Examining geological controls on baseflow index (BFI) in the Thames Basin

Baseflow Index, or BFI, is a measure of the ratio of long-term baseflow to total stream flow and it represents the slow continuous contribution of groundwater to river flow.

For streams and rivers on permeable aquifers, such as the Chalk, baseflow may provide the majority of flow in the river and in the summer months is the entire flow. Understanding these flows is therefore important in managing river flows.

However, the relationship between aquifer characteristics, geology and baseflow was relatively poorly understood. Using geological mapping, information on the distribution and hydraulic properties of the aquifers in the Thames Basin, we used statistical techniques, linear regression models and Monte Carlo simulations to investigate the correlations between geological and hydrogeological factors and know BFI for rivers across the Basin.

The study showed that geological and hydrogeological mapping could explain the distribution of BFI values across the Basin and that the hydraulic conductivity of the aquifers correlated well with the know BFI values.