Cohesive and mixed sediment in the Regional Ocean Modeling System (ROMS v3.6) implemented in the Coupled Ocean–Atmosphere–Wave–Sediment Transport Modeling System (COAWST r1234)

Christopher R Sherwood,Romaric Verney,J Paul Rinehimer,Courtney K Harris,Bénédicte Ferré,Alfredo L Aretxabaleta

doi:10.5194/gmd-11-1849-2018

Abstract

Abstract. We describe and demonstrate algorithms for treating cohesive and mixed sediment that have been added to the Regional Ocean Modeling System (ROMS version 3.6), as implemented in the Coupled Ocean–Atmosphere–Wave–Sediment Transport Modeling System (COAWST Subversion repository revision 1234). These include the following: floc dynamics (aggregation and disaggregation in the water column); changes in floc characteristics in the seabed; erosion and deposition of cohesive and mixed (combination of cohesive and non-cohesive) sediment; and biodiffusive mixing of bed sediment. These routines supplement existing non-cohesive sediment modules, thereby increasing our ability to model fine-grained and mixed-sediment environments. Additionally, we describe changes to the sediment bed layering scheme that improve the fidelity of the modeled stratigraphic record. Finally, we provide examples of these modules implemented in idealized test cases and a realistic application.

Highlights

1.1 MotivationFine cohesive sediment is present in almost every coastal environment and influences water clarity, benthic habitats, shoaling of harbors and channels, storage and transport of nutrients and contaminants, and morphologic evolution of wetlands, deltas, estuaries, and muddy continental shelves (Winterwerp and van Kesteren, 2004; Edmonds and Slingerland, 2010; Caldwell and Edmonds, 2014; Mehta, 2014; Li et al, 2017)
The improvements were implemented in the COAWST version of ROMS, which provides a framework for realistic two-way nested models with forcing from meteorology (WRF; Michalakes et al, 2001) and waves
The cohesive and mixed-bed algorithms we have introduced in ROMS provide tools that should be useful for both numerical experimentations and realistic applications for fine-grained and mixed-bed environments

Summary

Introduction

Fine cohesive sediment (mud) is present in almost every coastal environment and influences water clarity, benthic habitats, shoaling of harbors and channels, storage and transport of nutrients and contaminants, and morphologic evolution of wetlands, deltas, estuaries, and muddy continental shelves (Winterwerp and van Kesteren, 2004; Edmonds and Slingerland, 2010; Caldwell and Edmonds, 2014; Mehta, 2014; Li et al, 2017). The properties and behavior of mud depend on more than the size, shape, and density of the individual particles, so they are more difficult to characterize and model than properties of non-cohesive material like sand. Cohesive sediment often forms flocs that have lower densities, larger diameters, and faster settling velocities than the primary particles. Sherwood et al.: Cohesive and mixed sediment model werp, 1999, 2002; Winterwerp et al, 2006; Xu et al, 2008, 2010; Verney et al, 2011; Slade et al, 2011; MacDonald et al, 2013; Thorne et al, 2014)

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Conclusion