Getting Started with lakefetch

Introduction

The lakefetch package calculates fetch (open water distance) and wave exposure metrics for lake sampling points. Fetch is an important physical parameter that influences wave energy, sediment resuspension, and habitat characteristics.

Installation

install.packages("lakefetch")

# Optional packages for extra features:
# install.packages("nhdplusTools")                      # NHD integration
# install.packages(c("shiny", "leaflet", "base64enc"))  # Interactive app

Quick Start

library(lakefetch)

# From CSV file
sites <- load_sites("my_lake_sites.csv")

# Or create manually
sites <- data.frame(
  Site = c("Site_A", "Site_B", "Site_C"),
  latitude = c(43.42, 43.43, 43.41),
  longitude = c(-73.69, -73.68, -73.70)
)
sites <- load_sites(sites)

# Automatically download from OpenStreetMap
lake <- get_lake_boundary(sites)

# Or load from a local shapefile
lake <- get_lake_boundary(sites, file = "lake_boundary.shp")

results <- fetch_calculate(sites, lake)

# View results
head(results$results)

# Map of sites
plot_fetch_map(results)

# Bar chart
plot_fetch_bars(results)

# Interactive app
fetch_app(results)

Understanding the Results

The fetch_calculate() function returns a list containing:

• results: An sf object with one row per site, containing:
  • fetch_0, fetch_5, …, fetch_355: Fetch distance in each direction (meters)
  • fetch_mean: Average fetch across all directions
  • fetch_max: Maximum fetch (longest open water distance)
  • fetch_effective: Mean of the three longest fetch values
  • orbital_effective: Estimated wave orbital velocity (m/s)
  • exposure_category: Classification as “Sheltered”, “Moderate”, or “Exposed”
• lakes: The lake polygon(s) used for calculation
• angles: The angles (in degrees) used for ray-casting

Exposure Categories

Sites are classified based on effective fetch:

Configuration Options

Customize the calculation parameters:

# View current options
lakefetch_options()

# Change options
lakefetch_options(
  buffer_distance_m = 20,      # GPS accuracy buffer
  angle_resolution_deg = 10,   # Direction resolution (degrees)
  max_fetch_m = 30000,         # Maximum fetch distance
  use_parallel = TRUE          # Parallel processing for multiple lakes
)

# Reset to defaults
lakefetch_reset_options()

NHD Integration

If the nhdplusTools package is installed, lakefetch can add hydrological context from the National Hydrography Dataset: - Lake outlet and inlet locations - Distance and direction to outlet/inlets from each site - Connectivity classification (Headwater, Drainage, Terminal, Isolated) - Outlet stream order - Watershed area

# NHD context is added automatically if available
results <- fetch_calculate(sites, lake, add_context = TRUE)

# Check connectivity
table(results$results$connectivity_class)

Working with Multiple Lakes

If your sites span multiple lakes, lakefetch handles this automatically:

# Sites are assigned to their containing lake polygon
sites_with_lakes <- assign_sites_to_lakes(lake$sites, lake$all_lakes)

# Check assignment
table(sites_with_lakes$lake_name)

Exporting Results

# To CSV (without geometry)
write.csv(sf::st_drop_geometry(results$results),
          "fetch_results.csv", row.names = FALSE)

# To GeoPackage (with geometry)
sf::st_write(results$results, "fetch_results.gpkg")

# Export ray geometries for GIS
rays <- create_ray_geometries(results)
sf::st_write(rays, "fetch_rays.gpkg")