title: Fate and pathways of dredged estuarine sediment spoil in response to variable sediment size and baroclinic coastal circulation.
abstract: 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 studies.
authors.affiliation: National Oceanography Centre, Liverpool, UK. Electronic address: jebro@noc.ac.uk.
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: Brown
authors.affiliation: National Oceanography Centre, Liverpool, UK.
authors.forename: Laurent O
authors.initials: LO
authors.lastname: Amoudry
authors.affiliation: National Oceanography Centre, Liverpool, UK.
authors.forename: Alejandro J
authors.initials: AJ
authors.lastname: Souza
authors.affiliation: Centre For Environment, Fisheries and Aquaculture Science, Lowestoft, UK.
authors.forename: Jon
authors.initials: J
authors.lastname: Rees
mesh_terms: D004739:England; D063366:Estuaries; D019015:Geologic Sediments; D057446:Hydrodynamics; D008962:Models, Theoretical; D010316:Particle Size; D011312:Pressure; D014872:Water Movements
keywords: Baroclinic circulation; Estuarine modelling; Mersey Estuary; POLCOMS; Particle tracking; Sediment dynamics