1,721,005 research outputs found
Sea surface temperature trends in the coastal zone of southern England
No full textSea surface temperature (SST) trends along the south coast of England (northern English Channel) were examined based on data from systematic buoy measurements deployed by the National Network of Regional Coastal Monitoring Programmes of England (NNRCMP) since 2003. These data were supplemented with the following: 1) long-term, coastal SST measurements by the Centre for Environment, Fisheries and Aquaculture Science (CEFAS); 2) global data sets compiled by the Hadley Centre since 1900, and 3) satellite-derived observations from Moderate Resolution Imaging Spectroradiometer (MODIS Aqua) since 2002. These data sets were used to evaluate de-seasoned nearshore trends in SST along the south coast of England, and examine links to regional ocean-atmosphere teleconnections. The analyses of long-term, CEFAS data (collected at five sites along the Southern English Coast) support the proposal that prior to the mid-1980s there were no de-seasoned trends in SST and conditions from year to year were relatively stable. Subsequently, inter-annual fluctuations appear to have increased and are , associated with a period of warming between 1985 and 2003 (0.28oC/decade). Post 20052003, interannual fluctuations in SST monitored by the NNRCMP data buoys continued, and the warming trend appears to be greater (0.42 oC/decade). This trend in SST is greatest in the nearshore and decreases with distance offshore in a systematic fashion. The warming in SST also varied greatly from month to month. The greatest warming took place from December to March, whilst the least heating (and sometimes cooling) occurred between September and November. Analysis of Hadley (HadSST1.1) and MODIS data sets substantiated these trends. The greatest warming (post 2003) was found west of Portland Bill (up to 0.76 oC/decade) and decreased towards the Strait of Dover. Despite this west-to-east trend, all 12 NNRCMP stations between Penzance and Folkestone showed remarkably similar results, suggesting regional and global sources of heat rather than local sources. This is further corroborated through wavelet coherence analysis linking SST anomalies to regional/global ocean-atmosphere teleconnection indices at seasonal scales
BARDEX II: Nearshore sediment resuspension and bed morphology
No full textSediment resuspension in the region outside the surf zone is known to contribute to the morphological response of barrier beaches to wave forcing, such as onshore bar migration processes. However, few measurements in this region exist, limiting our ability to quantify its contribution. These processes are complicated by the presence of bedforms in the nearshore, which alter the sand transport processes while modifying bed roughness in a complex feedback mechanism. The Hydralab IV funded BARDEX II experiments, which took place in the Delta Flume in 2012, were used to provide measurements of these processes in the nearshore of a sandy barrier beach (D50 = 0.42mm) under a range of wave conditions (Hs = 0.3 - 0.8 m; Tp = 4 – 2 s) and water levels, through deployment of a suite of acoustic instruments measuring flow velocity, near-bed turbulence, sediment resuspension profiles and bed morphology in cross-section and plan view. Initial findings indicate that sediment suspension in the nearshore appears to be controlled by a combination of near-bed turbulent bursting processes which results in near-instantaneous low concentration suspensions restricted to the bottom boundary layer, and vortex shedding from bedforms which results in higher concentration suspensions which are larger in scale than vertical eddy sizes, and perpetuate outside of the bottom boundary layer
Beach monitoring: do we need to survey to spring low tide?
No full textWhen collecting coastal monitoring data, it is common practice to survey down to spring low tide to capture the maximum extent of the exposed subaerial beach. However, collecting topographic beach data is possible for only a few days per month. By reducing the seaward extent of the survey, the incurred costs and risks to the survey schedule could be greatly reduced. However, this would result in information loss at the lowest extremes of the subaerial beach. This study assesses the feasibility of predicting this part of the beach using deep learning neural networks based on partial beach profile data. A range of network architectures were tested alongside linear extrapolation, which was used as a baseline model. Each model was tested on three beaches with varying morphology, ranging from steep (reflective) to mildly sloping (dissipative). The presence of morphological features was found to play a dominant role in the accuracy of the predicted profiles; profiles with more pronounced cross-shore morphological features, such as sandbars, produced the highest error. While local connectivity of each network architecture was found to be the key factor in producing realistic profiles, the 1D Convolutional Neural Network was found to be the most effective with an average RMSE of between 0.026-0.119 m. This RMSE is not substantially larger than the vertical accuracy of current survey techniques (0.03 m), and the study found that errors of this magnitude have negligible effects when the survey data is used to calculate beach volumes and conduct numerical wave runup analysis to assess coastal flood risk
Re-processing Datawell Directional Waverider MkIII heave data affected by breaking waves
No full textObservations of nearshore waves are essential for coastal management, planning and operations. However, shallow water deployments often encounter breaking waves, causing anomalous measurements that are rejected during quality control. A new methodology for re-processing wave data containing breaking waves has been developed, utilising data from the National Network of Regional Coastal Monitoring Programmes of England which operates 37 Datawell Directional Waverider MkIII buoys. Heave data affected by breaking waves is reviewed, anomalous heaves removed, and the remaining data re-processed. Validation through a two-stage process confirms that re-processed wave parameters closely match those derived from the established Datawell processing and ensures strong agreement between parameters derived from shorter re-processed records and full-length data. Applying this new approach to all measured storm wave data, 7.3% (928.5 hours) of storm wave data is recovered across the 37 sites. At some sites, the retention of additional storm wave data has considerable impacts on significant wave height (Hm0) return periods. At five sites, the 1 in 100 year return period increased by over one meter. The enhanced dataset now includes more individual storm events and more complete records of storm events, providing a more robust foundation for coastal management and planning
Datasets from 'Mixed sand and gravel beach morphodynamics: observations and modelling across the nearshore' PhD project.
No full textDatasets gathered as part of the PhD project ' Mixed sand and gravel beach morphodynamics: observations and modelling across the nearshore'.
Pevensey Bay Bathymetric and Topographic Surveys 2020-2022: This dataset includes elevation data across 18 profiles which relate to the following National Network of Coastal Monitoring Programme transects 4c01677 to 4c01729. The profiles extend approximately 1km offshore with 3 profiles extending out to the outer depth of closure (Hallermeier, 1983). The positional data is provided in the cartesian co-ordinate system British National Grid, and the height data is relative to Ordnance Datum Newlyn. Further information included within datasheet.
Pevensey Bay Particle Size Distribution: This dataset includes particle size distribution data from the nearshore (array and transverse finger bar areas) and from across the beach face. The positional data of the grab samples is provided for the array area and transverse bar area, but is approximate for the upper beach area. The in the cartesian co-ordinate system British National Grid, and the height data is relative to Ordnance Datum Newlyn. Further information included within datasheet.
Pevensey Bay X-Band Radar Sea Surface Roughness Images: This dataset includes a series of sea surface roughness images calculated weekly between November 2020 until February 2023. The raw data was obtained from a X-band radar tower and processed by Marlan Maritime Ltd. Further information is included within datasheet.</span
Exploring nearshore bed dynamics of a mixed beach using the depth of closure conceptual model
No full textMixed sediment beaches are globally commonplace, yet little is understood of the extent and behaviour of their nearshore zones, potentially underestimating total cross-shore change. This paper is the first study to investigate the lateral and vertical extent of the active zone of the gravel-rich mixed beach in Pevensey Bay, a study site on the South East UK coastline. Morphodynamic change in the nearshore zone was studied at a range of timescales (days, months, years) suggesting that the width of the active nearshore zone correlated with the magnitude of the peak morphological change, whilst the depth of closure was influenced by bed slope, grain size and local variation in wave conditions. A conceptual model detailing the physical parameters responsible for local variations in the depth of closure was used to help understand differences between the observed and predicted depths of closure. Finally, ongoing chronic loss of sediment from below Mean Sea Level (MSL) was examined, which was shown to be independent of the depth of closure, but closely linked to the wider geomorphic setting of the bay
The effects of disturbance on the microbial mediation of sediment stability
No full textIn coastal areas, biofilms are often subject to disturbance by hydrodynamic forcing, bioturbation and human activities. These factors affect the influences biofilms have on the sediment. To reveal these effects, we studied laboratory-incubated and field-collected biotic sediments reworked by disturbances, and examined their stabilities and three-dimensional microstructures using laboratory annular flume tests and a wet-staining X-ray microcomputed tomography method. We find that, when subject to disturbance, biofilms do not always establish mat-like matrices that firmly armor the seabed and bio-stabilize sediments, but instead, have a range of effects on sediment stability, including both bio-stabilization and destabilization. Disturbance considerably alters microbial influences on sediment stability, but is not the only control. Given equal disturbance, whether or not sediments are bio-stabilized largely depends on the state of bio-sediment formation. At a relatively well-developed state, an organic-rich, adhesive polymer network tightly interconnects large amounts of sediment particles into aggregates, forms complex internal structures, and enhances sediment stability. By contrast, some bio-sediment formations only ever reach a less well-developed state, where scattered organic patches bind relatively few particles into aggregates and reduce sediment stability. Microbial growth likely has two opposing effects on sediment stability, by enhancing either weight/friction or lift/drag on aggregated particles. The former has the positive effect of enhancing sediment stability, whereas the latter can result in greater flow resistance and so have the opposite effect. A conceptual framework is put forward to characterize the different states of bio-sediment formation and their distinct effects on sediment stability.</p
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Micro-abrasion of flint artifacts by mobile sediments: a taphonomic approach
No full textFluvial redeposition of stone artifacts is a major complicating factor in the interpretation of Lower Palaeolithic open-air archaeological sites. However, the microscopic examination of lithic surfaces may provide valuable background information on the transport history of artifacts, particularly in low energy settings. Replica flint artifacts were therefore abraded in an annular flume and examined with a scanning electron microscope. Results showed that abrasion time, sediment size, and artifact transport mode were very sensitive predictors of microscopic surface abrasion, ridge width, and edge damage (p?<?0.000). These results suggest that patterns of micro-abrasion of stone artifacts may enhance understanding of archaeological assemblage formation in fluvial contexts
Morphological evolution of creek networks in 10 restored coastal wetlands in the UK
Full text linkCoastal wetlands provide crucial ecosystem services including flood protection and carbon storage, but are being lost rapidly worldwide to the combined effects of sea-level rise, erosion and coastal urbanisation. Managed Realignment (MR) aims to mitigate for these losses by restoring reclaimed land to tidal influence. Data of creek evolution is critical to assess the performance of design strategies and improve design and implementation practices. This data descriptor provides a dataset of the horizontal morphological evolution of creek systems from various initial conditions in 10 MR schemes across the UK. Using a semi-automated workflow, morphological creek parameters were extracted from 52 lidar datasets at 1 m horizontal resolution spanning 2 to 20 years post-breach. This constitutes the most comprehensive systematic monitoring of MR creek morphology to date. The dataset will assist future MR design and provide baseline morphological information for ecological and biogeochemical surveying
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