R/getminmaxatdam.R

In damAOI: Create an 'Area of Interest' Around a Constructed Dam for Comparative Impact Evaluations

getminmaxatdam <- function(reservoir, fac) {
  dam_buffer <- st_buffer(reservoir, 2000)
  # crops the flow accumulation raster to the dam buffer
  fac_dam <- crop(fac, dam_buffer, snap = "out")
  # removes low/insignificant values of flow accumulation
  fac_dam[fac_dam <= 50] <- NA
  # creates a raster for the dam extent
  dam_binary <- rasterize(vect(reservoir), fac_dam)
  x <- fac_dam * dam_binary
# takes x, a one-band flow accumulation in rast format
  x <-   as.data.frame(x, xy = TRUE)
# makes the column names standard
  colnames(x) <- c("x", "y", "var")
# arranges by flow accumulation
  x <- x %>% arrange(.data$var) %>%  
# calculates the difference with the last value
    mutate(diffvar = c(0,diff(.data$var)))
# selects the minimum (the place where the difference in accumulated flow is the highest (pour point in))
# and the maximum (place where the accumulated flow is the highest, pour point out)
  minmax <- rbind(x[x$diffvar == max(x$diffvar),1:3], 
                  x[x$var == max(x$var),1:3])
  return(minmax)
}