Calculating flow path length in R

Question

I am currently trying to calculate the flow path length in a DEM towards a streamnetwork. My desired outcome would be a raster with values of how long the flowpath to the nearest streamcell would be for every cell.

The streams are generated by flow accumulation and are also available as binary raster files.

I am working in R but am unable to find a function that provides this functionality.

I stumbled upon a similar function that might work in GRASS however I would like to forego setting up rgrass. For my Watersehd deliniation and flowpath prerpocessing im using whiteboxtools for R which works like a charm.

Answer 1

You can use the R package {whitebox} to bring whitebox tools to your R session. The tool you might be looking for is called wbt_downslope_distance_to_stream. Below you will find an example how to extract the distance to the nearest slope end-to-end. Note, that you will have to chose sensible settings for your area of interest.

library(whitebox)
library(terra)
#> terra 1.7.40
library(sf)
#> Linking to GEOS 3.11.1, GDAL 3.6.2, PROJ 9.1.1; sf_use_s2() is TRUE


loc <- tempfile()
dir.create(loc)

dem_file <- system.file("ex/elev.tif", package="terra")


install_whitebox()
#> Performing one-time download of WhiteboxTools binary from
#>   https://www.whiteboxgeo.com/WBT_Linux/WhiteboxTools_linux_amd64.zip 
#> (This could take a few minutes, please be patient...)
#> WhiteboxTools binary is located here:  /home/darius/.local/share/R/whitebox/WBT/whitebox_tools 
#> You can now start using whitebox
#>     library(whitebox)
#>     wbt_version()
wbt_version()


wbt_fill_depressions(
  dem = dem_file,
  output = file.path(loc, "dem_filled.tif")
)


wbt_flow_accumulation_full_workflow(
  dem = file.path(loc, "dem_filled.tif"), 
  out_dem = file.path(loc, "out_dem.tif"),
  out_pntr = file.path(loc, "out_pntr.tif"),
  out_accum = file.path(loc, "out_accum.tif"),
  out_type = "sca"
)

wbt_extract_streams(
  flow = file.path(loc, "out_accum.tif"),
  output = file.path(loc, "streams.tif"),
  threshold = 1
)


wbt_downslope_distance_to_stream(
  dem = file.path(loc, "dem_filled.tif"),
  streams = file.path(loc, "streams.tif"),
  output = file.path(loc, "flow_path_length.tif") 
)

flow_path <- rast(file.path(loc, "flow_path_length.tif"))

plot(flow_path)

^{Created on 2023-06-30 with reprex v2.0.2}