Depositional and erosional behaviour of cohesive sediments in estuarine environments

Cohesive muddy sediments are abundant across estuarine ecosystems and these sediments are typically composed of mineral grains and biological matter. The erosional characteristics of such sediments are impacted by micro-organisms providing bio-stabilisation. Deposition may be impacted by biochemical composition and turbulence properties, in turn influencing the flocculation of suspended particulate matter. Such flocculation processes impact settling velocity, porosity and density characteristics. Interactive processes between sedimentary dynamics and hydrodynamics are influenced by the various bio-physical attributes of these cohesive sediments, thus prediction of muddy sediment transport processes via numerical modelling is beneficial to improve the understanding of intertidal sediment dynamics. The accuracy of such models relies on quantitative erosional and depositional data for calibration. Sediment erodibility in intertidal habitats was investigated utilising sediment stability data collected during the CBESS (Coastal Biodiversity and Ecosystem Service Sustainability) programme. This project collected landscape-scale field measurements for biodiversity and ecosystem service flows in coastal wetlands to quantify patterns between ecosystem service provision and biodiversity (Paterson et al., 2015). An additional case study on saltmarsh sediment stability was conducted using geotechnical samples from Tillingham Marsh, Essex (UK), investigating composition and stability variability of open coast marsh substrates (Brooks, 2021). The studies investigate within- and between-marsh variation in sediment erosion thresholds from a cohesive strength meter, including various sediment compositions for comparison (clay, silt, sand composition; colloidal carbohydrate concentration). The aim of this chapter is to provide a state-of-the-art review of key research on intertidal sediment dynamics, including sediment stability and erodibility (erosion thresholds), drawing on case studies and key research contributions for quantitative analysis. This presentation includes a background and literature review of such topics in intertidal habitats, drawing from key case studies using CBESS and geotechnical sediment sample data sets