STELAR-S2S

morphodynamic modelling

In this project we are developing a generic morphodynamic model that will quantify all components of the Lower Mekong’s sediment budget. The model will consist of two linked components addressing:

  1. flood hydraulics and floodplain sedimentation, and
  2. bank erosion, river migration and long profile evolution.

For the channel hydraulics and floodplain sedimentation we will represent flow and suspended sediment transport by solving the 1D St. Venant equation and a 1D advection-diffusion equation for multiple sediment size fractions, following our earlier work (Nicholas, 2009). Floodplain flow is represented by solving the 2D shallow water equations and a 2D advection-diffusion equation for sediment transport. The 1D and 2D model components are coupled by representing mass (water and sediment) and momentum (water) exchanges between the channel and the floodplain. For channel planform evolution, we will couple a bank erosion model we have developed in prior work (Darby et al., 2010) with a channel migration model. We plan to run the model for a multi-decadal historical period, from around 1960 to present.

The simulation data derived from the model will be unique: the first annually resolved mega-river sediment budget encompassing a multi-decadal period. These data will enable us to explore a series of specific research questions:

  • What is the net effect on the Mekong sediment load of sediment exchanges within its alluvial transfer reach?
  • Do sediment fluxes associated with floodplain storage and bank erosion promote a net increase or reduction in efflux from the transfer zone?
  • How strong is the interannual variability in this modulation, and what factors drive this?
Example modelling output demonstrative of future STELAR results.

Simulated flow velocity structure in a divided channel reach

references

Nicholas, A.P. (2009), Reduced-complexity flow routing models for sinuous single-thread channels: intercomparison with a physically-based shallow-water equation model, Earth Surface Processes and Landforms, 34, 641-653, doi:10.1002/esp.1761.

Darby, S.E., Trieu, H.Q., Carling, P.A., Sarkkula, J., Koponen, J., Kummu, M., Conlan, I. and Leyland, J. (2010), A physically-based model to predict hydraulic erosion of fine-grained river banks: The role of form roughness in limiting erosion, Journal of Geophysical Research, 115, F04003, doi:10.1029/2010JF001708.