Truong, S.H.; Ye, Q., and Stive, M.J.F., 2017. Estuarine mangrove squeeze in the Mekong Delta, Vietnam.

Although the protective role of mangroves for coasts has been increasingly recognized, that of estuarine mangroves is less well acknowledged. The complex root, stem, and canopy system of healthy estuarine mangroves efficiently reduces the impact of a strong, along-bank flow during high tides and high river discharge, protecting the riverbank from eroding. If a sediment source is available, a healthy mangrove forest also offers a higher potential for sedimentation to compensate for sea-level rise. Unfortunately, along the Mekong, Vietnam, estuaries, mangroves have been rapidly destroyed. In many regions, estuarine mangroves have degraded into narrow strips of <50 m. Riverbanks at those locations are eroding at a rate of 2–4 m y⁻¹. The main reason for this “estuarine mangrove squeeze” phenomenon is due to the increasing demand to create more space for local fish farming. Hence, squeeze is used in a broader sense than in the context of sea-level rise impact alone. The hypothesis is that there is a critical minimum width for an estuarine mangrove forest strip to maintain its ability to survive. The analysis of available data, both from literature and from satellite observations, supports the hypothesis: An average critical width for Mekong estuaries was found to be approximately 80 m. To obtain insight into the efficiency of a mangrove forest in reducing the impacts of alongshore flow, the state-of-the-art Delft3D model was applied to the data. The model showed that the penetration-length scale of the shear layer into a mangrove forest requires a certain minimum space to develop fully. It is hypothesized that the minimum width of a mangrove forest, which equals this maximum penetration-length scale, has a crucial role for the health of a mangrove system.

Liu, H. and Wu, J., 2017. Determining topographically controlled flows through a combined contraction and hollow in the Pearl River estuary, China.

The modern Pearl River delta, with a two-fifths area of rocky islands or hills, is estuarine accumulation dominated, where most river-borne sediments are still trapped within the estuary. However, the role of topographic flows in controlling riverine sediment dispersal and delta development is not straightforward. In this paper, the topographically controlled flows through a combined contraction and hollow were investigated to understand their roles in modern delta development. Moving shipboard surveys, bottom-mounted tripods, and water-level gauging along the Yamen Channel were undertaken in the 2012 wet season to measure mean flows, bottom boundary layer flows, tidal elevation, and water depth. During the peak tidal flows, an accelerating high-speed zone occurred on the stoss (upstream) side of the hollow. Under the unstratified conditions, the momentum balance in the hollow is roughly achieved among barotropic pressure gradient, horizontal advection, and local acceleration. The form drag induced by the hollow was estimated to be one order of magnitude larger than the skin friction generated by bed roughness. The form drag can speed the upstream current in the hollow, forming the high-speed zone on the stoss slope of the hollow. Theoretical investigations reveal that a self-adjustment mechanism of the combined hollow and contraction can calm the channel flow speed, so that more flow energy can be dissipated and more river-derived sediments can be trapped within the estuary. This recognition implies that the Pearl River delta is estuarine accumulation dominated.

Bugajny, N. and Furmańczyk, K., 2017. Comparison of short-term changes caused by storms along natural and protected sections of the Dziwnow Spit, southern Baltic coast.

This paper focuses on a comparison of changes caused by weak storms (significant wave height [H_s] <2.5 m) along a dune coast on a nontidal sea. Repeated observations were made along two 2 km long sections of the southern Baltic coast; one section is a natural coast, and the other features protective structures. Several real-time kinematic GPS surveys were carried out in 2012. The surveys included cross-shore profiles measured from the dune foot to a water depth of 1 m. The profiles were spaced at constant 100 m intervals. In addition, offshore wave data and water level data were collected. Using statistical methods, three types of hydrodynamic conditions were identified and the data grouped accordingly; these groups had different effects on the coast. The coastal changes that occurred along the natural and protected sections of the coast were compared using two parameters: shoreline displacement and volume changes. The net, total, and maximal values and means of shoreline displacement and beach volume changes were calculated and are discussed in this paper. The analysis confirms that both natural processes of erosion and accumulation take place in relation to the location of shoreline displacement and the volume changes under all hydrodynamic conditions on both the natural and protected coasts. The proportion of these changes depends on the hydrodynamic conditions and the type of coast. The accumulative effect of the groynes is particularly seen under the hydrodynamic conditions of group 2. The ratio of volume changes to shoreline displacement exhibits stronger correlation for the natural coast (group 1, R = 0.82; group 2, R = 0.75; group 3, R = 0.80) than for the protected coast (group 1, R = 0.79; group 2, R = 0.74; group 3, R = 0.61), while the slope of regression is greater for the natural than for the protected coast.

Darwish, K.; Smith, S.E.; Torab, M.; Monsef, H., and Hussein, O., 2017. Geomorphological changes along the Nile Delta coastline between 1945 and 2015 detected using satellite remote sensing and GIS.

This study describes geomorphologic changes along the Nile Delta coastline between 1945 and 2015. The study used topographic maps produced by the Egyptian Geological Survey in 1945 and Landsat satellite imagery taken between 1973 and 2015. The study found that the coastline's geomorphology greatly changed during this time period, especially at Damietta and Rosetta promontories, which were highly eroded after construction of the Aswan High Dam. Other stretches of the coastline also eroded, while some accretion occurred along the coastline down-drift from the promontories. The trend has been erosion of the beaches along the Nile promontories and accretion within the embayments between the promontories, resulting in an overall smoothing of the coastline. A portion of the eroded material has accreted in the form of spits or shoals near the inlets. The principal causal factors of coastline change were the impacts of the Aswan High Dam, sea-level rise, land subsidence, storms, and coastal protection devices. Efforts to stop erosion have had mixed results. Seawalls built along the city of Alexandria have maintained the coastline, while other coastal protection devices have not impeded erosion. Areas of cultivated land are highly susceptible to saltwater intrusion due to sea-level rise and the fact that much of the delta is at or near sea level.

Hsu, C.-E.; Hsiao, S.-C., and Hsu, J.-T., 2017. Parametric analyses of wave-induced nearshore current system.

To date, a few investigations have focused on the interaction and sensitivity analysis of different factors affecting the nearshore current system. This paper attempts to present detailed parametric analyses by analyzing a widely adopted experiment using a model based on shallow-water and mild-slope equations. Discussions and conclusions are then made by the numerical experiments in this paper. Various factors, including bed roughness and bed slope, are taken into account to figure out their impact on the velocity field. Moreover, estimation of effective bed roughness, turbulent diffusion effects, and surface roller are considered and discussed in this study. After a series of analyses, bottom roughness is found to be the most significant variable in the system, whereas surface roller is proved to be indispensable in such two-dimensional nearshore current models. When the bed slope is too large, the present model gives poor computed results. Finally, suggested choices of formula and determination of important coefficients (e.g., the energy dissipation coefficient in the surface-roller model) are provided.

Krvavica, N.; Travaš, V., and Ožanić, N., 2017. Salt-wedge response to variable river flow and sea-level rise in the microtidal Rječina River Estuary, Croatia.

A finite-volume model for two-layer shallow-water flow is presented and applied to study the dynamic response of a salt wedge in a microtidal estuary to changes in river flow rate and sea-level rise (SLR). First, the shape of the arrested salt wedge was computed for different hydrographic conditions. Next, the response of the salt wedge to highly variable river flow was investigated. Finally, this model was applied to predict the impacts of the SLR on salinity intrusions in the Rječina River Estuary. To assess the model performance and to examine the salinity structure in the estuary, a field-sampling campaign was conducted during 2014 and 2015. Field observations revealed negligible longitudinal density variations in both freshwater and saltwater layers and highly stratified conditions for all considered river flow rates and sea levels. Furthermore, the maximum buoyancy frequency, computed as a measure of vertical stratification, was among the highest ever reported in field investigations. The behavior of the salt-wedge intrusion depends mainly on the river flow rate, although sea level and channel geometry become more influential under low-flow conditions. Computed salt-wedge shapes and propagation rates agreed well with field observations. The salinity structure in the Rječina River Estuary is not expected to change in the future for tested SLR scenarios, although stronger salt-wedge intrusion is predicted by the numerical model.

Meyers, S.D.; Moss, A.J., and Luther, M.E., 2017. Changes in residence time due to large-scale infrastructure in a coastal plain estuary.

The alteration of residence time in a coastal plain estuary due to dredging and building of barrier-type structures is found to vary with freshwater conditions. Two identical 3-year simulations with realistic boundary conditions were performed using numerical circulation models of Tampa Bay, Florida, that differ only in their bathymetry. The first simulation used present-day bathymetry. The second used bathymetry based on depth soundings from the preconstruction year 1879. Both models were seeded evenly with over 456,000 passive tracers at the beginning of three separate 90-day time periods. These times were initially chosen according to the relative change in subtidal circulation but found to correspond to different vertical mixing conditions. Two types of Lagrangian residence time were studied: The first, baywide residence time (T_R), is based on the total number of particles in the bay. The largest change in T_R was found during a weakly mixed time period with strong baroclinic circulation. In other time periods best described as well- or partially mixed, T_R was relatively unaffected. The second, grid scale residence time (), is based on the total number of particles in each model grid cell. Increased was found near bridges and causeways, and decreased was found where relatively deep dredging has occurred. Some regions within the estuary experienced increased in well-mixed conditions but decreased in weakly mixed conditions. The Lagrangian method reveals a rapid, largely transverse redistribution of particles that indicates the results are not sensitive to the initial particle distribution.

Huiru, R.; Guosheng, L.; Linlin, C.; Yue, Z., and Ninglei, O., 2017. Simulating wave climate fluctuation in the Bohai Sea related to oscillations in the East Asian circulation over a sixty year period.

Wave climate in the Bohai Sea from 1950 to 2011 was simulated with the Simulating Waves Nearshore model. Results showed that the following: (1) The significant wave height decreased; wave direction and wave period all increased in the past 62 years; the average decrease in significant wave height was 0.3 cm/y, and the increase in the wave angle was 0.12°/y. (2) The abrupt change of significant wave height occurred around 1968; the abrupt change of wave direction occurred around 1960. The characteristics of wave climate were affected by a complicated long-term process of the East Asian circulation. Four patterns for the effects of the East Asian circulation on the wave climate in the Bohai Sea were found by analysing the variation in the summer significant wave height and correlations of the significant wave height with the East Asian monsoon, West Pacific subtropical high, and west wind circulation.

Mahabot, M.-M.; Pennober, G.; Suanez, S.; Troadec, R., and Delacourt, C., 2017. Effect of tropical cyclones on short-term evolution of carbonate sandy beaches on Reunion Island, Indian Ocean.

Carbonate sandy beaches in Reunion Island show various forms of evidence of erosion. Extreme waves associated with tropical cyclones (TCs) play a major role in beach dynamics. The present study analyzes and quantifies back-reef beach response and recovery from forcing generated by TCs Dumile, Felleng, and Bejisa, which occurred in 2013 and 2014. The study focuses on carbonate beaches of Reunion Island from Cap Champagne to the Passe de Trois-Bassins. Morphological and volumetric changes on beaches were analyzed by comparing 19 beach profiles. The results show that TCs are able to cause significant morphosedimentary change on the back-reef beaches of Reunion Island. These changes affect beach topography and involve longshore and cross-shore sediment transport. An alongshore variation in beach response is observed, which varies according to tropical storm intensity and coastal morphology. The intensity of impact seems to be related to reef width. The most severe erosion occurred at Boucan Canot, where reef is absent with a loss of −24 ± 2 m³ after TC Dumile, −38.7 ± 1.2 m³ after Felleng, and −42.5 ± 1.6 m³ after Bejisa. Elsewhere, the volumetric changes is less than 5 m³ under TC Dumile and vary between 2 and 11 m³ under TC Felleng and between 2 and 23 m³ under TC Bejisa. No significant impact occurred at La Saline where the reef flat is large and provides good protection for the beach; however, relative coastline orientation and prestorm beach-profile morphology also play an essential role in storm impact. Wave height and water level are also determinant factors of storm erosion potential. After storms, the beaches show a relative capacity for recovering because of calm conditions; however, different behaviours are observed along the same beach compartment. This suggests local influence of coastal structure and/or reef geomorphology in sediment transport processes.

Lee, J.; Kim, S.-g., and An, S., 2017. Dynamics of the physical and biogeochemical processes during hypoxia in Jinhae Bay, South Korea.

Bottom-water hypoxia occurs during the summer in Jinhae Bay, a semienclosed embayment in South Korea, and can have detrimental effects on marine ecosystems around the region. Measurements of the oxygen demand in the bottom water and sediments and time-series measurements of hydrographic characteristics were conducted in Jinhae Bay in 2015. Variations in dissolved oxygen (DO) can be divided into three distinct time periods. During period I (late March to late May), bottom DO decreased linearly with thermocline development. During period II (late May to late August), hypoxia persisted. During period III (after late August), bottom DO increased as the thermal stratification began to break down. The seasonal bottom-water oxygen concentration was significantly correlated with the temperature difference between surface and bottom water, indicating that hypoxia development and maintenance is strongly dependent on thermal stratification. Although high oxygen demand in the water column and sediments must affect summer bottom-water hypoxia, biogeochemical oxygen consumption may not be significantly correlated with the time of formation and dissipation of hypoxia. The sediment oxygen demand was comparable with the water-column oxygen demand (WOD) in period I, whereas WOD dominated the total oxygen demand in the bottom water in period II, indicating that water-column respiration played a major role maintaining the hypoxic conditions. The results suggest that physical processes, especially thermal stratification, are more important to the development of hypoxia than biogeochemical oxygen consumption in Jinhae Bay, where freshwater input is insignificant and water circulation and exchange with the outer bay are restricted.

Fellowes, T.E.; Gacutan, J.; Harris, D.L.; Vila-Concejo, A.; Webster, J.M., and Byrne, M., 2017. Patterns of sediment transport using foraminifera tracers across sand aprons on the Great Barrier Reef.

Sediment dynamics exert large control over coral reef geomorphological evolution and are vital to understanding past and present geomorphic responses. Large benthic foraminifera (LBF) live in the algal reef flats, and their tests (shells) are transported post-mortem by waves and currents onto back-reef environments, including sand aprons. This study investigated the patterns of transport linking surficial and downcore sediments in samples from three sand aprons with different wave exposures at One Tree Reef on the southern Great Barrier Reef (Australia). Six LBF genera represented up to 32% of the sediments analysed. Lagoonward transport increased LBF test abrasion and sediment bulk density. Sediment grain size and LBF abundance in sediments also decreased with lagoonward transport. Sediment transport patterns indicated by LBF species used as tracer were consistent with the prominent E-SE wave environment. A novel taphofacies approach was used to describe stratigraphic layers in downcore sediments based on LBF test abrasion and abundance. Varied sediment deposition rates did not affect the LBF test abrasion signature downcore. It appears that Baculogypsina sphaerulata has been the dominant species for at least 3 ka. Tests that were deposited slowly exhibited less or the same levels of abrasion than those that were rapidly deposited. It appears that test abrasion is primarily determined by the distance travelled rather than the influence of increased age or chemical dissolution.

Kim, J.; Choi, J.; Choi, C., and Hwang, C., 2017. Forecasting the potential effects of climatic and land-use changes on shoreline variation in relation to watershed sediment supply and transport.

This study investigated the potential effects of future climatic and land-use changes on sediment supply and shorelines in the Hoeya River estuary, Korea. Historical shoreline variations were determined along Jinha and Solgae Beaches for the period 1975–2013 using the Digital Shoreline Analysis System. Sediments during future periods were simulated in this watershed under the Representative Concentration Pathways 4.5 and 8.5 scenarios using the soil and water assessment tool model. Subsequently, this study analyzed the correlations between the beaches and the sediment supply. For the natural beaches BS-I (0.805) and BS-II (0.700) in 1975–2013, the river-supplied sediment was closely correlated to shoreline changes. The area of beach sediment for future periods was assessed based on R-squared values. The artificial beach BS-III (0.203), which had remained relatively stable in 1975–92, showed shoreline erosion following this period. This beach is now artificially supplied with sediment because of a training dike. In 1986, because of the presence of a dam, a decrease in the discharge volume of suspended solids from the watershed caused a clear erosional trend in artificial beach BS-IV (0.432) from 1975. Artificial activity in the study area has caused major changes to the shoreline, but the R-squared values are relatively low. In the future, the area of the natural beach will increase during spring and winter and will decrease during summer and autumn. Furthermore, these seasonal trends in future periods may be amplified by seasonal variability in the wave direction. These results are expected to improve the understanding of shoreline changes that contribute to sediment supply and transport in river watersheds, which has significant implications for the effective management of the coastal environment.

Han, M.; Yang, D.Y.; Yu, J., and Kim, J.W., 2017. Typhoon impact on a pure gravel beach as assessed through gravel movement and topographic change at Yeocha Beach, south coast of Korea.

This study investigated sediment movement and topographic change using radio frequency identifier (RFID) tracers and real-time kinematic (RTK)–global positioning system (GPS) data to examine the response of a gravel beach under typhoon conditions. Yeocha Beach, the study site and a pure gravel beach, was affected by strong wind and waves produced by Typhoon Goni on 24–26 August 2015. On 26 August, the main direction of the tracer movement was toward the upper part of the beach and toward the west relative to the onshore-offshore and alongshore directions. The average movement distance of the tracers differed according to the insertion points. The tracers inserted in the beach face showed a longer average movement distance of 12.07 m compared with 1.89 m for those inserted in the storm berm. In addition, the tracers inserted in the beach face showed an average movement of 0.44 m in height toward the upper part of the beach. The result of topographic change showed that sedimentation was dominant within most parts of the beach. Moreover, this study clarified sediment movement patterns according to various patterns of localized topographic changes and tracer movement. This study investigated the relationship between tracer properties and movement distance and found that significant statistical differences did not occur under the typhoon conditions; thus, the beach gravel moved collectively rather than individually under strong wave energy conditions. In addition, 3 months after the typhoon, the beach recovered back to its original topography under normal wave conditions. The beach response and recovery indicate that the pure gravel beach exhibited an outstanding natural seawall effect. However, this study investigated the beach response based on a single typhoon; future research is necessary to understand the response under various environmental conditions.

Delgado, A.L.; Menéndez, M.C.; Piccolo, M.C., and Perillo, G.M.E., 2017. Hydrography of the inner continental shelf along the southwest Buenos Aires Province, Argentina: Influence of an estuarine plume on coastal waters.

Estuarine plumes have a significant influence on the characteristics and biology of the adjacent inner shelf. In the sector occupied by the plume, several transformations occur to the sediment and nutrients exported from the continent to the oceans. The coastal zone of Pehuén Co (PC) and Monte Hermoso (MH) is located in a highly complex oceanographic and ecological regional system, which creates the basis of one of the most valuable Argentinean habitats for fishing of commercial species. In this work, the physical oceanographic characteristics of the inner shelf of the southwest Buenos Aires Province and the influence of the Bahia Blanca estuarine (BBE) waters are introduced. The in situ data obtained from oceanographic cruises included vertical profiles of water temperature, salinity, and turbidity. The spatial variability of the parameters was studied with a multivariate statistical analysis. Temperature and salinity presented high seasonal variability (6.1–22.9°C; 33.5–36, respectively). Maximum turbidity occurred throughout the summer (64 nephelometric turbidity units [NTU]) and showed a minimum during spring (24 NTU). The study area was characterized by a significant spatial variability, especially in terms of salinity and turbidity, while water temperature showed a more homogeneous pattern. Salinity and turbidity values decreased from PC (closer to BBE) to MH (further from BBE) stations, with the highest values located near the mouth of the BBE. The PC and MH (to a lesser extent) inner shelves are transitional environments between the estuary and the open beaches of Buenos Aires Province, creating a habitat where benthic and zooplankton estuarine and marine species are found.

Liu, C.; Huang, Z., and Chen, W., 2017. A numerical study of a submerged horizontal heaving plate as a breakwater.

Using a nonlinear numerical wave tank (NWT) based on potential flow, a submerged horizontal plate heaving in regular waves was simulated, and its performance as a breakwater was examined. The NWT is based on a Mixed Eulerian-Lagrangian formulation and a de-singularized boundary integral equation method. The viscous effect on the motion of the plate is estimated by a linear damping coefficient, and the natural frequency of the heaving plate is controlled by the system stiffness. Compared with a fixed submerged horizontal plate, our results showed that the heaving motion of the plate with a critical stiffness could reduce the wave-transmission coefficient to almost zero and effectively suppress the free and locked waves on the leeside of the plate. The new type of breakwater can be an ideal alternative for small marinas and recreational harbors.

Lv, F.; Wang, T.; Liu, F.; Yebing, Y.; Qiao, G.; Wang, Z., and Qi, Z., 2017. De novo assembly and characterization of transcriptome in somatic muscles of the polychaete Perinereis aibuhitensis.

The polychaete Perinereis aibuhitensis is a common species distributed throughout coastal and estuarine regions with growing importance in aquaculture. However, the knowledge of molecular mechanism of physiology and pathology of this polychaete has been limited. In this study, the transcriptome of somatic muscles of P. aibuhitensis was sequenced using the Illumina HisSeq 2000 sequencing platform. As a result, 53,204 unigenes with a length of 63,967,647 base pairs (bp) were obtained, among which 29,797, 9951, and 24,844 unigenes were matched in the nonredundant, nucleotide, and Swiss-Prot databases, respectively. Gene ontology analysis revealed that 9938 unigenes were classified into three categories: biological process, cellular component, and molecular function. In addition, 21,756 unigenes were grouped into 257 annotated pathways in the Kyoto Encyclopedia of Genes and Genomes database. More importantly, genes involved in fatty acid biosynthesis and metabolism, muscle contraction, and innate immunity of P. aibuhitensis were analyzed in detail. In addition, 4682 simple sequence repeats and 32,202 candidate single nucleotide polymorphisms were identified from the P. aibuhitensis transcriptome. These data facilitate further studies of the physiology and molecular response of P. aibuhitensis. Furthermore, these results contribute to the molecular basis for coastal research worldwide, using P. aibuhitensis as a model animal in the fields of environmental ecology, toxicology, etc.

Rivera-Guzmán, N.E.; Moreno-Casasola, P.; Espinosa, E.C.; Lazos Ruiz, A.E.; Vega, C.M.; Peralta-Peláez, L.A.; Sánchez Higueredo, L.E.; Rodríguez Medina, K.P.A., and Santana Aguayo, K.V., 2017. The biological flora of coastal dunes and wetlands: Halodule wrightii Ascherson.

Information on the seagrass Halodule wrightii was assembled describing its taxonomy, phylogeny, and geographic distribution and its plant communities, ecology, population biology, reproduction, and biotic interactions. The objective was to review the current understanding of its role as a pioneer species that thrives in nutrient-rich waters and has a broad tolerance range to abiotic factors, such as salinity, temperature, depth, and light. Its short life cycle, high degree of vegetative reproduction, and rapid growth allow it to colonize areas that have undergone disturbances, e.g., those affected by hurricanes. It occurs in monospecific stands or mixed with other seagrasses (Ruppia maritima, Thalassia testudinum, Syringodium filiforme, Zostera marina) and exhibits both vegetative and sexual reproduction but does not flower often. Worsening water quality is the main cause of seagrass decline in the world, along with other human activities, such as fishing, dredging, boating, and tourism. Given its usefulness, it is important to establish programs for the restoration and management of this species.

Nijland, W.; Reshitnyk, L.Y.; Starzomski, B.M.; Reynolds, J.D.; Darimont, C.T., and Nelson, T.A., 2017. Deriving rich coastal morphology and shore zone classification from LIDAR terrain models.

Comprehensive mapping of shore-zone morphology supports evaluation of shore habitat, monitoring of environmental hazards, and characterization of the transfer of nutrients between marine and terrestrial environments. This article shows how rich shore-zone morphological metrics can be derived from LIDAR terrain models and evaluates the application of LIDAR to classify shore-zone substrates. The utility of LIDAR methods was tested in comparison with the current best-practice method of photo interpretation (i.e. the BC ShoreZone system) on Calvert Island, British Columbia, Canada. Wider applications are considered. Indicators of shore-zone morphology (i.e. slope, width, roughness, backshore elevation) were calculated from LIDAR terrain models for regularly spaced transects perpendicular to the coastline. A combination of boosted regression-tree modeling and direct-rule application was used to classify the shore-zone morphology according to the British Columbia (BC) ShoreZone system. Classification accuracy was assessed against existing ShoreZone classification data. Shore-zone substrate was classified from LIDAR-derived morphometric indicators with 90% accuracy (five classes). A full classification, which combined substrate with shore width and slope, results in lower correspondence (40%; 25 classes) when compared with ShoreZone classes. Differences can likely be attributed, in part, to variation in spatial resolution of elevation-based methods and photo interpretation. It is concluded that LIDAR data can be used to support characterization of shore-zone morphology. Differences in processing and interpretation cause a low direct correspondence with the current image-based classification system, but LIDAR has the advantage of higher resolution, rich terrain information, speed, and an objective and repeatable method for monitoring future change in coastal environments.

Zhang, Z.; Wang, L.; Yao, X., and Lang, J., 2017. Dynamics of an underwater explosion bubble near a rigid wall: Effect of slenderness ratio, installation, and distance parameter.

Structural damage of maritime construction (e.g., dams, warships, etc.) has received considerable international attention in recent years because of underwater explosions from accidental events and terrorist bombing attacks. Therefore, research studies on underwater explosion load characteristics will have a great influence on the future of coastal and maritime engineering. Here, level set–direct ghost fluid–Runge Kutta discontinuous Galerkin method and boundary element method are combined to establish a model of underwater explosion near a rigid wall. First, the hybrid algorithm is used to simulate the process of underwater explosion in free field; the results agree well with experimental data, proving the effectiveness of the algorithm. Second, the process of underwater explosion near a rigid wall is simulated by the presented method. Finally, effects of parameters – slenderness ratio, installation (horizontal and vertical), and distance from the center of the explosive to the rigid wall – are investigated on shock waves and bubble dynamics. It is found that during the detonation process, the ellipsoidal bubble gradually turns into a spherical one. The radial pressure peak value is higher than the axial one. During the collapse phase, the slenderness ratio and the installation have little effect on bubble shape, maximum radius, and pulsation cycle. During the bubble-jet process, a high-speed jet penetrates the bubble toward the rigid wall and generates a high-pressure region on the bubble wall. For the charge placed vertically, the jet velocity rises while the jet width decreases as the slenderness ratio increases; results for horizontal cases are opposite. The jet velocity in the vertical case is lower than that in the horizontal case; on the contrary, the jet width is larger. With the increase of the distance parameter, the pressure on the upper surface of the bubble and the jet velocity are higher, whereas the jet width is smaller.

Rogers, J.E.; Russell, M.J., and Harwell, M.C., 2017. Improved method for calibration of exchange flows for a physical transport box model of Tampa Bay, FL, U.S.A.

Results for both sequential and simultaneous calibration of exchange flows between segments of a 10-box, one-dimensional, well-mixed, bifurcated tidal mixing model for Tampa Bay are reported. Calibrations were conducted for three model options with different mathematical expressions for evaporative loss. Evaporation was subtracted from freshwater inputs in the first option. Evaporative losses were replaced by water from the adjacent down-bay segment in the second option. Evaporative losses in the third option described a complete water balance. For example, when starting at the head of the bay, water drawn from Segment II to replace evaporative losses from Segment I must be replaced by water from Segment III, and so on. Three questions were asked in approaching this project: does simultaneous calibration or sequential calibration yield better box model performance, which evaporation option best predicts observed salinities, and how well does model performance compare to more complex hydrodynamic models? Sequential calibration followed the classical salt balance and steady-state approach. A nonlinear parameter estimator was used for simultaneous calibration. The sequential approach proved useful in evaluating the three evaporation options. However, simultaneous calibration proved superior in predicting observed salinities but was ineffective in discerning differences between evaporation options. Simultaneously calibrated model option 3 produced residence times that fell within the range of more complex hydrodynamic models of Tampa Bay.

He, R.; Zhang, J., and Chen, W., 2017. Using the elastic vertical vibration of a rigid caisson at low frequencies to stabilize the foundation of coastal engineering structures.

A suction caisson or a bucket foundation offers a suitable and economic foundation type for many coastal structures (such as breakwaters and wind turbines). Because of the relative stiffness of a caisson foundation compared with the surrounding soil is high, the caisson is treated as a rigid cylindrical shell in this article. Seawater and seabed are treated as a coupled seawater–seabed half-space. In that way, the elastic, vertical vibration of a caisson can be modeled as the vertical vibration of a rigid shell embedded in a fully saturated, porous seabed. The solution to the problem is obtained with the ring-load Green's function and proper boundary conditions at the caisson–soil interface. With integral equations, the governing equations are transformed to Fredholm equations and are solved numerically. Numerical results show that, for a rigid shell embedded in a homogeneous sandy seabed, the dynamic contact-load transfer mechanisms are similar, and the nondimensional dynamic impedances are almost the same for various kinds of sands. By the obtained dynamic stiffness and damping of the caisson, the dynamic responses of a caisson-supported coastal structure can be obtained easily.