Adjacent Coast Research Articles

Monitoring the evolution of nearshore nourishments along Barra-Vagueira coastal stretch, Portugal

Maintenance of existing harbors implies regular dredging activities. Where the combined use of dredging and disposal of dredged material on nearby sediment-starved beaches can induce major changes in the beach morphology and generate unexpected impacts in the environment, monitoring becomes a concern. This paper was designed to analyze, interpret and evaluate a set of monitoring data collected along a regular-nourished coastal stretch with dredged sand (Barra-Vagueira coastal stretch, northwest coast of Portugal), surrounded by an energetic hydrodynamic environment with a scarce natural sediment input. Based on a field data set, collected between 2009 and 2015, the present study brings together a set of correlated analyses, intended to assess the morphodynamic evolution of the fills as well as their impact to the adjacent coast. The available data set encompasses topo-hydrographic surveys collected for 12 cross-sections (with 1 km spacing) distributed along the coastal stretch and bathymetric measurements collected for the dumping areas. Considering the concurrent offshore wave forcing, dominant temporal and spatial patterns, morphological changes, evolution trends, sediment budgets, and short- and medium-term responses of the fills are investigated by the use of ArcGIS tools and application of a multivariate statistical method based on Empirical Orthogonal Functions (EOFs). Overall, during the monitoring period, almost 2.8 Mm3 of sand was dumped in different locations and periods to control the erosion observed downdrift of the inlet. However, bathymetric surveys and profile indicators still point out the erosional longshore pattern diagnosed decades ago as a result of a negative longshore sediment balance. Observations also revealed that short-term changes arising from the seasonal cycles of cross-shore material exchange are mainly linked to the largest variations in the beach profile shape, also affecting the sediment budget. Profiling indicated cross-shore volume variations ranging from ±250 m3/m and ±1500 m3/m in the subaerial and subaqueous portion of the profile, respectively, along the monitored period. After the first completed seasonal cycle the sand bar, artificially created by the nourishments, could not be visually detected in the profiles, suggesting a cross-shore redistribution of the fill material. All the analyses developed in this paper stress the importance of establishing proper monitoring programs based on adequate surveying instruments and data collection strategies, in order to ensure high-density data that could be used in support to the decision-markers.

Dynamic preservation of Texel Inlet, the Netherlands: understanding the interaction of an ebb-tidal delta with its adjacent coast

AbstractTidal inlets and the associated ebb-tidal deltas can significantly impact the coastal sediment budget due to their ability to store or release large quantities of sand. Nearly 300 million m3(mcm) of sediments were eroded from Texel Inlet's ebb-tidal delta and the adjacent coasts following the closure of the Zuiderzee in 1932. This erosion continues even today as a net loss of 77 mcm was observed between 1986 and 2015. To compensate, over 30 mcm of sand has been placed on the adjacent coastlines since 1990, making maintenance of these beaches the most intensive of the entire Dutch coastal system.Highly frequent and detailed observations of both the hydrodynamics and morphodynamics of Texel Inlet have resulted in a unique dataset of this largest inlet of the Wadden Sea, providing an opportunity to investigate inlet sediment dynamics under the influence of anthropogenic pressure. By linking detailed measurements of bathymetric change to direct observations of processes we were able to unravel the various components that have contributed to the supply of sediment to the basin, and develop a four-stage conceptual model describing the multi-decadal adaptation of the ebb-tidal delta.Prior to closure of the Zuiderzee a dynamic equilibrium state (stage 1) existed with a stable ebb-tidal delta. The largest morphological changes occurred in roughly the first 40 years since the closure, and were dominated by the rotation and scouring of large tidal channels and landward retreat of the Noorderhaaks ebb shoal (stage 2; adaptation). Between 1975 and 2001 the general layout of main channels and shoals was stable, but large sediment losses continued to occur (stage 3; equilibrium erosional state). Since 2001, the erosion rates have significantly reduced to 2 mcm a−1(stage 4; stabilisation).Twenty-five years of data on ‘Dynamic Preservation’ prove that sand nourishments are well capable of keeping the coastlines adjacent to the Texel Inlet in place. Moreover, the abundant supply of sediment may also have compensated for the sediment losses on the larger scale of the southern part of the ebb-tidal delta, resulting in a recent stabilisation of its volume. This response illustrates the potential benefits of Dynamic Preservation not only for coastline resilience but also on the larger scale of the inlet system. Such knowledge is essential for future preservation, management and maintenance of inlet systems in the scope of climate change and accelerated sea-level rise.

Numerical modelling of erosion rates, life span and maintenance volumes of mega nourishments

Mega-nourishments, aiming at providing long-term coastal safety, nature qualities and recreational space, have been applied recently at the Holland coast and are considered at various other places in the world. Methods to quickly evaluate the potential and lifetime of these coastal mega nourishments are therefore very much desired, which is the main objective of this research. Two types of mega nourishments can be distinguished: feeder-type mega nourishments may erode freely to feed adjacent coasts for a more natural, dynamic dune growth while permanent mega-nourishments are designed to preserve safety levels and need to maintain their size and shape and thus needs to be nourished themselves. The design and impact assessment studies for both types of mega nourishments require detailed morphological studies to determine the morphological evolution. In this paper 2DH (Delft3D) and 1D (UNIBEST-CL+ and LONGMOR) numerical models were calibrated using data of the Sand Motor mega-nourishment and were then applied to model a series of mega-nourishments with various width over length ratios and volumes in order to derive relations and design graphs for erosion rates, life span and maintenance volumes. These relations and design graphs can be used in project initiation phases and feasibility studies. The magnitude of the modelled wave-driven longshore sediment transport rates in 1D coastline models depend on the representation of wave refraction on the lower shoreface, since a distinction should be made between the non-rotating lower shoreface and active surfzone. It was shown that the life time of nourishments is mainly determined by the dimensions of the nourishment and incoming wave energy.

Larval fish dispersal along an estuarine–ocean gradient

The present study investigated the larval fish dispersal along an estuarine–ocean gradient to explore connectivity between ocean and estuaries. During spring 2009, a combined ocean–estuarine survey was conducted along the Lima estuarine salinity gradient and in two transects off the adjacent coast (northwestern Iberian Peninsula), until the 100 m isobaths. Salinity, total particulate matter, particulate organic matter, total dissolved carbon, and dissolved organic carbon reached higher values at the ocean, and chlorophyll a and nutrients increased at the estuary. From the total 56 taxa identified, 14 were present along the gradient, including estuarine species (ES), marine stragglers (MS), and migrants (MM). Canonical correspondence analysis showed that species were separated along the gradient according to their ecological functional classification. MM associated with high salinity were separated from ES correlated with lower salinities and high chlorophyll a concentrations of inner estuary. Flounder (Platichthys flesus) showed a typical spatial gradient of MM, with abundance increasing from the ocean towards inner estuary. The dispersal of larvae along the Lima estuarine–ocean gradient was indicative of connectivity between habitats, emphasizing the need to consider this feature in management plans, mainly for species exploited by commercial fisheries.

Status of Multi-Geared Small Scale Fishery Operated in Koggala Lagoon and Adjacent Coastal Area

Management of multi-species and multi-geared fisheries is challenging due to conflicts and competitions of fishers. However, such a complex fishery exists for the last 100 years in Koggala lagoon, which extends only for 727 ha area, in southern Sri Lanka. This study evaluated the fish catch and income sharing mechanisms which enable to survive these fisheries in highly dynamic biological and socio-economical environments. Eight landing sites at the lagoon body, lagoon mouth and adjacent coast were weekly visited from April to August 2015 in drawing random samples to determine gear-based catch per unit effort (CPUE), species diversity and income levels. Questionnaires and discussions among fishers were used to identify potentials and threats for the fishery. Dominant 25 fish species and 6 shrimp species were observed in the catches of 11 fishing methods including snares, a fish trap which was not recorded from Koggala lagoon. During the study period high variations of CPUE were observed within and among fishing methods. Hierarchical cluster analysis based on present-absent data showed two clearly separated clusters (P<0.05). Though the educational level and years of experience significantly differed between lagoon and coastal fishers (P<0.05), the respective income was not significantly different. Targeting different species and different life history stages by different types of gear seems to be the key in sustaining multi-geared fisheries in the lagoon for last 100 years. Though school education does not have any effect on selecting fishing location, fishing experience seems to be important in operating some specific gear. Species aggregation and their susceptibility for different gear reveled in this study must be important in developing fishery management strategies for the lagoon. Despite to the effective catch sharing mechanism, the sand bar formation, which is the most concerned issue by both lagoon and coastal fishers, will determine whether Koggala lagoon fisheries will survived for another 100 years due to its effects on altering species diversity. Keywords: Artisanal fisheries, Catch composition, Socio-economic status

INTEGRATED COASTAL PROCESS MODELING AND IMPACT ASSESSMENT OF FLOATING AND SEDIMENTATION IN COASTS AND ESTUARIES

In this study, an integrated coastal process model was applied to assess impact of coastal flooding and sedimentation in an estuary in Taiwan and to evaluate performance of proposed engineering plans for flood prevention and sedimentation management. This in-situ validated model was used to simulate and predict hydrodynamic processes and morphological changes induced by multiple hydrological forcing such as river flood flows, waves, tides, and storms surges from rivers to the estuary and its adjacent coasts. Simulation results quantified coastal flooding risks, erosions, sedimentation, and channel refilling. Predicted dynamic responses to typhoons and monsoons were utilized for identifying the most effective engineering plan to reshape the geometry of the estuary. After the selected engineering plan was accomplished, this model was applied again to further predict morphological changes in the newly-developed estuary. This paper demonstrates effectiveness of a simulation-based coastal and estuary planning approach to manage flood and sedimentation driven by complex physical processes from river flows, waves, tides, and sediment transport.

Bioaccumulation of heavy metals in eight fish species of the Khur-e Khuran International Wetland in the Persian Gulf, Iran

Heavy metals are among the most toxic pollutants in aquatic ecosystems. This study was conducted to evaluate the concentration of heavy metals viz. lead, cadmium, chromium, zinc, cobalt, and copper in eight commercial fishes of Khur-e Khuran international wetland (KIW), Iran. The results showed that the highest concentration of heavy metals attributed to Zn as 176.5 µg g -1 dry weight in Platycephalus indicus and the lowest to Pb as 0.12 µg g -1 dry weight in Sillago sihama . Average concentrations of heavy metals in eight examined fish species were 29.15, 49.73, 1.39, 0.45, 1.43 and 1.56 µg g -1 dry weight for Cu, Zn, Cd, Pb, Co and Cr, respectively. The results also show that measured values of most heavy metals in some examined fishes of KIW were higher than those maximum permissible limit (MPL) according to international standards. The high concentrations of some metals in some examined fishes of KIW may be due to industrial and residential activities in adjacent coast i.e. in mainland and Qeshm Island, and marine traffic

An improved spectral optimization algorithm for atmospheric correction over turbid coastal waters: A case study from the Changjiang (Yangtze) estuary and the adjacent coast

Remote sensing-based retrieval of the concentrations of water components relies largely on the accuracy of the atmospheric correction. Although a variety of atmospheric correction algorithms have been developed for turbid waters, the water-leaving reflectance is still underestimated in extremely turbid waters, such as in the Changjiang (Yangtze) estuary and the adjacent coast. To address this issue, this paper proposes an improved algorithm that is based on a spectral optimization algorithm (ESOA) with a coupled water-atmosphere model. The model combines an aerosol model that is constructed from Aerosol Robotic Network (AERONET) observation data and a simple semi-empirical radiative transfer (SERT) model (Shen et al. 2010) for water component retrieval. Four unknown parameters are involved in the coupled model: the relative humidity (RH), fine-mode fraction (FMF), aerosol optical thickness in the near-infrared (NIR) wavelength τa(λ0) and suspended particulate matter (SPM) concentration (Cspm). These parameters are estimated by a global optimization approach that is based on a genetic algorithm (GA) without any initial inputs. Validation results of the atmospherically corrected remote sensing reflectance Rrs(λ) from matchups between Geostationary Ocean Color Imager (GOCI) data and in situ data show that the algorithm has satisfactory accuracy. The root mean square error (RMSE) and the absolute percentage difference (APD) are 0.0089 and 35.12, respectively. By contrast, the Rrs(λ) values retrieved from the same matchups using the GOCI data processing system (GDPS) have higher RMSE and APD of 0.0104 and 69.15, respectively. The ESOA method can be implemented conveniently within the open source code of SeaDAS (v7.1) as an alternative and operational tool for atmospheric correction of ocean color data, including GOCI, MERIS and MODIS, over highly turbid estuarine and coastal regions, such as the Yangtze estuary, the Hangzhou Bay and most of the coastal ocean in Eastern China.

On a possible origin of the anomalous effects that were observed during the May 24, 2013 earthquake in the Sea of Okhotsk

The deep-focus Sea of Okhotsk earthquake that occurred on May 24, 2013 (h = 630 km, Mw = 8.3) was accompanied by anomalous effects that were unknown previously. A combined analysis of published data concerning the source rupture evolution and some features of the deep structure provided an explanation of some anomalous effects, such as the large number of aftershocks and the low level of ground shaking in the epicentral area. However, GPS observations revealed high coseismic vertical displacements in the area. The seafloor uplift in the Sea of Okhotsk and the adjacent coasts was 3–12 mm, peaking at the approximate center of the sea, while Kamchatka and the North Kuril Islands subsided by 3–18 mm, peaking at the Apacha station 190 km east of the earthquake epicenter. These maximum estimates are 1.2–1.8 times the analogous values (10 mm) for the Chile mega-earthquake of May 20, 1960 (Mw ~ 9.5). It is known that the large distances at which ground shaking is felt during deep-focus earthquakes are due to the fact that the body waves travel through the high-Q lower mantle. However, this does not explain the paradox of the present earthquake in the Sea of Okhotsk, viz., a constant intensity of shaking (two grades) in the range of epicentral distances between 1300 and 9500 km. The explanation requires consideration of the earth’s free oscillations excited by the earthquake.

Beach Evolution Adjacent to a Seasonally Varying Tidal Inlet in Central Vietnam

ABSTRACT 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 trend...

Long-term and gender-related variation in the feeding ecology of common bottlenose dolphins inhabiting a subtropical estuary and the adjacent marine coast in the western South Atlantic

ABSTRACTWe combined stomach content analysis and stable isotopes to investigate long-term changes in the feeding ecology of common bottlenose dolphins (Tursiops truncatus) from the Patos Lagoon estuary and adjacent marine coast, southern Brazil, during the past 35 years. Stomach contents of bottlenose dolphins collected between 2002 and 2012 (Period II) were compared to those previously described for this population (1977–1980, Period I), and δ13C and δ15N values in tooth dentine from specimens collected between 1977 and 2012 were used to assess temporal changes in contribution of the main prey to the diet of dolphins over time. Additionally, these data were used to verify the magnitude of trophic overlap between males and females from Period II. Bottlenose dolphins consumed a wide variety of prey. Demersal and demersal–pelagic teleost fish predominated. These results show that bottlenose dolphins from the Patos Lagoon estuary are opportunistic feeders and confirm the plasticity of the species, which preys upon the most available prey. Differences in diet were found between seasons and periods. Stable isotopes and stomach contents detected a significant long-term change in the proportions of their main prey. The contribution of Micropogonias furnieri and Menticirrhus sp. decreased after 1990 while a significant increase in the importance of Trichiurus lepturus was observed. Males consumed a significantly higher proportion of T. lepturus while Mugil liza was the main prey for females. These changes might be due to fishing-related changes in fish abundance.

Exhumation history along the eastern Amundsen Sea coast, West Antarctica, revealed by low‐temperature thermochronology

AbstractWest Antarctica experienced a complex tectonic history, which is still poorly documented, in part due to extensive ice cover. Here we reconstruct the Cretaceous to present thermotectonic history of Pine Island Bay area and its adjacent coasts, based on a combination of apatite and zircon fission track and apatite (U‐Th‐Sm)/He thermochronology. In addition, we report petrographic information for the catchments of Pine Island, Thurston Island, and Thwaites glaciers. Our data suggest that the underlying bedrock of the Pine Island and Thwaites Glacier catchments are very different and vary from granitoids to (Cenozoic?) volcanogenic sequences and low‐grade metamorphics. Our thermochronology data show that the upper crustal rocks of Pine Island Bay experienced very rapid cooling during the late Cretaceous. We attribute this rapid cooling of basement rocks and associated reduction in mean elevation to tectonic denudation driven by gravitational collapse of the Cretaceous orogen along the proto‐Pacific Gondwana margin. Rapid Cretaceous crustal cooling was followed by very slow cooling during the Cenozoic, with no erosional response—within the limits of thermochronological methods—to the onset of glaciation and subsequent climatic changes. Cenozoic rifting within the West Antarctic Rift appears to have had little effect on erosion processes around Pine Island Bay; instead, our data suggest Cenozoic crustal tilting toward Pine Island Trough, a major geomorphic feature previously suggested to be a branch of the rift system.

Development and extension of an aggregated scale model: Part 2 — Extensions to ASMITA

Whilst much attention has been given to models that describe wave, tide and sediment transport processes in sufficient detail to determine the local changes in bed level over a relatively detailed representation of the bathymetry, far less attention has been given to models that consider the problem at a much larger scale (e.g. that of geomorphological elements such as a tidal flat and tidal channel). Such aggregated or lumped models tend not to represent the processes in detail but rather capture the behaviour at the scale of interest. One such model developed using the concept of an equilibrium concentration is the Aggregated Scale Morphological Interaction between Tidal basin and Adjacent coast (ASMITA). In a companion paper (Part 1), we detail the original model and provide some new insights into the concepts of equilibrium, and horizontal and vertical exchange that are key components of this modelling approach. In this paper, we summarise a range of developments that have been undertaken to extend the original model concept, to illustrate the flexibility and power of the conceptual framework. However, adding detail progressively moves the model in the direction of the more detailed process-based models and we give some consideration to the boundary between the two.

Surface water subduction during a downwelling event in a semienclosed bay

AbstractThe Ría de Vigo is a bay strongly influenced by upwelling‐downwelling cycles along the adjacent coast of NW Iberia. Moored and ship‐board observations during September 2006 showed that subduction, initially associated with an estuarine circulation, strengthened when a strong downwelling circulation, resulting from northward wind over the coastal ocean, was generated in the outer Ría causing ambient waters to be advected outward in the lower layer. Incoming surface waters confined the estuarine circulation to the shallow interior and displaced isopleths downward through the water column at ∼10 m d−1. As the estuarine circulation retreated inward, strong flow convergence developed between middle and inner ria in the layer above 15 m, while divergence developed beneath. The convergence increased through the period of downwelling‐favorable wind at a rate consistent with the observed isopleth displacement velocities. The coefficient of turbulent diffusion Kt, from a microstructure profiler, indicated that mixing was strong in the estuarine circulation and subsequently in the downwelling zone, where localized instabilities and temperature‐salinity inversions were observed. During the downwelling, concentrations of phytoplankton, including potentially harmful species, increased, especially in the middle and inner ria, as a result of inward advection, subduction, and the ability of the dinoflagellates to maintain their position in the water column by swimming. In the course of the 5 day event, the water mass of all but the innermost Ría was flushed completely and replaced by waters originating in the coastally trapped poleward flow along the Atlantic coastline.

Pigment-based chemotaxonomy of phytoplankton in the Patos Lagoon estuary (Brazil) and adjacent coast

ABSTRACTThe composition and distribution of phytoplankton assemblages were studied monthly at two sites in the Patos Lagoon estuary and at one site on the adjacent coast over three years (May 2012–April 2015). Samples were collected for microscopic examination and high-performance-liquid-chromatography pigment analysis. The pigment data were analysed using CHEMTAX software to estimate the contribution of different taxonomic groups to total chlorophyll a (Chl a). Phytoplankton assemblages were generally dominated by diatoms, which contributed, on average, 51% of the total Chl a, especially at the Cassino Beach surf zone, where Asterionellopsis guyunusae was the main species contributing to the high diatom-associated biomass. Cyanobacteria appeared as an important group at the lagoon’s mouth station, contributing, on average, 37% of the total Chl a. Cryptophytes, chlorophytes, prasinophytes and dinoflagellates were less important and contributed, on average, 13, 7, 5 and 3%, respectively, of the total phytoplankton biomass in the region. A good correlation was found between microscopy counts and CHEMTAX biomass estimates for most phytoplankton groups. The relationship, however, was poor for cyanobacteria and green algae, where the pigment-based approach estimated relatively higher biomasses. This discrepancy may be related to either the presence of plant/algae detritus in the samples (captured by the pigment method) and/or an underestimation by the microscopic method. Despite some differences, the pigment-based method successfully described the overall phytoplankton community pattern during the study period. Canonical Correspondence Analysis showed that temperature, salinity and dissolved inorganic nutrients are important driving forces of the observed variation in the phytoplankton community.

Development and extension of an aggregated scale model: Part 1 – Background to ASMITA

Whilst much attention has been given to models that describe wave, tide and sediment transport processes in sufficient detail to determine the local changes in bed level over a relatively detailed representation of the bathymetry, far less attention has been given to models that consider the problem at a much larger scale (e.g. that of geomorphological elements such as a tidal flat and tidal channel). Such aggregated or lumped models tend not to represent the processes in detail but rather capture the behaviour at the scale of interest. One such model developed using the concept of an equilibrium concentration is the Aggregated Scale Morphological Interaction between Tidal basin and Adjacent coast (ASMITA). In this paper we provide some new insights into the concepts of equilibrium, and horizontal and vertical exchange that are key components of this modelling approach. In a companion paper, we summarise a range of developments that have been undertaken to extend the original model concept, to illustrate the flexibility and power of the conceptual framework. However, adding detail progressively moves the model in the direction of the more detailed process-based models and we give some consideration to the boundary between the two. Highlights • The concept of aggregating model scales is explored and the basis of the ASMITA model is outlined in detail; • The relationship between dispersion as used in fast-scale process-based models and the horizontal exchange used in aggregated models is explored; • The basis for formulating suitable equilibrium relationships is explained; • Alternative ways to include advection and dispersion are examined.

Analytical model of sea level elevation during a storm: Support for coastal flood risk assessment associated with cyclone passage

Sea level oscillations are a result of continuous astronomic, oceanographic, and atmospheric interactions on different time and intensity scales. Thus, the collective action of forcing factors such as tide, wind, atmospheric pressure, and wave action may lead to elevated sea levels during cyclone events over the continental shelf, abruptly impacting adjacent coasts. The objective of this study is to evaluate the potential risks of sea level rise and coastal flooding associated with the passage of cyclones in southern Brazil. An analytical model was developed based on extreme storm events from 1997 to 2008. The model identifies the impact of each forcing factor during temporary sea level rise. Through the development of a digital terrain model, it was possible to identify the areas most vulnerable to flooding by superimposing the terrain model onto calculated sea levels. During storm events, sea level elevations ranged from 2 to 5m and show wind as the major forcing factor, followed by swells waves, astronomical tide and finally atmospheric pressure.

Tidal energy budget in the Zhujiang (Pearl River) Estuary

Tidal energy budget in the Zhujiang (Pearl River) Estuary (ZE) is evaluated by employing high-resolution baroclinic regional ocean modeling system (ROMS). The results obtained via applying the least square method on the model elevations are compared against the tidal harmonic constants at 18 tide stations along the ZE and its adjacent coast. The mean absolute errors between the simulation and the observation of M2, S2, K1 and O1 are 4.6, 2.8, 3.2 and 2.8 cm in amplitudes and 9.8°, 15.0°, 4.6° and 4.6° in phase-lags, respectively. The comparisons between the simulated and observed sea level heights at 11 tide gauge stations also suggest good model performance. The total tidal energy flux incoming the ZE is estimated to be 343.49 MW in the dry season and larger than 336.18 MW in the wet season, which should due to higher mean sea level height and heavier density in the dry season. M2, K1, S2, O1 and N2, the top five barotropic tidal energy flux contributors for the ZE, import 242.23 (236.79), 52.97 (52.08), 24.49 (23.96), 16.22 (15.91) and 7.10 (6.97) MW energy flux into the ZE in dry (wet) season, successively and respectively. The enhanced turbulent mixing induced by eddies around isolated islands and sharp headlands dominated by bottom friction, interaction between tidal currents and sill topography or constricted narrow waterways together account for the five energy dissipation hotspots, which add up to about 38% of the total energy dissipation inside the ZE.

Initial spreading of a mega feeder nourishment: Observations of the Sand Engine pilot project

Sand nourishments are a widely applied technique to increase beach width for recreation or coastal safety. As the size of these nourishments increases, new questions arise on the adaptation of the coastal system after such large unnatural shapes have been implemented. This paper presents the initial morphological evolution after implementation of a mega-nourishment project at the Dutch coast intended to feed the surrounding beaches. In total 21.5millionm3 dredged material was used for two shoreface nourishments and a large sandy peninsula. The Sand Engine peninsula, a highly concentrated nourishment of 17millionm3 of sand in the shape of a sandy hook and protruding 1km from shore, was measured intensively on a monthly scale in the first 18months after completion. We examine the rapid bathymetric evolution with concurrent offshore wave forcing to investigate the feeding behaviour of the nourishment to the adjacent coast. Our observations show a large shoreline retreat of O (150m) along the outer perimeter of the peninsula, with locally up to 300m retreat. The majority (72%) of the volumetric losses in sediment on the peninsula (1.8millionm3) were compensated by accretion on adjacent coastal sections and dunes, confirming the feeding property of the mega nourishment. Further analyses show that the morphological changes were most pronounced in the first 6months while the planform curvature reduced and the surf zone slope flattened to pre-nourishment values. In the following 12months the changes were more moderate. Overall, the feeding property was strongly correlated to incident wave forcing, such that months with high incoming waves resulted in more alongshore spreading. Months with small wave heights resulted in minimal change in sediment distribution alongshore and mostly cross-shore movement of sediment.

Identifying critical areas to reduce bycatch of coastal common bottlenose dolphins Tursiops truncatus in artisanal fisheries of the subtropical western South Atlantic

Many anthropogenic actions have an impact on coastal dolphins, with bycatch being one of the main threats. We describe the distribution patterns of common bottlenose dolphins Tursiops truncatus and periods of higher entanglement risk by the artisanal gillnet fishery in the Patos Lagoon estuary and along the adjacent coast of southern Brazil. A total of 136 dolphin groups and 187 gillnets were encountered in 69 surveys conducted between September 2006 and July 2009. Data were analyzed in relation to environmental, spatial and temporal variables using generalized additive models and a spatially adaptive local smoothing algorithm for model selec- tion. In both areas, dolphin densities increased as distance to the estuary mouth decreased. For the estuary area, water salinity and temperature influenced dolphin distribution. Along the adjacent coast, dolphin densities were higher with distance to shore as well as in the north area during the warm period. Patterns of dolphin distribution were probably a response to the presence of pre- ferred prey or avoidance of human-related disturbance. Kernel density showed that fishing effort was distributed along the entire surveyed area inside the estuary, while along the adjacent coast it was higher in the south compared to the north area in the warm period. The overlap between gillnets and dolphins increased considerably from the cold (33.8%) to the warm (48.6%) period. Seasonal variation in fishing effort and distribution affect the overlap and the risk of dolphin entanglement. Based on the findings of this study, a fishing exclusion area aimed at reducing bycatch was established by the Brazilian Environmental Agency.