NAME
r.sim.sediment - spatially distributed, 2D water
erosion, sediment transport and deposition simulation model based on
the continuity equations solved by Green's function Monte Carlo method.
GRASS raster program
SYNOPSIS
r.sim.sediment
r.sim.sediment help
r.sim.sediment [-tm] elevin =name wdepth=name dxin=name
dyin=name detin=name tranin=name tauin=name
manin=name [tc=name] [et=name] [conc=name] [flux=name]
[erdep=name] [nwalk=value] [niter=value] [outiter =value]
[density=value] [diffc=value]
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 files:
elevation ( elevin), flow gradient given by the first-order partial
derivatives of elevation field ( dxin and dyin),
overland flow water depth ( wdepth), detachment capacity coefficient (detin),
transport capacity coefficient (tranin), critical shear stress (tauin)
and surface roughness coefficient called Manning's n (manin raster file).
Partial derivatives can be computed by
s.surf.rst or r.slope.aspect
module. The data are automatically converted data from feet to metric
system using database/projection information. 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 file tc in [kg/ms],
transport capacity limited erosion/deposition raster file
et [kg/m2s], sediment flow rate raster file
flux [kg/ms], and net erosion/deposition raster file [kg/m2s].
Simulation time is controled by niter parameter. The default value is 1000,
depending on complexity of terrain, land cover and size of the area, several thousand
iterations may be needed to reach the steady state. Output
files can be saved during simulation using outiter parameter
defining simulation time step for writing output files. This option requires
time series flag -t. Files are saved with suffix containing
iteration number (e.g. name.500, name.1000, etc.).
OPTIONS
The user can run this program either interactively
or non-interactively. The program will be run non-interactively
if the user specifies program arguments and flag settings on
the command line using the form:
r.sim.sediment [-tm] elevin=name wdepth=name
dxin=name dyin=name detin=name tranin=name tauin=name
manin=name [tc=name] [et=name] [conc=name] [flux=name]
[erdep=name] [nwalk=value] [niter=value] [outiter=value]
[ density =value] [diffc=value]
Alternately, the user can simply type r.sim.water on the command line
without program arguments. In this case, the user will be prompted
for parameter values using the standard GRASS parser interface.
Flag:
- -t
- time series output
- -m
- multiscale (not ready yet)
Parameters:
- elevin =name
- Use the existing elevation raster file name as input [meters or feet].
- dxin=name
- Use the existing raster file with x-derivatives as input [-]
- dyin=name
- Use the existing raster file with y-derivatives as input [-].
- detin=name
- Use the existing raster file with detachment capacity coefficient
- train=name
- Use the existing raster file with transport capacity coefficient
- tauin=name
- Use the existing raster file with critical shear stress
- manin=name
- Use the existing raster file with Manning's surface roughness n raster file [-].
- tc=name
- Output transport capacity raster file
- et=name
- Output transportcapacity limited erosion/deposition raster file
- conc=name
- Output sediment concentration raster file
- flux=name
- Output sediment flux raster file
- erdep=name
- Output erosion/deposition raster file
- nwalk=val
- Set the number of walkers to val (default:2000000)
- niter=val
- Set the number of iterations to val (default:1200)
- outiter=val
- Set the time step for saving output maps to val (default: 300)
- density=val
- Set the density of output walkers to val (default: 200)
- diffc=val
- Set the diffusion constant to val (default: 0.8)
NOTES
SEE ALSO
s.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
REFERENCES
Mitas, L., and Mitasova, H., 1998, Distributed soil erosion
simulation for effective erosion prevention. Water Resources Research,
34(3), 505-516.
Neteler, M. and Mitasova, H., 2002, Open Source GIS: A GRASS GIS Approach,
Kluwer Academic Publishers.
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