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Almarshed, B.; Figlus, J.; Miller, J., and Verhagen, H.J., 2020. Innovative coastal risk reduction through hybrid design: Combining sand cover and structural defenses. Journal of Coastal Research, 36(1), 174–188. Coconut Creek (Florida), ISSN 0749-0208. Worldwide, sand dunes and hard coastal structures help to minimize loss of lives and property from storm impact and flooding along or behind coastlines. Both sand dunes and hard coastal structures have their benefits and shortfalls in terms of protective capacity, cost, flexibility, and impact to coastal systems. Combining these two inherently different coastal risk reduction measures into a single hybrid system can preserve some of the individual benefits of each while creating an Engineering-with-Nature™ system that fulfills the requirements of high levels of protection, adaptability to future challenges related to climate change, sustainability, and pleasing natural aesthetics. Although such hybrid systems have the potential to become viable alternatives to conventional coastal risk reduction schemes, there are still many unknowns related to the interaction between the soft and hard structural components and their effectiveness in storm surge mitigation and flood prevention that require targeted research efforts to create acceptable design guidelines. Specifically, the combination of hard and soft alternatives into a single structure has not been studied in detail. Here, hybrid coastal risk reduction systems consisting of traditional hard structures (levees, revetments, and sea walls) covered by sand layers attempting to mimic dunes are investigated. It is emphasized that these sand covers can look like natural dunes, but they cannot evolve like natural dunes in the long term due to spatial constrictions along developed coasts and lack of natural sediment supply in eroding coastal systems. Just like any engineered beach and dune system, these hybrid structures require episodic maintenance nourishment, particularly after storm impact. The present overview covers design advances and issues related to both hard structures and engineered sand dunes for coastal risk reduction and investigates existing hybrid approaches. Future research goals to better understand hybrid coastal risk reduction systems and to create applicable design guidelines are discussed.

Based on high-tide shoreline data extracted from 87 Landsat satellite images from 1986 to 2019 as well as using the linear regression rate and performing a Mann-Kendall (M-K) trend test, this study analyzes the linear characteristics and nonlinear behavior of the medium- to long-term shoreline evolution of Jinghai Bay, eastern Guangdong Province. In particular, shoreline rotation caused by a shore-normal coastal structure is emphasized. The results show that the overall shoreline evolution over the past 30 years is characterized by erosion on the southwest beach, with an average erosion rate of 3.1 m/a, and significant accretion on the northeast beach, with an average accretion rate of 5.6 m/a. Results of the M-K trend test indicate that significant shoreline changes occurred in early 2006, which can be attributed to shore-normal engineering. Prior to that engineering construction, the shorelines are slightly eroded, where the average erosion rate is 0.7 m/a. However, after shore-normal engineering is performed, the shoreline is characterized by significant erosion (3.2 m/a) on the southwest beach and significant accretion (8.5 m/a) on the northeast beach, thus indicating that the shore-normal engineering at the updrift headland contributes to clockwise shoreline rotation. Further analysis shows that the clockwise shoreline rotation is promoted not only by longshore sediment transport processes from southwest to northeast, but also by cross-shore sediment transport processes. These findings are crucial for beach erosion risk management, coastal disaster zoning, regional sediment budget assessments, and further observations and predictions of beach morphodynamics.

The present study makes a qualitative and quantitative assessment of inundation limit, the structural damage and shoreline change due to very severe cyclonic storm Phailin and also estimates the rate of recovery along different parts of south Odisha coast. At the time of landfall of Phailin along Odisha and adjoining Andhra Pradesh coast on October 12, 2013, maximum sustained surface wind speed reached up to 200–210 kmph gusting to 220 kmph with an estimated pressure drop 66 mbar at the center. Significant wave heights reached up to more than 7 m with a mean period range between 4 and 12 s from southeast direction during the event. Strong gale wind and high wave followed by massive rainfall brought irreparable damage to the coastal structures and shoreline along south Odisha. Real-time kinematics global positioning system and differential global positioning system Arcpad were used to monitor the shoreline change before and after Phailin and the inundation limit. The study indicates maximum inundation at southernmost part of Odisha coast (Ramayapatnam) followed by inside the Gopalpur Port area and minimum near Gopalpur port north. Shoreline change from pre- (September 2013) to post-storm period (October 2013) is landward all along south Odisha coast with maximum (48.7 m) near Rushikulya turtle nesting beach and minimum (12.6 m) near south of Gopalpur tourist beach. The recovery of the beach and dune areas assessed during October 2014 (after 1 year from the post-storm observation) is uneven. Percentage of recovery is maximum at south side of Gopalpur port, while recovery is minimum on north of the port.

Research on wave forces attacking a vertical structure has been conducted worldwide. Morison's equation commonly used to describe the phenomenon of the action for offshore structures, while for nearshore structures Goda's equation is more reliable. Wave impact on vertical breakwaters is dangerous for vertical structures, both for walls and columns. Wave pressure distinguished for wave crest and wave trough, assumed to be distributed as a trapezoidal shape like along the vertical wall. The wave force consists of wave pressure on the front of the vertical wall and buoyancy, and uplift pressure in the vertical direction. In this research, a 2-dimensional physical modelling is carried out to observe the response of a vertical structure due to a wave action. Wave forces are measured using a flexi force sensor for both horizontal and vertical forces. Time series of incident wave and waveforces acting on the structure are recorded simultaneously and it clearly depicts the relation between them. The wave forces at the structure are linear to the height of the action waves. Periodical wave action results in the pushing forces at the structure to be higher than the pulling forces, as extra drift forces appear due to the shallow water wave condition.

Some new results and preliminary remarks about the Plio–Quaternary structural and evolutionary characteristics of the outer Marche Apennines south in the Conero promontory are presented in this study. The present analysis is based on several subsurface seismic reflection profiles and well data, kindly provided by ENI S.p.A. and available on the VIDEPI list, together with surface geologic–stratigraphic knowledge of Plio–Quaternary evolution from the literature. Examples of negative vs. positive reactivation of inherited structures in fold and thrust belts are highlighted. Here, we present an example from the external domain of the Marche Apennines, which displays interesting reactivation examples from the subsurface geology explored. The study area shows significant evolutionary differences with respect to the northern sector of the Marche region previously investigated by the same research group. The areal distribution of the main structures changes north and south of the ENE–WSW oriented discontinuity close to the Conero promontory. Based on the old tripartite classification of the Pliocene, the results of this work suggest a strong differential subsidence with extension occurring during the Early Pliocene and principal compressive deformation starting from the Middle Pliocene and decreasing or ceasing during the Quaternary. The main structure in this area is the NNW–SSE Coastal Structure, which is composed of E-vergent shallow thrusts and high-angle deep-seated normal faults underneath. An important right-lateral strike–slip component along this feature is also suggested, which is compatible with the principal NNE–SSW shortening direction. As mentioned, the area is largely characterized by tectonic inversion. Starting from Middle Pliocene, most of the Early Pliocene normal faults became E-vergent thrusts.

Over recent years, many coastal engineering projects have employed the use of soft solutions as these are generally less environmentally damaging than hard solutions. However, in some cases, local conditions hinder the use of soft solutions, meaning that hard solutions have to be adopted or, sometimes, a combination of hard and soft measures is seen as optimal. This research reviews the use of hard coastal structures on the foreshore (groynes, breakwaters and jetties) and onshore (seawalls and dikes). The purpose, functioning and local conditions for which these structures are most suitable are outlined. A description is provided on the negative effects that these structures may have on morphological, hydrodynamic and ecological conditions. To reduce or mitigate these negative impacts, or to create new ecosystem services, the following nature-based adaptations are proposed and discussed: (1) applying soft solutions complementary to hard solutions, (2) mitigating morphological and hydrodynamic changes and (3) ecologically enhancing hard coastal structures. The selection and also the success of these potential adaptations are highly dependent on local conditions, such as hydrodynamic forcing, spatial requirements and socioeconomic factors. The overview provided in this paper aims to offer an interdisciplinary understanding, by giving general guidance on which type of solution is suitable for given characteristics, taking into consideration all aspects that are key for environmentally sensitive coastal designs. Overall, this study aims to provide guidance at the interdisciplinary design stage of nature-based coastal defence structures.

There is great interest in the restoration and conservation of coastal habitats for protection from flooding and erosion. This is evidenced by the growing number of analyses and reviews of the effectiveness of habitats as natural defences and increasing funding world-wide for nature-based defences–i.e. restoration projects aimed at coastal protection; yet, there is no synthetic information on what kinds of projects are effective and cost effective for this purpose. This paper addresses two issues critical for designing restoration projects for coastal protection: (i) a synthesis of the costs and benefits of projects designed for coastal protection (nature-based defences) and (ii) analyses of the effectiveness of coastal habitats (natural defences) in reducing wave heights and the biophysical parameters that influence this effectiveness. We (i) analyse data from sixty-nine field measurements in coastal habitats globally and examine measures of effectiveness of mangroves, salt-marshes, coral reefs and seagrass/kelp beds for wave height reduction; (ii) synthesise the costs and coastal protection benefits of fifty-two nature-based defence projects and; (iii) estimate the benefits of each restoration project by combining information on restoration costs with data from nearby field measurements. The analyses of field measurements show that coastal habitats have significant potential for reducing wave heights that varies by habitat and site. In general, coral reefs and salt-marshes have the highest overall potential. Habitat effectiveness is influenced by: a) the ratios of wave height-to-water depth and habitat width-to-wavelength in coral reefs; and b) the ratio of vegetation height-to-water depth in salt-marshes. The comparison of costs of nature-based defence projects and engineering structures show that salt-marshes and mangroves can be two to five times cheaper than a submerged breakwater for wave heights up to half a metre and, within their limits, become more cost effective at greater depths. Nature-based defence projects also report benefits ranging from reductions in storm damage to reductions in coastal structure costs.

Coastal structures are regarded as an effective defense for protecting the coastal area from tsunami disasters, considering that the tsunamis cannot be predicted. Therefore, much attention should be focused on tsunami–structure interaction (TSI). We must determine dynamic characteristics of the TSI such as wave height, free-surface elevation, dynamic wave pressure, and overtopping volume, all of which are essential to the design of coastal structures. The traditional mesh-based numerical method fails to accurately model TSI, because of large deformations that cause numerical diffusion. The moving particle simulation (MPS) is a pure Lagrangian mesh-less method, which can track free-surfaces with large deformations. The original MPS suffers from serious pressure fluctuations that affect the accuracy of the simulation. We modified three aspects of the original MPS: the kernel function, the source term, and the search of free-surface particles. We verified that these changes improved the pressure stability using two benchmark problems. Then, we applied the modified MPS to simulate the TSI, using a solitary wave to model the tsunami. We quantitatively and qualitatively compared our numerical results with the experimental data. The numerical results were consistent with the experimental data, which indicates that the modified MPS can capture the essential dynamic characteristics of the TSI and reproduce the entire interaction between the tsunami and structure.

The aim of coastal structures for the defense from erosion is to modify the hydrodynamic fields that would naturally occur with the wave motion, to produce zones of sedimentation of solid material, and to combat the recession of the coastline. T-head groin-shaped structures are among the most adopted in coastal engineering. The assessment of the effectiveness of such structures requires hydrodynamic study of the interaction between wave motion and the structure. Hydrodynamic phenomena induced by the interaction between wave motion and T-head groin structures have three-dimensionality features. The aim of the paper is to propose a new three-dimensional numerical model for the simulation of the hydrodynamic fields induced by the interaction between wave fields and coastal structures. The proposed model is designed to represent complex morphologies as well as coastal structures inside the domain. The numerical scheme solves the three-dimensional Navier–Stokes equations in a contravariant formulation, on a time-dependent coordinate system, in which the vertical coordinate varies over time to follow the free-surface elevation. The main innovative element of the paper consists in the proposal of a new numerical scheme that makes it possible to simulate flows around structures with sharp-cornered geometries. The proposed numerical model is validated against a well-known experimental test-case consisting in a wave train approaching a beach (non-parallel with the wave front), with the presence of a T-head groin structure. A detailed comparison between numerical and experimental results is shown.

The most massive design on the Baltic shore used geosynthetic materials, the landslide protection construction in Svetlogorsk (1300 m long, 90,000 m2 area, South-Eastern Baltic, Kaliningrad Oblast, Russian Federation) comprises the geotextile and the erosion control geomat coating the open-air cliff slopes. Due to changes in elastic properties during long-term use in the open air, as well as due to its huge size, this structure can become a non-negligible source of microplastic pollution in the Baltic Sea. Weather conditions affected the functioning of the structure, so it was assessed that geosynthetic materials used in this outdoor (open-air) operation in coastal protection structures degraded over time. Samples taken at points with different ambient conditions (groundwater outlet; arid places; exposure to the direct sun; grass cover; under landslide) were tested on crystallinity and strain at break. Tests showed a 39–85% loss of elasticity of the polymer filaments after 3 years of use under natural conditions. Specimens exposed to sunlight are less elastic and more prone to fail, but not as much as samples taken from shaded areas in the grass and under the landslide, which were the most brittle.