Coastal Features Research Articles

Constraints on extractable power from energetic tidal straits

National efforts to reduce energy dependency on fossil fuels have prompted examination of macrotidal nearshore sites around the United Kingdom (UK) for potential tidal stream resource development. A number of prospective tidal energy sites have been identified, but the local hydrodynamics of these sites are often poorly understood. Tidal energy developers rely on detailed characterisation of tidal energy sites prior to device installation and field trials. Although first-order appraisals may make macrotidal tidal straits appear attractive for development, detailed, site-specific hydrodynamic and bathymetric surveys are important for determining site suitability for tidal stream turbine (TST) installation. Understanding the ways in which coastal features affect tidal velocities at potential TST development sites will improve identification and analysis of physical constraints on tidal energy development. This paper presents and examines tidal velocity data measured in Ramsey Sound (Pembrokeshire, Wales, UK), an energetic macrotidal strait, which will soon host Wales' first TST demonstration project. While maximum tidal velocities in the strait during peak spring flood exceed 3 m s−1, the northern portion of Ramsey Sound exhibits a marked flood-dominated tidal asymmetry. Furthermore, local bathymetric features affect flow fields that are spatially heterogeneous in three dimensions, patterns that depth-averaged velocity data (measured and modelled) tend to mask. Depth-averaging can therefore have a significant effect on power estimations. Analysis of physical and hydrodynamic characteristics in Ramsey Sound, including tidal velocities across the swept area of the pilot TST, variations in the stream flow with depth, estimated power output, water depth and bed slope, suggests that the spatial and temporal variability in the flow field may render much of Ramsey Sound unsuitable for tidal power extraction. Although the resource potential depends on velocity and bathymetric conditions that are fundamentally local, many prospective tidal energy sites are subject to similar physical and hydrodynamic constraints. Results of this study can help inform site selection in these complicated, highly dynamic macrotidal environments. In order to fully characterise the structure of the tidal currents, these data should be supplemented with 3-D modelling, particularly in areas subject to a highly irregular bathymetry and complicated tidal regime.

Expanding coastal urban and industrial seascape in the Great Barrier Reef World Heritage Area: Critical need for coordinated planning and policy

Coastal freshwater and tidal wetland habitats are being transformed as a result of increasing demand for commercial, residential and tourism activities. The consequence is a habitat seascape complex, comprising a mosaic of natural and engineered coastal features. This study used the freely available mapping tool (Google Earth) to define the extent of coastal engineering structures in the Great Barrier Reef World Heritage Area (GBR; Australia), a marine ecosystem of global biodiversity and cultural significance. Continuing threats to the heritage estate concomitant with expanding urban and industrial developments has raised concerns directed at the future conservation and resilience of the reef ecosystems, along with maintaining expected human lifestyles and livelihoods it provides. The data here shows that break walls and pontoons/jetties dominate development, contributing to approximately 10% (equivalent) of the coastline linear length. Most (60%) development occurs along the coastline or within the first few kilometres upstream along estuaries. While conservation and protection of natural coastal habitats is still preferred for the objective of fisheries production and biodiversity, managers must consider seascape implication/benefits more broadly when approving new marine infrastructure rather than a case-by-case approach which further contributes to an ad hoc mosaic seascape of natural and engineered habitats. Not only within the GBR heritage estate, but more broadly, coastal managers need to regard wider seascape connectivity processes during the assessment of any new development. There is an urgent need for policy and planning instrument reform that is inclusive of accumulative impacts of urban and industrial development in this heritage estate. Opportunities to include eco-friendly (green engineering) solutions, in the repair and revitalisation of existing artificial structures, is necessary in any new proposed urban and industrial development and expansion.

Wave exposure as a predictor of benthic habitat distribution on high energy temperate reefs

The new found ability to measure physical attributes of the marine environment at high resolution across broad spatial scales has driven the rapid evolution of benthic habitat mapping as a field in its own right. Improvement of the resolution and ecological validity of seafloor habitat distribution models has, for the most part, paralleled developments in new generations of acoustic survey tools such as multibeam echosounders. While sonar methods have been well demonstrated to provide useful proxies of the relatively static geophysical patterns that reflect distribution of benthic species and assemblages, the spatially and temporally variable influence of hydrodynamic energy on habitat distribution have been less well studied. Here we investigate the role of wave exposure on patterns of distribution of near-shore benthic habitats. A high resolution spectral wave model was developed for a 624 km2 site along Cape Otway, a major coastal feature of western Victoria, Australia. Comparison of habitat classifications implemented using the Random Forests algorithm established that significantly more accurate estimations of habitat distribution were obtained by including a fine-scale numerical wave model, extended to the seabed using linear wave theory, than by using depth and seafloor morphology information alone. Variable importance measures and map interpretation indicated that the spatial variation in wave induced bottom orbital velocity was most influential in discriminating habitat the classes containing canopy forming kelp Ecklonia radiata, a foundation kelp species that affects biodiversity and ecological functioning on shallow reefs across temperate Australasia. We demonstrate that hydrodynamic models reflecting key environmental drivers on wave exposed coastlines are important in accurately defining distributions of benthic habitats.

Applicability of data mining algorithms in the identification of beach features/patterns on high-resolution satellite data

The available beach classification algorithms and sediment budget models are mainly based on in situ parameters, usually unavailable for several coastal areas. A morphological analysis using remotely sensed data is a valid alternative. This study focuses on the application of data mining techniques, particularly decision trees (DTs) and artificial neural networks (ANNs) to an IKONOS-2 image in order to identify beach features/patterns in a stretch of the northwest coast of Portugal. Based on knowledge of the coastal features, five classes were defined. In the identification of beach features/patterns, the ANN algorithm presented an overall accuracy of 98.6% and a kappa coefficient of 0.97. The best DTs algorithm (with pruning) presents an overall accuracy of 98.2% and a kappa coefficient of 0.97. The results obtained through the ANN and DTs were in agreement. However, the ANN presented a classification more sensitive to rip currents. The use of ANNs and DTs for beach classification from remotely sensed data resulted in an increased classification accuracy when compared with traditional classification methods. The association of remotely sensed high-spatial resolution data and data mining algorithms is an effective methodology with which to identify beach features/patterns.

Autotrophic net productivity patterns at four artificial reef sites in the Mississippi Sound

Nearshore artificial reefs are common coastal features, for instance the Mississippi Sound has 67 inshore artificial reefs, the goal of which is to increase fisheries production. The success of artificial reefs depends in part on the primary production potential available to support the reef-based food web. In this study, we used settlement plates to estimate periphyton community net productivity, chlorophyll-a (chl-a), and biomass at sites adjacent to four artificial reefs in the Mississippi Sound in order to evaluate the potential of these artificial reefs to enhance local primary production. Water column primary productivity, chl-a, and biomass were also measured to assess the contribution of phytoplankton to total net primary production at these four sites. The largely negative net productivity measurements obtained for the periphyton community suggest that artificial structures deployed in the Mississippi Sound are potentially net heterotrophic and that the autotrophic component of the periphyton is not likely to be a major source of primary production to the reef food web for much of the year except in winter. The higher water column productivity measurements suggest that phytoplankton is a more important source of primary production to the reef food web than the benthic periphyton community especially during the summer.

The Geomorphology of Gola, North-West Ireland

© 2015 Royal Irish Academy. The island of Gola, offshore north-west County Donegal, Ireland, shows a range of geomorphic and sedimentary features of Pleistocene and Holocene age, but hitherto these features have not been described. This study reports on the main glacigenic (Pleistoceneage) and coastal (Holocene) geomorphic features, their associated sediments and their environmental interpretations in the context of regional Pleistocene and Holocene climate change. The contemporary geomorphology of Gola is strongly controlled by its underlying geology and Pleistocene glacial history (which includes its paraglacial inheritance), and its exposed Atlantic-facing location.

Ports and Digital Ports: The Narrative Construction and Social Imaginaries of the Island City of Mumbai

A city is a physical structure in one sense. In another sense, it is an organic body, poetically and metaphysically portrayed as having a soul. Most urban formations around the world, especially island cities, have a clear anthology of narratives that mesh the physical and the metaphysical of a city-body. The island city of Mumbai possesses characteristic socioeconomic traits have been counter-intuitively shaped by narratives and social imaginaries that would not have emerged if not for coastal features and forms. This aspect has been insufficiently explored. This paper will bring three unexplored dimensions to the fore. The first is how this island city’s main ports, historically connected to West Asia and later to Europe, become the main entry points for material and non-material foundations of modern cultural production. The second is how these bases became the primary nodes for narratives that inform the city’s distinctive ethos and its inhabitants’ social imaginaries in such a way as to fundamentally differ from the pre- and postcolonial narratives of India. The third is how digital ports (global undersea Internet cables), initially connected to the city because of the calm waters of the Arabian Sea, have made the Internet a powerful and dominant mode of cultural production in Mumbai.

Design of Submerged Offshore Reefs for the Coastal Protection Measures

Coastline is an interface between the ocean and the land. Coastal erosion is recession of the shoreline and loss of land area due to action of waves, currents and wind. Human interference also contributes to the adverse effects along the coastline, including the erosion. The physical regime of the Indian coastline is characterized by different types of coastal features. In order to mitigate the coastal erosion, the coastal protections are provided and are broadly classified as soft and hard solutions, and also combination of both. The coastal protection for the erosion at Ullal, Mangalore in Karnataka was taken up for detail study as a sub-project by the (Asian Development Bank) ADB Consultants. An integrated development plan prepared by the ADB Consultants for sustainable coastal protection includes construction of two offshore reefs & four inshore berms to trap the sediments, Beach nourishment of the Ullal beach and Re-habilitation of breakwaters to allow more sand movement towards south. Two delta shaped offshore reefs have been proposed as a part of sustainable coastal protection at Ullal. Based on desk and wave flume studies carried out at CWPRS, the design of cross-sections of these offshore reefs as low-crested rubblemound structures has been evolved. Three alternative design cross-sections of submerged offshore reefs were confirmed through wave flume studies. The wave transmission characteristics of the submerged offshore reef were also evolved through the wave flume tests with different wave height and tidal level conditions.

Determination of Coastal Belt in the Disaster Prone Area: A case study in the Coastal area of Bantul Regency, Yogyakarta, Indonesia

Mitigation strategy development is needed for protecting coastal communities and preserving coastal resourc-es from the impact of coastal hazards. It is believed that coastal land use planning can be proposed to reduce impact of coastal hazards. ἀe coastal belt boundary development is one of the mitigation approach which is common use in many countries as an inexpensive solution compared to hard structure development. Our study was located in the coastal area of Bantul regency, a low lying coastal area and densely populated region, where some clustered people lives proximity to the sea. In this study, a new method for determining coastal belt boundary was developed in the study area. ἀe Spatial Multi Criteria Evaluation (SMCE) tool of Ilwis plays as powerful tool for assessing coastal vulnerability in term of multi-hazard events. To calculate the width of the coastal belt boundary, the Ilwis-SMCE outcomes were employed. By apply-ing this method, there were three scenarios of the setbacks wide for both direct and pairwise method to be proposed. In general, the coastal area of Bantul Regency is dominated by high vulnerable area respectively impacted by multi-hazard events (tsunami, high wave and erosion-accretion), by incorporating some coastal features, such as topography, bio-physics, economic, and social-culture. ἀe results of the analysis are consistent with what was observed in the actual areas. Taken into account for hazard and vulnerability indices, the coastal belt boundary established in this area should wider than those already determined by existing regulations.

Impact of increased grid resolution on global marine biogeochemistry

Here we examine the impact of mesoscale processes on the global marine biogeochemical system by performing simulations at two different resolutions, 2° (LO-res) and 1/4° resolution (HI-res) using the PELAGOS model. Both the LO-res and HI-res simulations are set up with the same forcings and biogeochemical parameterizations, while the initial conditions are provided by a spinup of the LO-res simulation. This allows us to perform a direct inter-comparison of the two cases with a view to understanding how the introduction of mesoscale features affects the biogeochemical system, specifically how differences in the resolved horizontal and vertical motions are reflected in the plankton biomass and the nutrient availability. While the global large-scale oceanographic features (fronts, gyres, etc.) are captured in both the LO-res and HI-res simulations, differences in the mesoscale flow structures, and in particular the resolved vertical physics in the HI-res simulation generate very different behavior in the biogeochemical system. These differences in the physics drive what is a spun-up biogeochemical system in the LO-res simulation into a new regime in the HI-res simulation with significant reduction of typical low resolution biases. Coastal features are well reproduced due to stronger Ekman upwelling at the continental margins and increased eddy kinetic energy in the Southern Ocean significantly reduces the winter overestimation. These biases in the LO-res model are a result of inadequate vertical dynamics. The enhancement of surface chlorophyll can be attributed to improvements in the winter mixed layer in some regions such as the North Atlantic, while it is overall the difference in the Ekman vertical velocity which improves surface production allowing to simulate more realistic deep chlorophyll maxima as well. While the HI-res is better than the LO-res at capturing the timing of the spring bloom in the Southern Ocean, it still overestimates the peak of the bloom, hinting at the need to better understand the driving forces of the seasonal cycle of sub-Antarctic plankton dynamics.

Landscapes on the edge: examining the role of climatic interactions in shaping coastal watersheds using a coastal–terrestrial landscape evolution model

AbstractIncised coastal gullies (ICGs) are dynamic features found at the terrestrial‐coastal interface. Their geomorphic evolution is driven by the interactions between processes of fluvial knickpoint migration and coastal cliff erosion. Under scenarios of future climate change the frequency and magnitude of the climatological drivers of both terrestrial (fluvial and hillslope) and coastal (cliff erosion) processes are likely to change, with an adjunct impact on these types of coastal features. Here we explore the response of an incised coastal gully to changes in both terrestrial and coastal climate in order to elucidate the key process interactions which drive ICG evolution.We modify an extant landscape evolution model, CHILD, to incorporate processes of soft‐cliff erosion. This modified version, termed the Coastal‐Terrestrial‐CHILD (CT‐CHILD) model, is then employed to explore the interactions between changing terrestrial and coastal driving forces on the future evolution of an ICG found on the south‐west Isle of Wight, UK. It was found that the magnitude and frequency of storm events will play a key role in determining the future trajectory of ICGs, highlighting a need to understand the role of event sequencing in future projections of landscape evolution. Furthermore, synergistic (positive) and antagonistic (negative) interactions were identified between coastal and terrestrial parameters, such as wave height intensity and precipitation duration, which act to modulate the impact of changes in any one parameter. Of note was the role played by wave height intensity in driving coastal erosion, which was found to play a more important role than sea‐level rise in determining rates of coastal erosion. This highlights the need for a greater focus on wave height in studies of soft‐cliff erosion. Copyright © 2014 John Wiley & Sons, Ltd.

Storms impact on morphodynamics of human controlled coastal features in western France: the prevailing role of local management practices.

Storms impact on morphodynamics of human controlled coastal features in western France: the prevailing role of local management practices.

English

Sea waves are the powerful agent of seashore erosion. Once waves attacked on coasts; beaches and headlands are the landforms which faces first and finally influenced by wave energy in terms of erosion. In the coastal areas; beaches, sand bars, sand spits and sand dunes are the depositional landforms which continuously interact with tidal waves. Among these, sand dunes are the coastal feature which also significantly protects the landward ecosystem and settlements by the disastrous effects of tidal waves, storms, cyclone, tsunamis etc. The present research work attempted to study the sand dunes of Mithmumbari and Kunkeshwar- the coastal areas of Devgad, Maharashtra. The study also focussed on degradation of sand dunes in the study area.

Prediction of ocean currents with artificial neural networks

The prediction of ocean currents on real time basis is a complex exercise due to the variability of coastal features like topography and bathymetry as well as uncertainty of driving forces and also interaction among various met-ocean parameters. Although numerical methods are commonly used for this purpose, they need large and detailed exogenous information along with high computational resources and at times can have less tolerance to noise and gaps in data. At this backdrop and when site-specific information is sought for, data-driven techniques like artificial neural network (ANN) might appear attractive. Although there are some past applications of ANN to online current forecasting, lower prediction accuracy at higher values and over longer prediction intervals together with unequal accuracy levels for zonal and meridional current components have remained as problems. This paper attempts to address these issues. At two locations in North Atlantic and North Pacific Oceans the ANN-based time series models have been developed to predict currents over time horizons of 1hr to 24 h. After considerable experimentation, it was found that if the input is pre-processed with the help of a carefully selected smoothing technique and if its sequence length is methodically selected, then together with an empirical correction the long interval and extreme predictions significantly improve in case of both meridional and zonal current components.

Tectonic constraints on the late Pleistocene-Holocene relative sea-level change along the north-eastern Adriatic coast (Croatia)

In spite of very favourable coastal features, late Pleistocene-Holocene relative sea-level changes along the eastern Adriatic coast are still not completely resolved mostly due to the intensive and complicated regional and local neotectonics. We gathered current knowledge that generally presents the north Adriatic area as subsiding one, and proposed a reconstruction in new light of possible very slow (local) uplift (average rate of 0.1–0.25mm/a for last 80ka) which is supported by well-dated submerged speleothems and tectonic reconstruction. In addition, such a scenario supports also the formation of tidal notches that are common in the north Adriatic region, but not yet entirely understood. However, according to the latest Mediterranean data on sea level during the marine isotope stage (MIS) 5.1 being at +1m 80ka ago, we do not dismiss the possibility of subsidence which would have been 0.18–0.23mm/a on average for the last 80ka, but notch formation under such condition would not have been realistic. Apparently, the position of the north-eastern Adriatic coast on a convergence area requires extensive palaeoenvironmental studies, including structural, lithostratigraphical, palaeontological, archaeological and radiometric data and application of isostatic modelling.

Landscape metrics as indicators of coastal morphology: A multi-scale approach

In this study, the aim was to assess how commonly used landscape metrics perform as predictors of coastal shape. I examined nine metrics computed in FRAGSTATS to model the distribution of three coastal features of the Iberian Peninsula: beaches, capes and gulfs. A multi-scale approach was used combining three extents, three resolutions and five moving-window sizes to implement generalized linear models (GLMs). This study has found that three landscape metrics (edge density, mean perimeter-area ratio and percentage of landscape) were good indicators for the three coastal features, while mean shape index was only for beaches and gulfs. Differences in performance were found among the coastal features and scales studied. GLMs revealed that the smallest extent (Levante coast) and resolutions (250m2 and 1km2) achieved better validation results, suggesting a higher suitability of these scales for detecting changes in vectorial shorelines. Differences in sensitivity and specificity were also found among models estimated from different moving-window sizes. The present study confirms previous findings on the high multicollinearity of landscape metrics, and the convenience of testing correlations in advance. Raster-based metrics computed from vectorial coastlines were effectively incorporated in spatial modeling. This research provides new insight into the use of coastal shape to predict species distributions and other coastal processes, serving as a base for future studies.

A LABORATORY MESOCOSM AS A TOOL TO STUDY PAH DEGRADATION IN A COASTAL MARSH WETLAND

ABSTRACT Polycyclic aromatic hydrocarbons (PAHs) are one of the contaminants of concern in coastal marsh environments which are subject to crude oil spills. A laboratory scale mesocosm can be used to complement field study of PAH degradation in coastal marshes. Coastal marsh wetland features, such as its soil, tidal cycles, and flushing, that may play roles in PAH degradation can be simulated in a laboratory mesocosm. The laboratory mesocosm tank is made of acrylic as the main construction material with an air chamber inside the tank which functions as a pneumatic system and tidal water storage compartment. Two trays filled with contaminated marsh wetland soil are situated at two different levels: the lower one is constantly submerged while the higher one is intermittently drained. When the air pressure inside the air chamber is high, the water will flow out from the air chamber to the tank to create high tide. When the air pressure inside the air chamber is low, the water will flow back from the tank to the air chamber to create low tide inside the tank. The tidal water sits in the air chamber until the next high air pressure. The cycles of air pressure inside the tank are controlled by an electrical air pump connected to a timer. The experimental setup can consist of several replicates with an air chamber inside each replicate is controlled by a master pneumatic tank. The model PAH contaminant used in the experiment was phenanthrene, a three-benzene-ring PAH, which was spiked to the wetland soil. The experimental results show that the phenanthrene degradation in the intertidal wetland soil is higher than that of in the subtidal wetland soil presumably due to the availability of oxygen in the intertidal wetland soil. The laboratory mesocosm developed in this study can be used as a tool for examining PAH degradation and other non-volatile organic contaminants.

Image classification methods applied to shoreline extraction on very high-resolution multispectral imagery

Comprehension of vulnerability to coastal erosion in dynamic coastal environments strongly depends on accurate and frequent detection of shoreline position. The monitoring of such environments could benefit from the semi-automatic shoreline delineation method, especially in terms of time, cost, and labour-intensiveness. This article explores the potential of using a semi-automatic approach in delineating a proxy-based shoreline by processing high-resolution multispectral WorldView-2 satellite imagery. We studied the potential and differences of basic and easily accessible standard classification methods for shoreline detection. In particular we explored the use of high spatial and spectral resolution satellite imagery for shoreline extraction. The case study was carried out on a 40 km coastal stretch facing the Northern Adriatic Sea (Italy) and belonging to the Municipality of Ravenna. In this area a frequent monitoring of shoreline position is required because of the extreme vulnerability to erosion phenomena that have resulted in a general trend of coastal retreat over recent decades. The wet/dry shorelines were delineated between the classes of wet and dry sand, resulting from different supervised (Parallelepiped, Gaussian Maximum Likelihood, Minimum-Distance-to-Means, and Mahalanobis distance) image classification techniques and the unsupervised Iterative Self-Organizing Data Analysis Technique (ISODATA). In order to assign reliability to outcomes, the extrapolated shorelines were compared to reference shorelines visually identified by an expert, by assessing the average mean distance between them. In addition, the correlation between offset rates and different types of coast was investigated to examine the influence of specific coastal features on shoreline extraction capability. The results highlighted a high level of compatibility. The average median distance between reference shorelines and those resulting from the classification methods was less than 5.6 m (Maximum likelihood), whereas a valuable distance of just 2.2 m was detected from ISODATA and Mahalanobis. Heterogeneous coastal stretches exhibited a larger offset between extracted and reference shorelines than the homogeneous ones. To finally evaluate the coastal evolution of the area, results from Mahalanobis classification were compared to a shoreline derived from airborne light detection and ranging (lidar) data. The fine spatial resolution provided by both methodologies allowed a detailed Digital Shoreline Analysis System (DSAS) comparison, detecting an erosive trend within a wide portion of the study area.

Ptolemy's map of Ireland: a modern decoding

Claudius Ptolemy (roughly AD 90-168) presents us the oldest surviving account of Ireland in the form of a set of coordinates showing different geographical features or a ‘virtual map’. While Ptolemy’s map looks roughly like today’s Ireland there are a number of discrepancies. Likewise, while some locations are obvious, others are disputed or obscure. After reviewing earlier attempts at reconciling Ptolemy’s map with modern ones we adjust Ptolemy’s coordinates to modern references with two equations. We find Ptolemy’s map is consistent with some intimate Mediterranean knowledge of Ireland, its peoples, coastal features and principal places with their respective locations. We correct some of the modern locations attributed to Ptolemy, offer possible explanations for certain disputed or uncertain locations and offer some external validation to the prehistoric division of Ireland passed down from pre-Patrician sources.

Coastal wetlands reveal a non-synchronous island response to sea-level change and a palaeostorm record from 5.5 kyr to present

Here, we describe environmental change on Lord Howe Island (LHI; 31°30′S, 159°05′E) over the last 5500 cal. BP, derived from the analysis of the accumulating sediments in four coastal wetlands. Grain-size analyses, loss on ignition (LOI) and micrometre-resolution x-ray fluorescence (XRF) geochemical data were combined with 10 accelerator mass spectrometry (AMS) 14C dates to determine a chronology of environmental change. Sedimentary coastal features were initiated on the drowned LHI basalt coastline after ~4500 cal. BP, which was followed by gradual development of wetland environments from 4200 cal. BP to present. Within this period, a series of high-intensity storm events are recorded, perhaps related to low-pressure systems, including cyclones and East Coast Low (ECL) events. A lack of synchronicity between the studied sites resulted from their position in the landscape relative to the coast, features within the lagoon and greater sediment availability after 2800 cal. BP as sediment filled sinks in the lagoon floor. Increasing westerly wind strength from 600 cal. BP also combined with late-Holocene falling sea levels and lagoon infilling to facilitate the rapid growth of the coastal plain at ~500 cal. BP. The coastal wetlands of LHI preserve a record of rapid changes superimposed over more gradual environmental change since the mid-Holocene. The findings of this study further the understanding of the development of this ‘World Heritage Area’ as well as provide an increased understanding of how small oceanic islands respond to rising sea levels.