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USGS NLDI workflows

GeoLibre includes a USGS NLDI plugin for tracing a point to the National Hydrography Dataset (NHD) network and displaying the result on the map.

Trace a map point

  1. Open Plugins → USGS NLDI.
  2. Choose Complete flowline, Upstream only, or Downstream only.
  3. Click a point on the map.

The plugin calls the NLDI nldi-flowtrace process. It draws the returned NHD flowline in blue, and, when the point is not already on a flowline, the elevation-based raindropPath in orange. The clicked point is marked in red.

Basin workflow

After a trace, GeoLibre calls NLDI hydrolocation for the clicked coordinate. When a COMID is available, use Basin from hydrolocation to request the simplified upstream basin. The selected COMID also enables navigation options for upstream mainstem, upstream tributaries, downstream mainstem, and downstream diversions. Set a distance in kilometres and choose 1. Load sources & plot navigation to load the available catalogs. You can then choose NHD flowlines, streamgages (ca_gages or nwissite), groundwater wells (nwisgw), Geospatial Fabric points (gfv11_pois), HUC12 pour points (huc12pp), New Mexico water sites (nmwdi-st), or another catalog returned by NLDI. Choose Plot another navigation layer to draw the selected features on the map; flowlines are purple and point catalogs are also rendered by the navigation layer. These are chained workflows: the selected map point feeds hydrolocation, its COMID feeds the basin or navigation request, and the result is rendered on the map.

Use Export rendered results to GeoJSON to save the selected point, flowline, raindrop path, basin, and any plotted navigation features as one GeoJSON FeatureCollection. The _nldiLayer property identifies each result group in the exported file.

Use Add rendered results to GeoLibre Layers to copy the current NLDI results into the Layers panel. GeoLibre creates one USGS NLDI results group containing the flowline, raindrop path, selected point, basin, and every navigation result plotted so far. These copied layers remain in the project even after the temporary NLDI map overlays are cleared.

The plugin uses the public USGS service at https://api.water.usgs.gov/nldi; network access and the service’s CORS policy are required.