Sediment Characterisation in an Estuary-Beach System

Abstract

Spatial sedimentological characteristics of surface and shallow intertidal sediments at an estuary-beach system (using the Hayle-St Ives system as a case study) is presented in this study. Short sediment cores obtained from 80 samples are sliced at 1cm intervals and the grain size analysis is undertaken on these subsamples, using a Malvern MasterSizer 2000. The resulting distributions are processed to yield a range of grain size statistics through the GRADISTAT software package. Grain size parameters are examined to explore the evidence for the system's sediment mixing and extensive sediment transport processes. Sediment statistics at the coastlines/beaches (Carbis Bay, Black Cliff and Godrevy Towans) show that sediments are well sorted, near symmetrical/positively skewed medium-coarse sand while the inner estuary samples are predominantly medium sand, well sorted, symmetrical and only negatively skewed at 10-15 cm depth. A Principal Component Analysis, supported by a cluster analysis, shows that 82% of the variance in the grain size distribution is represented by fine-medium-coarse sand, and 14% is represented by the coarse/very coarse sand component. Comparison of grain-size statistics and cluster analysis reveals clear populations associated with specific sub-environments of the system. Importantly, this analysis shows that sediment characteristics can be discriminated clearly by sub-environments, but not on the basis of sub-surface shallow depth.