Research Topics

Estuarine sediments and coastal change

The post-glacial estuarine alluvium preserved beneath the Severn Estuary Levels is dominated by alternating silts, representing intertidal salt marshes and mudflats, and peats, formed in organic marshes in the highest parts of the intertidal zone or above tide levels. Investigations based on exposed sections and borehole records, especially along the Gwent coast, show that the sequence is laterally very variable and that the boundaries between the silt and peat beds can change considerably in age from place to place, depending on such factors as distance from the coast or the main rivers and the thickness of the sediments already present.

The general evidence that relative sea-level has risen in a fluctuating manner since the last glaciation is to a degree blurred by these local variations. The investigations have also demonstrated that the evolving estuarine shoreline was very changeable. From time to time the coast retreated significantly because of erosion, only to advance again when the regime changed. Annual sedimentary banding has proved to be common in the silts, demonstrating that new salt marshes can grow upward very rapidly. Because 'summer' and 'winter' parts of the bands can be distinguished, it is proving possible to show when humans and animals where present on the prehistoric wetlands.


Fishing in the Severn Estuary

The Severn Estuary contains some of the best evidence for fishing from the British Isles. Remains of fishtraps preserved within intertidal muds attest to the important role that fishing played in all periods to those living along the estuary. The earliest known fishtraps date to the late Bronze Age, but fish bones from late Mesolithic occupation sites at Goldcliff (c. 5700-4500 cal BC) show fishing was also important to earlier hunter-gatherers. Most fishtraps are medieval or later. Documentary evidence for fish weirs in the estuary begins in the 7th century AD. Saxon fishtraps (5th-6th century) occur at Redwick, but most, such as those at Sudbrook and Magor Pill, date between the 11th to 15th centuries. These various forms, typically facing the ebb-tide, include v-shaped post settings (Figure 1), individual baskets (Figure 2), weirs and hurdle fencing. From the 18th century, larger fishing structures were built of two main types. Putts, large closely woven, wide-mouthed baskets, were used to catch fish from shrimp upwards. The smaller putchers, however, were specifically for salmon, and came in hundreds or even thousands contained within scaffolding, often ranging hundreds of metres across the foreshore. Although the last putchers fell out of use in the early 1990’s, a few local fishermen, using lave nets, continue to catch fish from the estuary at low-tide. The tradition of fishing extends back at least 1000 years, and, on a smaller scale, back into prehistory when people hunted and foraged within the wetlands.


Roman and medieval reclamation

In their natural state, without any human interference, the wetlands that fringe the Severn Estuary would be vast areas of mudflats and saltmarsh that are regularly flooded by the tide. In the Roman period, however, people started to construct earthen embankments to keep the tide at bay, and then to dig ditches in order to drain the land. This is the process known as reclamation, which has been investigated at various places around the estuary, including Puxton on the North Somerset Levels. In the post Roman period all this hard work was destroyed as rising sea levels, and a failure to maintain the flood defence systems, led to the Severn Estuary levels being flooded and a thick layer of alluvium deposited over much of the Roman landscape.

In the medieval period there was a second phase of reclamation and it was this process that led to the creation of the patterns of sea walls, drainage ditches, settlements, fields, and roads that still form the basic framework of today’s landscape. This medieval reclamation began in coastal areas around the 10th century AD, though it was only completed in the 19th century when the last of the lower-lying areas, such as the peat bogs of the Brue Valley and Sedgemoor in Somerset, were drained.

Image 5. The Congresbury Yeo in North Somerset showing the irregular field patterns created by the gradual process of reclamation and drainage in the medieval and post-medieval periods. In the foreground are the sea walls that protect the area from tidal inundation – Dr. Steve Rippon