Seawall Construction Research Articles

Seawall construction alters soil carbon and nitrogen dynamics and soil microbial biomass in an invasive Spartina alterniflora salt marsh in eastern China

Seawalls have increasingly been constructed to control the invasion of an exotic perennial grass, Spartina alterniflora, in coastal wetlands of eastern China. We investigated soil organic carbon (C) and nitrogen (N), available and microbial C and N, soil microbial community composition and biomass in a seawall-reclaimed S. alterniflora salt marsh compared with an adjacent natural S. alterniflora salt marsh. Seawall reclamation in S. alterniflora salt marsh significantly decreased soil salinity, moisture, litter and root biomass, and strongly decreased soil total organic C by 57% and total organic N by 59%, and also lowered soil available C and N in S. alterniflora salt marsh. Seawall reclamation significantly decreased soil microbial biomass C and the quantities of the total phospholipid fatty acids (PLFAs), and bacterial, fungal, gram-negative bacterial, gram-positive bacterial, saturated straight-chain, and monounsaturated PLFAs in deeper soil layers (10–30cm). Our results suggested that seawall construction could greatly decrease soil C and N accumulation of S. alterniflora salt marsh by decreasing S. alterniflora residuals input into the soil and lowering soil salinity and moisture, which further decreased soil microbial biomass by lowering soil available C and N in S. alterniflora salt marsh. Changes in soil microbial community composition and biomass could in turn affect soil C and N accumulation in a seawall-reclaimed S. alterniflora salt marsh in eastern China.

Influence of near-shore marine structures in a beach nourishment project on tidal currents in Haitan Bay, facing the Taiwan Strait

The Longfengtou Beach in the Haitan Bay, located in Fujian Province of China and facing the Haitan Strait, has been suffering severe erosion due to the construction of seawalls. A simple beach nourishment project implemented has not achieved the anticipated beach restoration. Thus a practical solution has to rely on a combination with near-shore marine structures. In this study, a 2-D calibrated flow model is set up to investigate the effects of three different layouts of near-shore marine structures on the tidal current. It is shown that the breakwaters situated in both the north and south ends play a vital part in the protection against erosion. The offshore breakwaters can serve as a barrier to obstruct the current circulation then reduce the current velocity. The groyne linking the Guimo islet and the coast significantly reduces the south-to-north water exchange through the channel and redirects the current direction nearly perpendicular to the north breakwater, which cuts off the longshore transport that may have a negative influence on the beach, especially, the northern part. It is also noted that the monsoon at the site with different directions increases the current velocity. In general, proper layouts of marine structures can reduce the current velocity thus lead to less intense sand transport near the beach.

Reclamation of tidal flats and shorebird declines in Saemangeum and elsewhere in the Republic of Korea

Saemangeum, in the Republic of Korea (ROK, commonly called South Korea) was one of the most important shorebird staging sites in the Yellow Sea. It supported at least 330 000 shorebirds annually between 1997 and 2001, including ∼30% of the world population of Great Knots (Calidris tenuirostris) during both northward and southward migration. Construction of a 33-km long sea-wall was completed in April 2006. We show that shorebird numbers at Saemangeum and two adjacent wetlands decreased by 130 000 during northward migration in the next two years and that all species have declined at Saemangeum since completion of the sea-wall. Great Knots were among the most rapidly affected species. Fewer than 5000 shorebirds were recorded at Saemangeum during northward migration in 2014. We found no evidence to suggest that most shorebirds of any species displaced from Saemangeum successfully relocated to other sites in the ROK. Instead, by 2011–13 nearly all species had declined substantially in the ROK since previous national surveys in 1998 and 2008, especially at more heavily reclaimed sites. It is likely that these declines were driven by increased mortality rather than movement to alternate staging sites given that other studies have shown concurrent declines in numbers and survival on the non-breeding grounds. This is the first study in the East Asian—Australasian Flyway to confirm declines of shorebirds at a range of geographical scales following a single reclamation project. The results indicate that if migratory shorebirds are displaced from major staging sites by reclamation they are probably unable to relocate successfully to alternate sites.

Master Plan Jakarta, Indonesia: The Giant Seawall and the need for structural treatment of municipal waste water

In order to take actions against the annual flooding in Jakarta, the construction of a Giant Seawall has been proposed in the Master Plan for National Capital Integrated Coastal Development. The seawall provides a combination of technical solutions against flooding, but these will heavily modify the mass transports in the near-coastal area of Jakarta Bay. This study presents numerical simulations of river flux of total nitrogen and N,N-diethyl-m-toluamide, a molecular tracer for municipal waste water for similar scenarios as described in the Master Plan. Model results demonstrate a strong accumulation of municipal wastes and nutrients in the planned reservoirs to extremely high levels which will result in drastic adverse eutrophication effects if the treatment of municipal waste water is not dealt with in the same priority as the construction of the Giant Seawall.

Inter-annual Variation of Tides on the Western Coasts of Korea

서해 연안해역에서 국립해양조사원이 관측한 기왕의 조위자료를 분석하여 조석 조화상수를 ì‚°ì¶œí•˜ê³ , 조화상수와 비조화상수의 변화추세와 원인을 ê³ ì°°í•˜ì˜€ë‹¤. ì „ë°˜ì ìœ¼ë¡œ 반일주조의 진폭은 거의 변화하지 않았으나 위상은 빨라졌으며, 일주조의 진폭과 위상은 거의 변화하지 않았다. 그러나 내만에 위치한 목포에서는 하구언과 ë°©ì¡°ì œ 건설로 인해서 반일주조의 진폭은 크게 ì¦ê°€í•˜ê³ , 위상은 크게 빨라졌다. ì „ë°˜ì ìœ¼ë¡œ 일주조의 진폭과 위상은 변화하지 않았으나, 목포에서만 위상이 ëšœë ·í•˜ê²Œ 빨라졌다. 대조기 조석간만의 차는 목포를 ì œì™¸í•˜ê³ ëŠ” 크게 변화하지 않았으며, 목포에서는 조석확폭 현상으로 조차가 ì¦ê°€í•˜ê³ , 간사지의 폭이 넓어졌다. ì•½ìµœê³ ê³ ì¡°ìœ„ëŠ” ì „ë°˜ì ìœ¼ë¡œ 과거에 비해서 상승하여 서해 연안에서 범람으로 인한 위험성이 ì¦ê°€í•˜ê³ ìžˆì—ˆë‹¤. ì•½ìµœê³ ê³ ì¡°ìœ„ì™€ ì•½ìµœì €ì €ì¡°ìœ„ì˜ 변화는 í‰ê· í•´ìˆ˜ë©´ 상승과 ë°€ì ‘í•œ 관계를 ê°€ì§€ê³ ìžˆì—ˆë‹¤. 핵심용어: 서해안 조석, 조화상수, ì¡°ì°¨, 설계조위

Attitudes toward disaster-prevention risk in Japanese coastal areas: analysis of civil preference

Facing potential coastal disasters such as storm surges, storm waves, and tsunamis, Japan has planned the construction of coastal structures such as seawalls or breakwaters along its coastal areas. However, some conflicts exist among the public whether such constructions should be undertaken or whether the natural coast should be conserved. This study uses a choice experiment to investigate opinions of coastal citizens about (1) the acceptable loss of coastal wildlife species as a tradeoff for seawalls; (2) the willingness to pay (WTP) for conservation of coastal wildlife as a compromise for disaster risk reduction; (3) the influence on popular preferences in coastal management of individual characteristics, such as frequency of visiting the sea and public recognition of disaster risk; and (4) civil trust in scientific information. The survey was conducted among 7496 respondents in municipalities around the Japanese coast. As a result, the acceptable loss of coastal wildlife species was 18.7 %. The marginal WTP for conserving the coastal wildlife was 680.95 JPY per percent in the number of species per capita. We found that people who frequently visit the sea preferred ecosystem conservation and disliked seawall construction, whereas people strongly recognizing disaster risks preferred seawall construction. Furthermore, we found that civil trust in scientific information affects civil preferences regarding coastal management. Our study indicates the need to reduce negative effects of coastal constructions on coastal ecosystems and to consider other options, such as ecosystem-based disaster risk reduction. It also indicates the social influences of raising public trust in scientific information to enable citizens to make better decisions regarding coastal management.

When a Seawall Is Visible: Infrastructure and Obstruction in Post-tsunami Reconstruction in Japan

The triple disaster of March 11, 2011 posed a formidable challenge for Japanese society in general, and for affected coastal communities in particular. In the immediate aftermath of the catastrophe, there was widespread support for the construction of high seawalls to protect communities. However, many communities began questioning this approach. In Maehama, the question of land reconstruction and protection gave rise to a set of complex responses. The government aimed to put in place even higher seawalls; however, the local community proposed instead to mark the boundary of high water with trees and stakes. These solutions instantiate different ways of infrastructuring the post-tsunami environment for safety; they carry different assumptions about infrastructure itself. Whereas the seawall solution was technical and quantitative, centering on the question of height, the boundary markers embedded qualitatively different assumptions about what makes a workable infrastructure. In particular, this difference centered on issue of visibility. On the one hand, the seawall was meant to slowly become unremarkable, whereas the boundary markers were specifically intended to maintain community memory. On the other hand, the seawall would make the sea itself invisible, whereas keeping the sea in sight is very important to villagers. However, the opposition between these forms of infrastructuring the environment was not total. A solution was gradually negotiated in which the sea wall and the boundary markers could complement each another. This situation highlights the intricate, transformable relation between visible and invisible forms of infrastructure.

Destruction or persistence of coral atoll islands in the face of 20th and 21st century sea‐level rise?

The future of low‐lying reef islands has been the subject of international concern, scientific debate, and media interest in the last decade. As a result of sea‐level rise, atoll islands are expected to become increasingly unstable and to be susceptible to potential depopulation by the end of the 21st century. Some have suggested that sea‐level rise has already resulted in widespread erosion and inundation of atoll islands. Here, we analyze the physical changes in over 200 islands on 12 atolls in the central and western Pacific in the past few decades when sea level in the region increased at rates three to four times the global average. Results show little evidence of heightened erosion or reduction in island size. Instead island shores have adjusted their position and morphology in response to human impacts such as seawall construction and to variations in climate–ocean processes. These changes are reviewed and the role of sea‐level rise is evaluated. The implications of this analysis are addressed in two parts. First, we consider the proposition that future sea‐level rise will destabilize atoll islands to such an extent that their inhabitants will be forced to migrate offshore. And second, we identify a series of new challenges relating to risk reduction and adaptation policy for atoll island governments, international agencies, and island communities. These require a substantial shift away from the present adaptation paradigm of external migration and focus on the persistence of atoll islands and in‐country solutions. WIREs Clim Change 2015, 6:445–463. doi: 10.1002/wcc.350This article is categorized under: Paleoclimates and Current Trends > Earth System Behavior Assessing Impacts of Climate Change > Evaluating Future Impacts of Climate Change Vulnerability and Adaptation to Climate Change > Learning from Cases and Analogies

Detecting Flood Variations in Shanghai over 1949–2009 with Mann-Kendall Tests and a Newspaper-Based Database

A valuable aid to assessing and managing flood risk lies in a reliable database of historical floods. In this study, a newspaper-based flood database for Shanghai (NFDS) for the period 1949–2009 was developed through a systematic scanning of newspapers. After calibration and validation of the database, Mann-Kendall tests and correlation analysis were applied to detect possible changes in flood frequencies. The analysis was carried out for three different flood types: overbank flood, agricultural waterlogging, and urban waterlogging. The compiled NFDS registered 146 floods and 92% of them occurred in the flood-prone season from June to September. The statistical analyses showed that both the annual flood and the floods in June–August increased significantly. Urban waterlogging showed a very strong increasing trend, probably because of insufficient capacity of urban drainage system and impacts of rapid urbanization. By contrast, the decrease in overbank flooding and the slight increase in agricultural waterlogging were likely because of the construction of river levees and seawalls and the upgrade of agricultural drainage systems, respectively. This study demonstrated the usefulness of local newspapers in building a historical flood database and in assessing flood characterization.

Consideration for effective height of sea walls against tsunami

Tsunami wave height data at several sites in Tohoku district in Japan were examined and an empirical extreme value distribution with both upper and lower bounds was applied to model the cumulative probability distribution function of annual maximum wave height. Then by estimating the construction cost of sea walls against the tsunami and the expected damage cost due to a tsunami attack, the expected total cost was studied. Observation of the tendency of expected total cost with the design height of a sea wall indicates that sea wall construction is not economically justified, unless the height exceeds the upper bound of tsunami wave height.

Rising tides: adaptation policy alternatives for coastal residential buildings in Australia

In this work, a risk-based assessment method and benefit-cost analysis to support policy decisions for adapting Australian coastal residential buildings to future coastal inundation hazard is presented. Future coastal inundation is mainly influenced by storm surge and rising sea level. The sea level rises projected by the A1FI, A1B and B1 emissions scenarios developed by the Intergovernmental Panel on Climate Change are considered. The effects of economic and population growth are accounted for by three urban development scenarios: (a) business as usual, (b) urban consolidation and (c) regional development. The adaptation policy actions investigated include a ‘protect’ stance (involving the construction of seawalls), an ‘accommodate’ stance that mandates raising house floors to a certain height (e.g. at heights of 100-year events) and an ‘avoid’ stance that limits new developments in hazardous areas. Policy stances classified as reactive (i.e. action taken after damage being incurred) and anticipatory (i.e. action taken anticipating what will happen) are developed for asset investment choices. In general, adaptation costs are an order of magnitude lower than benefits gained from avoided damages. The results highlight that adaptation action for coastal inundation has a no-regrets character and provides a strong case for reform to ensure that Australia-wide adaptation opportunities are realised.

Anthropogenic Effects on Fluxes of Ecosystem Respiration and Methane in the Yellow River Estuary, China

To evaluate the influence of human activities on ecosystem respiration (CO2) and CH4 fluxes and determine the seasonal and spatial variations, we measured CO2 and CH4 fluxes at four sampling sites (west side of the seawall, WSS; oilfield, OF; Spartina alterniflora coastal marsh, SCM; aquaculture pond, ACP) in the Yellow River estuary from June to December in 2013. Both CO2 and CH4 fluxes showed seasonal and spatial variations in the Yellow River estuary. The average CO2 fluxes from WSS, OF, SCM and ACP were 125.36, 111.03, 241.97 and −39.49 mg CO2 m−2 h−1, while CH4 fluxes were −0.0110, −0.0165, 0.2012 and 0.0034 mg CH4 m−2 h−1, respectively. Spatial variations of CO2 and CH4 fluxes were mainly affected by vegetation and soil moisture. There were significant relationships between both CO2 fluxes in WSS and SCM and CH4 flux in SCM with temperature. CO2 and CH4 fluxes were mainly affected by the interactions of thermal conditions and other abiotic factors in OF and ACP. Human activities have great effect on greenhouse gas emission, especially in the area where exotic-species S. alterniflora invaded. The construction of seawall blocked sea water transporting into the study area leading to low soil moisture which accelerated CO2 emission. Aquaculture ponds act as an emission of CH4 and consumption of CO2.

Anthropogenic impact on macrobenthic communities and consequences for shorebirds in Northern France: A complex response

Shorebird populations are declining worldwide due to the combined effect of climate change and anthropogenic forcing, the ongoing coastal urbanisation amplifying the alteration of their habitat in both rate and magnitude. By focusing on a highly anthropogenically-influenced region in Northern France, we studied the impact of a seawall construction on wintering shorebird populations through potential alterations in the abundance and availability of their food resources. We concurrently investigated changes in the spatial distribution of muddy-sand beach macrobenthic communities between two periods of contrasting anthropogenic impacts and examined year-to-year trends of wintering shorebirds. Our study reveals that the seawall construction led to a major spatial reorganisation of the macrobenthic communities with a drastic reduction of the muddy-sand community. However, no relation between macrobenthic changes and shorebird abundances was detected. Fluctuations in shorebird abundances appeared to be congruent with flyway population trends. This result suggests that the response of shorebirds to human-induced perturbations is much more complex than expected. While an assessment of potential disturbances induced by coastal engineering constructions is needed, the pathways by which alterations could propagate through an ecosystem are not linear and as such difficult to determine. Ecosystems appear as complex adaptive systems in which macroscopic dynamics emerge from non-linear interactions at entangled smaller/larger scales. Our results confirm that an in-depth knowledge of the local, regional and global factors that influence trends of shorebirds and their habitat use is essential for accurate and effective management and conservation strategies.

Essential Aspects of Beach Erosion - Lessons from Devastation of Ichinomiya Coast, Japan

The fundamental issues of the beach erosion including the difficulty in social and comprehensive adjustments of the beach erosion were discussed through a case study, taking the Ichinomiya coast on south Kujukuri Beach as an example. On this coast, sand supply from the sea cliffs markedly decreased as a result of the preventive measures against cliff erosion on upcoast, resulting in the downcoast erosion. Artificial headlands have been constructed since the 1990 as a measure against shoreline recession, but this caused further downcoast expansion of the beach erosion. Finally, it became difficult to escape from a vicious cycle of seawall construction - downcoast erosion - seawall construction - downcoast erosion, permitting further expansion of the erosion area. Such difficulties were analyzed.

Pressures on Gabion Boxes as Artificial Reef Units

Naturally occurring shoals and near-shore reefs act as good wave attenuators. Artificial reefs have been looked into as potential solutions for creation of surf waves. Recently, artificial reefs are being examined as soft solutions for coastal protection. Conventional hard approaches like construction of sea wall, groins, revetments, bulkheads and break waters have been successful over the past. However, they may sometimes create adverse impacts on the coastal environment. Thus, employing artificial reefs for shore protection would yield multiple benefits as they attenuate the waves away from shoreline and does not interact with the shoreline directly. Because of this, they are often called multipurpose reefs. Construction of reefs has been primarily based on geo bags and geo tubes. Sometimes, rubble mound construction has been used. However, there are construction and handling difficulties. Hence, gabions may be considered in artificial reefs due to their ease of construction and porous nature. Gabions also reduce the construction time, hence making it suitable to construct during adverse weather window. The porosity of gabions may also add favorable effects on the near shore environment. On the other hand, several installations of artificial reefs over the past decade have faced severe stability issues. Since literatures relevant to artificial reef are scanty, the present study brings out the experimental measurement of pressures on Gabion Boxes as artificial reefs. In order to relate the pressure to stability, pressures are measured over units at critical locations. An attempt has been made to use the measured pressures to obtain forces and thus stability factors of Gabion Box units in reef applications. The pressure measurement is made varying, the reef parameters and wave parameters. The purpose of varying the reef parameters (width of reef and height of the reef) is to come out with the optimum configuration of reef for a given wave climate. The pressure measurement corresponding to a particular reef configuration is presented in the paper.

Shoreline Change Analysis of Mangalore Coast and Morphometric Analysis of Netravathi-Gurupur and Mulky-pavanje Spits

Various developmental projects have come up in the coastal zone of Dakshina Kannada and Udupi districts in the last few decades. A number of beaches are subjected to erosion and lots of coastal properties are destroyed specially during SW monsoon season along the Mangalore coast in recent years. In order to protect the beaches and the properties, a number of seawalls - each ranging in length between 100 m and 2500 m - are built since 1980s. A very few of them built scientifically, but most of them are just dumping of granite blocks directly on the shoreline. In the present study, an attempt is made to understand long-term (1967-2013) shoreline changes as well as erosion / deposition patterns due to natural (including sea-level rise) and anthropogenic activities along this coast. The study area extends from Yermal in the north to Talpady in the south covering a total length of 45.63km. Topomap of 1967 and multi-temporal satellite images have been analyzed using Remote Sensing and GIS techniques to demarcate shoreline positions and to assess the impact of anthropogenic and hydrological factors on coastal morphology of this region. An integrative approach of Remote Sensing and GIS techniques as well as seasonal field studies clearly illustrates the reasons for shoreline and beach morphological changes. Construction of seawalls has resulted in shifting of erosion sites from one place to another adjacent place, whereas, breakwaters have been acting as barriers for littoral drift. Overall, areas subjected to erosion are higher compared to those subjected to accretion in the study area. Applications of Remote Sensing and GIS have led to understanding shoreline and beach morphological changes. These have also provided data analysis tools and methods to evaluate the geospatial patterns in short-term and long-term changes. The results of this study will be useful for shoreline, coastal zone management and implementation of CRZ act.

Rethinking China's new great wall.

Massive seawall construction in coastal wetlands threatens biodiversity

Sedimentary impacts of anthropogenic alterations on the Yeongsan Estuary, South Korea

Abstract Over the last half-century, coastal zones within the Republic of Korea (S. Korea) have experienced a wide range of engineered coastal modifications including construction of seawalls, extensive land reclamation, and installation of estuarine dams. The Yeongsan Estuary has experienced all of these modifications and provides an ideal case study on how sedimentation changes within a macrotidal estuary in response to these alterations. Combined, these alterations have considerably modulated the timing and intensity of river discharge, prevented natural tidal exchange, modified the shoreline profile, and altered the transport of sediment and organic matter within the coastal zone. These impacts have been investigated using 30 gravity cores analyzed for 210 Pb radioisotope geochronology, laser diffraction particle size analyses, δ 13 C and δ 15 N isotope ratio mass spectrometry, and X-radiography. Average sediment accumulation rates range from 0.9 ± 0.6 cm yr − 1 to 10.0 ± 2.9 cm yr − 1 , with the highest rates proximal to the downstream side of the dam, and some areas determined to be either actively eroding or recently dredged. These results are supported by comparison of multiple bathymetric surveys, and CHIRP seismic data suggest an order of magnitude increase from average Holocene sediment accumulation rates. Side scan sonograms collected adjacent to the dam reveal distinctive scouring, transitioning to areas accumulating fine-grained sediments. Shifts in the organic matter source inputs are apparent in pre/post-dam sediments and reflect the occluding of tidal influence above the dam, resulting in increasingly terrestrial dominated signatures. Additionally, a time series of cores collected during periods of limited and high discharge analyzed for 7 Be, indicates sediment deposition occurs episodically corresponding to high discharge dam releases. Our observations record a shift in depositional environments as a response to an extensive array of anthropogenic alterations. Ultimately, land reclamation and dam construction have severely altered the fate and transport of sediment within the estuarine system. As a consequence, sedimentation rates have increased dramatically and depositional events are primarily controlled by discharges from the estuarine dam.

Two-Dimensional Finite Element Analysis of Laboratory Seawall Model

Two-Dimensional finite element analysis was used to investigate the performance of seawall construction over weak subgrade soil using artificial base layer material consisted of cemented sand cushion comprising geosynthetics materials. Two types of base layer materials pure sand and cemented sand comprising husk rich ash and two types of geosynthetics materials geogrid and geotextile were used. Constitutive models were used to represent different materials in numerical analysis. The competence of two-dimensional numerical analysis was compared with experimental results. Numerical results showed a superior harmony with the experimental results. Finite element analysis model proved to be a great tool to determine the parameters that are difficult to measure in laboratory experiments. In addition, finite element analysis has the benefit of cost and time saving when compared to experimental investigation work. Numerical results showed strain induced in geosynthetics eliminated beyond a distance approximately equal six times of footing width.

Are natural beaches facing extinction?

Pilkey, O.H. and Cooper, J.A.G. 2014. Are natural beaches facing extinction? In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa) Journal of Coastal Research, Special Issue, No. 70 pp. 431–436. ISSN 0749-0208.On a generational scale, on developed shorelines, the world's recreational beaches are doomed. This is largely because of the widespread assumption that preservation of buildings is a higher priority than preservation of beaches in response to sea level rise. Continuing beach degradation will be inevitable through active or passive processes. Active degradation means the actual removal of the beach, mostly as a result of shoreline engineering or mining. By far, the most important cause of beach loss in this category will be hard structures, especially seawalls. The incorrectly but widely perceived panacea of each replenishment will become economically impossible because of raised sea levels. Replenishment leads to intensified beachfront development and this ironically and inevitably will increase the future construction of seawalls. Passive degradation refers to reduction of the quality of the beach to the point that human usage drops, along with political support for costly beach preservation by nourishment. Passive degradation includes trash accumulation, oil spills, beach driving and most importantly, pollution, which is increasing rapidly apace with population growth and remains largely unrecognized by the beach-using public.