r.sim.sediment(1)

NAME
r.sim.sediment - Sediment transport and erosion/deposition simulation using path sampling method (SIMWE).

KEYWORDS
raster, hydrology, soil, sediment flow, erosion, deposition, model, parallel

SYNOPSIS
r.sim.sediment
r.sim.sediment --help
r.sim.sediment [-s] elevation=name water_depth=name [dx=name] [dy=name] detachment_coeff=name transport_coeff=name shear_stress=name [man=name] [man_value=float] [observation=name] [transport_capacity=name] [tlimit_erosion_deposition=name] [sediment_concentration=name] [sediment_flux=name] [erosion_deposition=name] [logfile=name] [walkers_output=name] [nwalkers=integer] [niterations=integer] [mintimestep=float] [output_step=integer] [diffusion_coeff=float] [random_seed=integer] [nprocs=integer] [--overwrite] [--help] [--verbose] [--quiet] [--ui]

  Flags:

-s
    Generate random seed
    Automatically generates random seed for random number generator (use when you don’t want to provide the seed option)

--overwrite
    Allow output files to overwrite existing files

--help
    Print usage summary

--verbose
    Verbose module output

--quiet
    Quiet module output

--ui
    Force launching GUI dialog

  Parameters:

elevation=name [required]
    Name of input elevation raster map

water_depth=name [required]
    Name of water depth raster map [m]

dx=name
    Name of x-derivatives raster map [m/m]
    Computed from elevation map if not given

dy=name
    Name of y-derivatives raster map [m/m]
    Computed from elevation map if not given

detachment_coeff=name [required]
    Name of detachment capacity coefficient raster map [s/m]

transport_coeff=name [required]
    Name of transport capacity coefficient raster map [s]

shear_stress=name [required]
    Name of critical shear stress raster map [Pa]

man=name
    Name of Manning’s n raster map

man_value=float
    Manning’s n unique value
    Default: 0.1

observation=name
    Name of sampling locations vector points map
    Or data source for direct OGR access

transport_capacity=name
    Name for output transport capacity raster map [kg/ms]

tlimit_erosion_deposition=name
    Name for output transport limited erosion-deposition raster map [kg/m2s]

sediment_concentration=name
    Name for output sediment concentration raster map [particle/m3]

sediment_flux=name
    Name for output sediment flux raster map [kg/ms]

erosion_deposition=name
    Name for output erosion-deposition raster map [kg/m2s]

logfile=name
    Name for sampling points output text file. For each observation vector point the time series of sediment transport is stored.

walkers_output=name
    Base name of the output walkers vector points map

nwalkers=integer
    Number of walkers

niterations=integer
    Time used for iterations [minutes]
    Default: 10

mintimestep=float
    Minimum time step for the simulation [seconds]
    A larger minimum time step substantially reduces processing time, but at the cost of accuracy
    Default: 0.0

output_step=integer
    Time interval for creating output maps [minutes]
    Default: 2

diffusion_coeff=float
    Water diffusion constant
    Default: 0.8

random_seed=integer
    Seed for random number generator
    The same seed can be used to obtain same results or random seed can be generated by other means.

nprocs=integer
    Number of threads which will be used for parallel computation.
    Default: 1

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]i 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
hofierka@geomodel.sk
Chris Thaxton
North Carolina State University
csthaxto@unity.ncsu.edu
csthaxto@unity.ncsu.edu

SOURCE CODE

Available at: r.sim.sediment source code (history)

Latest change: Wednesday Feb 04 10:35:18 2026 in commit: 017db7e1df9b84130ca5b0549ecfed07a848daa8

Main index | Raster index | Topics index | Keywords index | Graphical index | Full index

© 2003-2026 GRASS Development Team, GRASS 8.5.1dev Reference Manual