Environmental Changes and the River Thames
Between the 1960’s and 1990’s major redevelopment works took place along the river Thames at Bankside and the City. Archaeological evidence gathered during these redevelopments has allowed archaeologists to find out more about the ancient landscape or “palaeogeography” of this area. Understanding the changing shape of the river over time allows us to understand how the river Thames has influenced human settlement – as well as understanding how the river responded to human interference.
Since Roman times, London’s need to import and export goods and increasing commercial wealth lead to continuous improvements of the wharves and quays where boats and ships loaded and unloaded. These improvements extended the waterfront towards the river through land reclamation. This difficult process involved the construction of strong riverfront walls and timber bulwarks/revetments on the foreshore which were then back-filled with rubbish, debris or landfill to form flat new working areas. This land reclamation had an important impact on the River Thames. The new riverfronts made the river narrower, the current faster and the tidal range wider, which increased the risk of severe floods. Archaeological evidence for early land reclamation shows that the original course of the Thames is located quite far back from the present-day riverfront. The presence of large structures related to bargebeds (structures where boats rested at low tide for repair) shows that land reclamation continue right up until the 20th century
The Thames is a tidal river; this means that twice a day, every day, the water level rises (flood tide) and falls (ebb tide) by around 4.6-6.6 meters (at London Bridge) as the river flows in and out of the North Sea. Climate change and land reclamation affects the level of the sea and tide. In Roman times, the variations between high and low tide were much smaller – only around two metres. (source: Milne G., Batterbee R., Straker V. and Yule B., 1983. The River Thames in London in the Mid 1st Century AD. Trans London Middlesex Archaeol Soc 34, 19 -30). As a result, archaeologists and researchers can use these changes in river level to examine the variation in climate and effect of human settlement on the riverside through time. These changes can also be recorded and tracked on the river walls, especially if you look closely at the improvements and extensions of the river walls. For example, near the pier of Tower Bridge, you can see a series of extensions upwards on the river wall, which represent continuing river-level changes.
Erosion of the foreshore
The movement of water due to the tidal nature of the river Thames produce oscillating currents known as “tidal streams”. These currents are responsible for erosion (the “wearing away” of the foreshore) and deposition (where the river deposits things it sweeps up, such as sand or gravel).
All along the river, you can see evidence for these processes. Lots of the archaeology that can be found on the foreshore is being washed away or covered up as a result, and this is the reason that you can find so many exciting archaeological finds on the foreshore one day, and it is covered in mud the next!
Where structures like bridges or floating pontoons are built, the erosion is accelerated, which causes the foreshore to erode away very quickly. This is seriously damaging various structures such as the bargebeds and timber revetments located on the foreshore.
The fast pace of the erosion in this location at Bankside shows that in only 20 years, the structures that support the foot of the Globe stairs have been exposed.
Elsewhere, erosion is easily detected by the presence of newly exposed surfaces, i.e. the occurrence of clear surfaces or areas which show no signs of green algal growth.