Do, T.K.A.; de Vries, S., and Stive, M.J.F., 2018. Beach evolution adjacent to a seasonally varying tidal inlet in central Vietnam.

Cua Dai Inlet is a typical, seasonally varying tidal inlet in central Vietnam. Since 1995 the northern adjacent coast, known as Cua Dai Beach, has experienced serious erosion. The decadal scale behavior of this inlet appears to reflect a nonperiodic cyclic process. Inlet channel shifting from north to south has welded the abandoned ebb-tidal delta with Cua Dai Beach, leading to accretion but subsequently triggering erosion. Although erosion of Cua Dai Beach was exacerbated by decrease of sediment supply from the estuary and ebb-tidal delta and by coastal developments, the channel shifting to the south, and the ebb shoal development were important primary controlling mechanisms. This study aims to quantify the main erosional processes in and near the Cua Dai coastal inlet and adjacent beaches since 1995. First, satellite data were used to detect shoreline change trends and to estimate volume changes. Second, alongshore, wave-driven sediment transports were estimated using numerical models. Observed shoreline changes indicate that, during the period from 2000 to 2010, erosion rates at the northern side of the inlet were on average 12 m/y. Close to the inlet, erosion rates were larger, up to 19 m/y. At the same time, the southern coast of the inlet was found to accrete with a mean rate of 11 m/y. Calculated alongshore sediment transport rates explain the observed erosion and accretion patterns. The overall system lost a significant sediment volume, which is estimated to amount to 243,000–310,000 m³/y. A logical conclusion is that the effects of the shifting of the inlet channel to the south caused erosion of the northern adjacent coast, whereas human interventions in the river catchment, the estuary, and along the coast contributed importantly to the overall sediment deficit of the inlet system and its beaches and to the shifting erosion pattern toward the north.

Burnette, C. and Dally, W.R., 2018. The longshore transport enigma and analysis of a 10-year record of wind-driven nearshore currents.

Previous analysis of a 10-year record of nearshore directional wave spectra collected with an Acoustic Doppler Current Profiler (ADCP) installed outside the surf zone in Melbourne Beach, Florida, unexpectedly revealed that the long-term average wave-induced radiation stress (S_xy) was nearly balanced between northerly and southerly forcing. More than 4 years of wind data collected at the site with a directional anemometer also showed a nearly balanced net longshore wind stress. However, shoreline offsets at nearby jettied inlets clearly indicate a predominant north-to-south net sediment transport. This enigma was investigated by analyzing the nearshore currents measured by the ADCP, and examining their correlation with the wind and incident waves. Significant correlation was found between the depth-averaged wind-driven longshore current and the incident wave conditions; e.g., the average energy-based significant wave height ____mo is typically larger (0.95 m) when the current is directed to the south than when the current is directed to the north (0.73 m). Guided by the classic Coastal Engineering Research Center (CERC) formula for longshore sediment transport, it is found that is significantly more correlated with southerly directed longshore currents (r = 0.47) than northerly currents (r = 0.21). Also, if a “storm” is defined as whenever H_mo exceeds 1.75 m, 40% of this time, the mean wave direction is out of the northeast quadrant, 33% is from the southeast, and 27% approaches shore-normal. Additionally, during storms, a stronger correlation between S_xy is found with southerly directed wind-driven currents (r = 0.51) than with northerly directed currents (r = 0.32). These findings indicate that net longshore sediment transport may in fact be heavily influenced by the correlation of the local wind with the waves, a feature not included in traditional longshore sediment transport formulas.

Carrasco, L.; Vera, P.; Belda, E.J., and Monrós, J.S., 2018. Combining remote sensing and field mapping methods to study the vegetation dynamics within a coastal wetland and determine the habitat effects of a threatened bird species (Emberiza schoeniclus witherbyi).

Coastal wetlands are highly dynamic changing ecosystems because of the effects of meteorology, wildlife interactions and human activities. They are one of the world's most threatened ecosystems, and threats to them drive the most specialist species to unfavorable conservation status and population trends. Therefore, it is important to frequently monitor the coverage changes of the different vegetation types to understand these species' population dynamics. However, frequent and detailed cartography entails costly efforts. Here, satellite images with field mapping were combined to create vegetation classification maps for past years from SPOT-5 images in the Pego-Oliva coastal wetland (Spain) and obtained classification accuracies above 85%. Together with habitat selection models, this information was used to understand the changes in the habitat of a threatened bird species, the Eastern Iberian reed bunting (Emberiza schoeniclus witherbyi), whose population has sharply declined in recent decades in Spain. A statistically significant reduction in reed–rush patches (positively selected habitat) and an increase in homogeneous reed patches (negatively selected habitat) were observed in those areas where the species disappeared as breeders. This study shows the potential of remote sensing and GIS techniques for the a posteriori monitoring of variation in the habitats available for threatened species to set up management and conservation measures.

Schedel, J.R., Jr. and Schedel, A.L., 2018. Analysis of variance of flood events on the U.S. East Coast: The impact of sea-level rise on flood event severity and frequency.

This is an investigation to quantify the severity and frequency of coastal flood events on the U.S. East Coast. Flood events are defined as instances during which the water level exceeds a predetermined threshold. An examination of monthly water-level data from 13 locations on the U.S. East Coast shows an increasing mean sea-level trend. Analysis of variance was used to compare the frequency of flood events. At all 13 locations, flood events were compared to established moderate and minor flood stages in the pre-1990 and post-1990 time frames. Flood stages are defined as water-level heights associated with various levels of flooding. For all locations, compared to absolute water heights based on a fixed datum, these flood stages were exceeded more frequently today than in the past. However, when the effects of sea-level rise were negated, flood events were shown to occur at similar rates today as in the past. Flood events that were significantly higher than the mean sea level occurred with the same frequency over the past century. Based on absolute water levels, flood events are more severe and more frequent than in the past. However, if the effects of sea-level rise are negated, flood events show little to no change in severity or frequency. Coastal flood events are starting from a higher baseline height because of sea-level rise. Thus, the same severity of a flood event today reaches a greater absolute height than an identical flood would have reached 50 or 100 years ago.

Feher, L.C.; Willis, J.M., and Hester, M.W., 2018. Importance of site history and environmental setting on soil properties in restored Louisiana back-barrier island salt marshes.

Although previous studies have identified significant differences between the soils of salt marshes restored with dredged material and natural marshes, it is unclear how these differences might affect plant community composition, soil development, and the overall stability of the marsh through time. Using soil shear strength as a metric of soil integrity and resistance to erosion, this study utilized field surveys of one natural and two restored back-barrier island salt marshes in coastal Louisiana to examine differences in shear strength and other soil properties in relation to site history and environmental setting. Soil properties at both restored sites were largely dependent on the source of the fill material in addition to site-specific restoration approaches. Soils at the younger restored marsh were significantly more finely grained than soils at either the older restored marsh or the natural marsh. High soil conductivity resulting from limited tidal exchange likely hindered plant establishment at the younger restored marsh, whereas the soil properties and vegetation cover of the older restored marsh were relatively similar to that of the natural marsh. Soil shear strength was comparable between the natural and restored marshes but was significantly higher in areas with finely grained soils. Therefore, differences in soil properties between the natural and restored marshes may reflect site-specific restoration approaches. As such, sediment source and hydrologic regime are important drivers of back-barrier marsh restoration success that can exert strong influences on soil development and likely the resilience and sustainability of these habitats.

Allahdadi, M.N. and Li, C., 2018. Numerical simulation of Louisiana shelf circulation under Hurricane Katrina.

The response of currents on the Louisiana shelf to Hurricane Katrina was studied using the 3-D Finite Volume Community Ocean Model (FVCOM). The study area encompassed the Louisiana shelf covering both sides of the Mississippi River's Birdsfoot Delta. The model was forced by a wind field prepared by combining the Hurricane Research Division Wind Analysis System data for the hurricane with background winds outside of the hurricane's influence from National Centers for Environmental Prediction (NCEP)/North American Regional Reanalysis (NARR). Current and water-level data recorded at Wave-Current-Surge Information System (WAVCIS) stations over the inner shelf provided a unique opportunity to examine shelf hydrodynamics in response to Katrina. Model performance was evaluated by examining water-column stratification under different scenarios and using a range of parameters of the Mellor-Yamada level 2.5 turbulence closures for vertical eddy viscosity. This resulted in a set of appropriate closure parameters for the response of a shallow shelf to a hurricane. Simulated near-surface currents followed the overall pattern of hurricane wind structure over the outer shelf and to some extent over the inner shelf; however, currents over the shallow Louisiana shelf were affected by coastal geometry. Investigation of bottom currents showed a possible baroclinic response over both the inner and outer shelves. Over the Louisiana shelf, this was similar to the baroclinic response of stratified shallow waters for regions outside of the radius of maximum wind (R_mw), as identified in previous studies. A part of this baroclinic response can be explained by the horizontal baroclinic pressure gradient that resulted from the inhomogeneous hurricane-induced surface cooling.

Mo, S.; Li, Z.; Gou, K.; Qin, L., and Shen, B., 2018. Quantifying the effects of climate variability and direct human activities on the change in mean annual runoff for the Bahe River (Northwest China).

Evaluating the impacts of climate change and human interference on runoff is critically important for regional water security. This study investigated the effects of climate variability and direct human activities on the change in mean annual runoff for the Bahe River in Northwest China. Precipitation, evaporation, and runoff data from 1959 to 2010 were analyzed at the Luolicun and Maduwang hydrologic gauge stations, and their temporal trends were explored using the Mann-Kendall test. A Mann-Kendall-Sneyers test and the double mass curve were applied to detect the statistically significant transition points in the hydrometeorological records. Results indicated no change point in upstream runoff in the Bahe River from 1959 to 2010; however, a clear transition point existed in midstream runoff in 1989, indicating a significant decrease in stream-flow. While climate change could be a major factor leading to runoff variation in the upstream, human activities had significantly contributed to the decline of the midstream runoff after 1989. A decomposition method based on a Budyko equation was used to quantify the relative impacts of climate change and direct human activities on the midstream runoff. Results show that 35.3% of the reduction in annual runoff was caused by human activities and that a 2.2% increase in annual runoff could be attributed to climate change. This finding means that human impact rather than climate exerts the dominant influence on runoff decline in the Bahe River basin.

Camara, E.M.; Caramaschi, É.P.; Di Dario, F., and Petry, A.C., 2018. Short-term changes in two tropical coastal lagoons: Effects of sandbar openings on fish assemblages.

Sandbar openings (SBOs) are among the largest possible disturbances in coastal lagoons. This study investigated the mechanisms of the responses of fish assemblages to short-term environmental changes resulting from several SBOs during 1 year in two coastal lagoons in southeastern Brazil. Lagoons were sampled monthly in sites closer to, and more distant from, the sandbars. A principal component analysis summarized limnological differences between periods of contact and isolation from the sea, and site- and lagoon-based variation partitioning and independent redundancy analyses (RDAs) quantified the unique and shared effects of limnology, space, and period on species and groups of species (marine, estuarine, and freshwater). Limnological differences between periods were associated with a higher marine influence during SBOs and an increasingly eutrophic state influenced by the lagoon and days of isolation. Limnology explained most of the variance in composition and abundance of species, and large fractions were shared with, or explained exclusively by, lagoons and distance of sites from the sandbar. The responses of groups of species were less evident in lagoon-based analyses and more associated with trophic state, most likely because of the short intervals between SBOs, which reduced temporal differences in the marine influence. Responses at the group level were more relevant in site-based analyses, given the predominance of species based on their tolerances or affinities in sites with different salinities. Therefore, the responses of groups of species to limnological changes associated with the features of lagoons and sites (e.g., morphometry, human impacts, and freshwater inflow) determined the effects of SBOs on the fish assemblages.

Gao, X.; Wang, M.; Wu, H.; Wang, W., and Tu, Z., 2018. Effects of Spartina alterniflora invasion on the diet of mangrove crabs (Parasesarma plicata) in the Zhangjiang Estuary, China.

Spartina alterniflora , an exotic invasive plant, has become the most serious threat colonizing mangrove areas in China in the past two decades. The diets of a dominant mangrove crab, Parasesarma plicata, in two mangrove habitats (Kandelia obovata forest and Avicennia marina forest) and adjacent S. alterniflora marsh in a subtropical mangrove estuary in Fujian, China, were investigated using stable isotopes, while a feeding experiment was carried out. The results showed that in the Avicennia forest, Parasesarma was herbivorous, feeding mainly on macroalgae. In the Kandelia forest, the contribution of mangrove leaves, macroalgae, and sediment to the diet of Parasesarma were about 75.5%, 24.2%, and 0.2%, respectively. While Parasesarma had a higher δ¹³C value and also a higher δ¹⁵N value in the Spartina marshes relative to the two mangrove habitats, suggesting that they were feeding on Spartina detritus as well as some small invertebrates. The feeding experiment showed that the δ¹³C value of Parasesarma after 90-day feeding only on Spartina leaves was very close to the δ¹³C value of the crab caught from the Spartina marshes, indicating that Spartina was the main carbon source. These results demonstrated that the invasion of Spartina has changed the main food resources of native crabs by providing food resources, which could affect the impact of crabs as ecological engineers and eventually affect the integrity and function of native ecosystems.

Yu, P.; Zhong, X., and Zhou, Y., 2018. Impact of model resolution on radar imaging of underwater sand waves.

Radar sensors are capable of imaging varying sea-surface roughness attributable to divergent and convergent current flow over underwater sand waves. This manifestation can be simulated and explored through a flow model combined with a radar-imaging model by explaining the interaction between bathymetry, currents, and surface waves. Accuracy of numerical models is usually limited by grid resolution; however, a lack of studies is present regarding the influence of grid resolution on the combined flow and radar-imaging model, which can determine the research scale of oceanic phenomena based on radar-imaging theory. To examine the role of grid size on imaging of distinct scales of sand ridges and to ignore other sources of surface-roughness variations in coastal areas, the authors designed an idealized flow model integrated with a radar-imaging model with different resolution. The results indicate that high-resolution synthetic aperture radar (SAR) images may be possible to detect bottom features smaller than 100 m. As the increasing grid resolution, surface-roughness variations can gradually reach a stable phase, indicating that the grid spacing should be elaborately selected according to the scale and complexity of underwater topography to fully present performance of the two-dimensional combined model. This model offers a reference to study the application of a radar-imaging mechanism or to analyze morphological changes based on SAR images and the combined system in coastal areas for future work.

Moffitt, D.L. and Kumar, L., 2018. Remote sensing of a shallow, fringing reef platform for analysis of island sector susceptibility and development of a coastal vulnerability index.

Like many islands in middle latitudes, Pacific islands are often fringed by protective coral reefs that attenuate wave energy impacting the coastline. Measurement of the extent and distribution of shallow reef platforms by remote sensing of bathymetry enables an assessment of the relative exposure or protection of each part of an island. Fringing reefs are one of a number of physical variables relevant to the coastline's susceptibility to erosion and inundation resulting from extreme weather and conditions exacerbated by climate change and rising sea levels. In this research the extent of shallow reef platform around Lifuka Island, Tonga, was determined using a modified Stumpf band ratio method applied to Landsat 8 and high-resolution Quickbird satellite imagery, with aerial LIDAR data available for ground-truth purposes. The results indicate that both sets of satellite imagery provide a means of measuring the bathymetry to at least 15 m with a correlation (R²) value of 0.87 for Landsat 8 and to 15 m with a correlation (R²) value of 0.86 for Quickbird, when compared with the LIDAR survey. This article forms part of the research into the preparation of a coastal vulnerability index to inform decision-making and risk assessment for Pacific Island nations at the subisland scale. The mapping of the fringing reef by remote sensing allows its spatial distribution to be considered in the assessment of risk to coastal regions to inundation and erosion processes. Further, it demonstrates the value of freely available Landsat data for planning adaptation to climate change in developing nations at a level pertinent to local governance of villages and communities.

El Khattabi, J.; Carlier, E., and Louche, B., 2018. The effect of rock collapse on coastal cliff retreat along the chalk cliffs of northern France.

Coastal retreat is a topic that concerns all countries located on the coastal edge. This is the case for the chalky cliffs located in the north of France. Here, the cliff base is characterized by chalk rock rich in clay with low mechanical characteristics. To understand the appearance of rock collapses causing cliff retreat, the methodology applied in this report is based on an analytical study and numerical modeling. The model developed with CESAR (i.e. finite element software dedicated to stability) shows deformation affecting gray and blue chalk with separations reaching 3 cm. Simulations carried out with UDEC (i.e. Universal Distinct Element Code) show that constraints are organized around joints when the blocks rearrange themselves, and the effects are mainly seen at the base of the cliff. This study demonstrates the appearance of irregular conjugate fractures within the marly levels of the blue chalk. This type of fracture appears as a result of pressure from the overlying layers and the influence of lateral stress induced by the “Grand Blanc Nez” formation. These fractures propagate towards the gray chalk and set the limits of different blocks. The displacement of these blocks leads to the obstruction of conduits, which increases the water pressure. The destabilization of the cliff is reflected in the appearance of release cracks, which are strongly influenced by variations in groundwater level. These findings were verified by numerical modeling. This example demonstrates that rock collapses are responsible for coastline retreat in this area. The combination of unpredictable natural phenomena associated with a concentrated spatial area creates a high-risk coastal area retreating at around 0.25 m/y.

Gong, J.; Guo, C.-Y.; Wu, T.-C., and Song, K.-W., 2018. Numerical study on the unsteady hydrodynamic performance of a waterjet impeller.

Numerical simulations of the internal flow field of a waterjet-propelled ship have been performed to evaluate the unsteady hydrodynamic performance of the impeller. Hydrodynamic performance of the impeller provides a great influence on ships with waterjet propulsion when sailing in coastal environments and zones farther out to sea. Nonuniform axial velocity entering the channel causes unsteady loading of the impeller blades, resulting in noise and vibration, and it increases the risk of impeller cavitation. The hull modeled in this study is the INSEAN 2340, fitted with a waterjet-propulsion system. Numerical simulations are for unsteady, multiphase flow and include free-surface effects. Meshing of the hull and waterjet, selection of the turbulence model, and calculation conditions set to satisfy all research objectives are discussed. The simulation results showed that the internal flow field featured with gas–liquid mixed flow and reflow phenomena in the channel. A varied pressure distributed over the blade surface, and the surface pressure pulsation was considered to be more intensely close to the channel during a cycle. It is found that the thrust and torque coefficients of the impeller were periodically fluctuating within one period. The average fluctuation range of thrust coefficient is −4.07%∼3.39% to its mean value, which demonstrated the unsteady quantitatively. Additionally, thrust deduction existed when the impeller rotated to a particular position of a single blade, and the loads on the impeller blade surface tended toward stabilization as the rotating speed increased.

Sigren, J.M.; Figlus, J.; Highfield, W.; Feagin, R.A., and Armitage, A.R., 2018. The effects of coastal dune volume and vegetation on storm-induced property damage: Analysis from Hurricane Ike.

In response to numerous recent high-profile cases of tropical storm and hurricane damage to coastal communities, there has been increasing attention on the storm protection services provided by coastal ecosystems. However, substantial knowledge gaps exist regarding the quantitative economic benefits of such services, particularly for coastal vegetated dune ecosystems. A novel geographic information system (GIS)-based technique for delineating, quantifying, and relating coastal dune volume, vegetation area, and geographic and built-environment covariates to sustained property damage was used for the upper Texas coast following Hurricane Ike in 2008. The multivariate regression analysis contained more than 1000 homes spanning both sides of the storm's path. Dune volume and vegetation were both significantly related to reduced sustained property damage for the west side of the storm. For this area, model results showed that dune sediment was worth roughly $50 per cubic meter and dune vegetation was worth roughly $140 per square meter. However, because these variables were collinear and modeled separately, these amounts should not be viewed additively. The total property damage offset value of dunes across the study area was estimated to be more than $8 million, or approximately $8200 per homeowner. Based on the frequency of storms for this area over the last 115 years, coastal vegetated dunes were valued at roughly $86,000 per hectare per year. The results indicate that dunes could play an integral role in coastal hazard mitigation strategies and offer a unique opportunity where bioengineered, green infrastructure can be used as an alternative to hard coastal structures.

Belmonte, G.; Moscatello, S.; Hajdëri, E.; Vaglio, I., and Denitto, F., 2018. Composition and spatial distribution of mesozooplankton along confinement and anthropogenic-impact gradients in the Gulf of Vlorë (Albania).

The composition of mesozooplankton and their space-time distribution in the Gulf of Vlorë (southern Albania, Mediterranean Sea) are described for the first time. Sampling was carried out during two oceanographic cruises (May 2007, January 2008) with two replicates at each of 17 stations at each time, making a total of 68 samples. The study aimed to describe the influence of confinement (defined as distance from the open sea) and anthropogenic impact (defined as vicinity to the east coast of the gulf) on zooplankton composition. A total of 198 taxa were recognised in the whole zooplankton assemblage, with only 136 taxa common to both periods and only two species present in all samples. Statistical analysis of data distinguished the Mezokanal area (the boundary between the gulf and the open sea) from three other areas inside the gulf. Differences were also found among the areas inside the gulf at increasing degree of confinement. Mesozooplankton varied more sharply with confinement than with anthropogenic impact and yielded more-detailed space partitioning of the gulf than microzooplankton, which had been used in a previous study.

Yang, W.; Yu, M., and Yu, G., 2018. Stratification and rheological properties of near-bed cohesive sediments in West Lake, Hangzhou, China.

To understand the transport of cohesive sediments better, their vertical stratification characteristics must be known. In this study, the nature of the stratification and the rheological properties of near-bed cohesive sediments in West Lake, Hangzhou (China) were investigated. In the first step, basic properties such as concentration, density, and particle size were measured; thereafter, the rheological properties of the sediments were determined, including apparent viscosity, shear stress, and yield stress, under different shear loads. On the basis of the results, the stratification characteristics were analyzed, and the relationship between yield stress and incipient shear stress was evaluated. It was found that the bed sediments showed strong non-Newtonian and shear thinning behavior that can be described by the Carreau rheological model. Findings of particular interest are that the yield stress increased linearly with mud concentration and that the incipient bed shear stress was closely related to the yield stress.

Guerra-Santos, J.J. and Kahl, J.D.W., 2018. Redefining the seasons in the Términos Lagoon region of southeastern México: May is a transition month, not a dry month.

The Términos Lagoon is the largest estuary in Mexico, with numerous important animal and plant interrelationships. Its dominant feature is the largest mangrove surface in Latin America. A Natural Protected Area under Mexican law as well as an internationally recognized Ramsar site, this unique ecosystem is a frequent location for research projects concerning marine, wetlands, and terrestrial ecosystems. Located in the southern Gulf of Mexico and characterized by a tropical climate, the primary characteristic determining the region's meteorological seasons is the annual variation in rainfall. In 1982, an oft-cited article was published that defined the seasons as dry (February–May), wet (June–September), and an overlapping season of “nortes” or winter storms (October–March). Here evidence is presented, on the basis of an analysis of diverse meteorological parameters including 220 station-years of rainfall observations in the region, that May should be considered a transitional month, not part of the dry season. Because sampling and analysis protocols are often based on the definition of meteorological seasons, this result has implications for a wide range of environmental science research in the Términos Lagoon region.

Yang, Z.; Cheng, H.; Cao, Z.; Guo, X., and Shi, X., 2018. Effect of riverbed morphology on lateral sediment distribution in estuaries.

An idealized model is applied to a set of eight estuaries with various transverse depth cross-sections to examine the effect of riverbed morphology on suspended sediment concentration (SSC) distribution. Five estuaries consist of a single deep channel, and three estuaries consist of double deep channels. All estuaries share a set of boundary conditions, including tidal flow, density gradient, river discharge, in an attempt to represent a typical estuary. Under these conditions, model results suggest that both tidal and residual flow fields vary significantly among eight estuaries, resulting in significant differences on SSC distribution, e.g., maximum mean SSC (), location of (), and space uniformity of mean SSC. In most estuaries, the SSC is higher over the left channel than that over the right channel mainly due to the lateral density gradient-generated residual flow (). However, the space distribution of mean SSC is more uniform over the estuaries with a rightward deep channel than those estuaries with a leftward deep channel. Furthermore, the former estuaries get a higher value of , which is mainly caused by the decreasing lateral density gradient across the estuary. Lateral residual flow generated by nonlinearities would transport sediment from two sides of the estuary to the central channel (convergent transport). This transport component would play an important role in a narrow deep estuary, and would shift the location of to the central orientation. On the contrary, a much lower value of is examined in the broad wide estuary because of the extreme weak nonlinearity. Sensitivity analysis of tidal asymmetry indicates that both the amplitude and phase of M₄ tidal flow would affect the transverse sediment distribution though the M₄ tidal transport () and the influence of M₄ tidal flow on the M₂ tidal transport (), resulting in a significant variance of and over estuaries.

Whiley, H.; Austin, J.; da Silva, G.M., and Ross, K., 2018. Faecal indicator bacteria present in sand at South Port Beach, South Australia.

Research has demonstrated that bacterial pathogens present in beach sand may be a risk to human health. The indicator species enterococci, total coliforms, and Escherichia coli were measured in beach sand collected from South Port Beach, South Australia, a popular recreational beach. Samples were collected from five distances from the low tide mark (low tide, 10 m, 20 m, 30 m, and 40 m), at three depths (surface, 10 cm down, and 30 cm down), and at five sampling times over a 3-month period. During this time there was a storm that resulted in significant movement of sand from the beach and high flow of the nearby river, and coincided with increased bacterial load. Within a week the bacterial load had returned to previously measured levels. In general, higher bacterial counts were at the surface level compared with 10 and 30 cm below the surface, and the lower counts were at the low tide mark, with increasing distance from the low tide resulting in increasing bacterial loads, and the highest load at the dune edge. This research provides information about the potential health risk of beach sand and a baseline for future studies exploring the microbial risks of Australian beach sand.

Wang, J. and Deng, Z., 2018. Development of a MODIS data–based algorithm for retrieving gage height in nearshore waters along the Louisiana Gulf Coast.

Gage height is one of most important physical parameters commonly used for the description of daily sea levels and generally monitored at sparsely scattered tidal stations. This paper presents a novel remote sensing algorithm for the retrieval of spatially distributed gage height data in coastal waters with emphasis on nearshore waters using the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data. The algorithm was trained using the Artificial Neural Networks toolbox in the MATLAB program and over 4 years (2007–11) of cloud-free MODIS Aqua data for water-leaving reflectance as well as ground truth measurements collected daily from U.S. Geological Survey stations along the Louisiana Gulf Coast. The algorithm was validated using 3 additional years of independent data sets, which were not used in the algorithm training and collected from 2012 to 2014. Cross-validation results indicated that the gage heights derived from the new algorithm were in good agreement with observed height, as evidenced by the high linear correlation coefficient of 0.8465 and low root mean square error of 0.2238 m. The new algorithm makes it possible to produce daily, spatially distributed gage height data for coastal management and resources development in shallow coastal areas where there are no gages.

Lim, H.S., 2018. Open channel flow friction factor: Logarithmic law.

The friction factor in open channel flow is considered to increase proportionally with wall roughness compared to that of pipe flow because of undulation at the free surface. The undulation is considered to be driven from the bottom and side walls. The increment factor associated with free surface undulation, shape distortion, and meandering is related to the Manning coefficient, and the incremented friction factor is substituted into the friction factor of circular pipe smooth (stretching) turbulent flow so as to yield the friction factor for open channel flow. The new equation for friction factor or mean velocity provides similar results to the Manning equation and the Ganguillet-Kutter (GK) equation for small streams. However, it is found that the Manning equation results in larger values of mean velocity in wide rivers compared with the GK equation and the new logarithmic equation based on the concept termed as “smooth turbulent,” which appears inappropriate in describing the turbulent flow mechanism. Smooth turbulent may have to be denoted as “stretching turbulent” because of stretching of the velocity profile as the Reynolds number increases. Based on the comparison results with the other two empirical equations, the new logarithmic equation could be suitably adopted in open channel flows.

Hu, J.; Guo, L., and Sun, S., 2018. Numerical simulation of the potential flow around a submerged hydrofoil with fully nonlinear free-surface conditions.

Hydrofoils have been utilized worldwide to facilitate coastal vessels for transportation, surveillance, and patrol with high speed. Inevitably, the free surface has a significant effect on the hydrofoils because of the shallow draft. In this paper, a numerical procedure based on a boundary-element method is developed for simulating a uniform incoming flow passing a two-dimensional submerged hydrofoil with free-surface effects. In the proposed technique, the boundaries of the computational domain are discretized by small elements over which the known and unknown variables are linearly distributed. To avoid the numerical instabilities induced by the sudden start of the flow through a sharp-edged foil, it is assumed that a vortex sheet with uniform strength Γ has been placed within the foil at the initial time step. The unknown vortex strength Γ, the velocity potential ϕ and ϕ_n on the boundaries are obtained simultaneously by solving the boundary integral equation together with an added auxiliary function at each time step. The free surface is assumed to be undisturbed at the initial time step. Then, it is traced by a Eulerian scheme. Both linear and nonlinear free-surface conditions have been applied. Convergence studies with respect to the element size, the time step, and the size of far-field boundaries have been undertaken. Comparison of the present numerical results with experimental data and previous numerical results shows that the present method gives fairly good results on the force, circulation, and wave excitation of the foil.