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Identify watershed basins and direction and accumulation of flow

Source: R/flow.r
flow.Rd

The flow() function uses a raster representing elevation to compute other rasters representing:

  • Flow accumulation;

  • Direction of flow;

  • Watershed basins;

  • Flooded areas; and/or

  • Topographic convergence (log of flow accumulation divided by local slope).

More details about the computations can be found at the help page for the GRASS module r.terraflow] (see grassHelp("r.terraflow"))

Usage

# S4 method for class 'GRaster'
flow(
  x,
  direction = "multi",
  return = "accumulation",
  dirThreshold = Inf,
  scratchDir = NULL
)

Arguments

x

A GRaster with a single layer, typically representing elevation.

direction

Character: Either "single" or "multi". This indicates whether a single-direction flow or multi-direction flow model is used. The default is "multi". Partial matching is used and case is ignored.

return

Character vector: Indicates what rasters to return. Partial matching is used and case is ignored. Options include:

  • "accumulation" (default): Flow accumulation raster.

  • "basins": Watershed basins

  • "direction": Flow direction

  • "flooded": Flooded areas

  • "TCI": Topographic convergence index

  • "*": All of the above

dirThreshold

Numeric (default is Inf): For the multi-direction flow model, this indicates the amount of accumulated flow above which the single-direction flow rule is used to locate the egress of water from a cell. This is the d8cut parameter in r.stream.extract.

scratchDir

Character or NULL (default): Directory in which to store temporary files. The GRASS module r.terraflow makes a lot of temporary files. If this is NULL, then a temporary folder in the user's working directory will be used (see getwd()).

Value

A GRaster.

See also

flowPath(), streams(), the GRASS module r.terraflow (see grassHelp("r.terraflow"))

Examples

if (grassStarted()) {

# Setup
library(terra)

# Example data
madElev <- fastData("madElev")
elev <- fast(madElev)

# Calculate flow accumulation and watershed basins
water <- flow(elev, return = c("accum", "basins"))
water

elevWater <- c(elev, water)
plot(elevWater)

}