Construct a raster of channel locations from vector or topographic data

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Description

The discretise and make.routing.table methods both require a raster defining the locations of the channel cells and the proportion of each river cell occupied by the channel. A detailed river network (DRN) may be available in vector format. If not, the channel location can be inferred from a spatially-distributed metric, typically the topographic wetness index.

Usage

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build_chans(dem = NULL, drn = NULL, atb = NULL, chan.width = 5,
  buffer = 10, atb.thresh = 0.8, single.chan = TRUE)

Arguments

dem

Elevation raster (DEM) using a projected coordinate system (e.g UTM) and regular grid spacing. Not required if atb raster supplied.

drn

Detailed river network (DRN) in vector (ESRI Shapefile) format. Not required if atb raster supplied.

atb

Raster whose values provide a criteria for locating the channel. This is typically the value of the topographic wetness index (TWI) determined from the elevations. Should be in a projected coordinate system (e.g UTM) and regular grid spacing.

For the TWI to be meaningful this raster should have a resolution of a least 30m. It can be calculated using the upslope.area method applied to the DEM and atb=T.

chan.width

Channel width, in m, which by default will be applied across entire network.

buffer

If using a vector input then buffer the DRN by this width to capture all river cells.

atb.thresh

If drn not supplied then this specifies the threshold value above which cells are identified as containing part of the channel network

single.chan

If using a vector input then individual reach IDs are ignored and the first raster layer returned contains either 1 for a river cell or NA for a non-river cell. Otherwise the discretise method will create an entry for ecah channel ID

Value

A two-band raster with the same dimensions as the elevation or ATB raster whose first layer comprises non-zero cells where identified with the channel and whose second layer holds the proportions of those cells occupied by the channel.

References

Kirkby, M. (1975). Hydrograph modelling strategies. In Peel, R., Chisholm, Michael, Haggett, Peter, & University of Bristol. Department of Geography. (Eds.). Processes in physical and human geography : Bristol essays. pp. 69-90. London: Heinemann Educational.

Examples

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## Not run: 
# Build channel raster in two ways and compare the results (each with a
# nominal 2m channel width). Artificial drainage in this catchment has
# apparently introduced many channels with dimensions below the scale. Their
# existence would not have been inferred simply from examining the topography.
# This high-network connectivity is suggested as a cause of the unexpectedly
# high responsiveness of the catchment given high antecedent moisture conditions.

require(dynatopmodel)
data("brompton")

# (1) Using the wetness index

a.atb <- upslope.area(brompton$dem, atb=TRUE)
chan.rast.1 <- build_chans(atb=a.atb$atb)

# (2) using the DRN
chan.rast.2 <- build_chans(dem=brompton$dem, drn=brompton$drn, buff=5, chan.width=2)

sp::plot(chan.rast.2[[1]], col="green", legend=FALSE)
sp::plot(chan.rast.1[[1]], col="blue", legend=FALSE, add=TRUE)
legend(fill=c("green", "blue"), legend=c("TWI", "DRN"), title="Method", x="bottomright")

## End(Not run)