USGS, with assistance from Horizon Systems, is well into a project to produce High Resolution NHDPlus (NHDPlus HR). NHDPlus HR will be built from:

• The High Resolution National Hydrography Dataset (1:24,000-scale or better),
• The 1/3 arc-second National Elevation Dataset (approximately 10 meter ground spacing), and
• The Watershed Boundary Dataset.

For more information about these input datasets, visit: NHD at http://nhd.usgs.gov, NED at http://ned.usgs.gov and WBD at http://nhd.usgs.gov/wbd.html.

NHDPlus HR will differ from NHDPlusV2 in several ways:

• There is generally better spatial correspondence among the input datasets for NHDPlus HR.
• The native data format of NHDPlus HR will be file geodatabase and raster tif's rather than shapefiles and grids.
• The unit of processing and distribution will be HUC4s rather than HUC2s.
• The hydro-enforcement process has been significantly improved.
• In NHDPlus HR, EROM flow estimates will be mean annual, rather than mean annual and mean monthly as in NHDPlusV2.

The project has 5 phases:

• Phase 1: NHDPlus HR Build/Refresh Software Development

During this phase, the software to produce the NHDPlus vector components, raster components, and attributes was designed, programmed and validated.

• Phase 2: Data Validation

During this phase, the Build/Refresh software was used in production to produce NHDPlus HR for hydrologic regions 06 and 01. These data were subjected to extensive review to determine that the Build/Refresh software and workflow were producing expected results.

• Phase 3: Data Production and Release

This phase is on-going and produces NHDPlus HR data by 4-digit hydrologic units for the entire conterminous U.S. and parts of Alaska. As data is produced, it is distributed on the NHD website http://nhd.usgs.gov. As different hydrographic conditions are encountered, the Build/Refresh software is adjusted to handle the new data.

Production of NHDPlus HR begins with the USGS National Geospatial Technical Operations Center (NGTOC) running the NHD data through the NHDPlus QAQC checks and fixing any data problems found. A 4-digit hydrologic unit (HUC4) dataset of NHD and WBD is delivered to the NHDPlus HR Build/Refresh process. The 19 step NHDPlus HR Build/Refresh process is performed which includes QA throughout. Finally, the data is delivered to the USGS Staged Products group for distribution.

• Phase 4: User Error Reporting

As the water resources community begins to use the data, data errors in NHD and WBD will be discovered and corrected both by state stewards and by USGS. Also during this time, state stewards will continue to update and improve high resolution NHD and WBD. Both data corrections and enhancements will lead to phase 5.

• Phase 5: Data Refresh

As each 4-digit hydrologic unit of NHDPlus HR data moves into Data Refresh, it will be regenerated with the updated NHD, WBD and NED. Change thresholds will be used for the NHD, WBD, and NED to determine when a HUC4 should be refreshed.

PROJECT STATUS: Phases 1 and 2 of the project are completed. Phase 3 of the project has produced NHDPlus HR data for most of the conterminous U.S. Phases 4 is on-going as data is published in Phase 3.