The role of scour in shipwreck site formation processes and the preservation of wreck-associated scour signatures in the sedimentary record – evidence from seabed and sub-surface data

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.     

Processes and patterns of flow,erosion, and deposition at shipwreck sites: a computational fluid dynamic simulation

Shipwreck sites are open systems, allowing the exchange of material and energy across system boundaries. Physical processes dominate site formation at fully submerged wreck sites, and in turn influence chemical and biological processes at many stages of site formation. Scouring presents a fundamental yet poorly understood threat to wreck sites, and the processes and patterns of erosion and deposition of sediments and artefacts at wreck sites are poorly understood. Laboratory and field-based experiments to study these phenomena are time-consuming and expensive. In this study, open-source computational fluid dynamic (CFD) simulations are used to model the processes and patterns of flow, erosion, and deposition at fully submerged wreck sites. Simulations successfully capture changes in the flow regime in the environment of the wreck as a function of incidence angle, including flow contraction, the generation of horseshoe vortices in front of the wreck, the formation of lee-wake vortices behind the structure, and increased turbulence and shear stress in the lee of the wreck site. CFD simulations demonstrate that horseshoe vortices control scour on the upstream face of structure but play a minimal role in scouring on the lee side. Lee-wake vortices dominate behind the structure, with low-pressure zones in the lee of the wreck capturing flow. The amplification and reduction of wall shear stress and turbulent kinetic energy in the lee of the vessel form distinctive patterns in relation to flow direction, with areas of amplified and reduced wall shear stress and turbulent kinetic energy demonstrating excellent spatial correlation with erosional and depositional patterns developed at real-world wreck sites.     

Process-based models for port evolution and wreck site formation at Mombasa,Kenya

Mombasa Island, settled for almost 2000 years, 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.     

The 'Mardi Gras' Shipwreck: Results of a Deep-Water Excavation, Gulf of Mexico, USA

The 'Mardi Gras' Shipwreck is the remains of an early-19th-century sailing vessel lost in approximately 1220 m of water in the Gulf of Mexico. A recent archaeological investigation documented the wreck and recovered several artefacts, including glassware, ceramics, navigational instruments, a cannon, and a stove. Analyses of these artefacts and the surviving hull have led to preliminary conclusions on the nature of the vessel and its crew.
© 2009 The Authors     

Identification of Suspected Horn from the Queen Anne's Revenge (1718), North Carolina,USA

Infrared spectroscopy can be a valuable tool for conservators and archaeologists to help identify archaeological artefacts. We present a case‐study on the identification of an artefact recovered by North Carolina Department of Cultural Resources (NCDCR) Underwater Archaeology Branch from an early‐18th‐century shipwreck (31CR314). The wreck is assumed to be the remains of Queen Anne's Revenge, which sank off the North Carolina coast in 1718. A sample of the artefact was analysed by infrared spectroscopy to identify it. Prior to spectroscopic analysis it was speculated that the sample could be animal horn or leather. © 2011 The Authors     

Fishing Gear from a 7th-Century Shipwreck off Dor, Israel

The ancient anchorage of Dor, Israel, contains wreck-sites from several periods. Underwater exploration of one Byzantine wreck discovered the remains of a medium-size boat constructed with iron nails. Coin-finds dated it to c .665 AD, after the Muslim conquest. The wreck was probably caused by natural agents, but an event in the Byzantine-Muslim conflict can not be discounted. The artefacts include a group of objects testifying to the practice of light-fishing. Literary sources indicate a prevalence of light-fishing, but archaeological finds are very rare. This discovery clearly indicates light-fishing in late antiquity. A sounding-lead and steelyard can be seen as auxiliary to the fishing.
© 2007 The Authors     

The Western River Steamboat Heroine, 1832–1838, Oklahoma,USA: excavations,summary of finds,and history

This paper describes the excavation, discoveries relating to the hull, machinery, and artefacts, and the history of an early steamboat wreck discovered in the Red River between Oklahoma and Texas. The wreck has been identified as the side‐wheel steamer Heroine, a vessel in service on the Mississippi, Ohio, and other western rivers of North America during the 1830s. It is the earliest example of this famous type of vessel yet studied.     

Navigational Equipment from 't Vliegend Hart (1735)

The Dutch United East-India Company ship 't Vliegend Hart sank in the mouth of the River Scheldt in 1735. With archival sources the wreck was located in 1979, and in the following years researched and excavated, a process still continuing. This article gives a brief historical introduction on the ship, followed by a paragraph on the art of navigation and navigational instruments at the time of 't Vliegend Hart 's sailing. Thereafter this is compared with the navigational artefacts retrieved from the wreck. In the final paragraph the exploration of the 't Vliegend Hart wreck is briefly dealt with.
© 2006 The Authors     

Shipwreck Evidence from Kilwa,Tanzania

This article reports on the artefacts and environment of marine ballast and pottery sites identified through inter‐tidal and underwater survey around Kilwa, Tanzania, one of the most important medieval sultanates along the east African coast. An inter‐tidal site on the limestone fringing reef on the approaches to Kilwa Kisiwani Harbour and an underwater site within the harbour have been dated from associated pottery to c.8th–10th century and the 13th–16th century respectively. The presence of exotic basalt ballast is discussed as an indicator of wreck‐sites.     

Report on Finds from the Saint-Quay-Portrieux Wreck, France

In 1987, some divers discovered the cargo of a merchant ship which was wrecked off the rocks of the Saint-Quay Islands in Brittany. Several expeditions were conducted by the discoverer, DRASSM and the Art and History Museum of Saint-Brieuc on the site between 1987 and 2003 but the wreck remains unidentified. The ship is believed to have traded with Africa in the first part of the 18th century. Though no remains of the ship's structure were found, the artefacts recovered, including trading goods, ship's equipment, and domestic utensils, allow comparisons to be made with other contemporary materials.
© 2004 The Nautical Archaeology Society     

The Management of the Maritime Archaeological Heritage in the Bailiwick of Guernsey: a Case Study

Guernsey and the other islands in its Bailiwick have been visited and settled by people arriving by sea for thousands of years. Guernsey Museum manages the display and interpretation of this maritime heritage and, in conjunction with the Receiver of Wreck, administers the legal protection of historic wreck. Over the last 25 years a considerable amount of research has been undertaken on many aspects of the islands' maritime past. Museum displays and media presentations have been made to disseminate information about the islands' maritime archaeology to the wider world. This paper will highlight the various aspects of maritime archaeology in Guernsey and illustrate how Guernsey Museum manages this rich archaeological resource.
© 2004 The Nautical Archaeology Society     

The Mechanism and Kinetics of In Situ Conservation of Iron Cannon on Shipwreck Sites

Analysis of the pre‐disturbance values of the in situ corrosion parameters on historic iron shipwrecks and artefacts has established that the arithmetic product of the pH and corrosion potential is dependent on the burial environment and provides a unique insight into the objects' state of decay. The value of the product changes during in situ conservation treatment with sacrificial anodes, and reaches a minimum at which point the treatment is completed. Treatment times vary with water‐depth, being faster on shallower sites and shorter for more extensively corroded artefacts. The model was developed using data from the Duart Point wreck (1653), the Monitor‐styled warship HMVS Cerberus (1926) and a series of wrecks in Australia and the USA.     

Managing a Monitor — the Case of HMVS Cerberus in Port Phillip Bay: Integration of Corrosion Measurements with Site Management Strategies

Abstract

The hull of the former HMVS Cerberus (1926) collapsed two metres during gales in December 1993, leaving the vessel half-submerged. Sunk as a breakwater in 1926, the vessel is one of the few remaining and accessible twin-turret Monitor-style warships from the 1870s. This paper presents the complex history of attempts to stabilize the site and to preserve the wreck. A series of in situ corrosion studies of corrosion potentials, pH, and residual metal thickness have provided a special insight into the processes of decay and have paved the way for future site stabilization. Removal of the four 16-tonne 10 inch Armstrong rifled muzzle loading guns and their in situ treatment alongside the wreck have assisted in relieving some of the stress on the remaining structure. The paper reports on correlations between the corrosion rate and the formation of concretions and how to determine the end point of an in situ treatment for cannon.     

The Odyssey Case: press,public opinion and future policy

The Odyssey Case refers to the dispute between Odyssey Marine Exploration Inc. (OME) and the Kingdom of Spain in the US courts to determine the ownership of more than 500,000 coins, as well as other artefacts, that OME recovered from a wreck‐site it had code‐named Black Swan. However, the process was much more than a dispute over the coins. It reflected many of the components involved in the protection of underwater archaeological heritage, especially when economic and political interests are at stake. Written from the perspective of an archaeologist working for the regional authority responsible for developing archaeological policy, this paper tries to assess the case's impact on future policy development.     

Mapping of the Buried Yarmouth Roads Wreck, Isle of Wight, UK, using a Chirp Sub-Bottom Profiler

Remains of the 16th-century Yarmouth Roads wreck, buried in sediments, were imaged using high-resolution geophysical techniques. The remains appear as strong reflectors underlain by an acoustic blanking zone, which was used to create maps of the wreck material. Close survey line-spacing allowed the construction of contour maps and hull sections, which revealed that the bow and stern sections are tilted to port at different angles, implying that they are detached. The seismic data have enhanced our understanding of the site beyond what was known from conventional archaeological investigations and confirms that this wreck was once a large carrack.
© 2007 The Authors     

The Roman wreck of c. AD 200 at Plemmirio, near Siracusa (Sicily): Interim report

A Roman wreck, named Plemmirio B^[1]i, lies on the rocky talus below the southern cliffs of Capo Murro di Porco, near Costa Bianca del Plemmirio (Penisola della Maddalena), prov. Siracusa, Sicily. The cargo of amphoras and iron bars, relatively well-preserved, is situated between 22 m and 47 m depth. Following brief examinations in 1974–1982, a University of Bristol expedition spent four weeks surveying the site in July-August 1983^[2] This paper presents an interim summary of these campaigns; a comprehensive report will be published after completion of excavations at the site^[3]. The archaeological deposit at Plemmirio B is characterized by concentrations of fragmented amphoras. There is no direct evidence for the structure of the ship, much of which may have disintegrated during the initial wreck process, but study of the artefact distribution suggests a vessel of fairly large capacity. The amphora consignment (which may have numbered no more than 200) comprised cylindrical African containers, 80% of which were form Africana 2A and 20% Africana 1^[4] w. The Africana 2A amphoras had internal resinous linings, and so may have contained a fish product rather than olive oil. Other amphoras exposed on the site were at least one Mauretanian Dressel 30 (Keay type 1) and two possibly intrusive amphoras of unclassified types. Ferrous concretions contained voids (hollow casts) which may once have been about 39 wrought iron bars, of two distinctive shapes. These, and several other concretions of unidentified forms, may represent a consignment of iron originally weighing approximately one tonne. Other finds from the wreck are two cooking pots, a small bowl or cup, a sounding lead, three fragments of tegula rooftiles, and two small stone blocks. One of the cooking pots confirms a date for the wreck based on the amphora association of circa AD 180–250, most likely in the first decade of the 3rd century. The amphora assemblage belongs to an important phase of commerce from North Africa represented by at least 20 known wreck cargoes; however, few of these sites have been scientifically recorded or are as closely dated as Plemmirio B, and the diversity of container types and cargo consignments on this wreck is of particular interest.     

Site Charting and Environmental Studies of the Monitor Wreck

Abstract

Marine geological and geophysical techniques have been applied to studies of the Monitor wreck to chart the fragments of the wreck and to determine the corrosion state of the remaining iron and the state of the geological and oceanographic environment in the immediate area of the wreck. Methods included magnetic surveying of the wreck site, computer calculations of the magnetization of the Monitor iron, and comparisons with magnetic measurements on iron artifacts from the wreck. Piston coring of the strata immediately beneath the wreck and near-bottom current measurements revealed evidence on the sedimentation rates and sediment transport at the site; these data confirmed interpretations made from high-resolution subbottom reflection profiles across the site.     

The Wreck of the Warship Northumberland on the Goodwin Sands,England, 1703: an interim report

The Northumberland, a third‐rate man‐of‐war was lost with all hands during the Great Storm of 26–27 November 1703 on the Goodwin Sands—famously known as ‘the ship swallower’. It was rediscovered in 1980 by local divers following the location of a sister ship, the Stirling Castle. Since, the primary concern has been to record exposed structural remains, ordnance and artefacts, and interpret the wreck formation of the site. This paper describes the results of this work, and discusses in particular the size of the keel, the use of chocks, and standardization of ordnance in the Restoration Navy through reference to comparable ship‐finds and historical records.