r.sim.sediment(1grass)

💖 r.sim.sediment 💖

okay bestie, buckle up, because this is the GRASS User's Manual page for r.sim.sediment — the sediment transport and erosion/deposition simulation using the path sampling method (SIMWE). literally the girlboss of overland flow modeling, no cap. 💅

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🎀 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. it automatically makes a random seed for the random number generator, so use this when you're feeling chaotic and do NOT want to provide the seed option yourself 🙈
• --overwrite — lets output files overwrite files that already exist. (careful bestie, it does exactly what it says 💀)
• --help — prints the usage summary so you can read it again like a good student 🌸
• --verbose — verbose module output, aka it tells you everything it's doing
• --quiet — quiet module output, aka it says nothing, it just works 😌
• --ui — forces launching the GUI dialog

🧚 Parameters

• elevation=name [required] — name of the input elevation raster map
• water_depth=name [required] — name of the water depth raster map, in [m]
• dx=name — name of the x-derivatives raster map [m/m]. if you don't give one, it gets computed from the elevation map ✨
• dy=name — name of the y-derivatives raster map [m/m]. same deal, computed from elevation map if not given
• detachment_coeff=name [required] — name of the detachment capacity coefficient raster map [s/m]
• transport_coeff=name [required] — name of the transport capacity coefficient raster map [s]
• shear_stress=name [required] — name of the critical shear stress raster map [Pa]
• man=name — name of the Manning's n raster map
• man_value=float — one single unique Manning's n value. default: 0.1
• observation=name — name of the sampling locations vector points map, or a data source for direct OGR access
• transport_capacity=name — name for the output transport capacity raster map [kg/ms]
• tlimit_erosion_deposition=name — name for the output transport limited erosion-deposition raster map [kg/m2s]
• sediment_concentration=name — name for the output sediment concentration raster map [particle/m3]
• sediment_flux=name — name for the output sediment flux raster map [kg/ms]
• erosion_deposition=name — name for the output erosion-deposition raster map [kg/m2s]
• logfile=name — name for the sampling points output text file. for every observation vector point, the time series of sediment transport gets 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 the random number generator. the same seed can be used to obtain the same results, or the random seed can be generated by other means
• nprocs=integer — number of threads that will be used for parallel computation. default: 1

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🌈 DESCRIPTION 🌈

okay so, r.sim.sediment is a landscape scale simulation model of soil erosion, sediment transport and deposition caused by flowing water 🦋 and it was designed for spatially variable terrain, soil, cover and rainfall excess conditions. it's giving versatility, periodt.

the soil erosion model is based on the theory used in the USDA WEPP hillslope erosion model, but plot twist — it's 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 the Green's function Monte Carlo method, which provides the robustness necessary for spatially variable conditions and high resolutions (Mitas and Mitasova 1998). academic AND iconic.

key inputs of the model include these raster maps, bestie:

• elevation (elevation [m])
• flow gradient, given by the first-order partial derivatives of the 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])
• the surface roughness coefficient called Manning's n (the man raster map)

partial derivatives can be computed by v.surf.rst or the 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 ⚠️ (yes, always — don't play with her). the water depth file can be computed using the r.sim.water module. the other parameters must be determined using field measurements or reference literature (see the suggested values in Notes and References).

output includes:

• the transport capacity raster map transport_capacity in [kg/ms]
• the transport capacity limited erosion/deposition raster map tlimit_erosion_deposition [kg/m2s] — these two are output almost immediately and can be viewed while the simulation continues 👀

and then:

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

those last ones can take a longer time depending on time step and simulation time ⏳. simulation time is controlled by the niterations [minutes] parameter. and if the resulting erosion/deposition map is noisy? higher number of walkers, given by nwalkers, should be used 💅.

heads up: increasing the number of threads with nprocs does not really speed up the simulation. ngl, she said what she said.

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📚 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 bestie, that email is listed twice, and honestly? double credit, we love to see it 🙈)

🧚 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

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© 2003-2026 GRASS Development Team, GRASS 8.5.0 Reference Manual

and that's the whole manual page, bestie 💖 this was r.sim.sediment from the GRASS 8.5.0 Reference Manual, and yeah she's still serving the exact same energy she was serving in the source docs. slay, go simulate some sediment, drink water, and remember: it's giving erosion but make it distributed ✨🌊🎀