| dc.description.abstract | Lowland chalk streams in the UK are experiencing increased deposition of fine
sediment due to changes in land-use practices, channel modifications, and groundwater
abstraction. The fine sediment is linked to benthic habitat degradation, the obstruction
of surface-groundwater flow, and the storage of contaminants, such as nutrients and
pesticides. Whilst research has been conducted on the provenance, transport, deposition,
and storage of fine sediment in chalk streams, none has expressly investigated erosion.
To help fill this gap in knowledge, a yearlong field survey was conducted in two
reaches of the Frome-Piddle Catchment (Dorset) to quantify the erodibility of surficial
fine sediment deposits. Sediment erodibility was measured in the field using a cohesive
strength meter (CSM) and a shear vane. These measurements were paired with sediment
cores for analysis of the physical, chemical and biological properties of the sediment.
The large environmental dataset was analysed using a comprehensive suite of modern
analytical techniques, including regression trees, linear regression, and mixed effects
modelling. The results indicate that the erodibility of fine sediment varies significantly
over time and within a stream reach due to variations in hydraulic conditions and
sediment properties. Effective particle size and chlorophyll-a content were identified as
the major sediment properties influencing CSM-derived erodibility, whereas root
density was key for shear vane-derived strength. To date, the erosion thresholds
generated by CSMs have been largely restricted to relative uses, and a calibration based
on cohesive sediment is needed to permit their future incorporation into sediment
transport models. This study developed an empirical calibration using laboratory
experiments that estimated critical shear stress from CSM-derived erosion thresholds.
By quantifying the erodibility of fine sediment deposits in chalk streams, and
representing the erosion thresholds as critical shear stress, we can better gauge their
local environmental impacts and help to inform models of fine sediment transport | en_US |
