r.sim.sediment(1)

📦
version 8.4.2 · 8 versions
, in fedora 44

r.sim.sediment 💖

okay bestie, gather round, because this is the GRASS GIS User's Manual page for r.sim.sediment — yes, the (1) one, section 1, we're in the big leagues. Sit down, hydrate, we're simulating sediment transport with path sampling and it's gonna be iconic. ✨

🌸 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. yes she will bulldoze your old files, that's the deal 💅
  • --help — Print usage summary
  • --verbose — Verbose module output. she will yap (affectionately)
  • --quiet — Quiet module output. she will NOT yap
  • --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 [required] — Name of x-derivatives raster map [m/m]
  • dy=name [required] — Name of y-derivatives raster map [m/m]
  • 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 🌈

So r.sim.sediment is a landscape scale, simulation model of soil erosion, sediment transport and deposition caused by flowing water, and it's designed for spatially variable terrain, soil, cover and rainfall excess conditions. Basically she eats variable conditions for breakfast. 💅

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). no cap, that's the actual technique.

Key inputs of the model include the following raster maps, and bestie, we're listing ALL of them:

  • elevation (elevation [m]) — the terrain itself, main character energy
  • 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])
  • 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).

Now, the outputs, because she's giving range:

  • transport capacity raster map transport_capacity in [kg/ms]
  • transport capacity limited erosion/deposition raster map tlimit_erosion_deposition [kg/m2s]

Those two are output almost immediately and can be viewed while the simulation continues. lowkey the best part.

  • Sediment flow rate raster map sediment_flux [kg/ms]
  • net erosion/deposition raster map [kg/m2s]

Those 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. 🫶

Also, heads up: increasing the number of threads with nprocs does not really speed up the simulation. like, at all. it's giving placebo 😭

📚 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

(yes, that last email is listed twice in the original, and I am NOT about to erase a single character of it, that's her lore 💜)

💾 SOURCE CODE 💾

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

Accessed: Saturday Jan 17 05:41:00 2026

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

okay that's the whole page, every flag, every default, every reference, every email, periodt. 💖✨

And a lil sign-off for the girlies: this is GRASS GIS 8.4.2, © 2003-2025 GRASS Development Team, straight out of the GRASS GIS 8.4.2 Reference Manual, and the page itself signs off as GRASS 8.4.2 with r.sim.sediment(1). slay, go simulate some erosion, bestie 🌸🦋🎀

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