Review of hydrogeological knowledge of the Clyde basin

A short review of the current hydrogeological knowledge of the Clyde Basin, including the city of Glasgow, has been carried out, and activities to address knowledge gaps have been proposed. The hydrogeological datasets available or potentially available within BGS, Glasgow City Council and other sources are identified. These include national datasets such as maps of aquifer productivity, superficial deposits permeability and thickness, likely depth to water in superficial deposits, and groundwater vulnerability; and databases such as water boreholes, groundwater chemistry and aquifer properties. They also include local datasets such as mine plans, historical mine water pumping data, groundwater levels and groundwater discharges, and groundwater contamination events. The complex hydrogeology of the Clyde Basin is poorly understood. Groundwater flow in most of the bedrock aquifers, both sedimentary and volcanic, occurs dominantly in fractures. Extensive mining in many of the Carboniferous sedimentary rocks has significantly changed natural hydrogeological conditions. Groundwater flow paths in the sedimentary aquifers are likely to be relatively deep and long, with Glasgow acting as the focal point for much of the groundwater discharge from the Clyde coalfield area. Groundwater flow systems in Carboniferous volcanic rocks are likely to be predominantly local, with discharge occurring as baseflow to local rivers. The natural chemistry of groundwater in Carboniferous sedimentary aquifers is often moderately to highly mineralised. Groundwater quality was also affected by mining in the 19th century. There is little recent information on groundwater chemistry in either the sedimentary or volcanic aquifers. Little is known of the hydrogeology of the superficial deposits across the area, although they are likely to play an important role in controlling recharge to the underlying bedrock aquifers, and in influencing surface water drainage. Consultation with representatives from Glasgow City Council has highlighted the following hydrogeological issues: sustainable urban drainage (the role of groundwater in flooding and the potential for discharging surface water to the subsurface); the lack of good quality groundwater data; the hydrogeological characteristics of made ground; the hydrogeological impacts of mining; and the potential presence of poor quality groundwater. Improving understanding of the hydrogeology of the Clyde Basin, and addressing the hydrogeological issues, will require the development of hydrogeological conceptual models of the superficial deposits and the bedrock aquifers. Effective conceptual model development will depend on the availability and quality of data, and should be staged so that simple models are produced first to cover the whole area, which can be refined as new information becomes available. The development of more complex hydrogeological models should be linked to the current development by BGS of detailed 3D geological models for a small pilot study area in eastern Glasgow, whereby that the existing geological models are attributed with hydrogeological parameters and used as the basis for a numerical groundwater model. The creation of robust conceptual models will require the collection of new groundwater data, including monitoring of groundwater levels and chemistry. Existing data in borehole and site investigation records should also be digitally captured so that it is easily available.