r.sim.sediment - GRASS manual

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 [-sp] 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] [duration=integer] [mintimestep=float] [output_step=integer] [diffusion_coeff=float] [seed=integer] [nprocs=integer] format=name [--overwrite] [--help] [--verbose] [--quiet] [--ui]

Flags:

-s: Generate random seed (result is non-deterministic) [deprecated]; This flag is deprecated and will be removed in a future release. Seeding is automatic or use parameter seed.
-p: Print run summary to standard output
--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
duration=integer: Duration of the simulated water flow [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
seed=integer: Seed value for the random number generator; Using the same seed ensures identical results, while a randomly generated seed produces different outcomes in each run.
nprocs=integer: Number of threads which will be used for parallel computation.; Default: 1
format=name [required]: Output format; Options: plain, json; Default: plain; plain: Plain text output; json: JSON (JavaScript Object Notation)

DESCRIPTION
NOTES
- Run summary
REFERENCES
SEE ALSO
AUTHORS

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 module requires a projected coordinate system and does not run in a latitude-longitude project. 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 duration [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 speeds up the simulation. The random numbers, the seed and the reproducibility of the results with more than one thread are as in r.sim.water.

NOTES

Null cells in the elevation, dx, dy, water_depth, detachment_coeff, transport_coeff, shear_stress and man raster maps are excluded from the simulation, the outputs are null there, and walkers that reach them leave the area.

Run summary

With the -p flag, a summary of the run is printed to standard output after the maps are written. The format option selects plain text (one key: value pair per line) or JSON. Without -p, nothing is printed to standard output regardless of format. The values are also stored in the history of the sediment_flux raster map under the same keys (see r.info).

The keys are the same as for r.sim.water with these differences:

Key Meaning Unit

time_step_sediment Time step limit derived from the sediment transport parameters, null when no cell exceeds the critical shear stress s

velocity_max Maximum flow velocity over the defined cells m/s

sigma_max Maximum first order reaction coefficient (detachment to transport capacity ratio) over the defined cells 1/m

mean_source_rate Mean sediment source (detachment) rate kg/m^2s

mean_infiltration Not reported

transport_capacity, tlimit_erosion_deposition Names of these maps, which are written once before the simulation starts, or null when not requested

outputs A single entry with the simulated_time (s), timestamp and walkers_remaining at the time of writing, and the names of the sediment_concentration, sediment_flux, erosion_deposition and walkers maps, or null for maps which were not requested

Key	Meaning	Unit
`time_step_sediment`	Time step limit derived from the sediment transport parameters, `null` when no cell exceeds the critical shear stress	s
`velocity_max`	Maximum flow velocity over the defined cells	m/s
`sigma_max`	Maximum first order reaction coefficient (detachment to transport capacity ratio) over the defined cells	1/m
`mean_source_rate`	Mean sediment source (detachment) rate	kg/m^2s
`mean_infiltration`	Not reported
`transport_capacity`, `tlimit_erosion_deposition`	Names of these maps, which are written once before the simulation starts, or `null` when not requested
`outputs`	A single entry with the `simulated_time` (s), `timestamp` and `walkers_remaining` at the time of writing, and the names of the `sediment_concentration`, `sediment_flux`, `erosion_deposition` and `walkers` maps, or `null` for maps which were not requested

Summary of a run in JSON:

r.sim.sediment elevation=elevation water_depth=water_depth detachment_coeff=detachment \
    transport_coeff=transport shear_stress=shear_stress man_value=1 \
    sediment_flux=flux erosion_deposition=erdep transport_capacity=tc \
    duration=1 seed=1 -p format=json

{
    "walkers_requested": 60,
    "walkers_generated": 78,
    "walkers_remaining": 43,
    "seed": 1,
    "duration": 60,
    "simulated_time": 54.891343113611583,
    "time_step": 5.4891343113611581,
    "time_step_sediment": 70.517234241515013,
    "iterations_planned": 10,
    "iterations_completed": 10,
    "stopped_early": false,
    "mean_velocity": 0.1821780891624834,
    "velocity_max": 0.21544346900318839,
    "sigma_max": 0.052657639041437901,
    "mean_mannings_n": 1,
    "mean_source_rate": 0.56025284041612944,
    "threads": 1,
    "transport_capacity": "tc",
    "tlimit_erosion_deposition": null,
    "outputs": [
        {
            "simulated_time": 54.891343113611583,
            "timestamp": "1 minutes",
            "walkers_remaining": 43,
            "sediment_concentration": null,
            "sediment_flux": "flux",
            "erosion_deposition": "erdep",
            "walkers": null
        }
    ]
}

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.

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 Oct 07 16:51:13 2026 in commit: 40afb9f47208ffa5b7f90dbce890049c09c65841