Seabed dynamics in a large coastal embayment: 180 years of morphological change in the outer Thames estuary

This article analyses the morphological history of the outer Thames seabed, covering over 3,000 km 2 from Aldeburgh (Suffolk), to Southend-on-Sea (Essex) and Margate (Kent). The region has been depicted on bathymetric charts since the sixteenth century, and has been formally charted since the eighteenth century. Charts published since the early 1800s incorporate sufficient grid reference or ground control detail for georectification onto a common coordinate system (British National Grid). The morphological history of the outer seabed was thus reconstructed through the digitisation and interpolation of soundings onto a regular grid (3D surface). The evolution of seabed morphology was examined using transects, bathymetric change maps and spatial statistics. The results show considerable spatial variability in seabed behaviour. Within the central Thames, banks have experienced significant depth changes can be associated with lateral shifts in individual banks. Some of the outer banks in this region exhibit progressive elongation. Shifts in bank position across the Suffolk shoreface appear to be more subtle, and there is evidence here of both onshore and offshore migration. There is no clear evidence of any regionally coherent response to large-scale historical forcing such as sea-level rise

Understanding coastal change using shoreline trend analysis supported by cluster-based segmentation

Shoreline change analysis is a well defined and widely adopted approach for the examination of trends in coastal position over different timescales. Conventional shoreline change metrics are best suited to resolving progressive quasi-linear trends. However, coastal change is often highly non-linear and may exhibit complex behaviour including trend-reversals. This paper advocates a secondary level of investigation based on a cluster analysis to resolve a more complete range of coastal behaviours. Cluster-based segmentation of shoreline behaviour is demonstrated with reference to a regional-scale case study of the Suffolk coast, eastern UK. An exceptionally comprehensive suite of shoreline datasets covering the period 1881 to 2015 is used to examine both centennial- and intra-decadal scale change in shoreline position. Analysis of shoreline position changes at a 100 m alongshore interval along 74 km of coastline reveals a number of distinct behaviours. The suite of behaviours varies with the timescale of analysis. There is little evidence of regionally coherent shoreline change. Rather, the analyses reveal a complex interaction between met-ocean forcing, inherited geological and geomorphological controls, and evolving anthropogenic intervention that drives changing foci of erosion and deposition

Seabed mobility in the greater Thames estuary

This report presents results from a Caird-Crown Estate research project to investigate the geomorphic history of the seabed and associated features within the greater Thames estuary within a region of over 5000km2 bounded by Aldeburgh (Suffolk), Southend-on-Sea (Essex) and Margate (Kent). Bathymetric charts published over the last 180 years have been analysed to assess the geomorphological evolution of the greater Thames seabed. Charts published since the early 1800s comprise sufficient grid reference or ground control detail for georectification onto a common coordinate system (British National Grid), and a total of 10 charts were used here to reconstruct the historical changes in seabed morphology. Systematic errors in the positioning of offshore features proved only problematic for the earliest chart (1824). Soundings were digitised as points from each chart, and the depth measures at each point were converted to Ordnance Datum. The point data were interpolated onto a regular 100 x 100 m grid (3D surface), which formed the basis of further analysis. The historical evolution of the greater Thames seabed was examined using cross- estuary and shore-normal transects; bathymetric change maps and spatial statistics. The analyses illustrated considerable spatial variability in seabed mobility. Within the central Thames, the banks of Barrows, Sunk Sand, Long Sand and Kentish Knock have experienced significant depth changes associated with lateral shifts. In many cases, the bank surface comprises numerous bathymetric highs that appear to migrate along the banks. Progressive changes can be seen at Long Sand Head, which has been prograding northward over the last 180 years, and Kentish Knock, which has been lengthening and changing shape over this period. The Suffolk shoreface has also experienced some gradual shifts in bank position. Cutler bank has moved seaward, whereas Whiting and Aldeburgh Ridge have moved landward. Bawdsey Bank appears to be extending northward, and the Shipwash has shifted around a central axis, with more recent change in shape. It is not clear whether the offshore banks (Gabbards, Galloper) have moved due to systematic positional errors, but the head and tails of these banks do show evidence of growth and decay

Large-scale spatial variability in the contemporary coastal sand and gravel resource, Suffolk, eastern UK

The response of coastal systems to changes in sea level and storm events is often dependent on the availability of sediment and sustainability of sediment supply. This paper analyses the changing sediment resource of a driftaligned shoreline in eastern England, UK, over centennial and decadal timescales. Spatial variability in cross-shore extent and elevational distribution of this mixed sand and gravel system exerts a significant control on the ability of different stretches of this shoreline to respond dynamically to changes in marine forcing. Furthermore, anthropogenic interference has led to the development of unnaturally high beach ridges in some places, which contrasts with the absence of intertidal or supratidal sediment along stretches dominated by seawalls

The need for data integration to address the challenges of climate change on the Guyana coast

Guyana's capacity to address the impacts of climate change on its coastal environment requires the ability to monitor, quantify and understand coastal change over short-, medium- and long- term. Understanding the drivers of change in coastal and marine environment can be achieved through the accurate measurement and critical analyses of morphologies, flows, processes and responses. This manuscript presents a strategy developed to create a central resource, database and web-based platform to integrate data and information on the drivers and the changes within Guyana coastal and marine environment. The strategy involves four complimentary work packages including data collection, development of a platform for data integration, application of the data for coastal change analyses and consultation with stakeholders. The last aims to assess the role of the integrated data systems to support strategic governance and sustainable decision-making. It is hoped that the output of this strategy would support the country's climate-focused agencies, organisations, decision-makers, and researchers in their tasks and endeavours

The morphodynamics of transverse dunes on the coast of South Africa

Transverse sand dunes located within the supratidal zones of beaches are a significant geomorphic feature along sand-dominated coasts worldwide and are generated by strong alongshore winds in areas of high sediment availability. Transverse dunes are present along the South African coast, and these are known to migrate dynamically in response to wind forcing. However, the detailed dynamics of individual dune systems along the same coastal stretch have not been compared to one another, and the relationship of transverse dunes to their hosting beach systems has also not been examined. This study examines the properties and dynamics of transverse supratidal dunes from three systems along the coast of South Africa, using remote sensing methods. Results show that, although the underlying beach system appears to be relatively stable over the time period of analysis, there is a dominant aeolian-driven migration of transverse dunes towards the northeast, following prevailing wind direction, countered by less dominant movement to the southwest. There are also considerable variations in calculated annual dune migration rates between adjacent systems, between summer and winter seasons, and between dunes within a single site. This highlights that, although beach and dune landforms can be conceptually considered as part of the same sediment system, there is not a clear relationship between phases of beach aggradation and phases of dune aggradation. Instead, a primary control appears to be beachface erosion by waves that reduces beach width and influences dune morphodynamics, independent of sediment supply

Benchmark ultra-cool dwarfs in widely separated binary systems

Ultra-cool dwarfs as wide companions to subgiants, giants, white dwarfs and main sequence stars can be very good benchmark objects, for which we can infer physical properties with minimal reference to theoretical models, through association with the primary stars. We have searched for benchmark ultra-cool dwarfs in widely separated binary systems using SDSS, UKIDSS, and 2MASS. We then estimate spectral types using SDSS spectroscopy and multi-band colors, place constraints on distance, and perform proper motions calculations for all candidates which have sufficient epoch baseline coverage. Analysis of the proper motion and distance constraints show that eight of our ultra-cool dwarfs are members of widely separated binary systems. Another L3.5 dwarf, SDSS 0832, is shown to be a companion to the bright K3 giant Eta Cancri. Such primaries can provide age and metallicity constraints for any companion objects, yielding excellent benchmark objects. This is the first wide ultra-cool dwarf + giant binary system identified.Comment: 4 pages, 3 figures, conference, "New Technologies for Probing the Diversity of Brown Dwarfs and Exoplanets", oral tal