In jsta/nhdR: Tools for Working with the National Hydrography Dataset

knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>"
)

The goal of this vignette is to demonstrate how to pull the stream network associated with a waterbody catchment. We will use the extract_network function to accomplish this task using the built-in mendota dataset.

library(nhdR)
library(dplyr)
library(ggplot2)
library(sf)

Let's start by pulling the coordinates associated with Lake Mendota, which will be the largest object (by area) in the waterbody object.

data(mendota)

largest_waterbody <- which.max(st_area(mendota$sp$NHDWaterbody))
mendota_lake      <- mendota$sp$NHDWaterbody[largest_waterbody, ]
mendota_lake      <- st_transform(mendota_lake, crs = 4326)
mendota_centroid  <- st_coordinates(st_centroid(mendota_lake))

Next, we can use the extract_network function to pull the stream network associated with Lake Mendota. Notice that we have set the maxsteps parameter to Inf. If the network is anticipated to be very large it can be a good idea to set this to a discrete (lower) number to avoid returning very large lines objects.

mendota_network <- extract_network(lon = mendota_centroid[1],
  lat = mendota_centroid[2],
  maxsteps = Inf)

Finally, we compare the stream network from a geometric buffer around Lake Mendota against the output of extract_network to make sure everything is working properly.

data(mendota_network)

ggplot() +
  geom_sf(data = mendota$sp$NHDFlowLine) +
  geom_sf(data = mendota_lake, fill = "cyan") +
  geom_sf(data = mendota_network, color = "blue")