Understanding water table dynamics in relation to aggregate extraction sites

English Heritage ALSF summaries. 2004/2005

Proposed new research focusing on the floodplain sequences adjacent to the gravel extraction site of Newington, Notts. [SK675943]. These deposits are located on the northern side of the River Idle floodplain.

The proposed project represents the second stage in an ongoing program of archaeological research, which is assessing the impacts of de-watering in relation to waterlogged floodplain (organic) environments. The investigations to date (Lillie & Smith 2007) have demonstrated that reduced water levels are impacting on the floodplain resource. There is also a clear need to continue monitoring these sequences in order to produce higher-resolution, targeted, studies of the floodplain deposits in terms of their physico-chemical and biological status, in order to understand the impacts of de-watering at this location.

To date, this project has investigated water table dynamics over time during staged extraction at Newington, at the catchment-wide and site-specific levels. Targeted assessment of the burial environment through environmental analyses, redox potentials, and pH has identified the criteria by which controlled mitigation can be developed (ibid. 2007). However, these studies have also demonstrated that the Newington site, and the River Idle system, are in a negative water budget scenario, and as such are unsustainable. The Idle floodplain at Newington has been shown to exhibit variable states of preservation, and a fluctuating (seasonal) water table that can be drawn down to c. 2.0 m below the modern ground surface.

The proposed new research will target those areas of the floodplain that have demonstrated either a high or low potential for in situ preservation, and contrast the impacts of both scenarios on the physico-chemical and microbiological status of the contained sediments. This will provide significant information in relation to microbial community diversity and activity in relation to saturation/de-watering.

This investigation will enhance the data generated to date in order to further inform the Heritage sector, managers of extraction sites, and planning authorities on ‘best practice’ approaches to mitigation strategies in relation to the waterlogged resource. The results from this work will therefore provide further baseline data for the future management of aggregates extraction sites and provide interested parties with empirical data against which realistic mitigation strategies can be further developed.

Furthermore, the continued monitoring of water tables will enable an assessment of water recharge as extraction moves away from the floodplain areas; and the enhanced (through the profile) analysis of pH, redox, temperature, organic content, particle size distributions and microbiology, will greatly enhance our understanding of the in situ context of deeply stratified floodplain sequences. This data will provide only the second study of the specific microbial context of deeply stratified organic floodplain sequences (cf. Douterelo-Soler forthcoming) undertaken to date.

This page was published on 19/09/2007