Archaeological Resource Modelling in Temperate River Valleys: A Case Study from the Trent Valley, UK
Howard, A. J., Brown, A. G., Carey, C. J., Challis, K., Cooper, L. P., Kincey, M., Toms, P., Antiquity
Methods for mapping and determining the condition of archaeological resources while they are still underground have been in development for nearly half a century. The authors here offer an example from the frontiers of the art: the application of a package of remote sensing procedures not only designed to locate sites but to model the valley deposits which contain and cover them. The variation in success of different methods in different deposits offers a guide to the design of evaluation projects on sand and gravel terrain everywhere.
Keywords: Britain, Trent, prehistory, alluvial, floodplain, confluence, lidar, ERGI, geophysics, prospection, boreholes, radiocarbon
Archaeological remains within river valleys are often exceptionally well preserved through a combination of the presence of high water tables, stable terrace surfaces and substantial depths of alluvium (Brown 1997; Howard et al. 2003). However, recent archaeological research focused on British river valleys has shown that both cultural and taphonomic factors influence the wealth and spatial distribution of the archaeological resource across floodplains and terrace surfaces. A number of authors have demonstrated a direct link between the distribution and preservation potential of archaeology and the observed geomorphology (Howard & Macklin 1999; Passmore et al. 2006). Such patterns of preservation are not unique to the UK and have been observed in Europe (Howard et al. 2004), Africa (Pearl & Dickson 2004) and North America (Bettis & Mandel 2002; Bauer et al. 2004). Published studies are not just restricted to empirical observations; recent analytical work within meandering river systems has sought to predict the spatial distribution of archaeology on the basis of patterns of erosion and sedimentation, using a landscape evolution model (Clevis et al. 2006).
Archaeological research in Britain has indicated that river confluences and their adjacent floodplains are the focus of prolonged activities. In the Palaeolithic, terrace promontories of higher ground extending into confluence wetlands appear to have formed attractive localities for temporary hunting camps (Wymer 1999). Aerial photography of cropmarks first illustrated the importance of these areas in the Neolithic and Bronze Age for ritual and funerary activity often associated with the deposition of metalwork (Scurfield 1997; Barclay & Hey 1999; Malim 2000; Brown 2004).
River confluences and their immediate environments are complex, dynamic landscapes, where processes of erosion and sedimentation are extremely variable, reflecting the changing courses of the rivers through time (Best 1988; Bradbrook et al. 2001). The dominant mechanism of floodplain evolution will have an important influence on the preservation potential of the archaeological record. For example, an avulsive system (i.e. one where there is rapid switching of the stream within a pre-existing palaeochannel network, Ashworth et al. 2004) is liable to have a high potential for the preservation of in situ archaeological remains, due to limited channel migration. Such rapid channel movement can also result in the preservation of high densities of organic-rich palaeochannels (Brown 2003). In contrast, river systems that evolve through extensive lateral migration are liable to have a lower potential for the preservation of in situ archaeology. However, even in laterally mobile river systems, active channel migration should not be assumed to lead solely to the destruction of in situ archaeology and even where it does, careful recording of the archaeology can provide valuable information for the reconstruction of floodplain hydrology and human activity (Salisbury et al. 1984; Howard et al. 1999).
Using a case study in the middle Trent Valley (UK), this paper examines the distribution and preservation potential of archaeological resources within a geomorphologically dynamic confluence zone. …