Sutherland, T.F.; Garcia-Hoyos, L.M.; Poon, P.; Krassovski, M.V.; Foreman, M.G.G.; Martin, A.J., and Amos, C.L., 2018. Seabed attributes and meiofaunal abundance associated with a hydrodynamic gradient in Baynes Sound, British Columbia, Canada.

The distribution of seabed geotechnical, biochemical, and meiofauna attributes was examined in Baynes Sound, British Columbia, between 2009 and 2014. Among attributes measured were sediment porosity, organic carbon and nitrogen, and trace element concentrations (e.g., zinc, copper), which increased with increasing sediment fines content toward the head of the Sound. A ternary plot (sand-silt-clay percentages) revealed a constant clay/silt ratio across a range of sand proportions with textures ranging from well-sorted sand at the high-energy SE entrance to silt-dominated mud in the depositional basin. These sediment textures were related to modeled maximum velocity values within 5 m of the seabed (U_max,5), with highest values (restricted entrance) and lowest values (deep basin) representing sand depositional and mud depositional facies. Sediment porewater sulfide fell into an oxic category (0–700 μM), exhibiting a lack of variation and organic enrichment within the Sound. The first principal component analysis (PCA) factor described the alignment between fine sediments, organics, Cu and Zn, and meiofauna attributes and accounted for 49% of the total variance. The second PCA factor (19% of total variance) described the relationship between U_max,5 and sediment grain size fractions >0.5 mm and an indirect association with water depth and fine sand (0.105–0.250 mm). Meiofauna were associated with a medium sand fraction (0.25 mm) characterized by low-porosity and low-organic sand loam textures. Although the range in abundance was relatively greater for nematodes, harpacticoid copepods revealed a stronger response to changes in sediment geotechnical and organic attributes, suggesting these taxa may be used to describe seabed variations or potential perturbations.

Koster, K.; Cohen, K.M.; Stafleu, J., and Stouthamer, E., 2018. Using ¹⁴C-dated peat beds for reconstructing subsidence by compression in the Holland coastal plain of the Netherlands.

Subsidence in the Holland coastal plain of the Netherlands was reconstructed from the vertical displacement of Holocene peat layers below their reference groundwater levels at the time of peat formation. This quantifies the part of subsidence that is due to compression processes and allows specification of the current state of peat compression in a map. ¹⁴C-dating of peat layers found intercalated in the Holocene sequence were used in the reconstruction. This dataset was combined with results from a recent coastal-deltaic plain wide three-dimensional (3D) interpolation of reference palaeo-groundwater levels, at which the intercalated peats are thought to have formed before they were buried, compressed, and vertically displaced. Empiric relations between reconstructed displacement and the thickness of overburden were determined and deployed in a national 3D geological subsurface model to establish a subsidence map with continuous cover of the coastal plain. The resulting maps show compressed peat layers under urbanized areas with 1 to 8 m of natural and anthropogenic overburden have subsided 1 to 5 m below the original level of formation. In the agricultural area of the coastal plain, where overburden is merely decimetres thick, consisting of fluvial flood- and sea-ingression deposits, peat generally experienced less than 1 m subsidence. The reference-level reconstruction method is deployable over large coastal plain areas to reconstruct subsidence caused by postdepositional vertical displacement of intercalated peat layers. It could therefore serve as an alternative approach for methods based on soil mechanics, which require input often not available for coastal plains on regional scales.

Selman, W. and Collins, S.A., 2018. Observations of wintering piping plovers (Charadrius melodus) positively associated with rock breakwater-influenced shorelines in southwestern Louisiana.

Much of the coastline in southwestern Louisiana is undergoing high rates of shoreline erosion, but long-term plans are to armor the majority of this shoreline with offshore rock breakwaters. This area is also considered critical wintering habitat for Piping Plovers (Charadrius melodus). However, to date, little information is available to assess the influence of these shoreline protection measures on Piping Plovers. From 2009 to 2010, three experimental breakwater sections were built along the shoreline of Rockefeller Wildlife Refuge (RWR) in southwestern Louisiana to determine their effectiveness at combating shoreline encroachment. Thereafter, annual Piping Plover surveys were conducted from 2013 to 2017 at RWR along ∼14.5 km of shoreline inclusive of the test sections. Observations included 89 total Piping Plovers in the 5 survey years, and 56 of these (total mean 63%; annual range 33–94%) were observed immediately behind or closely associated with all three rock breakwater test sections (∼6% of the shoreline surveyed). Breakwater sections, regardless of construction type, supported higher Piping Plover densities than unprotected shoreline. However, it seems that only one of these test sections will be economically viable in the long-term to protect shorelines. Offshore segmented breakwaters may positively benefit wintering Piping Plovers given that they are designed appropriately and permit limited overwash to maintain an open shoreline behind the structure (i.e. no vegetative encroachment). However, shoreline stabilization measures could be a trade-off that benefits some shorebirds (e.g., Piping Plovers) but negatively affects others that prefer mudflats (e.g., Long-billed Curlew [Numenius americanus]).

Lindner, B.L. and Neuhauser, A., 2018. Climatology and variability of tropical cyclones affecting Charleston, South Carolina.

Communities benefit from site-specific examinations of tropical cyclone climatology. The impact data from a tropical cyclone climatology are useful for planning purposes for emergency managers, medical facilities, building and infrastructure codes, utility and communications design, insurance, and wildlife and resource management. To that end, per an analysis of National Hurricane Center data for the years 1851 to 2015, a chronological list of tropical cyclones that passed within 139 km (75 nautical miles) of Charleston, South Carolina was compiled. Date, intensity, approach angle, and translational velocity were catalogued for each system upon closest approach. The return period is approximately 1.5 years for tropical storms and hurricanes, 3.8 years for hurricanes, and 28 years for major hurricanes. The frequency of zero-strike and multistrike seasons is well reproduced by a Poisson distribution, implying random strikes. The seasonality of tropical cyclones in Charleston shows a secondary maximum early in the hurricane season, likely due to the numerous diminished tropical cyclones that originated in or passed through the Gulf of Mexico. In fact, there has been an increase in recent decades in the occurrence of early-season tropical cyclones. The large fraction of tropical cyclones that affect Charleston after originating in or passing through the Gulf of Mexico can also be seen in the data for approach angle (most strikes by tropical storms were by those that came over land) as well as in the data for translational velocities (higher for tropical storms than for hurricanes). Charleston not only experienced more tropical cyclones during the years 1871–1910, but these cyclones also had higher-than-average translational velocities at closest approach.

Peláez-Zapata, D.S.; Montoya, R.D., and Osorio, A.F., 2018. Numerical study of run-up oscillations over fringing reefs.

This work presents a numerical study of run-up oscillations over a typical fringing reef profile at the laboratory scale. The nonhydrostatic SWASH model was calibrated and validated using experimental data of free surface elevation for eight gauges and run-up oscillations. The model shows a high sensitivity to variations in the parameters of bottom friction and horizontal mixing length. A process of calibration found the optimal values to be 0.014 s m^−1/3 and 0.01 m, respectively. With these values, the model is good at reproducing bulk run-up parameters such as the mean run-up period (r² = 0.93), sea-swell significant run-up (r² = 0.93), and infragravity significant run-up (r² = 0.88). The ratio between the infragravity and sea-swell run-up is highly dependent on the surf similarity parameter. For dissipative and intermediate conditions, the run-up is mainly dominated by low-frequency or infragravity oscillations, whereas for reflective conditions, high-frequency or sea-swell oscillations become more important. The results show that the run-up spectrum at high frequencies is proportional to f⁻⁴. The energy level at high frequencies is apparently independent of the offshore wave conditions and the width of the reef flat. However, the depth of the reef crest seems to be the most influential variable on the high-frequency energy. A parametric equation that depends on both the energy level at high frequency and a function of the run-up period was obtained to analyze the spectral characteristics of the wave run-up. This equation can be considered a first approach to a general parameterization of the run-up spectrum for reef zones, which can be useful in coastal engineering applications, such as predicting both the run-up height and frequency, spectral response of sediment transport in the swash zone, and coupling with spectral wave models.

Yaukey, P.H., 2018. Bird distribution among marsh types on the northern Gulf of Mexico.

The wetlands bordering the northern coast of the Gulf of Mexico are among the most extensive in North America and are among the most threatened. Despite this, little information is available on the distribution patterns of birds across these fresh, intermediate, brackish, and saline marshes. To evaluate the species-specific use patterns of these avian habitats, birds were surveyed in nesting season from 2010 to 2012 along a network of 97 points. Species richness peaked at fresh/intermediate points and numbers of birds detected at saline points. Numbers of most species detected varied across wetland types, with approximately one-half progressively declining with increasing salinity. Marian's Marsh Wren (Cistothorus palustris marianae) was found at fewer points than expected, suggesting it may be vulnerable. A subsample of points followed from immediately before the 2010 Deepwater Horizon oil spill through 2014 continued to show decreased numbers of detections of a relatively sedentary species, the Clapper Rail (Rallus longirostris).

Beetham, E.; Kench, P.S., and Popinet, S., 2018. Model skill and sensitivity for simulating wave processes on coral reefs using a shock-capturing Green-Naghdi solver.

Wave-flume data from published benchmark experiments were used to extensively evaluate numerical model skill and sensitivity for applying a shock-capturing Green-Naghdi (GN) model to simulate nonlinear wave-transformation processes on complex coral reefs. Boussinesq-type models that utilise nonlinear shallow-water equations (NSWEs) to represent wave breaking and dissipation hold significant potential for understanding coastal hazards associated with global environmental change and sea-level rise. These fully nonlinear phase-resolving models typically require a threshold condition to switch from dispersive equations to shock-capturing NSWEs in areas of active wave breaking. However, limited information exists regarding how this splitting approach influences the behaviour of different surf-zone processes that contribute to wave runup and inundation on reef environments. This paper presents a comprehensive analysis of model sensitivity to explore how input parameters that control wave breaking and dissipation influence the behaviour of sea-swell waves, infragravity waves, wave setup, runup, and solitary waves on coral reefs. Results show that each wave process exhibits unique sensitivity to the free-surface slope threshold (B) that is used to represent areas of active wave breaking by locally switching from the weakly dispersive GN equations to the shock-capturing NSWEs. Accurate representation of all wave processes, however, can be achieved if the wave-face steepens to at least 35° (B ≥ 0.7) before breaking is initiated. Results from this research support and encourage the use of nonlinear phase-resolving wave models as tools for academic research, coastal management, coastal engineering, and hazard forecasting on atoll and fringing reef environments.

Day, F.P.; Adams, E.C.; Gibala-Smith, L.A.; Graziani, D.J.; McMillan, B.; Sedghi, N.; Shafer, J., and Smith, M., 2018. Determining change in coastal barrier island dune vegetation following a decade of nitrogen fertilization.

Nitrogen deposition from agricultural and industrial sources is a threat to terrestrial biodiversity, and impacts are likely to be greatest in nitrogen-deficient systems. The results of a 10 year fertilization treatment on nitrogen-deficient coastal barrier island dunes and the decade following cessation of fertilizer application are reported here. The study objective was to determine the resilience of the dune plant communities. Would these communities return to their former state in terms of density, species composition, and species diversity after nitrogen additions ended, and if so, how rapid was their recovery? Plant density by species and species diversity were determined over a 20 year period from permanent plots established on three different-aged dunes on a Virginia barrier island. Two dominant species responded differently to nitrogen additions. Ammophila breviligulata abundance was enhanced by the additions, and, in most cases, Spartina patens abundance was repressed. On the older Hog Island dunes, the addition of nitrogen over a 10 year period had a dramatic and rapid negative effect on diversity. However, recovery to diversity values observed in the control plots was rapid, beginning almost immediately after nitrogen additions were stopped. The dune vegetation on a Virginia barrier island appears to be quite resilient, as it rapidly recovered from diversity loss after 10 years of nitrogen additions.

Llopis, I.A.; Echeverria, A.G.; Trimble, S.; Brannstrom, C., and Houser, C., 2018. Determining beach user knowledge of rip currents in Costa Rica.

Rip currents account for over 50 drownings a year in Costa Rica, with most drownings involving young single male students at beaches in close proximity to San Jose. The hazard posed by a rip current in Costa Rica and elsewhere depends in part on beach user knowledge of the rip current hazard and their ability to identify the situations in which there is the potential for drowning or need for rescue. This study describes the results of beach user surveys (n = 171) completed in English and Spanish at Jacó Beach on the central Pacific coast and Cocles Beach on the Caribbean coast of Costa Rica in 2013 and 2014. Rip current knowledge amongst national (domestic) and foreign tourists was estimated on both beaches. Results suggest that the amount of time spent in the water, activities on the beach, and self-assessment of swimming abilities help to explain why more males drown despite similar populations of males and females at both beaches. The personal and group behaviors that increase the potential for drowning are exacerbated by problems with the rip current warning system used at each beach. Approximately 58% of respondents did not observe the warnings, and 41% self-reported not changing their behavior after observing the sign, with 40% of respondents noting that the messages on the signs were confusing. Results of the study highlight the need to design and employ more effective warning signs, to set up a national certified lifeguard corps, and to plan educational activities aimed at those who are at greatest risk to drowning. This assessment and the identified need to develop a national policy can serve as a model for other countries in Central America and elsewhere where rip current–related drownings are a public health concern.

Sheppard, J.N. and MacKay, C.F., 2018. Using historic land cover data to predict estuarine macrobenthos characteristics in South Africa.

Human socioeconomic activities affect natural environments worldwide. Coastal environments like estuaries are especially threatened by the disproportional population growth and development taking place within the coastal zone. Within semiarid South Africa, and especially within the KwaZulu-Natal (KZN) Province, estuaries face human development pressures from a growing coastal population ranging in socioeconomics and types of natural resource use, and many systems are degraded. Although estuary management is well legislated, it is slow to be implemented. Unlike biophysical data, land cover data (historical–present) for KZN's coastal zone is readily available. Of interest was whether land cover is related to estuary ecological condition. If so, there is potential to use land cover characteristics around estuaries in future development of a tool for short-term interim management that addresses common management challenges including a paucity of historical ecological information, money, and expertise. In a novel approach for this region, land cover and biophysical (water physicochemical, sediment, and estuary macrobenthic invertebrates) data sets for seven of the province's estuaries for three points within a 30-year period (1980–2010) were examined. Land cover around these estuaries ranged from seminatural, agriculturally dominated to highly urbanized systems. Macrobenthos communities within the systems showed a similar distinction in terms of taxonomic dominance, although species richness and abundances were variable. Land cover within the 20-m contour line was found to be a very strong predictor of estuary macrobenthos characteristics, with a subset of 8 land cover types and five invertebrate species identified in this study for use as potential future indicators.

Zarranz Elso, M.; Manent, P., and Robaina, R.R., 2018. Zostera noltii in the Canary Islands: A genetic description for conservation purposes.

The extremely delicate situation affecting the seagrass Zostera noltii in the Canary Islands (listed as ‘threatened with extinction') requires urgent measures to ensure its preservation. The genetic or genotypic description of populations and knowledge about their connectivity are important genetic issues that should be taken into account to accomplish appropriate conservation and restoration programmes, particularly for threatened habitats or species. Therefore, a genetic characterisation of the single remaining meadow located on the coast of Lanzarote was conducted using nine microsatellite loci, and its genetic relationship with the geographically closest Moroccan populations was studied for restoration purposes. Results showed that the Lanzarote population has recently suffered a significant reduction in effective population size and presents low levels of allelic or genotypic diversity in relation to other Z. noltii populations throughout its distribution range. Moreover, this population remains in an extremely isolated situation in which it lacks long-term gene flow with other Moroccan populations. These genetic factors, together with the lack of sexual reproduction (only vegetative growth via rhizomes has been reported) and high anthropogenic pressures, make the risk of extinction of this species in the Canarian archipelago more likely. Some considerations for future restoration plans for this valuable species are suggested.

Bonnici, L.; Borg, J.A.; Evans, J.; Lanfranco, S., and Schembri, P.J., 2018. Of rocks and hard places: Comparing biotic assemblages on concrete jetties versus natural rock along a microtidal Mediterranean shore.

The species composition and structure of littoral assemblages on concrete jetties were compared with those on natural rocky shores at two localities on the microtidal NE coast of Malta. Algal species richness and total algal biomass were significantly lower on jetties. Faunal species richness and faunal abundance were also lower on jetties, albeit not significantly so. Jetties and natural rocky shores differed in relative species composition. The algae Palisada perforata/Laurencia obtusa and several mobile animals, mostly crustaceans, molluscs, and polychaetes, were more abundant on rocky shores. In particular, the supralittoral gastropod Melarhaphe neritoides had a density ranging between 8 ind./m² to 98 ind./m² on rocky shores but was never recorded on jetties. Conversely, the algae Cladophoropsis spp., the barnacle Chthamalus stellatus, and the limpets Patella caerulea and P. ulyssiponensis were more abundant on jetties. The rocky shores of sites with jetties were compared with those of a reference site (Dahlet ix-Xmajjar) that lacked jetties. No significant differences occurred in algal biomass and faunal abundance; however, faunal species richness was significantly higher at the reference site. These results may be linked to a number of abiotic factors inclusive of increased exposure to waves, decreased area for colonisation, and habitat homogeneity. The present case study has implications for coastal zone management.

Berkowitz, J.F.; VanZomeren, C.M., and Priestas, A.M., 2018. Potential color change dynamics of beneficial use sediments.

Sediment color is important in determining aesthetic and habitat suitability for beach nourishment projects; however, sediment derived from dredging operations must meet locally established color compatibility requirements (i.e. cannot be too dark). Often, potential sediment sources are close to meeting specified thresholds, and previous observations suggest that sediments may lighten over time following beach nourishment. This work seeks to characterize the degree of color change potential based on the removal of constituents affecting sediment color. Thus, a sequential chemical treatment was developed to examine color changes associated with the removal of carbonates, organic matter, and iron oxide coatings from sediments collected from eight U.S. Army Corps of Engineers dredging operations. The results show that Munsell values increased by an average of 1.0 unit (became lighter in color) upon removal of these secondary constituents. In addition, five of the eight sediments examined surpassed established color thresholds (Munsell value ≥ 5) from their pretreated state. This procedure is meant to serve as a proxy for removal of these constituents by natural processes. Study findings suggest that sediments with initially unacceptable color, and high capacity for color change, may increase potential use of limited sediment resources. Future work will further relate color shifts to sediment composition, sediment mixing, and solar bleaching to predict sediment color changes under real-world scenarios.

Grizzle, R.E.; Bricelj, V.M.; AlShihi, R.M.; Ward, K.M., and Anderson, D.M., 2018. Marine molluscs in nearshore habitats of the United Arab Emirates: Decadal changes and species of public health significance.

This paper describes the results of three qualitative surveys of marine molluscs conducted in December 2010 and May 2011 and 2012 in nearshore benthic habitats along the Arabian Gulf and Gulf of Oman coasts of the United Arab Emirates. Findings are compared with historical studies, focusing on extensive surveys from the 1960s and 1970s. Molluscan species of public health significance are identified on the basis of their potential as vectors of algal toxins in light of the recent occurrence of harmful algal blooms (HABs) in the region. Habitats sampled included intertidal sand or gravel beaches, rocks and jetties, sheltered soft-sediment flats and mangroves, and shallow subtidal coral reefs. The present study showed differences in taxonomic composition and decreased species richness of gastropods compared with a previous mollusc survey conducted in the early 1970s, reflecting the probable impacts of extensive, ongoing coastal development activities, although other environmental stressors may play a contributing role. The major habitat change found in the current survey was replacement of natural “rocky” substrates with man-made jetties and breakwaters. Of the 27 live gastropod species collected, seven predatory or scavenging species were identified as potential biotoxin vectors: Thais savignyi, T. tissoti, T. lacera, Murex scolopax, Nassarius persicus, Hexaplex kuesterianus, and Rapana sp. Of the 22 live bivalve species collected, the following 11 suspension feeders were deemed to be potential vectors of HAB toxins on the basis of their body size and feeding mode: three venerid clams (Circenita callipyga and Tivela ponderosa, which are consumed locally, and Amiantis umbonella); the widespread encrusting rock oyster, Saccostrea cuccullata, also consumed locally; two pearl oyster species; Pinctada spp.; the prickly pen shell Pinna muricata; the scallop Chlamys livida; the cockle Acrosterigma lacunosa; and the facultative suspension-feeding tellinids Asaphis violascens and Hiatula rosea.

Giménez-Casalduero, F.; Gomariz-Castillo, F.; Canales, R., and Calvín J. C., 2018. Identifying the conservation state of marine rocky habitats along the western Mediterranean using focal species.

Marine management in Europe has progressed in implementing a European legal framework. The directives stand out among the legal instruments of such framework; their main objective is to conserve biodiversity in the marine environment in order to maintain a good ecological status. For the application of the directives, it is necessary to improve knowledge of the reef habitat by identifying its ecological value as a first step to define its conservation and ecological status. This study has identified the state of conservation in the rocky coastal habitat of the Region of Murcia (SE Spain) by using the presence of benthic focal species for each type of landscape as an indicator. To identify the landscape units, a hierarchical classification of rocky habitats was carried out. The existence of comparable units makes it possible to search for indicators of ecological status and compare the units within each category. After the definition of landscape units, the specific reference level for rock habitat, adapted to each of the “landscape types,” was defined, allowing its ecological value to be determined; the focus on focal species can help in defining conservation objectives. Of the rocky landscape units analysed, 94% have a high ecological value. In conclusion, with the methodology proposed in this paper, it is possible to easily define the specific reference level for rock habitat and determine its status in relation to it. This way it is possible to provide rapid information on the environmental status of rocky landscape units.

Ma, W.; Wang, Y.; Yang, S.; Wang, S., and Xue, Z., 2018. Observation of internal solitary waves using an underwater glider in the northern South China Sea.

Internal solitary waves (ISWs) are frequently observed in the ocean, in particular in the South China Sea. Petrel-II, the autonomous underwater glider developed by Tianjin University, conducted ISW observations in the northern South China Sea in August 2017. With the payload conductivity, temperature, and depth, Petrel-II can obtain the repeating thermohaline profiles from the surface to nearly 1500-m depth. Combined with the analysis of a moderate-resolution imaging spectroradiometer true-color image, it is verified that the thermohaline fluctuation is caused by the ISWs. The features of the ISW are estimated by calculation of vertical velocity using a glider flight model. The ISW captured by Profile-46 of the glider was a depression wave, with a period of about 24 minutes and an amplitude of about 127 m. The application of underwater gliders will contribute to studies on the features, generation, propagation, and evolution of ISWs in the South China Sea.

Lipiec, E.; Ruggiero, P.; Mills, A.; Serafin, K.A.; Bolte, J.; Corcoran, P.; Stevenson, J.; Zanocco, C., and Lach, D., 2018. Mapping out climate change: Assessing how coastal communities adapt using alternative future scenarios.

Coastal communities are increasingly experiencing climate change–induced coastal disasters and chronic flooding and erosion. Decision makers and the public alike are struggling to reconcile the lack of “fit” between a rapidly changing environment and relatively rigid governance structures. In efforts to bridge this environment-governance gap in Tillamook County, Oregon, stakeholders formed a knowledge-to-action network (KTAN). The KTAN examined alternative future coastal policy and climate scenarios through extensive stakeholder engagement and the spatially explicit agent-based modeling framework Envision. The KTAN's results were further evaluated through a two-step mixed methods approach. First, KTAN-identified metrics were quantitatively assessed and compared under present-day vs. alternative policy scenarios. Second, the feasibility of implementing these policy scenarios was qualitatively evaluated through a review of governmental regulations and semistructured interviews. The findings show that alternative policy scenarios ranged from significantly beneficial to extremely harmful to coastal buildings and beach accessibility in comparison to present-day policies, and they were relatively feasible to almost impossible to implement. Beneficial policies that lower impacts of flooding and erosion clearly diverge from the existing regulatory environment, which inhibits their implementation. In response, leadership and cross-sector cooperation and coordination can help to overcome mixed interests and motivations, and increase information exchange between and within the public and government organizations. The combination of stakeholder engagement, an alternative futures modeling framework, and the robust quantitative and qualitative evaluation of policy scenarios provides a powerful model for coastal communities hoping to adapt to climate change along any coastline.

Gu, L.; Ni, F.; Xu, L., and Li, Z., 2018. Determining the threshold pressure of clay-cutting by a mobile jet for coastal construction.

Trailing suction hopper dredgers (THSD) are widely used in channel excavation and coastal construction projects. In such projects, clay is a common soil that is difficult for the drag head of THSDs to dredge. Jet-cutting using a mobile jet is often adopted to improve the efficiency of the drag head, since it can create grooves into the clay surface and reduce cutting forces for the drag head. The jet pressure is an important factor for jet-cutting, so it is necessary to accurately grasp the threshold pressure of clay-cutting by the mobile jet. In this paper, clay samples with three different strengths (undrained shear strength S_u = 16 kPa, 35 kPa, and 51 kPa) were prepared, and clay-cutting experiments using a mobile jet were conducted. The effects of parameters such as the nozzle diameter, the moving speed, and the jet pressure on the cutting results were investigated, and the cutting depths under different jet pressures were measured. The threshold pressure was measured, and the cause of clay failure under jet-cutting was analyzed. The results show that the nozzle diameter and the moving speed changed the cutting depth via the exposure time during the clay-cutting, and that the cutting depth increased linearly with cumulative cutting time. The threshold pressure was independent of the jet diameter and moving speed and only increased linearly with the undrained shear strength of the clay. In the cutting process using a mobile jet, shearing slippage was the main failure mode of clay, and the jet was only able to effectively cut the clay when its pressure was higher than the ultimate bearing capacity of the clay bed.

Appeaning Addo, K.; Nicholls, R.J.; Codjoe, S.N.A., and Abu, M., 2018. A biophysical and socioeconomic review of the Volta delta, Ghana.

Delta regions are dynamic and rich environments with diverse economic activities and are often densely populated. Deltas are being shaped by multiple drivers, including changes in sediment delivery to the coastal zone due to catchment changes, especially construction of dams on major rivers, intensified agriculture and/or aquaculture, mining, urbanisation, human-induced subsidence, climate change, and sea-level rise. These environmental challenges have significant implications for the livelihoods of delta residents. Thus, the integrated assessment of deltas is now attracting the attention of the scientific research community to analyse and understand deltas as coupled biophysical and socioeconomic systems. Most attention has been focussed on the major deltas. This review focusses on the smaller but regionally significant Volta delta, Ghana. Previous scientific studies are limited, with more focus upstream on the Volta River basin. Many contemporary problems are recognised in the Volta delta, especially erosion and flooding of the open coast fringe, such as at the town of Keta. However, these problems are treated independently, which may hinder identifying the root causes and the most effective solutions. Equally, the emergence of new problems might be anticipated and hence better managed or even avoided. This paper reviews the present delta with emphasis on biophysical processes and socioeconomic characteristics and considers in particular the current drivers and challenges. With this information, a research agenda will be established for a more systemic approach to understanding the Volta delta, including its residents and development.

Zuckerman, S. and Anderson, S., 2018. Bathymetry and water-level estimation using X-band radar at a tidal inlet.

Knowledge of bathymetry in coastal areas is a key factor for maintaining shipping channels, identifying hazards to navigation, and measuring sediment transport processes. Remote-sensing techniques are crucial for this purpose, because in situ methods are often costly, time-consuming, and less frequent in occurrence. This paper presents a derived bathymetry and water-level retrieval algorithm that operates on time-series X-band marine radar data. The algorithm is designed to operate on a long-term continuous data stream, generating updated water-level measurements and bathymetry maps as new data are collected. In step 1, individual data sets are first processed to retrieve dominant wave numbers over a pyramid of overlapping tiles. In step 2, depths are estimated at each pixel location in the domain using the shallow-water wave dispersion relation. Last, results from step 2 are used to estimate the current water level. Updated water levels are used to tide correct a series of individual depth estimates, which are averaged together to produce an updated bathymetry map. In this way, no a priori or external data sources from the survey area are required. A 2-month-long experiment was conducted at Beaufort, North Carolina, to test the algorithm and quantify the frequency at which adequate signal levels were present for valid retrievals. Derived bathymetry and water-level results are presented and compared against ground truth. Derived measurements agree well with ground truth, although bathymetry accuracy degrades in areas of the domain with large bottom gradients or strong tidal currents.

Gallagher, J.B. and Chuan, C.H., 2018. Chlorophyll a and turbidity distributions: Applicability of using a smartphone “app” across two contrasting bays.

Turbidity from suspended particulate matter and chlorophyll a concentrations are first-level indicators of the health of coastal waters. Coastal regions, typically several kilometers in scale, require a sampling resolution sufficient to identify the extent of turbidity and chlorophyll a sources and sinks. An inexpensive smartphone “app” (HydroColor™), which uses color reflectance to measure turbidity and chlorophyll a concentration, was tested for both accuracy and practicality. Two separate and contrasting coastal regions were chosen, the proposed Silam Coastal Conservation Area, and Sepanggar Bay, serving Kota Kinabalu city (Sabah, Malaysia). It was found that results produced by HydroColor's built-in turbidity calibration agreed well with those from a laboratory nephelometer across the range encountered within the two regions (0 to 26.4 nephelometric turbidity units). Chlorophyll a concentrations, calculated using a function developed with a previous less-convenient underwater camera setup, showed a response closely proportional to chlorophyll a water extractions, but greater by 1.30 μg L⁻¹. Nevertheless, the differences and similarities between turbidity and chlorophyll a patterns between bays were compelling, especially as they were consistent with land use and river and coral reef proximity. The study identified several practical difficulties and sampling design constraints. The extent of the survey was limited to regions of the bay where the bottom could not be seen. Large tidal variations required three small, fast boats for rapid random site visits before onset of sea breeze to normalize for tide and wind variability. Reflectance measurements and accuracy were also hampered by screen glare, avoiding changing cloud cover, and rain staining the reflectance grey card, as well as the difficulty in avoiding interference from shadows from restricted open deck space. In contrast, the accuracy and precision of the regional calibration appeared to be dependent on obtaining a sufficient number and range of values over different turbidity and cloud conditions across the region and over different times.

Moloney, J.G.; Hilton, M.J.; Sirguey, P., and Simons-Smith, T., 2018. Coastal dune surveying using a low-cost remotely piloted aerial system (RPAS).

Monitoring coastal morphodynamics is important for understanding the response of coasts to short-term storm events, for understanding coastal response to long-term environmental change, and for managing beach-dune systems. Remotely piloted aerial systems (RPAS), or “drones,” present new opportunities for coastal monitoring. They are inexpensive and efficient, require minimal expertise, and provide high-resolution aerial imagery. This paper investigates the efficacy of low-cost RPAS for coastal foredune monitoring. Comparisons among total station, real-time kinematic global navigation satellite system, terrestrial laser scanner, and RPAS surveys were made based on the efficiency of point acquisition, cost, accuracy of the output surface, and the method's sensitivity to atmospheric and environmental limitations. Temporal elevation and volumetric changes in sand were quantified using RPAS photogrammetry and conventional survey methods. An intentionally notched section of foredune was monitored over a 12 month period. The RPAS survey was the most efficient method and had a high level of accuracy. The digital surface model (DSM) derived from the RPAS survey had a vertical root mean square error of 8 cm. However, RPAS was more sensitive to environmental and atmospheric conditions, although the survey rapidity means undesirable weather conditions can be avoided. The RPAS did not accurately quantify total sand deposition downwind of the notches due to an elevational offset caused by vegetation, which is dense throughout the study site. Comparison of the DSMs derived from RPAS surveys indicated a decrease in elevation (between 10 and 20 cm) during the survey period. The method affords the advantages of point acquisition efficiency and flexibility. However, low-cost red-green-blue RPAS is more suited to quantifying the morphology of bare sand or sparsely vegetated areas, quantifying large-scale changes, or for long-term morphologic monitoring due to its inability to penetrate vegetation. It is expected that future sensors capable of penetrating vegetation will become more accessible for low-cost platforms.

Jara, M.S.; González, M.; Medina, R., and Jaramillo, C., 2018. Time-varying beach memory applied to cross-shore shoreline evolution modelling.

A new cross-shore Shoreline Evolution Model Based on the Equilibrium Wave Energy—the SE-WE Model—is presented in this article. This simple model predicts the shoreline position S as the equilibrium shoreline response under a specific wave forcing, i.e. the proposed Equilibrium Wave Energy (E_eq) is computed as a weighted average of antecedent wave conditions, according to a new formulation. This new approach allows for the prediction of S at any time from a small fragment of the incident wave-energy time series as the only input of the model. In contrast, previous, similar models needed to evaluate the entire time series from an initial shoreline position to the target time. The proposed model addresses shoreline changes derived from wave-driven, cross-shore sediment transport. Consequently, the SE-WE Model has limited applicability in beaches in which the gradient in the longshore sediment transport or the longshore sediment transport itself are not negligible. The time frame considered for the computation of E_eq refers to the set of antecedent wave conditions having significant influence on the current shoreline position and, therefore, alludes to a certain beach memory (BM). In contrast to existing, similar models, the SE-WE Model BM varies over time. This time-varying BM is in agreement with observations in which high wave energy events erase all trace of past configurations of the beach (“short beach memory”), whereas at the same beach, the effects of past events usually remain after long periods of calm conditions (“long beach memory”). Results from the SE-WE Model applied at the beach of Nova Icaria, Spain, show a good agreement with observations. Additionally, the new model is compared with existing similar models, showing remarkably similar skills in spite of the differences in model approach and model input.