shadow (version 0.6.4.1)

flowlength: Calculate flow length

Description

Calculates flow length for each pixel in a Digital Elevation Model.

Usage

flowlength(elev, veg, res = 1)

Arguments

elev

A numeric matrix representing a Digital Elevation Model (DEM)

veg

A logical matrix representing vegetation presence. TRUE values represent vegetated cells where flow is absorbed (i.e. sinks), FALSE values represent cells where flow is unobstructed

res

numeric vector of length 1, specifying DEM resolution. Default is 1, i.e. pixel size is 1*1

Value

A numeric matrix where each cell value is flow length, in res units

References

The algorithm is described in:

Mayor, A. G., Bautista, S., Small, E. E., Dixon, M., & Bellot, J. (2008). Measurement of the connectivity of runoff source areas as determined by vegetation pattern and topography: A tool for assessing potential water and soil losses in drylands. Water Resources Research, 44(10).

Examples

# NOT RUN {
# Example from Fig. 2 in Mayor et al. 2008

elev = rbind(
  c(8, 8, 8, 8, 9, 8, 9),
  c(7, 7, 7, 7, 9, 7, 7),
  c(6, 6, 6, 6, 6, 5, 7),
  c(4, 5, 5, 3, 5, 4, 7),
  c(4, 5, 4, 5, 4, 6, 5),
  c(3, 3, 3, 3, 2, 3, 3),
  c(2, 2, 2, 3, 4, 1, 3)
)
veg = rbind(
  c(TRUE,  TRUE,  TRUE,  TRUE,  FALSE, FALSE, TRUE),
  c(TRUE,  TRUE,  TRUE,  TRUE,  TRUE,  FALSE, FALSE),
  c(FALSE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE),
  c(FALSE, TRUE,  FALSE, FALSE, FALSE, FALSE, TRUE),
  c(TRUE,  TRUE,  FALSE, FALSE, FALSE, FALSE, FALSE),
  c(TRUE,  TRUE,  TRUE,  FALSE, FALSE, FALSE, FALSE),
  c(FALSE, TRUE,  TRUE,  FALSE, FALSE, TRUE,  TRUE)
)

# Calculate flow length
f = flowlength(elev, veg)

# Plot
library(raster)
r = raster(f)
pnt = rasterToPoints(r)
plot(r, main = "Flow length")
text(pnt[, 1:2], as.character(round(pnt[, 3], 1)))

# }