Temporal and spatial variations in intertidal sediment stability are fundamentally
governed by the intricate physicochemical properties of cohesive sediment. To
further our knowledge of the geomorphological development of these systems and
their response to a changing climate, a greater understanding of this relationship
between sediment properties and temporal and spatial variations in stability is
Clay mineralogy is a key sediment property that has received little attention within
estuarine erosion studies. The differing characteristic properties of the clay mineral
groups are known to be a significant factor in erosion resistance in terrestrial
sediment studies. Despite this knowledge there has been little consideration in
assessing the significance of this within intertidal settings.
Temporal and spatial variations in the surface sediment strength were measured
using a Cohesive Strength Meter (CSM) alongside bulk sediment property analysis
at 14 sites within four UK estuaries. The influence of clay mineralogy was
assessed through a series of CSM laboratory experiments using reconstructed
sediments with varying ratios of kaolinite and smectite clays.
Multiple regression identified wet bulk density and organic matter (R2
particle size, mud content, dry bulk density and porosity (R2 0.84) as the key
controls on stability variations within two field study sites. Bed elevation change
was identified as a further driver of variations in stability, with strong negative
Spearman’s correlations of -0.727 and -0.645 at one study site and a positive
correlation of 0.80 observed at a further site.
The laboratory study results identify clear differences in erosion thresholds based
on clay mineralogy under marine shearing fluids. The greatest erosion thresholds
were observed in sediments containing the highest concentrations of smectite.
Erosion thresholds reduced in a linear trend (R2
0.97) with decreasing smectite to
kaolinite ratio. The use of fresh water as the shearing fluid resulted in a
considerable decline in the erosion thresholds of the smectite rich sediments,
highlighting the susceptibility of this clay mineral to change in water chemistry.
The results of this study contribute essential information on the influence of
sediment properties on sediment stability, bridging a crucial gap in the knowledge
of cohesive sediment stability within intertidal locations. Furthermore the
identification of a relationship between clay mineralogy and sediment stability may
lead to improved identification of estuaries that are more likely to be susceptible to
erosion under a changing climate.
|Date of Award