Monument record RLM 109 - Prehistoric palaeochannels, river valley geoarchaeological survey, Rendlesham

2021: Geoarchaeological fieldwork was conducted in the river valley and water meadow immediately south of the early medeival royal settlement (RLM 013), with volunteers as part of Rendlesham Revealed NLHF project . 67 boreholes made by hand in 10 transects and 4 further drilled boreholes revealed evidence of at least three palaeo-channels within the present day floodplain. A major palaeo-channel is located within the centre of the Deben floodplain near the present day sluice and river foot-bridge. It is c. 2.5 to 3.6m deep, well preserved and waterlogged, and appears to date from at least late 9th millennium BC to the end of the Roman period. It is suggested that after an early Neolithic impact of arable and pastoral activities in the 4th millennium BC, the landscape became more pastoral in later prehistory. This was followed by increasing arable/pastoral intensification and opening-up of the landscape from the Iron Age onwards. The consequent increased soil erosion led to alluvial aggradation, thus infilling and flattening the Deben floodplain to produce the landscape as seen today.
There are at least two other palaeo-channels evident on the western and eastern edges of the floodplain. At the base of slope on the eastern side of the valley, there are indications of a shallow palaeo-channel infilled with organic silts and detrital peat over a depth of c. 1–1.5m which was contemporary with the main palaeo-channel, with a date range from the late Mesolithic to Late Bronze Age periods. In a similar location but on the western edge of the floodplain, there is another possible palaeo-channel, as yet undated. But in contrast to the eastern edge palaeo-channel, it contains organic, fine sandy/silt muds in its lower c. 0.4m which may indicate tidal creek influence. Nonetheless, its upper fills of detrital humic muds and alluvium mirror those of the main and eastern palaeo-channels, suggesting that it also a contemporary later prehistoric channel.
There does not appear to be any widespread finger-print of the influence of brackish water tidal creek conditions in the valley, except perhaps in the very base of this main palaeo-channel and in the possible shallow channel on the western edge of the valley. This suggests that the fluvial channels identified were outside the influence of tidal limit from about the mid-5th millennium BC or late Mesolithic, at least in this part of the floodplain at Rendlesham.
It is also clear from the extensive and intensive geoarchaeological survey and its analyses that we were unable to identify a clear early medieval river channel. There are two main possibilities for this. Perhaps the wide alluvial floodplain was a braid plain with many shallow creeks seasonally active across it, but which went undetected as they are confined within the alluvium itself and infilled with the same type of eroded soil material. The corollary of this is that the main channel extending inland from the estuary at Woodbridge was not a well-defined channel all the way to Rendlesham. Or, it is possible that the today’s channel more or less follows the course of the early historic channel, and its repeated dredging, cleaning out and canalisation in more recent times has destroyed any trace of channel deposits from the past 1000 years or so. Or, it could be some combination of all of these scenarios. (S1, S2).

Geophysical Survey over this area following the auger survey was conducted by Prof Chris Gaffney, University of Bradford with the aim of identifying the palaochannels and the possibility of structural remains relating to past water-side activity. Three geophysical survey techniques were used to target several areas: Ground Penetrating Radar (GPR) which surveyed sections at increasing depths, Electromagnetic Induction (EM) which measured the conductivity and magnetic susceptibility at three different depths, and Electrical Resistivity Tomography which takes sections through the ground. The results showed very typical responses to an environmental area and show some correlation with the possible palaeochannel. The responses do not indicate any settlement in the survey areas. (S3)

See RLM 066 for earthworks of an area of banks and drainage ditches of probable medieval to post medieval date visible on aerial photographs and LIDAR, identified by NMP in 2015.