Fracture flow and preferential groundwater flow paths in hard rocks : illustrations from Precambrian and lower Palaeozoic strata in Wales

Groundwater in the Lower Palaeozoic and Precambrian hard rocks is mainly constrained to limited storage and circulation in an upper weathered and fractured zone. Some deeper circulation via favourable fractures is possible and there may be hydraulic connection with storage in Quaternary gravels and with surface waters. Examples from Wales illustrate some of the features typical of the small aquifer units that occur in these hard rocks and provide some of the methodologies that have been attempted in understanding groundwater recharge, storage and transport on a catchment scale.