Hydrological monitoring of an alluviated landscape in the lower Great Ouse valley at Over, Cambridgeshire: the quarry restoration phase

Abstract

This paper sets out the results of the last phase of the hydrological monitoring programme conducted at the Hanson Over quarry in Cambridgeshire, during the first full year (March 2004 to March 2005) in which the area of the first phase of gravel extraction was reinstated as reed beds under the management of the Royal Society for the Protection of Birds. It follows on from the studies of the pre-extraction and extraction phases, both published previously in Environmental Archaeology (French et al. 1999; French 2004). It is reassuring to report that the groundwater table in the formerly quarried area and the landscape immediately upstream and downstream has ostensibly been restored to pre-extraction levels, along with a return to previous pH, conductivity, redox and dissolved oxygen values in the groundwater system. Significantly, the continuing gradual fall in groundwater levels observed beyond 500 m from the quarry face for a distance of at least 1·5 km was seen to be arrested, although these had not quite recovered to pre-extraction levels downstream to the northeast. In addition, the soil moisture within the alluvial overburden and the buried palaeosol has also almost returned to pre-extraction levels. This indicates that the clay bunding of the formerly quarried areas acts as an effective barrier against further water abstraction, both inside and outside the sealed area, and allows the natural aquifer to begin to return to its previous levels of influence.The study dramatically indicates that both the mineral operator, drainage authority and archaeological curator need to collaborate from the outset of any quarrying operation to ensure the continuing maintenance of the groundwater and soil moisture system regardless of how well the combined gravel and water abstraction processes are conducted, and how successful the post-quarry conservation is. As every site's landscape dynamics contribute to its individual hydrological setting, each case is different and requires tailored monitoring programmes to protect the archaeological and palaeo-environmental record from the adverse effects of water abstraction associated with development schemes.