Fate and pathways of dredged estuarine sediment spoil in response to variable sediment size and baroclinic coastal circulation

Brown, Jennifer ORCID:; Amoudry, Laurent; Souza, Alejandro; Rees, Jon. 2015 Fate and pathways of dredged estuarine sediment spoil in response to variable sediment size and baroclinic coastal circulation. Journal of Environmental Management, 149. 209-221.

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Most of the world’s megacities are located in estuarine regions supporting commercial ports. Such locations are subject to sedimentation and require dredging to maintain activities. Liverpool Bay, northwest UK, is a region of freshwater influence and hypertidal conditions used to demonstrate the impact of baroclinicity when considering sediment disposal. Although tidal currents dominate the time-varying current and onshore sediment movement, baroclinic processes cause a 2-layer residual circulation that influences the longer-term sediment transport. A nested modelling system is applied to accurately simulate the circulation during a three month period. The hydrodynamic model is validated using coastal observations, and a Lagrangian particle tracking model is used to determine the pathways of 2 sediment mixtures representative of locally dredged material: a mix of 70% silt and 30% medium sand and a mix of 50% fine sand and 50% medium sand. Sediments are introduced at 3 active disposal sites within the Mersey Estuary in 2 different quantities (500 and 1500 Tonnes). Following release the majority (83% or more) of the particles remain within the estuary due to baroclinic influence. However, particles able to leave follow 2 distinct pathways, which primarily depend on the sediment grain size. Typically the finer sediment moves north and the coarser sediment west. Under solely barotropic conditions larger sediment volumes (up to 5 times more) can leave the estuary in a diffuse plume moving north. This demonstrates the necessity of considering baroclinic influence even within a hypertidal region with low freshwater inflow for accurate particle tracking.

Item Type: Publication - Article
Digital Object Identifier (DOI):
ISSN: 0301-4797
Additional Keywords: POLCOMS; Baroclinic circulation; Sediment dynamics; Particle tracking; Estuarine modelling; Mersey Estuary
NORA Subject Terms: Management
Marine Sciences
Date made live: 11 Nov 2014 13:28 +0 (UTC)

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