The impact of geological control on flow accretion in lowland permeable catchments

The results of two comprehensive catchment-scale flow accretion surveys that were conducted in the lowland permeable catchments of the Rivers Frome and Piddle in Dorset, UK are presented. The surveys, undertaken as part of the NERC lowland catchment and research (LOCAR) program, were conducted under baseflow conditions during the summer of 2005. Results were adjusted for seasonal variation, the occurrence of intense precipitation events and anthropogenic inputs. A number of significant groundwater–surface water interactions related to various geological formations and boundaries were identified in this study. These included inputs of groundwater associated with the Greensand/Chalk (18–51 L s-1 km-1) and Chalk/Palaeogene (68–152 L s-1 km-1) boundaries and the Oakdale Clay Member (52–79 L s-1 km-1), as well as substantial surface water losses associated with the Broadstone Sand Formation (158–171 L s-1 km-1). The study suggests that it may be possible to predict groundwater–surface water interactions from basic information on solid geology, which would be of considerable benefit to the implementation of the Water Framework Directive in England and Wales.