Quantifying the differential contributions of deep groundwater to streamflow in nested basins, using both water quality characteristics and water balance

This paper describes use of a hydro-chemical mixing model and a water budget to investigate the presence of deep runoff pathways in two small, nested sub-catchments of the Eden basin, UK (8.8 km² Blind Beck and 1.0 km² Low Hall stream). A linear relationship between bicarbonate concentration and electrical conductivity was used in a two-component mixing model. End-members were identified as a high-solute, deep groundwater and a low-solute, soil-water. The mixing model indicated 69% ± 10% deep groundwater in Low Hall for September–December 2008 and 46% ± 8% in Blind Beck for the same period. The water budget also indicated more deep groundwater in Low Hall stream. These results were consistent with the findings of rainfall–runoff models which also indicated the presence of high storage, deeper pathways.