Seawall Research Articles

Spatial variability assessment of La and Nd concentrations in coastal China soils following 1000 years of land reclamation

Rare earth elements (REE) play a prominent role in the understanding of geochemical processes. Lanthanum (La) and neodymium (Nd) are considered as two representative examples of REE. The objectives of this study were to investigate their concentrations and spatial variability in coastal soils and to assess the effect of long-term reclamation. The coastal plain of Cixi City (China) has undergone reclamation for over 1000 years, providing an ideal place to perform such research. In total, 329 soils samples were collected by means of a nested sampling methodology, combined with grid and transect techniques. The total contents, as well as their diethylenetriamine penta-acetic acid (DTPA) extractable concentrations, were measured by an inductively coupled plasma-mass spectrometry (ICP-MS). Statistics and geostatistics tools were used to analyze their spatial variability. Combined variogram models were developed to quantitatively describe their spatial structure. Variance components were estimated to assess the proportion of their total variance captured by reclamation history and different sampling stages. Both the La and Nd concentrations showed great variability in space. Reclamation activity accounted for 42–84% of their total variance. There were significant differences in their contents between reclaimed zones (P < 0.05). They exhibited moderate spatial dependence, and the discontinuity in space generally occurred around sea dikes, as indicated by the spherical components of the La and Nd concentration variogram models. A gradually increasing tendency of elemental contents with reclamation time was observed, which was also reflected in the linear component of the variogram models. However, in the areas covered by the 3rd to the 10th zones, intensive application of phosphorus fertilizer, land consolidation, or household appliance factories led to large fluctuations of elemental contents being superimposed on the relatively homogeneous content distributions, thus causing the observed periodic features of their variogram models. Additionally, a 100-m sampling distance was found to be appropriate for future REE investigations. Geostatistical modeling showed a great potential to analyze quantitatively the spatial variability of La and Nd and to assess human forces on soil genesis. The investigation of the spatial distribution of REE identified the prominent role played by the geogenic component. By means of spatial analysis, a time-series of elemental contents on a millennium scale was also reconstructed. Accumulation of their concentrations with time, as well as pollution, occurred in the surface soils. Reclamation history was the most important factor controlling La and Nd spatiotemporal variability.

Are American Coasts Under-Protected?

This study tests whether potential coastal sea walls would pass a cost benefit test given current risks of flooding. The paper combines detailed GIS property data with local scientific measurements of relative SLR and storm risks to measure expected benefits and applies this methodology to measure the optimal strategy for the coastal town of East Haven, Connecticut. The paper finds that East Haven should build sea walls that are about 1 m high along its entire coastline. The benefit to cost ratio is about 2 to 1.

Geospatial Modeling of Blue Carbon Ecosystem Coastal Degradation in Jakarta Bay

Jakarta Bay is shallow water which is used for various activities, currently experiencing environment, soil,and sediment degradation. Jakarta Bay experienced rapid development, population growth, increased economic activity and utilization of coastal resources. The development of Jakarta Bay is carried out to balance land necessity and overcome the problem of land subsidence through reclamation and construction of sea dikes. Ecosystem services arethe contribution of various interrelated ecological structures and functions, mangrove ecosystems provide services as an important part of the carbon cycle. Mangroves use CO2 for photosynthesis and store it in Biomass and sediment stock. Mangrove ecosystems in Jakarta Bay have been degraded and deforested due to land conversion for settlement, facilities, and other activities, in line with the increasing population. The calculation of the service value of mangrove ecosystems is limited to economic valuation and descriptive account, geospatial modelling has not been widely carried out, this has caused widespread and temporal unknown data on ecosystem services. The Coastal Blue Carbon geospatial modelling used in this study requires land use classification data input based on the interpretation of Landsat satellite's images and global carbon deposits in mangrove ecosystems while carbon prices are based on Social Cost Carbon (SCC), Greenhouse Gas Initiative (RGGI) and International Voluntary Market Price (IVMP). This study produced a map of the dynamics of carbon stock, sequestration, emissions, accumulation and net present value of carbon. The output of these maps is expected to be a referencefor sustainable mangrove management, coastal area planning optimization with mangrove ecosystem protection so it can be part of climate change mitigation efforts in Jakarta Bay.

Assessment of physical properties of a sea dike using multichannel analysis of surface waves and 3D forward modeling

Seismic surface waves analysis methods have been widely developed and tested in the context of subsurface characterization and have demonstrated their effectiveness for sounding and monitoring purposes. Given their efficiency, surface waves methods have been used in a variety of contexts, including civil engineering applications. However, at this particular scale, many structures exhibit 3D geometries which drastically limit the efficiency of these methods since they are mostly developed under the assumption of a semi-infinite 1D layered medium without topography. Taking advantages of wave propagation modeling algorithm development and high-performance computing center accessibility, it is now possible to consider the use of a 3D elastic forward modeling algorithm for the inversion of surface wave dispersion. We use a parallelized 3D elastic modeling code based on the spectral element method which allows to obtain accurate synthetic data with very low numerical dispersion and a reasonable numerical cost. In this study, we choose a sea dike as a case example. We first show that their longitudinal geometry and structure may have a significant effect on dispersion diagrams of Rayleigh waves. Then, we investigate the sensitivity of the dispersion diagrams to small velocity and layer thickness perturbations, and show the limitations of the standard 1D surface wave methods approach. Finally, we demonstrate in this context the benefits of using both a 3D forward modeling engine and the whole dispersion diagram, instead of the dispersion curves only.

Application of steady flow model to overcome inundation based on eco drainage system in the Port Area of Dobo City, Aru Islands Regency

This research was carried out in inundation that occurred in the Port area of Dobo City, Aru Islands Regency. Inundation that occurs is due to the unavailability of adequate and well-arranged drainage. This research aims to plan a drainage system in the Port area of Dobo City that can overcome the inundation that arises and the influence of tides. Data processing is carried out with two analyzes including hydrological analysis and hydraulic analysis. For hydraulics analysis, this includes cross section planning and drainage system modeling with HEC-RAS 4.0. In conventional drainage in the case of high tides, the results of the modeling show that the overflow of water on the channel that will occur is at an elevation of +2.48 m. After adding a long storage with dimensions of 1.2 m x 3.5 m along 101.6 m and sea walls as high as + 2.48 m. The results of the modeling show that the inundation height that will occur is at an elevation of +0.61 m. Of the several scenarios that are performed for the most optimal two-door openings, which are opened by 30 cm which later the water will be at + 12 cm elevation. Whereas the most optimal one-door openings are opened by 70 cm which later the water will be at + 6 cm elevation.

Monitoring of a Sea-Dike in Northern Germany by Means of ERS-1, ENVISAT/ASAR, and Sentinel-1 SAR Interferometry

Flood events are one of the most severe natural hazards threatening billions of people living in coastal areas. Synthetic aperture radar (SAR) interferometry can contribute significantly to civil security by providing a highly accurate tool for spatially explicit monitoring of flood protection structures. This article analyzes multitemporal SAR interferometry techniques like persistent scatterer interferometry and small baseline subset (SBAS) for C -band radar data in order to show the potential for a precise dike monitoring. These techniques not only achieve accuracies of few millimeters, but they also enable to reconstruct the deformation process in time. Thus, critical deformation processes can be identified timely and precautions can be taken to prevent dike bursts during flood events. In this article, sea dikes located at the North Sea coast in Germany are analyzed in order to show the potential but also the difficulties of this approach, using 34 ERS-1/2, 55 Envisat ASAR, and 44 Sentinel-1 scenes. All results point out that long-term deformation processes can be measured quite well. Due to decorrelation effects, the results on vegetated dikes are ambiguous. Applying SBAS to Sentinel-1 data is very promising to serve as a tool to precisely detect and understand deformation processes of dike bodies on large spatial scales.

The queen is led? Bumblebee (Bombus spp.) nest-searching on sea wall banks may be influenced by cutting and sward height

English sea wall flood defences support an important grassland habitat for bumblebees (Bombus spp.). However, annual cutting in midsummer (July–August) could negatively affect them. The mowing regime on a sea wall at Goldhanger Creek in Essex was changed to a late cut (after 15 September) and nest-searching behaviour was compared with an adjacent sea wall cut in midsummer (normal cut in August). Sward height and the number of queens nest-searching were significantly higher on the normal cut sea wall than on the late cut one. Tall grass swards resulting from a cut early in the previous summer may be important for nest-searching compared to those mown late, although there is probably an interaction with sea wall aspect and soil type. The landward slope was also more attractive for nesting than the flat folding (berm) due to the longer vegetation where nests under construction were located (of Bombus humilis and B. terrestris).

Littoral Current Monitoring Techniques Along Ibeno Atlantic Coastline, South Eastern Nigeria

The coastline is a dynamic and complex environment due to the natural processes and the anthropogenic activities impacting it. The major current that affects the coastline is a surface current known as coastal or littoral current greatly influence by wave and wind action. This current which is popularly known as longshore current plays a very significant role in the morphology of the beach. The impact is dynamic. It can be positive when it result to accretion or sediment deposition and it can be negative resulting in sediment alteration or beach erosion. This current plays an important role in the distribution of sediment along the coastline. The features of longshore are Spit, Barrier Island, Tombolo, Lagoons etc. They are three major Littoral current direction in Nigeria, 1. The west-east littoral current along western coastline, 2. The littoral current off the north western flank of Niger Delta, 3. The west-east littoral current between Akasa point and Calabar Estuary. Littoral current can be monitored using Bouys, ADCP and RADAR. The techniques used are Langrarian and Eularian. Control Measures of Littoral Current Impact: Hard and Soft Engineering. Hard Engineering Includes: Goines, Gabions, sea wall, Revetment, Jetties etc. Soft Engineering includes: Beach Nourishment, Coastal realignment, Beach re-profiling and dune Regeneration. Recommendation 1. It is highly recommended that a permanent monitoring station be established along this coastline for continuous data collection that could be used for obtaining oceanographic models on hydrodynamic parameters along the coastline. With the use of modern equipment. 2. Government should use the information gathering from this research to monitor marine pollution, assess bathing-water quality of public beaches and the health of coastal ecosystem.

The Effect of Pole Density on Permeable Groin Due to Controlling Longshore Current

Erosion and sedimentation problems that occurs, usually solved firstly by finding the cause of erosion and sedimentation literally, due to determining the action to overcome them. In coastal engineering, there are two approaches that can be used to solve such kind of problems; which are the soft approach, i.e. beach nourishment, vegetation, sand by passing, coastal boundary policy; while the hard approach or structural approach are building breakwater, jetty, groin, sea wall and so on. In structural approach, the uses of permeable groin nowadays is one of the new ways to overcome the erosion and sedimentation problems in beaches. To find out how efficient the permeable groin can control the flow along the coast, so called longshore current, a research needed to be conducted focusing on the effect of pole density at permeable groin itself. The ability of controlling longshore current will be the main analysis, in such various variations of pole densities at the permeable groin. It found out that the pole densities of permeable groin can significantly controlled the longshore current; which is if the pole density become higher than the speed of longshore current can be reduced. It also found out that by implementing 40% of pole density, the longshore current can be reduce up 50% respectively.

Erosion Caused by Coastal Structure

Coastal structure such as jetties, groins, sea walls, breakwaters, etc. along the coast can alter the shoreline and morphological structure of coastline. Presence of the coastal structure gives impact like sediment trapping on upstream side of the structure and causing shore erosion along adjacent shorelines. Therefore, this paper presents attempts to describe the coastal erosion process effected by a different kind of coastal structure. Generally, it takes time to notes the impact of coastal erosion, therefore several methods are adapted to identify the erosion by surface sediment sampling and beach profile measurement. These measurements are conducted by conventional and high-technology method such as manual surface sediment sampling, Real-Time Kinematic (RTK) GPS, LiDAR and UAV. In terms of analysis, these methods can be approach with variable techniques and applications. However, this review paper briefly described the commonly used technique and application in finding the result of eroded coastal.

Validation of an operational forecasting system of sea dike risk in the southern Zhejiang, South China

In this study, an operational forecasting system of sea dike risk in the southern Zhejiang, South China was developed based on a coupled storm-surge and wave model. This forecasting system is important because of the high cost of storm-surge damage and the need for rapid emergency planning. A comparison with astronomical tides in 2016 and the validation of storm surges and high water marks of 20 typhoons verified that the forecast system has a good simulation ability. The system can forecast relatively realistic water levels and wave heights as shown under the parametric atmospheric forces simulated in a case study; the sea dikes in credible high risk were mainly located in the estuaries, rivers, and around the islands in the southern Zhejiang Province. Therefore, the forecast system is applicable in the southern Zhejiang with a support to the effective prevention from typhoon storm-surge damage.

Enhancing the Ecological Value of Sea Dikes

Sea dikes protect low-lying hinterlands along many coasts all around the world. Commonly, they are designed as embankments with grass covers or grey revetments accounting for the prevailing hydraulic loads. So far, incorporation of ecological aspects in the dike design is limited. With regard to increasing environmental awareness and climate change adaptation needs, the present study reviews methods for ecological enhancement of sea dikes and discusses limitations and challenges related to these methods. In doing so, one key aspect is to maintain dike safety while increasing the ecological value. Potential for ecological enhancement of sea dikes has been found regarding natural or nature-based solutions in the foreshore, dike surface protection measures (vegetated dike covers, hard revetments and dike roads) and the dike geometry. While natural and nature-based solutions in the foreland are investigated thoroughly, so far only few experiences with ecological enhancements of the dike structure itself were gained resulting in uncertainties and knowledge gaps concerning the implementation and efficiency. Additional to technical uncertainties, engineers and ecologists meet the challenge of interdisciplinary collaboration under consideration of societal needs and expectations.

Shelving the Coast With Vertipools: Retrofitting Artificial Rock Pools on Coastal Structures as Mitigation for Coastal Squeeze

Coastal squeeze caused by sea level rise threatens the size, type and quality of intertidal habitats. Along coastlines protected by hard defences, there is a risk that natural rocky shore habitat will be lost, with remaining assemblages characteristic of hard substrata confined to sea walls and breakwaters. These assemblages are likely to be less diverse and different to those found on natural shores as these structures lack features that provide moist refugia required by many organisms at low tide, such as pools and crevices. Engineering solutions can help mitigate the impacts of sea level rise by creating habitats that retain water on existing structures. However, as experimental trials are strongly affected by local conditions and motivations, the development of new techniques and solutions are important to meet the needs of local communities and developers. Following a small scale community project, a feasibility study retrofitted five concrete-cast artificial rock pools (‘Vertipools’) on to a vertical seawall on the south coast of England. After 5 years, the artificial pools increased the species richness of the sea wall and attracted mobile fauna previously absent, including fish and crabs. The Vertipools had assemblages which supported several functional groups including predators and grazers. Although disturbance of algal assemblages on the seawall from the retrofitting process was still evident after 3 years, succession to full canopy cover was underway. Collaboration between policy makers, ecologists, children and artists produced an ecologically sensitive design that delivered substantial benefits for biodiversity and that could be adapted and scaled-up to both mitigate habitat loss and enhance coastal recreational amenity.

Utilization of Industrial Waste in Cement in a Marine Environment with a Tropical Climate

This novel study on cement paste material was conducted with the aim of keeping up with the rapid development of urban construction and contributing to the continuous improvement of building materials to overcome environmental issues. In this study, several kinds of industrial waste were used to enhance the properties of cement paste for application in a marine environment with a tropical climate, such as in Vietnam. This study focuses on evaluating the properties of cement paste containing cement replacement combining 0–30% fly ash, 0–10% silica fume, and plasticizer accounting for 0.3% and 0.4% of the binder by mass. Water demand, chloride ion and sulfate ion permeability, and microstructural properties of the cement paste were determined by thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscope (SEM) and they were investigated after 28 and 56 days. The test results show that an optimum mixture could be obtained with the use of 20% fly ash, 10% silica fume (replacing Portland cement), and 0.4% plasticizer. The application of such materials to sea dikes affected by a tropical climate (characterized by heat, humidity, salty seawater, many big storms, large waves, and strong tides) was investigated for four years on the Vietnamese coast. The test results indicate that fly ash and silica fume can improve the corrosion and abrasion resistance of concrete in coastal areas with a tropical climate, such as in Vietnam.

Conserving unprotected important coastal habitats in the Yellow Sea: Shorebird occurrence, distribution and food resources at Lianyungang

The Yellow Sea coastline in East Asia, an important staging area for migratory shorebirds in the East Asian-Australasian Flyway (EAAF), is rapidly deteriorating. Conserving the declining shorebird populations that rely on the Yellow Sea requires habitat protection and management based on sound ecological knowledge, especially on the seasonal occurrence of shorebirds, their daily movements and their food resources. However, in this region such ecological data are scarce, and expertise to collect them are less-established. Here we gather and assimilate such information for the coastal wetlands at Lianyungang on the Chinese Yellow Sea coast, an understudied and unprotected area where we found 27% of intertidal soft sediment habitats have been destroyed in 2003–2018 by reclamation. In 2008–2018, 43 shorebird species were recorded along this coastline, including 12 globally threatened or ‘Near Threatened’ species. In terms of number of shorebird species exceeding 1% of the EAAF population, with 22 species meeting this criterion, Lianyungang ranks highest among the >300 shorebird sites in East Asia. The benthic mollusc community of the intertidal flats were dominated by small soft-shelled bivalve species at very high densities, including 9399 individuals/m2 of Potamocorbula laevis, which are high-quality food for shorebirds to refuel during migration. Satellite tracked bar-tailed godwits (Limosa lapponica) and great knots (Calidris tenuirostris) stopped at Lianyungang for 5–30 days during northward and southward migration. The tidal movements of satellite-tagged birds indicated high-tide roosts and low-tide foraging areas, some of which are inaccessible on-ground. These movements can also be used to evaluate whether roosts and foraging areas are close enough to each other, and direct where to create new roost sites. Potential measures to increase the capacity of Lianyungang to support shorebirds include reducing human disturbances, creating roosts at undeveloped parts of the reclaimed land, and removing recently-built sea dikes to restore intertidal flats.

Anthropogenic influences on benthic food web dynamics by interrupted freshwater discharge in a closed Geum River estuary, Korea

Stable isotope analysis was used to investigate the benthic food web dynamics in the Geum River estuary where continuous river flow has been blocked by a sea dike over the past 25 years. In order to address the dike effect(s) on distribution of food sources (i.e., organic matters and microphytobenthos) and their utilization by marine predators, a three years monitoring survey (total of 30 surveys) was seasonally conducted at four fixed locations at both inside of dike and outer tidal flats. All the collected biota (total of 19 species; >1100 individuals and microphytobenthos) and abiotic (n = 118) samples were analyzed for carbon (δ13C) and nitrogen (δ15N) stable isotopes. In particular, two dominant marine bivalves inhabiting outer reach of tidal flats, Mactra veneriformis and Cyclina sinensis, were targeted to identify their feeding strategies that being related to a year-round population growth. In general, the stable isotopic signatures of samples indicated dissimilarity in distribution of organic matters between inside and outside of dike, supporting geographical and/or trophic isolation. The taxa-dependent trophic levels are also evidenced in consistent manner, with two to three levels being positioned over the years. Meantime, their dietary contributions varied in time, i.e., seasonal chances in compositions of major food sources (microphytobenthos and particulate organic matters) were observed for two target bivalves. Such temporal variations could be further linked to selective feedings that evidenced by age(size)-dependent and/or tissue specific distributions. Altogether, the present study suggested seasonality, diet preference, and growth dependent food web dynamics in the Geum River estuary. Overall, the present study suggested that the stable isotopic technique could be a powerful tool for characterizing the long-term anthropogenic influences of a sea dike on marine food-web dynamics.

Numerical investigations for mitigation of tsunami wave impact on onshore buildings using sea dikes

Abstract A well tested mathematical model is used to bring out important counter intuitive results on the aspect of reducing tsunami impact forces on on-shore buildings using sea dikes. The mathematical model is based on numerical solution of the general Reynolds Averaged Navier Stokes equations, with SST–k–ω model for turbulence closure. Tsunami waves are allowed to propagate on a 1 in 40 sloped beach and over-top a sea dike before impacting on buildings. The combined effect of various parameters such as position of the dike and shape and size of the dike has been studied, for sloping beaches. A sea dike placed far from the building may increase the tsunami impact force, if its size is not appropriate. It is found that a sea dike positioned close to the building offers best protection only if the height of the wave is small. If the wave height is large, there is an optimal distance at which the dike should be located for minimizing the tsunami impact force. Placing a second sea dike in addition to an existing sea dike may not reduce the tsunami impact force, if the location and size of the sea dikes are not appropriate.

Climate risk assessments and management options for redevelopment of the Parliamentary Complex in Samoa, South Pacific

The site of the Samoan Parliament Complex Redevelopment Project is in a coastal environment hazard zone as a result of high risk of several hazards, including damaging winds and flooding due to stormtides. This paper presents the findings of detailed hazard, vulnerability, exposure and adaptation assessments, and prioritises risk reduction measures based on the findings of cost benefit analyses, as well as other considerations.As a result of higher intensity rainfall events in the future, as well as a general increase in sea level, the frequency and depth of localised flooding of the site during periods of heavy rainfall are expected to increase. No significant change is anticipated in the exposure of the buildings to extreme wind gusts between present day and 2045–2055, but projected increases in the frequency of extreme high temperatures have relatively high certainty and are substantial. Inundation as a result of a cyclone-related stormtides is the highest risk for the site. By 2065, 50- and100-year stormtides could be 3.0 m and 3.2 m above mean sea level, respectively, compared to 2.6 m and 3.0 m for the same events in 1990. Water velocities experienced during such stormtides are projected to increase from 1.5ms−1 (in 1990) to 1.9ms−1 by 2055.Relocating the Parliamentary Complex would alleviate all of the key risks that were identified. However, for cultural and historic reasons this response was not favoured by the Government of Samoa. Two key ways to manage the identified risk of damaging stormtides were assessed, namely to increase the height of building platforms above the business as usual case of meeting the design code in force at the time (i.e. finished floor level at 2.8 m above mean sea level), or to increase protection of the entire site by raising the heights of the surrounding sea wall and embankments. Cost benefit analyses showed that raising finished floor levels was the much more cost-effective option for protecting the new buildings from damage due to stormtides.The new Parliamentary Chamber was officially opened in March 2019. Its climate resilient design reflects the findings of the above assessments, including the prioritised risk reduction measures.

Wave impacts on structures with rectangular geometries: Part 2 decks, baffles and seawalls with impermeable or porous surfaces

This paper considers wave impacts on baffles, on baffles or decks adjacent to a vertical wall, and on porous seawalls and/or sea beds. For seawalls and vertical baffles, impacts can occur in steep waves, whilst a deck can be struck from below by a rising wave crest either in open sea or in a tank with standing waves (sloshing). A simple analytical model for the pressure impulse, P, due to a wave of idealized geometry and dynamics is developed and applied to the following geometries with impermeable surfaces:•horizontal wave impact onto a vertical wall with a deck at the waterline,•vertical wave impact under a deck in the same configuration (equivalent to vertical water impact of a horizontal plate),•horizontal wave impact onto a surface-piercing vertical baffle in open sea,•as for 3. but with the baffle in front of a wall,•as for 4. but with a deck extending from the vertical wall to the baffle,•bottom-mounted baffle in front of a wall with impact occurring on the wall.We also consider cases that complement part 1 of this paper to include the effect on impacts on a seawall with a porous sea bed and/or sea wall with/without a berm. Finally we reconsider case 3) above but with a porous baffle.The method uses eigenfunction expansions in each of the rectangular regions that satisfy some of the impermeable or porous surface conditions, and a simplified free-surface condition. Their unknown coefficients are determined from the impact boundary condition, impermeable or porous boundary conditions and by matching the solutions, in any two neighbouring rectangles, along their common boundary. Although the fluid motion is treated rather crudely, the method yields the pressure impulse throughout the entire region. Impulses, I, and moment impulses, M, on all or parts of the structure are also presented.

Stakeholder assessment of coastal risks and mitigation strategies

Perceptions of coastal hazards and risks and support for mitigation strategies among three different stakeholder groups (experts, businesses, and community members) are compared and analyzed in Waikiki, Hawaii. A justification for research on Waikiki, a world renown tourist destination and its relevance to other coastal communities is provided. It is shown that the three groups perceive risks, such as hurricanes, storm surge, erosion, tsunamis, and other natural and man-made hazards, differently which in turn influences support for mitigation strategies such as sea walls, beach nourishment, elevating or relocating at-risk structures and the preferences as to who should pay for risk reduction strategies. Data were analyzed using basic inferential statistics, GLM regression and correspondence analysis. Correspondence analysis is a novel technique for studying the relationships between stakeholder attributes (demographic, political, etc.) and the level of support for coastal interventions. The implications for researchers, engineers and coastal planners working in at-risk coastal communities are described.