Comparison of four snapshots of Watershed Boundary Dataset Twelve-Digit Hydrologic Units

This data release contains a registry and comparison of the representation of twelve-digit hydrologic unit code (HUC) hydrologic unit polygons from four snapshot versions of the Watershed Boundary Dataset (WBD). The four versions were chosen due to their pressence in broadly: National Hydrologic Dataset Plus V2.1 (nhdpv2) and National Hydrologic Dataset Plus High Resolution (nhdphr) products, use in the 2025 National Integrated Water Availability Assessment (niwaa), and the importance of the 2025 Watershed Boundary Dataset containing the final version of the Coterminous United States WBD (final). They are identified as “nhdpv2”, “nhdphr”, “niwaa”, and “final” respectively. Note that the niwaa WBD snapshot for the 2025 assessment is from 2020. File Summary: - The registry JSON file contains only the HUC identifier and date it was last edited for each of the four WBD snapshots. - The GPKG file contains the most recently geometry from one of the four snapshots for every HUC identifier in the registry. Note that polygons in this GPKG are the most recent and may overlap HUCs from earlier snapshots. It also contains attributes indicating whether a HUC was deprecated, which snapshots it exists in, and whether it changed from one snapshot to the next. - Four comma separated files, one for each snapshot comparison, contain polygon area attributes for the both the entire HUC polygon from each snapshot and each partial polygon implied by the spatial intersection of the compared pair of snapshots. Comparisons were performed for four pairs of snapshots: 1) nhdpv2 to nhdphr, 2) nhdpv2 to niwaa, 3) niwaa to final, and 4) nhdphr to final. The nhdphr snapshot is composed of several regional subset snapshots taken over the period that nhdphr was being produced. In contrast, the niwaa snapshot is a complete snapshot of the Watershed Boundary Dataset taken at a single point in time. Due to this, some hydrologic units defined in the nhdphr snapshot are older than those in the niwaa snapshot and others are newer. Because of this overlap, direct comparison of the nhdphr and niwaa snapshots was not possible. If additional comparisons not presented in this data release are required, the script used to generate the comparisons is included as an ancillary file.