NAME
r.traveltime - Estimation of travel times/isochrones.
Computes the travel time of surface runoff to an outlet
KEYWORDS
raster,
hydrology
SYNOPSIS
r.traveltime
r.traveltime --help
r.traveltime [-q] dir=name accu=name dtm=name manningsn=name out_x=string out_y=string threshold=string b=string nchannel=string dis=string [slopemin=string] out=name [--overwrite] [--help] [--verbose] [--quiet] [--ui]
Flags:
- -q
- Quiet
- --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:
- dir=name [required]
- Flow direction map (e.g. derived by r.watershed)
- accu=name [required]
- Flow accumulation map (e.g. derived by r.watershed)
- dtm=name [required]
- Depressionless, filled terrain model (e.g. derived by r.fill.dir)
- manningsn=name [required]
- Map with Manning's n value for surface roughness
- out_x=string [required]
- x coordinate of basin outlet
- out_y=string [required]
- y coordinate of basin outlet
- threshold=string [required]
- Minimum number of cells (threshold) that classify cell as channel
- b=string [required]
- Channel width
- nchannel=string [required]
- Channel roughness (Manning's n)
- dis=string [required]
- Specific discharge [l/s/km**2]
- slopemin=string
- Minimum slope for flat areas [m/m]
- out=name [required]
- Output travel time map [seconds]
r.traveltime computes the travel time of surface runoff to an
outlet. The program starts at the basin outlet and calculates the travel
time for each raster cell recursively. A drainage area related threshold
considers either surface runoff or channel runoff. Travel times are
derived by assuming kinematic wave approximation.
In order to derive channel flow velocities, an equilibrium discharge
for each cell is calculated (Q=Area*specific discharge).
The results can be used to derive a time-area function. This might be
useful for precipitation-runoff calculations (estimation of flood
predictions) with a lumped hydrological model (user-specified unit
hydrograph).
The program ist restricted to SI units (meters). The algorithm is
recursive. Maybe it will not work with extensive datasets. It is
assumed that the minimum slope is 0.001. For smaller gradients the
program uses this value.
Please not that the flow accumulation map must be defined as single
direction. Multiple flow directions are not supported. Thus, the
"SFD (D8) flow" option has to be set if, e.g., the r.watershed
module is used to generate the input files (parameter s). The flow
accumulation map should include positive values only (-a of
r.watershed). Flow direction definitions are in accordance to the
r.fill.dir program using the "agnps" format option.
The program does not work correctly if Manning's roughness grid is
defined as double (float expected). To define a simple uniform
roughness distribution try: r.mapcalc 'roughness = 0.1f'
This example uses the North Carolina sample dataset.
g.region raster=elevation
r.mapcalc "n = 0.1f"
r.fill.dir input=elevation output=fill direction=flowdir format=agnps
r.fill.dir input=fill output=fill2 direction=flowdir2 format=agnps
r.watershed -a -s elevation=fill2 accumulation=accu
r.traveltime --overwrite dir=flowdir2 accu=accu dtm=fill2 manningsn=n \
out_x=634613 out_y=217014 threshold=250 b=3 nchannel=0.03 slopemin=0.01 \
dis=900 out=ttime
r.colors ttime colors=blues
r.watershed,
r.fill.dir
http://jesbergwetter.twoday.net/stories/4845555/
- Kilgore, J. L. (1997): Development and evaluation of a GIS-based
spatially distributed unit hydrograph model, master thesis,
Virginia
Polytechnic Institute and State University.
- Melesse, A. M., Graham, W. D. (2004): Storm runoff predicition
based on a
spatially distributed travel time method utilizing remote sensing and
GIS, Journal of the American Water Resources Association, 8,
863-879.
- Muzik, I. (1996): Flood modelling with GIS-derived distributed
unit hydrographs, Hydrological Processes, 10, 1401-1409.
Kristian Foerster
SOURCE CODE
Available at:
r.traveltime source code
(history)
Latest change: Monday Jan 30 19:52:26 2023 in commit: cac8d9d848299297977d1315b7e90cc3f7698730
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GRASS Development Team,
GRASS GIS 8.3.dev Reference Manual