Advisian provided specialist groundwater services as part of a water resource management study to meet public water supply and ecological requirements in southwest England.
Low flows in several rivers in the southwest of England were under scrutiny due to the perception that abstraction of groundwater for public supply was having an adverse impact on river flows and associated ecosystems. Water supply companies have been working with the UK Environment Agency to investigate the causes of low flows and the effectiveness of potential mitigation measures.
In the Malmesbury area, a trial stream support system had been implemented, pumping over 10 megalitres per day of additional water from the main aquifer during dry periods to augment river flows. However, it was not known what the long-term effects of this scheme were likely to be and how it would function under conditions of prolonged water stress.
Advisian was retained to assist in the investigation of this groundwater system and predict its long-term behaviour under a variety of different management options.
The initial phase of work included a critical review of earlier phases of hydrogeological investigation and modelling work that had been undertaken, and identifying the limitations that prevented an earlier successful outcome. Recommendations were provided on the requirements for new field work to fill gaps in data coverage and improve understanding of the groundwater systems involved.
Advisian provided a key step in the development of the conceptual model of the area, with the recognition of the importance of an extensive siltstone unit underlying the limestone aquifer horizon that had been ignored in earlier studies. Significant quantities of water are stored in this part of the system.
Understanding how this storage interacts with groundwater in the main aquifer can lead to improvements in resource management arrangements, minimising the environmental impacts of short-term fluctuations in demand.
Advisian’s specialists subsequently developed a 3-D, 30 year transient numerical groundwater model of the main aquifer units and used it to help optimise the management strategy, meeting stream support requirements, protecting existing abstraction rights and demonstrating sustainability of the scheme under a variety of likely recharge scenarios.
This outcome enabled the client to apply for full licensing of the stream support system with the regulatory authorities, address stakeholder concerns, and negotiate shared responsibilities with other utility providers.
