Project Background

Low flows in several rivers in the southwest of England are under scrutiny due to the perception that abstraction of groundwater for public supply is 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 megaliters per day of additional water from the lower 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.

Our Services

Advisian engaged to assist in investigating this groundwater system and predicting its long-term behavior.

The initial phase of work included a critical review of the previous phases of hydrogeological investigation and modeling 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.

Our consultants provided a key step in the development of the conceptual model of the area, with the recognition of the importance of the siltstone unit underlying the main aquifer horizon that had been ignored in earlier studies. Significant quantities of water are stored in this part of the system. Understanding how this interacts with the limestone aquifer enabled improvement of resource management, minimizing the environmental impacts of short-term fluctuations in demand.

Our consultants subsequently developed a 3D, 30-year transient numerical model of the main aquifer units and used it to help optimize the management strategy, meeting stream support requirements, protecting existing abstraction rights and demonstrating sustainability of the scheme under a variety of likely recharge scenarios.

Results

This outcome enabled the client to apply for full licensing of the stream support system with the regulatory authorities.