Description Usage Arguments Details Value Examples
flowvelocity
applies Manning's equation to calculate flow velocity across all cells
of a digital elevation model. It is used to calculate which cells contribute to peak
flow.
1 2 | flowvelocity(dem, nr = 0.025, wf = 1e-04,
minslope = atan(0.005/mean(res(dem))))
|
dem |
a raster object of elevations |
nr |
an optional single numeric value, or a raster object, two-dimensional array or matrix of Manning's roughness coefficients (see details) |
wf |
n optional single numeric value, or a raster object, two-dimensional array or matrix of mean water volumes (see details) |
minslope |
an optional positive value specifying the minimum slope allowed (see details). |
If wf
is a single value it should approximate the mean proportion of land wetted.
If wf
is an array, matrix or raster object, then values should approximate the mean proportion of
land wetted seperately for each basin, but should not be variable within basins.
If slope is zero, infinite topographic wetness index values are returned. Thus,
flat areas are assigned a value specifed by minslope
. The default value, given by
atan(0.005 / mean(res(dem))), assumes that height differences between adjacent cells exceed
0.005. Accumulated flow is multiplied by the cell dimensions, thusdem
should have an
equal area projection. Values of nr
fora variaty of substrate types can be found
here: http://www.fsl.orst.edu/geowater/FX3/help/8_Hydraulic_Reference/Mannings_n_Tables.htm
.
a raster object of flow velocities (m / s)
1 | plot(flowvelocity(dtm100m), main = "Flow velocity")
|
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