## DESCRIPTION

r.sim.sediment is a landscape scale, simulation model of soil erosion, sediment transport and deposition caused by flowing water designed for spatially variable terrain, soil, cover and rainfall excess conditions. The soil erosion model is based on the theory used in the USDA WEPP hillslope erosion model, but it has been generalized to 2D flow. The solution is based on the concept of duality between fields and particles and the underlying equations are solved by Green's function Monte Carlo method, to provide robustness necessary for spatially variable conditions and high resolutions (Mitas and Mitasova 1998). Key inputs of the model include the following raster maps: elevation (elevation [m]), flow gradient given by the first-order partial derivatives of elevation field ( dx and dy), overland flow water depth (water_depth [m]), detachment capacity coefficient (detachment_coeff [s/m]), transport capacity coefficient (transport_coeff [s]), critical shear stress (shear_stress [Pa]) and surface roughness coefficient called Manning's n (man raster map). Partial derivatives can be computed by v.surf.rst or r.slope.aspect module. The data are automatically converted from feet to metric system using database/projection information, so the elevation always should be in meters. The water depth file can be computed using r.sim.water module. Other parameters must be determined using field measurements or reference literature (see suggested values in Notes and References).

Output includes transport capacity raster map transport_capacity in [kg/ms], transport capacity limited erosion/deposition raster map tlimit_erosion_deposition [kg/m2s] that are output almost immediately and can be viewed while the simulation continues. Sediment flow rate raster map sediment_flux [kg/ms], and net erosion/deposition raster map [kg/m2s] can take longer time depending on time step and simulation time. Simulation time is controlled by niterations [minutes] parameter. If the resulting erosion/deposition map is noisy, higher number of walkers, given by nwalkers should be used.

Increasing the number of threads with nprocs does not really speed up the simulation.

## REFERENCES

Mitasova, H., Thaxton, C., Hofierka, J., McLaughlin, R., Moore, A., Mitas L., 2004, Path sampling method for modeling overland water flow, sediment transport and short term terrain evolution in Open Source GIS. In: C.T. Miller, M.W. Farthing, V.G. Gray, G.F. Pinder eds., Proceedings of the XVth International Conference on Computational Methods in Water Resources (CMWR XV), June 13-17 2004, Chapel Hill, NC, USA, Elsevier, pp. 1479-1490.

Mitasova H, Mitas, L., 2000, Modeling spatial processes in multiscale framework: exploring duality between particles and fields, plenary talk at GIScience2000 conference, Savannah, GA.

Mitas, L., and Mitasova, H., 1998, Distributed soil erosion simulation for effective erosion prevention. Water Resources Research, 34(3), 505-516.

Mitasova, H., Mitas, L., 2001, Multiscale soil erosion simulations for land use management, In: Landscape erosion and landscape evolution modeling, Harmon R. and Doe W. eds., Kluwer Academic/Plenum Publishers, pp. 321-347.

Neteler, M. and Mitasova, H., 2008, Open Source GIS: A GRASS GIS Approach. Third Edition. The International Series in Engineering and Computer Science: Volume 773. Springer New York Inc, p. 406.

## SEE ALSO

v.surf.rst, r.slope.aspect, r.sim.water

## AUTHORS

Helena Mitasova, Lubos Mitas
North Carolina State University
hmitaso@unity.ncsu.edu
Jaroslav Hofierka
GeoModel, s.r.o. Bratislava, Slovakia
Chris Thaxton
North Carolina State University
csthaxto@unity.ncsu.edu