Improving understanding of shallow urban groundwater: the Quaternary groundwater system in Glasgow, UK

ABSTRACTAlthough many European cities use urban aquifers for water supply, groundwater from shallow urban aquifers is not widely exploited. Nevertheless, shallow urban groundwater is a key environmental resource – for example, in maintaining healthy urban river flows and attenuating some pollutants – and it can also be a threat, such as through groundwater flooding. However, shallow urban groundwater is frequently overlooked or ineffectively managed, in large part because it is often poorly understood. This paper demonstrates the need to improve understanding of the shallow groundwater system in a city where shallow groundwater is not widely abstracted and, consequently, relatively little groundwater data exist. Like many UK cities, Glasgow is underlain by complex unconsolidated Quaternary deposits, which form a heterogeneous shallow aquifer system that has been extensively impacted by urban activities, typical of a former industrial city. Balancing the potential benefits and risks of shallow groundwater in Glasgow requires a better understanding of Quaternary hydrogeology in order to support the transition to a more sustainable city. This paper presents an improved conceptual model of Glasgow's shallow groundwater system within a sequence of Quaternary deposits in the Clyde valley, drawing heavily on data collected during major site investigations for land development in the city. Postglacial Quaternary sediments in Glasgow form an elongate, variably thick (up to 30m) and variably permeable aquifer system. Aquifer units with high permeability and high storage capacity are partially separated by lower permeability, but still hydrogeologically active, units. Groundwater in the system is hydraulically connected with the River Clyde. Groundwater flow occurs both longitudinally down-valley and convergent from the edge of the valley aquifer towards the river. There has been extensive anthropogenic alteration to the urban surface and shallow subsurface, which has modified the natural physical and chemical groundwater system. Pollution associated with historical industry has also extensively impacted the quality of Quaternary groundwater.