Labs WMT ROMSLIte SettlingRates

Introduction to Regional Ocean Modeling - Settling Rates and Critical Shear Stress

This lab has been designed and developed by Courtney Harris, Julia Moriarty, and Danielle Tarpley, Virginia Institute of Marine Sciences, Gloucester Point, VA
with assistance of Irina Overeem, CSDMS, University of Colorado, CO

Classroom organization
This is the second lab in a mini series to introduce a Web-Based version of the Regional Ocean Modeling System (ROMS) for inexperienced users. ROMS is a three-dimensional hydrodynamic ocean model (see Shchepetkin and McWilliams 2005; myroms.org). ROMS solves the conservation of mass and three-dimensional momentum equations and includes transport equations for temperature and salinity. The version implemented here also accounts for suspended sediment transport and deposition, following Warner et al. (2008). Here we present a basic configuration of ROMS in the framework of the Web Modeling Tool (WMT). This series of labs is designed for inexperienced modelers to gain some experience with running a numerical model, changing model inputs, and analyzing model output. The example provided looks at the influence of a river plume on the hydrodynamics and sediment transport within an idealized continental shelf.

This lab focuses on sediment settling rates and critical shear stress for motion. Basic theory on settling rates and suspended sediment is presented in these slides File:ROMS Lite Introduction.pptx.

This lab will likely take ~ 3hours to complete in the classroom.

If you have never used the Web Modeling Tool, learn how to use it here. The WMT allows you to set up simulations, but once you are ready to run them, you will need an account on the CSDMS supercomputer to successfully submit and run your job. More information on getting an account can be found here HPCC Access. Note that getting permission for access takes a few days after your request.

Learning objectives

familiarize with a basic configuration of the Regional Ocean Modeling System
learn how to manipulate parameters in ROMS-Lite and set up different experiments

physics of settling rates
bed shear stress and threshold to incipient motion
Shields and Yalin diagrams
influence of settling velocity and critical shear stress on fluvial deposition

Lab Notes

>> Open a new browser window and open the Web Modeling Tool here and select the ROMS project
>> This WMT project is unique in that there is only a single driver, ROMS-Lite. It is a pre-compiled instance of the larger ROMS system specially configured to the river plume case for teaching use.

The numerical experiment has been designed to use idealized inputs and a configuration considered representative for a medium-sized river draining into the coastal ocean. This ROMS model implementation represents sediment using three separate categories: two are used to represent sediment discharged by the river, and the third represents sediment from the seabed. Each sediment class has fixed attributes of grain diameter, density, settling velocity, critical shear stress for erosion, and the erodibility constant. The user can modify the settling velocity, critical shear stress for erosion, and erodibility constant from the WMT GUI interface.
Sediment suspended in the water column is transported, like other conservative tracers (e.g., salinity) by solving the advection–diffusion equation with a source/sink term for vertical settling and erosion. The ROMS model represents sediment using separate cohesive and non-cohesive categories, in this ROMS-Lite model there are 3 non-cohesive sediment classes, and one non-cohesive sediment class. Each class has fixed attributes of grain diameter, density. In WMT settling velocity, critical shear stress for erosion, and erodibility constant. These properties are used to help determine the bulk properties of each bed layer.

References

Warner, Sherwood, Signell, Harris, and Arango, 2008 "Development of a three-dimensional, regional, coupled wave, current, and sediment-transport model", Computers & Geosciences.
Threshold of sediment motion under unidirectional currents, M. C. Miller, I. N. McCave, P. D. Komar, Sedimentology (1977) 24, 507-527.