A new FEH catchment descriptor has been added to our Peak Flow station pages: BFIHOST19.
The estimate of the base flow index (BFI) based on the Hydrology of Soil Types (HOST) classification, BFIHOST, provides a measure of catchment responsiveness. The HOST dataset is available as a 1km grid which records, for each grid square, the percentage associated with each HOST class present. Using IHDTM boundaries for each gauged catchment, the soil characteristics of the catchment can be indexed and by exploiting the relationship between soil typologies and runoff response an aggregated assessment of BFIHOST for the catchment can be derived. The new BFIHOST19 descriptor addresses a number of issues in the original BFIHOST developed in 1995, including:
- the BFI calculated through base flow separation tended to be underestimated in clay-dominated catchments,
- the calculation technique performed poorly in ephemeral catchments or those with missing data, and
- the pragmatic bounding of BFI coefficients for permeable soils overlying aquifer outcrops was also problematic for small catchments.
To resolve such issues, UKCEH has revised the regression method used to estimate BFIHOST and has improved the classification of rare soil types. The revision has been published in Hydrology Research.