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What does the output drainage raster map show?
Output drainage raster map contains drainage direction. Provides the “aspect” for each cell measured CCW from East. Multiplying positive values by 45 will give the direction in degrees that the surface runoff will travel from that cell. The value 0 (zero) indicates that the cell is a depression area (defined by the depression input map).
How are overland flow units calculated in a GIS?
Overland flow units represent the amount of overland flow each cell contributes to surface flow. If omitted, a value of one (1) is assumed. Raster retention map specifies correction factors per cell for flow distribution.
How to enable single flow direction in GRASS GIS?
Setting this flag causes the program to manage memory on disk which allows very large maps to be processed but is slower. Flag -s force the module to use single flow direction (SFD, D8) instead of multiple flow direction (MFD). MFD is enabled by default. By -4 flag the user allow only horizontal and vertical flow of water.
What does option threshold mean in GRASS GIS?
Blocking cells and streams stop the slope length for the RUSLE. All cells that are not NULL and not zero indicate blocking terrain. Option threshold specifies the minimum size of an exterior watershed basin in cells, if no flow map is input, or overland flow units when a flow map is given.
Which is the default MFD flag in r.watershed?
MFD is enabled by default. By -4 flag the user allow only horizontal and vertical flow of water. Stream and slope lengths are approximately the same as outputs from default surface flow (allows horizontal, vertical, and diagonal flow of water). This flag will also make the drainage basins look more homogeneous.
What is the universal soil loss equation for western rangelands?
Equations taken from Revised Universal Soil Loss Equation for Western Rangelands (Weltz et al. 1987). Since the LS factor is a small number (usually less than one), the GRASS output map is of type DCELL. The output slope_steepness raster map stores slope steepness (S) factor for the Universal Soil Loss Equation (RUSLE).
How to calculate the drainage area of grass?
Some other software, such as the ArcGIS extension “ArcHydro” can calculate the total upstream drainage area flowing through each stream reach. The same result is achieved in GRASS with a few hydrology modules and a database join. Begin by rerunning the r.watershed command as in the first section, but adding a flow accumulation raster as the output:
Which is the default flow direction in r.watershed?
Flag -s force the module to use single flow direction (SFD, D8) instead of multiple flow direction (MFD). MFD is enabled by default. By -4 flag the user allow only horizontal and vertical flow of water. Stream and slope lengths are approximately the same as outputs from default surface flow (allows horizontal, vertical, and diagonal flow of water).