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Shipwrecks are an integral part of our maritime archaeological landscape and are associated with diverse societal and cultural interests, yielding significant management challenges. Coupled hydrodynamic and geomorphological processes significantly impact the effective in situ preservation of these fragile sites. In this study, we assess sediment budget change and hydrodynamic triggers at metal‐hulled shipwrecks lost between 1875 and 1918, all located in the tidally dominated Irish Sea at depths between 26 and 84 m. This is conducted using time‐lapse, multibeam echosounder surveys at multiannual, annual, and weekly time steps, supported by sediment grain‐size analysis, modeled ocean currents, and shallow seismic data. Results indicate significant changes at all time steps for sites located in sand‐dominated environments, whereas the seabed around shipwrecks settled in multimodal sediments shows virtually no change outside of measurement errors (±30 cm). Variability in geomorphic change is attributed to local environmental factors, including bed shear stress, sediment supply, and spatial barriers to scour. We demonstrate that individual wrecks in similar shelf sea regions can be in very different equilibrium states, which has critical implications for the in situ management of underwater cultural heritage. [ABSTRACT FROM AUTHOR]

Conservation of historic shipwrecks is prohibitively expensive and in situ preservation and recording are the preferred archaeological approaches. Non-destructive high-definition 3D imaging is therefore essential for recording and managing submerged historic shipwrecks. Multibeam echosounders (MBES), the standard tool for hydrographic survey, can produce point clouds to image complex 3D structures. However, wreck imaging is often done using MBES in traditional survey mode optimised for morphological characterisation of the seafloor. This does not necessarily provide high-definition imagery required by archaeologists. This study demonstrates key factors influencing high-definition MBES imaging of wrecks through a controlled field experiment. Results show that optimal high-definition 3D imaging is achieved through maximising the pulse rate, narrowing the angular sector, using the highest frequency and shortest pulse lengths, applied to at least 3 to 5 overlapping centreline-parallel and offset passes with additional perpendicular/oblique lines. Variations in survey design are demonstrated to exert strong controls on sounding density and distribution, with high-density on horizontal and vertical wreck surfaces enabled by a combination of overlapping passes and offset lines. Adoption of this method would result in more widespread high-definition 3D imaging of wrecks to benefit archaeological research and develop effective mitigation strategies to minimise loss of the fragile underwater resource. [ABSTRACT FROM AUTHOR]

The large number of historic metal-hulled shipwrecks on the seabed is a major consideration for the marine environment, heritage management and spatial planning. Their stability is driven by linked hydro- and sediment-dynamics, which in turn influence chemical corrosion and biological encrustation. The dynamism at underwater sites is frequently expressed in elaborate patterns of depositional and erosional features developed due to seabed scour. These settings are complex, due to the variable morphologies of the wrecks, and diverse types of seabed geology and geomorphology. Not only are the flow patterns and geomorphic changes at shipwreck sites not fully understood, but how these influence the wreck structures remains under-researched. Here we combine high-resolution multibeam echosounder, ocean current and sediment data with 3D Computational Fluid Dynamics (CFD) to investigate interrelations between hydro- and sediment-dynamics and the deterioration of two complex, fully submerged tidally-influenced shipwrecks. Intricate patterns of wake and horseshoe vortices are observed, and modelled wall shear stresses predict geomorphic changes recorded in 4-year and one-week interval difference models. Moreover, substantial damage is detected on the wrecks, correlated with areas of elevated wall shear stress and pressure in CFD simulations. The combined approach aids site management and provides analogies for offshore engineering. • The sheer number of metal shipwrecks on the seabed creates perplexing management challenges. • Their structures significantly influence, and are influenced by, the local hydro- and sediment-dynamic settings. • Computational fluid dynamics and difference modelling using bathymetric data provide new insights into wreck deterioration. • Intricate patterns of simulated flows and wall shear stresses correspond to the areas of sediment erosion and deposition. [ABSTRACT FROM AUTHOR]

This paper describes Phase 1 of the project 'Archaeological Applications of the Joint Irish Bathymetric Survey (JIBS) Data', analysing bathymetric and backscatter data derived from multibeam surveys off the north coast of Ireland. In particular, the usability of the data for shipwreck detection, identification and site characterization is explored. In Phase 1, the data was screened for anomalous sea-bed features, which were subsequently described, catalogued and categorized according to their archaeological potential and cross-referenced against existing records. A planned second phase of this project will examine each anomaly in greater detail together with the local and regional hydrodynamic conditions. © 2010 The Authors [ABSTRACT FROM AUTHOR]

Abstract: Data from time-lapse single-beam and multi-beam bathymetric surveys are used to assess the rate and scale of morphological change at shipwreck sites caused by anthropogenic forcing. The technique is illustrated by characterizing changes in wreck site morphology over two sites located on the east coast of Ireland – the Drogheda Boat site on the River Boyne and the Arklow Bank site in the Irish Sea. Results indicate that repeated bathymetric surveys accurately and rapidly capture morphological change, with time-lapse accretion–erosion models indicating possible erosion rates of up to 0.04m per day and accretion rates of 0.36m per day at dynamic riverine and marine sites in response to external triggers. These data are valuable in understanding site formation processes at fully submerged archaeological sites and in the derivation of high-resolution site formation models. [ABSTRACT FROM AUTHOR]

Abstract: Mombasa Island, settled for almost 2000years, played a central role in the development of the central seaboard of East Africa, emerging by the 16th century as a centre of sustained port dominance. Marine geoarchaeological surveys were conducted in Mombasa Harbour in 2001 (i) to quantify the nature and extent of the submerged archaeological resource, (ii) to investigate site formation and preservation potential of historic shipwrecks, and (iii) to explore the natural evolution of the Old Port and adjacent basins in the context of hydrodynamic and sedimentary processes. Backscatter and single-beam echo-sounder data were acquired, interpreted and diver-truthed using surface-demand and SCUBA systems. It is proposed that sustained scour processes, resultant from the interaction of ebb and flood tidal currents with bedrock ridges, control the bathymetric evolution of Mombasa Harbour, negating requirement for mechanical dredging. The submerged archaeological resource in the area comprises fish traps and shipwrecks. Physical processes govern shipwreck site formation, with scour and bed-migration dominant, ultimately leading to structural instability and site degradation. The wreck of Santo António de Tanná (1697) has been subject to gravitational collapse and mass down-slope movement of material, concentrating wreck structure and material along the portside stern third of the vessel. [Copyright &y& Elsevier]

Northern Ireland has been subject to significant maritime influences throughout its known 9,000-year human history. In 1997, the University of Ulster, in partnership with the Environment and Heritage Service, embarked on a program of seabed mapping in an attempt to record the submerged and buried archaeological resources. To date, the geophysical research program has imaged about 80 19th- and 20th-century wrecks and about 100 targets of further ‘archaeological potential.’ One method of integrating the results of geophysical surveys into the Maritime Sites and Monuments Record (SMR) is the use of the classification scheme CEBESSt, an alphanumeric wreck-site classification scheme based upon six site-specific variables: Composition of hull, Energy of wreck environment, Burial, Exposure, Structural integrity, and Substrate type, with t corresponding to time (the year of wrecking, if known). The classification is designed for use within a database scheme that allows for interrogation through character recognition and pattern matching. [ABSTRACT FROM AUTHOR]

Fully submerged shipwreck sites act as open systems, with the exchange of material (sediment, water, organic and inorganic objects) and energy (wave, tidal, storm) across system boundaries. Formation processes at wreck sites are driven by some combination of chemical, biological and physical processes, with physical processes dominant in initial phases of site formation. Scouring and associated depositional patterns that form in response to hydrodynamic forcing are commonly the dominant physical processes acting at shipwreck sites. Scour is initiated by the introduction of a shipwreck to the seafloor, leading to increases in flow velocity and turbulent intensity around the structure. Near-field and far-field scour pits form at wreck sites due to the interaction of horseshoe and lee wake vortices with the mobile substrate. The morphology of resultant scour signatures are controlled by the orientation of the wreck structure in relation to the prevailing hydrodynamic regime, the morphology and size of the wreck and individual site components, the hydrodynamic regime (currents, waves or combined waves and currents), bathymetry and the geology of the site (seafloor and sub-surface conditions). Individual objects or artefacts may act as nuclei to promote scour at a local scale. Under high-energy conditions, groups of artefacts and/or disarticulated structural components emanating from a wreck may compound natural scour processes by rolling or sliding. Under suitable environmental conditions, wreck-associated scour features can be preserved in the sedimentary record. [Copyright &y& Elsevier]

The original version of this article was revised: Additional correction in Table 1: please delete (') in the second column heading was incorrectly carried out. It should read "Acquisition settings test"; by this, the author meant only to delete the apostrophe symbol, not the entire second column heading. [ABSTRACT FROM AUTHOR]