Bedrock groundwater influences on runoff generation in upland Wales
Haria, Atul Harakhchand
PublisherUniversity of Aberdeen
MetadataShow full item record
A detailed physico-chemical study was established in the forested Hafren catchment at Plynlimon, mid-Wales, UK. The focus of the study, the Hafren Transect, comprised nets of instrumentation from the stream riparian zone to the lower hillslope. Soil water and groundwater processes to 30 m depth were monitored in detail. Two supplementary studies (a detailed hydrochemical stream survey and sub-catchment water balance analysis) were conducted to determine the spatial importance of the processes identified at the Hafren Transect. Bedrock groundwaters were found to be active in depth-specific horizons where the deeper horizons were confined or semi-confined. Chemical stratification showed extremes in water quality between these horizons. Groundwaters from these different horizons, with different chemistries, were shown to discharge, by different mechanisms, into the stream channel. Shallow groundwaters were shown to rise up into the deeper soils and move rapidly laterally also a fast flow pathway at the soil-bedrock interface. By this mechanism aluminium sourced from the deeper soils was quickly transported to the stream channel. Spatial studies showed that the processes identified at the Hafren Transect could not account for the peak in ‘old’ pre-event water observed during storm response. However, they identified potentially significant groundwater discharge from discrete fractures and in-stream mixing in fluvial deposits that warrant further research. This study has shown how bedrock groundwater processes need to be considered when conceptualising upland streamflow generation, especially with regard to surface water quality.