While there are several hydrography datasets containing the acronym “NHD” available for download, there are major differences a user can use to determine which is the best choice for their work and which dataset they have downloaded. More information on the similarities and differences in these datasets will be covered in upcoming newsletter articles.
Which NHD Product Do You Need and Which Do You Have?
Which Dataset Should I Use?
The choice between the National Hydrography Dataset (NHD), NHDPlus Version 2 (NHDPlus V2), and NHDPlus High Resolution (NHDPlus HR) depends on your needs.
The datasets differ by currency, level of detail, and geographic area. If you need the most up-to-date and detailed hydrography (1:24K or more detailed), then downloading the most current version of the NHD is the best choice. It is also the only dataset with coverage of the conterminous U.S. (CONUS), Alaska, Hawaii, Puerto Rico, U.S. Virgin Islands, and several Pacific Island territories.
NHDPlus HR is based on 1:24K or more detailed NHD, Watershed Boundary Dataset (WBD), and a 10 meter digital elevation model (DEM), whereas NHDPlus V2 is based on 1:100K NHD, WBD, and a 30 meter DEM. Both NHDPlus V2 and NHDPlus HR cover CONUS, Hawaii, Puerto Rico and the U.S. Virgin Islands, and several Pacific Island territories. NHDPlus HR is being developed for Alaska; NHDPlus V2 is not available for Alaska.
The NHDPlus V2 and NHDPlus HR are geospatial models that can be used to represent the flow of water across the landscape and through the stream network. Both NHDPlus V2 and NHDPlus HR include elevation-derived catchment areas for each NHDFlowline in the NHD snapshots that come with the datasets. Additional Value-Added Attributes (VAAs) that assist with stream network navigation and analysis can be associated with the catchments, greatly adding to the ability to functionality of the dataset. The VAAs are available in both the NHDPlus V2 and NHDPlus HR. But, the VAAs sometimes differ between the datasets. Monthly and annual average flow estimates are available in NHDPlus V2, whereas NHDPlus HR has mean annual flow estimates, but not the mean monthly estimates.
|NHD||NHDPlus HR||NHDPlus V2|
|Currency||New edits available monthly (bimonthly for state downloads)||Based on snapshot of 1:24K NHD from 2015-2019 timeframe (differs by area)||Based on snapshot of 1:100K NHD from 2011 timeframe|
|Level of Detail||1:24K or more detailed (1:63,360 or more detailed in AK)||1:24K or more detailed||1:100K (more detailed for HI, U.S. Virgin Islands, Puerto Rico, and Pacific Island territories)|
|Geography||CONUS, AK, HI, Puerto Rico, U.S. Virgin Islands, and several Pacific Island territories||CONUS, HI, Puerto Rico, U.S. Virgin Islands, and several Pacific Island territories; in development in AK||CONUS, HI, Puerto Rico, U.S. Virgin Islands, and several Pacific Island territories; not available in AK|
|Additional Attributes||None||Value-Added Attributes, Mean Annual Flow Estimates||Value-Added Attributes, Mean Annual and Mean Monthly Flow Estimates|
|Additional Features||None||Elevation-derived catchment areas based on 1:24K NHD and 10 meter DEM||Elevation-derived catchment areas based on 1:100K NHD and 30 meter DEM|
There are good historical reasons for the existence of these similarly-named datasets. If you’re interested to learn more, please see The road to NHDPlus — Advancements in digital stream networks and associated catchments.
National Hydrography Dataset (NHD)
The NHD is a vector dataset with no accompanying raster datasets. Currently, NHD is available in both Esri file geodatabase and shapefile formats in the following extents:
- 8-digit hydrologic unit (HU8)
- 4-digit hydrologic unit (HU4)
NHD datasets are distributed in .zip files having beginning with “NHD_H_”, with the rest of the filename specifying the specific geographic area covered, the type of extent covered, and the format of the data. Figures 1a and 1b show examples of NHD distribution files. Note, the .jpg thumbnail view and .xml files are also contained in the .zip file. The .zip file is the only one you need to download.
NHD downloadable files are updated frequently (monthly or bimonthly). You can find the date the dataset was published in the .xml file. Look for the “<pubdate>” tag.
All NHDPlus V2 and NHDPlus HR datasets contain a snapshot of the version of NHD version used to create the dataset. These snapshot versions of NHD may be different from the most current NHD.
NHDPlus Version 2 (V2) is distributed by the Environmental Protection Agency (EPA), and was released in 2012 (NHDPlus V1 was released in 2006). NHDPlus V2 is based on a 2011 snapshot of the 1:100K NHD, which is a precursor to the NHD currently managed by USGS and mapped at 1:24K or more detailed. The 1:100K hydrography represented in the NHDPlus V2 is much less detailed than current NHD. The 1:100K NHD is no longer distributed by USGS, but is still available as part of the NHDPlus V2 dataset download.
The NHDPlus V2 is delivered in multiple compressed files containing raster or vector data for each vector processing unit (VPU). Figure 2 shows an example of NHDPlus V2 distribution files. The VPUs for NHDPlus V2 generally represent a 2-digit hydrologic unit. Filenames for NHDPlus V2 begin with “NHDPlusV21_” (for Version 2.1, the current minor sub-version of what is called NHDPlus Version 2 generally.)
The NHDPlus V2 User Guide is available from the "Documentation" section on the EPA National Hydrography Dataset Plus webpage.
For additional NHDPlus V1/V2 Support please email firstname.lastname@example.org.
Although the NHDPlus HR is modeled after the NHDPlus V2, the two datasets have slightly different content, table/field naming, and geographic availability. The biggest difference between NHDPlus HR and NHDPlus V2 is in the underlying NHD each is based upon. NHDPlus HR is based on relatively current NHD, at 1:24K or better. The NHDPlus V2 is based on an older, less detailed, 1:100,000-scale NHD, which has not been updated since 2012. NHDPlus HR updates using current NHD, WBD, and 3DEP elevation data are underway, and NHDPlus HR is being developed for Alaska.
The NHDPlus HR is distributed in two compressed datasets: one for the vector files in Esri file geodatabase format and a second for the raster components in GeoTIFF format. Figure 3 shows an example of NHDPlus HR distribution files. These files cover 4-digit hydrologic unit vector processing units (VPUs), except in Alaska, where the VPUs are 8-digit hydrologic units. NHDPlus HR distribution files begin with “NHDPLUS_H_”.
NHDPlus HR files are not updated as frequently as NHD. As with NHD, you can find the date the dataset was published in the .xml file. Look for the “<pubdate>” tag.
The user’s guide for the NHDPlus HR is available at the USGS Publications Warehouse.