using in situ data with multivariate analyses. Benthic and topographic features in the area were assessed using a towed drop camera system to relate to biological factors. Results that support breakwater topography should follow the natural spur and groove and depth of the adjacent reef and orient with wave direction. A deep area characterized by unconsolidated substrata and low coral cover would be replaced with the shallow, sloping hard bottom of the breakwater, and provide an exemplary area for corals to flourish while protecting the harbor from large ocean swells. Surfaces on shallow sloping hard bottoms receive higher levels of irradiance that benefits coral growth. Optimal levels of water motion facilitate sediment removal and promote coral recruitment and growth. The design of the Kahului Harbor submerged multi-purpose structure serves as a model for design of shoreline modification that enhances, rather than degrades, the local coral reef environment.

Natural vs. Anthropic Influence on the Multidecadal Shoreline Changes of Mediterranean Urban Beaches: Lessons from the Gulf of Cagliari (Sardinia)

Urban Mediterranean beaches are often characterized by a fragile and unstable equilibrium that can be easily altered by ongoing climate change and by the increase in human pressure. This may pose serious threats to the survival of beach systems that cannot accommodate these modifications. In this paper, the spatio-temporal shift of the shoreline was investigated along two urban beaches in the Gulf of Cagliari (Poetto and Giorgino; southern Sardinia, western Mediterranean Sea) across a time frame of 62 years (1954–2016). The Digital Shoreline Analysis System (DSAS) ArcGIS™ extension was used to extract different statistical parameters which allowed us to quantify the erosion and accretion rates. These data were further examined in relation to a number of anthropic and natural forcings in order to disentangle the factors controlling shoreline evolution. Eight sectors with interchanging net erosive and accretion trends were identified along the Poetto and Giorgino beaches. In six decades, some sectors of the two study sites appeared to have undergone great shoreline modification as a result of the intense anthropogenic activities impacting these coastal areas. The westernmost portions of both beaches were found to be the most vulnerable to erosion processes; such conditions were likely controlled by the interplaying of local hydrodynamics and by the intense coastal development which affected these sectors. The highest retreat rates (mean end point rate (EPR) = −0.51/year) were recorded in the western limit of Giorgino beach. Along the western limit of Poetto beach, EPR erosion rates (mean EPR = −2.92/year) considerably increased in the years after the artificial beach nourishment carried out in 2002, suggesting that the majority of the nourished material was lost offshore or partly redistributed along the beach. Coastal structures, urban development, river catchment modification, industrial and port activities, beach cleaning and touristic and recreational activities have been identified as the ongoing causes of coastal alteration. If these factors remain constant, under projected climate change scenarios, these beaches are at risk of further increased flooding and erosion. In this context, the application of DSAS appeared as an essential tool, supporting a monitoring system able to provide understanding and, potentially, predictions of the short- to long-term evolution of these beach systems.

Shoreline modification affects recruitment of invasive Phragmites australis

Shoreline hardening affects ecological processes in nearshore intertidal ecosystems and upland habitats. Invasive species establishment and spread is one consequence of shoreline alterations. Invasive Phragmites australis has spread throughout the U.S., including in subestuaries with hardened shorelines. It is unclear, though, by what mechanisms shoreline hardening facilitates P. australis establishment. We tested the hypothesis that shoreline structures are associated with seedling recruitment, resulting in higher levels of within stand genetic diversity. We used microsatellite analysis to examine the genetic diversity of P. australis stands associated with two types of shoreline structures (riprap, bulkhead revetments) compared to unaltered shorelines. Because P. australis seed viability depends on cross-pollination, higher levels of genetic diversity in stands associated with hardened shorelines are more likely to contribute to the spread of invasive P. australis. We conclude that the extent of shoreline modifications in the Chesapeake Bay has contributed to the spread of P. australis by seeds. The results have implications for the management of P. australis associated with the establishment of shoreline structures.

Encouraging Living Shorelines over Shoreline Armoring: Insights from Property Owners Choices in the Chesapeake Bay

This study uses data from shoreline modification permit applications in Gloucester County, Virginia to provide insights into how coastal managers can encourage the use of living shorelines over shoreline armoring. The data show that shorelines are more likely to be modified on properties with high neighboring property values and properties threatened by hurricane storm surge and high wave energy, while modifications are less likely in conservation areas and areas with high percentages of natural cover and agricultural use. Compared to armoring, living shorelines are more likely in FEMA Special Flood Hazard Areas and following recent flooding experiences but are less likely to be installed following an FEMA disaster declaration. Property owners are also significantly more likely to install a specific modification if their neighbors have already installed that modification. Based on these results, coastal managers may be able to increase the effectiveness of interventions to reduce shoreline modification by targeting unmodified high value properties in residential areas with high wave energy. To encourage property owners to install living shorelines over armoring, the results suggest that coastal managers should target properties with armored neighbors or properties in business zones and should develop interventions directly following significant storm events.

What Drives Property Owners to Modify Their Shorelines? A Case Study of Gloucester County, Virginia

This analysis uses data from a survey of shoreline property owners combined with data on shoreline modification permits to examine whether and how property owners modify their estuarine shorelines. We find that shoreline armoring is very popular among property owners that choose to modify their shoreline. While living shorelines are less common, applications for them are increasing both in absolute numbers and as a percentage of all shoreline modification requests. A number of different issues factor into the shoreline modification decision including effectiveness, cost, aesthetics, and property values. More valuable parcels are more likely to be modified, as are parcels that have been owned longer. Parcels with a high percentage of natural cover or agricultural use are less likely to be modified. Parcels with primary structures that are closer to the shoreline are more likely to have some sort of armoring. Regardless of their choice of shoreline modification, almost all survey respondents believe that their choices have had a neutral or positive impact on erosion and the health of the Chesapeake Bay.

Seawall as salmon habitat: Eco-engineering improves the distribution and foraging of juvenile Pacific salmon

Urban nearshore ecosystems are built environments that differ structurally and functionally from the natural ecosystems they replace. Eco-engineering offers the ability to enhance these ecosystems by reducing the impacts of shoreline modification. Recent studies have linked shoreline armoring and pier shade—common features of modified shorelines—to lower foraging rates, altered distribution patterns, and increased predation risk for juvenile salmon. The 2017 replacement of the Elliott Bay seawall in Seattle, WA, USA incorporated novel eco-engineering design elements, including glass light penetrating surfaces (LPS) in overwater structures, an elevated seafloor, and textured substrates in the seawall face to enhance nearshore habitat for juvenile Pacific salmon (Oncorhynchus spp.) migrating from natal streams to the ocean. To examine the effectiveness of seawall eco-engineering, we used snorkel surveys to assess changes in juvenile salmon spatial distribution and foraging patterns during peak outmigration (March–August), and measured ambient light penetration before and after seawall replacement. Overall, we found that juvenile salmon were distributed more evenly across a spatial mosaic of habitats following eco-engineering. LPS enhanced ambient light penetration in nearshore under-pier habitats, and juvenile salmon use of these habitats increased concurrently. Salmon densities under piers tended to be greatest at low tides, indicating that light availability may mediate selective habitat use. Feeding rates at sites immediately adjacent to the seawall increased both between and under piers following habitat enhancement. Our findings suggest that the elevated light levels facilitated by LPS, in concert with physical enhancements that provided more complex shallow water habitat, temper the negative effects of pier shade and shoreline armoring on juvenile salmon.

Shoreline infrastructure degradation and increasing littoral naturalization accommodates juvenile fish and crab assemblages in heavily urbanized Upper New York Harbor

Many estuarine shorelines are influenced by urbanization. Extensive shoreline modification in Upper New York Harbor (UNYH) included port development, landfilling marshes, and armoring. Recent sedimentation in constructed shipping terminal embayments, abandonment of shoreline structure maintenance, subsequent recruitment of upland and intertidal vegetation, and restoration projects have naturalized some shorelines in this urban setting. We determined the species composition and relative abundance of fishes and crabs in shallow shoreline habitats in constructed embayments of UNYH with seine sampling to determine the potential for restoring similar isolated shallow water sites as functional habitats. Twenty‐seven identified species of fishes and crabs, including seasonally transient and resident marsh species, were represented in samples dominated by Menidia menidia, but marsh resident and coastal ocean species were also periodically abundant. Differences in assemblage structure among the sampled embayments as measured by principal components analysis were weak despite some differences in the slope and colonization of vegetation along shorelines. The mere presence of shallow shorelines was sufficient to recruit numerous species. Assemblage differences relative to a nearby relatively unaltered estuary revealed a lack of southern, warm affiliated species reflecting a natural clinal gradient. Marsh resident species dominated in UNYH, but not as strongly as at the reference estuary. Together with a previously published evaluation of life cycle connectivity for several sentinel species, this study shows that even small, isolated projects seeking to restore shallow shorelines add value to the estuarine landscape and are worth pursuing.

Shoreline Change Observations in Gulf of Khambhat using Satellite Images

Sea shore or shoreline modification is one of the most common concern among natural processes that prevail upon coastal areas. The most important aspect in coastal areas is identifying the location and change over time of shoreline. This can be accomplished by frequent monitoring of the shoreline using satellite imagery over time. This study will evaluate short term shoreline modification from 2016 to 2018 in half yearly interval in Gulf of Khambhat. Following analysis is carried out using ArcGIS and Remote Sensing datasets from USGS. The proposed study and map prepared in the research will contribute to shoreline protection measures. This work will useful for forecasting the future trends and planning mitigation measures.

Coastal development and mangroves in Abu Dhabi, UAE

Mangrove forests are widely distributed in Asia, America, and Africa. These salt-tolerant bushes or trees grow at the intersection of fresh and saline waters in tidal lagoons, estuaries, and deltas creating rich ecosystems. They are used by communities for wood, and fish and shellfish harvesting, and they play an important role in soil stabilization and wave and flood modification by absorbing storm surges protecting coastal communities. Mangroves are threatened by human activities that include discharge of untreated wastewater that creates hypoxic conditions; structures, which interfere with material deposition and current circulation; and ship and boat movement, which create wake waves, or introduce ballast water. The highly salt tolerant species of Avicennia marina covers about 155 km2 of the Abu Dhabi shoreline. Mangroves’ existence in some locations there is endangered by the intense coastal development and engineered shoreline modification taking place. Cement factories with heavy metal and other particle sea deposition; marinas, ports, canals, and seawalls constructed to provide residential sea views, and motorized boats modify hydrodynamic conditions and affect the settling of particles directing them seaward. Finally, the dredging that accompanies construction removes benthic communities and material modifying the seabed and may create conditions adverse to mangrove survival.

Artificial wave breakers promote the establishment of alien aquatic plants in a shallow lake

We surveyed the occurrence of three emergent alien aquatic plants, Gymnocoronis spilanthoides, Alternanthera sessilis, and Alternanthera philoxeroides, in Lake Kasumigaura from 2013 to 2017. To determine the effects of shoreline modification on the expansion of alien aquatic plants, we compared the relative occurrence of alien aquatic plants in varying shoreline conditions modified by shoreline hardening and wave breakers. The distribution of alien aquatic species increased continually in Lake Kasumigaura over the study period, although the rate of expansion differed among years. Furthermore > 64.6% of the vegetative fragments were found within 2 km of the nearest patch. The construction of artificial wave breakers, which were installed parallel to the shoreline, had a positive influence on alien aquatic plant patch establishment. Especially, parallel wave breakers increased the patch establishment of G. spilanthoides by about 2.27-fold compared to the natural environment. Perpendicular wave breakers increased alien patch establishment by about 1.63-fold. For lakeshore management, it is important to consider both alien plant suppression and levee protection. We further suggest prompt action to prevent the expansion of alien aquatic species around pumping stations, which can also result in the relocation and expansion of invasive species.

Effects of Long-Term Anthropogenic Disturbance on the Benthic Episammic Diatom Community of an Ancient, Tropical Lake.

Habitat homogenization, nutrient enrichment and loss of biodiversity are broadly recognized as the consequences of human activity in aquatic systems. Diatoms (Bacillariophyceae) are frequently used in aquatic environmental assessment and impact monitoring, but in unique habitats dominated by endemic taxa, traditional approaches may not be appropriate. We examined the impacts of long term anthropogenic impacts upon the littoral episammic diatom community around the town of Soroako, located on Lake Matano, an ancient tropical lake. Lake Matano is located on central Sulawesi Island, Indonesia, and socio-economic conditions are typical of developing nations. Although differences in nutrient concentrations were undetectable with field-based spectroscopy approaches, mean Shannon diversity was decreased in association with proximity the town-site. However, mean ß-diversity was maintained despite several decades of shoreline modification at Soroako. Elevated abundances of early-successional diatom taxa in the disturbed area drove differences between areas immediately offshore of Soroako and those farther away. These findings suggest that increased physical disturbance and TSS loads around Soroako, rather than increased nutrient loading, influenced shifts in the diatom community. These results suggest that microscopy-based biomonitoring approaches are sensitive indicators of environmental modification that could be useful in areas where access to cutting-edge analytical equipment is limited.

Tracking shoreline evolution in central Cyclades (Greece) using beachrocks

Beachrocks represent a significant paleo-environmental proxy because they can record both the vertical and the horizontal evolution of the shoreline. They have often been used to assess Holocene shoreline evolution and crustally induced Relative Sea-Level (RSL) changes in the Mediterranean Sea. In this paper, we used submerged beachrocks from Paros and Naxos Islands (Aegean Sea, Greece) to reconstruct the shoreline modification and provide new insights on the RSL evolution in central Cyclades. Paros and Naxos Islands are of great importance in terms of archaeological evidence of coastal occupation. However, the evolution of their coastlines was seldom explored. In this study, we coupled detailed underwater surveys, analysis of aerial photogrammetry, microstratigraphic analysis and luminescence dating to study beachrock outcrops found down to about 6m below the present sea-level. We, then, spatially and chronologically constrained some major palaeogeographical changes of a number of coastal sectors of the two islands. Furthermore, the multiple analyses of beachrocks, sediment coring and archaeological data suggested that RSL rose by at least 3.8m in the last 4.0ka and that RSL variation in the last 2.0ka did not exceed 2m with respect to the present mean sea level.