Sediment dynamics of the Severn Estuary and inner Bristol Channel

McLaren, Patrick; Collins, Michael B.; Gao, Shu; Powys, Richard I. L.

doi:10.1144/gsjgs.150.3.0589

Cited by 33 publications

(21 citation statements)

References 48 publications

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“…The trend line opposes the height distribution of storm waves in Bristol Channel and the Severn Estuary (McLaren et al 1993). Storm wave heights are greatest in the outer channel, where they have been recorded at ≥10 m. Storm wave heights of 4.7 and 3.5 m occur in the inner channel and the Severn Estuary, respectively, both with 50-yr return periods.…”

Section: Discussionmentioning

confidence: 82%

Catastrophic Wave Erosion, Bristol Channel, United Kingdom: Impact of Tsunami?

Bryant¹,

Haslett²

2007

The Journal of Geology

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On January 30, 1607, a massive wave from the ocean surged up Bristol Channel in the United Kingdom, flooding more than 500 km2 of lowland along 570 km of coast. It killed 2000 people and is considered Britain's worst natural disaster on land. The wave occurred on a fine day and surprised inhabitants. Contemporary descriptions of the event have many of the characteristics of accounts of recent catastrophic tsunamis. Geomorphic evidence for tsunamis in the channel can be found in the form of transported and imbricated boulders, bedrock sculpturing on coastal platforms and ramps, and, at isolated locations, wholesale erosion of the coastal landscape. Hydrodynamic calculation of the height of the tsunami and flow velocities can be derived from boulder dimensions. Tsunami wave height increased from 4 m in the outer Bristol Channel to more than 6 m within the inner Severn Estuary. Theorized flow velocities range between 11.8 and 18.1 m s1, increasing up the estuary. Under topographic enhancement, these depths and velocities may be sufficient to generate bedrock sculpturing, which is indeed observed at a few locations on rocky headlands in the channel. Interpolation of the amount of cliff retreat at Dunraven Bay indicates that an imbricated boulder train was deposited by tsunami sometime between 1590 AD and 1672 AD, a time span that encompasses the January 30, 1607, event. A B S T R A C TOn January 30, 1607, a massive wave from the ocean surged up Bristol Channel in the United Kingdom, flooding more than 500 km 2 of lowland along 570 km of coast. It killed 2000 people and is considered Britain's worst natural disaster on land. The wave occurred on a fine day and surprised inhabitants. Contemporary descriptions of the event have many of the characteristics of accounts of recent catastrophic tsunamis. Geomorphic evidence for tsunamis in the channel can be found in the form of transported and imbricated boulders, bedrock sculpturing on coastal platforms and ramps, and, at isolated locations, wholesale erosion of the coastal landscape. Hydrodynamic calculation of the height of the tsunami and flow velocities can be derived from boulder dimensions. Tsunami wave height increased from 4 m in the outer Bristol Channel to more than 6 m within the inner Severn Estuary. Theorized flow velocities range between 11.8 and 18.1 m s Ϫ1

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Section: Discussionmentioning

confidence: 82%

Catastrophic Wave Erosion, Bristol Channel, United Kingdom: Impact of Tsunami?

Bryant¹,

Haslett²

2007

The Journal of Geology

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“…However, it is likely that this is a key influence near large estuaries. This can be seen in the high-energy Bristol Channel, where there is both a high level of rock and a relatively high level of mud due to the contradictory influences of strong tidal currents and the sediment deposits from the river Severn (McLaren et al, 1993). The influence of river outflows is implicitly captured by the inclusion of distance from the coast as a predictor.…”

Section: Limitations and Assumptionsmentioning

confidence: 99%

A synthetic map of the north-west European Shelf sedimentary environment for applications in marine science

Wilson

Speirs

Sabatino

et al. 2018

Earth Syst. Sci. Data

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Abstract. Seabed sediment mapping is important for a wide range of marine policy, planning and scientific issues, and there has been considerable national and international investment around the world in the collation and synthesis of sediment datasets. However, in Europe at least, much of this effort has been directed towards seabed classification and mapping of discrete habitats. Scientific users often have to resort to reverse engineering these classifications to recover continuous variables, such as mud content and median grain size, that are required for many ecological and biophysical studies. Here we present a new set of 0.125 • by 0.125 • resolution synthetic maps of continuous properties of the north-west European sedimentary environment, extending from the Bay of Biscay to the northern limits of the North Sea and the Faroe Islands. The maps are a blend of gridded survey data, statistically modelled values based on distributions of bed shear stress due to tidal currents and waves, and bathymetric properties. Recent work has shown that statistical models can predict sediment composition in British waters and the North Sea with high accuracy, and here we extend this to the entire shelf and to the mapping of other key seabed parameters. The maps include percentage compositions of mud, sand and gravel; porosity and permeability; median grain size of the whole sediment and of the sand and the gravel fractions; carbon and nitrogen content of sediments; percentage of seabed area covered by rock; mean and maximum depth-averaged tidal velocity and wave orbital velocity at the seabed; and mean monthly natural disturbance rates. A number of applications for these maps exist, including species distribution modelling and the more accurate representation of sea-floor biogeochemistry in ecosystem models. The data products are available from https://doi.org/10.15129/1e27b806-1eae-494d-83b5-a5f4792c46fc.

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“…Although the bed-material coarsens from chiefly medium sand in the outer estuary to very fine sand in the inner part (McLaren et al 1993), the suspended sediment becomes finer grained and more clay-rich down-estuary (Allen 1987 c ;French 1993). Roughly 10 % of this sediment consists of carbonate particles, chiefly shell debris, and a full range of claymineral species is present, about 25 % of the 2 mm fraction consisting of expandable minerals.…”

Section: (B) Sedimentological Backgroundmentioning

confidence: 99%

Subfossil mammalian tracks (Flandrian) in the Severn Estuary, S. W. Britain: mechanics of formation, preservation and distribution

Allen

1997

Phil. Trans. R. Soc. Lond. B

156

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Mammalian tracks and trackways are widely preserved at all stratigraphical levels in the Flandrian sediments of tidal mudflat and marsh origins which formed over the last 8000–9000 years on the marginal wetlands of the inner Bristol Channel and Severn Estuary. The fauna recorded in this way, however, is less diverse than that known from the few, small assemblages of skeletal remains, including some from archaeological sites, so far assessed. Missing or rarely represented in terms of tracks are the smaller of the large mammals. Humans are represented by tracks throughout the Flandrian deposits. In the earlier Flandrian, they were accompanied by deer and aurochs which gave way, in the later Flandrian, to domesticated cattle and sheep/goat; there are sporadic indications of the presence of horse. Wolf/dog, represented by just two records, is the only smaller large mammal so far recorded as a track. The tracks were made, modified, and eventually preserved under a wide variety of sedimentological conditions on the margins of the estuary. Those environmental conditions constrained the quality of the anatomical evidence preserved in the tracks but can be inferred from the character of the tracks. Field experiments suggest that the moisture content of the sediment at the time was crucial to the general nature of the tracks. The mudflat–marsh silts which received the tracks varied from semi–liquid to firm, depending on tidal and seasonal factors and on the elevation of the sedimentary surface relative to the tidal frame. Some tracks were made in marsh peats which offered little resistance. Deep tracks preserving little detail were produced in weak sediments of high moisture content; tracks formed in strong, firm muds retained full anatomical detail. Referring to mechanical theory, and to a series of laboratory experiments using plasticine, the act of making a track is shown to be similar in character and effect to the indentation of an ideal elastic–plastic material by a punch. The punch represents the descending limb of the animal, the face of the punch the sole of the animal's foot, and the elastic–plastic material the sediment which is pierced and deformed by the downward action of the limb. The character of the experimental tracks, and the range and relative size of the deformation structures they include, is qualitatively similar to what is recorded from the field. Many of the tracks recorded from the field were variously modified in a changeable and dynamic environment before final burial and preservation.

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Sediment dynamics of the Severn Estuary and inner Bristol Channel

Cited by 33 publications

References 48 publications

Catastrophic Wave Erosion, Bristol Channel, United Kingdom: Impact of Tsunami?

Catastrophic Wave Erosion, Bristol Channel, United Kingdom: Impact of Tsunami?

A synthetic map of the north-west European Shelf sedimentary environment for applications in marine science

Subfossil mammalian tracks (Flandrian) in the Severn Estuary, S. W. Britain: mechanics of formation, preservation and distribution

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