3D Sediment model

The 3D sediment model inside SCHISM (USE_SED, also referred to as ‘SED3D’ sometimes to differentiate it from the 2D sediment module ‘SED2D’) is adapted from Community Sediment Transport Model (Warner et al. 2008). The algorithm is implemented on UGs and we have also reworked several components and added a morphological module (Exner equation). Detailed are reported in Pinto et al. (2012). Also note that for best results this module should be run in conjunction with the wave model (WWM) to account for the wave-enhanced bottom stress.

The main parameter input is sediment.nml, which is a namelist file. The sample file has comments /explanations for each parameter; a few important ones are explained below:

  • sed_morph: This parameter controls active morphology.
  • Nbed: The # of bed layers affects the stability of the sorting, and Nbed=1 works robustly with sed_morph>0.

Other inputs include sed_class and output flags in param.nml, and a few .ic files: bedthick.ic, bed_frac_[1,2..].ic, and I.C. for concentrations of all classes (*_[hvar]_[1,2…].ic or (*_[vvar]_[1,2…].ic). The B.C. inputs may include SED_[1,2..].th, SED_3D.th.nc. The nudging inputs may be SED_nudge.gr3 and SED_nu.nc.

The outputs from SED3D can be combined and visualized just as other SCHISM outputs.

A common crash occurs when the active morphology is on. At a river inflow boundary, often the depths will decrease over time due to deposition there and eventually the boundary will become dry/blocked. A work-around is to use a combination of ‘bare-rock’ bed around the boundary (specified in bedthick.ic), and ‘clear-water’ inflow as B.C. (sediment concentration =0 in bctides.in) , and then input the incoming sediment concentration as point sources (msource.th) a distance away from the boundary.

References

Pinto, L., Fortunato, A.B., Zhang, Y., Oliveira, A. and Sancho, F.E.P. (2012) Development and validation of a three-dimensional morphodynamic modelling system, Ocean Mod., 57-58, 1-14.

Warner, J.C., Sherwood, C.R., Signell, R.P., Harris, C.K., Arango, H.G. 2008. Development of a three-dimensional, regional, coupled wave, current, and sediment-transport model. Comput. Geosci. 34 (10), 1284–1306. doi: 10.1016/j.cageo.2008.02.012