This data release contains a crosswalk between subwatersheds (12-digit hydrologic unit codes; hereafter, HUC12s) and hydrologic regions (sometimes called "Van Metre regions"). This crosswalk allows for data at the HUC12 scale to be summarized regionally. Hydrologic regions are boundaries of hydrologically distinct areas modified from hydrologic subregions (4-digit Hydrologic units; HUC4s) defined by Qi and Mason (2023; https://doi.org/10.5066/P98194QR) for use in Van Meter et al. (2020; https://doi.org/10.1007/s10661-020-08403-1). These hydrologic regions should not be confused with 2-digit hydrologic unit codes (HUC2 or HU2), also referred to as "hydroregions" or "HydroRegions." Although they are similar in number and size, they represent different concepts: HUC2s denote drainage basins of major rivers, while the hydrologic regions defined by Van Metre et al. (2020) are areas with similar hydrology and water availability concerns that were originally developed to help inform selection of basins for more in-depth sampling, analysis, and modeling. For comparative purposes, we further grouped the hydrologic regions into four CONUS aggregated hydrologic regions based on location and shared water-availability characteristics and challenges (Northeast through Midwest, Southeast, High Plains, and Western). The HUC12 boundaries used are those made available in the Mainstems data release (https://doi.org/10.5066/P92U7ZUT), which are modified from the stable NHDPlusV2 snapshot of the Watershed Boundary Dataset.

This data release contains fractional intersectional weights used to crosswalk data from the National Water Use Program to the National Integrated Water Availability Assessment (IWAAs) projects. The Watershed Boundary Dataset (WBD; https://www.usgs.gov/national-hydrography/watershed-boundary-dataset) is a companion dataset to the National Hydrography Dataset and contains polygons that define the spatial boundaries of hydrologic units (i.e., the area of land the landscape that drains into a portion of the stream network). These are periodically updated as these boundary definitions are refined by incorporating better, more localized data. When aggregating data from multiple sources that rely on data from the WBD, a situation can occur where different datasets rely on different versions (or “snapshots”) of the WBD. This was the case for the IWAAs National Report which relied upon data using a version of the WBD found in the Mainstem Rivers data release (https://doi.org/10.5066/P92U7ZUT) as well as data that relied upon a version used by the National Water Use Program (https://doi.org/10.5066/P9FUL880). This dataset is the output of a pipeline of R code published as a software release (https://doi.org/10.5066/P1UANON8) and contains the fraction of spatial overlap (i.e., weights) between the subwatershed (HUC12) boundaries from these two versions of the WBD. These weights can be used as a crosswalk between the two snapshots of the WBD.

This child item provides a snapshot of the watershed boundary dataset which consists of a shapefile with 87,020 12-digit hydrologic unit codes (HUC12) for the conterminous United States retrieved 10/26/2020. The National Watershed Boundary Dataset (WBD) is a comprehensive set of digital spatial data that represents the surface drainages areas of the United States. Although versions of the WBD are published as part of U.S. Geological Survey National Hydrography Products, the version used to produce the water-use reanalysis was not archived and is provided here. This dataset is part of a larger data release using machine learning to predict public supply water use for 12-digit hydrologic units from 2000-2020. Public-supply water use estimates for the HUC12s included in this shapefile are provided on the data release main landing page and on the public supply water use machine learning model child item. This page includes the following file: WBD_HUC12_CONUS_pulled10262020.zip - a zip file containing a shapefile with 12-digit hydrologic units in the conterminous United States

This USGS data release includes a shapefile of outlet point locations for selected 12-digit hydrologic units (HU12s) from the Watershed Boundary Dataset (WBD), dated August 13, 2020 (U.S. Geological Survey and others, 2020), draining to the Gulf of Mexico in the south-central and southeastern United States. The outlet locations were derived by combining the WBD boundaries with flow direction grids from the National Hydrography Dataset Plus (NHDPlus) v 2.1 (U.S. Environmental Protection Agency and U.S. Geological Survey, 2012). Most of the outlet locations were determined by finding the cell with highest flow accumulation from the NHDPlus flow-direction grids within each WBD HU12 boundary. Some locations were found to be inaccurate upon inspection, and other sources were used for the locations as described in the attribute description and process description sections of this document. A shapefile of the HU12 boundaries from the WBD (U.S. Geological Survey and others, 2020) for the study area also is included in this data release for comparison to outlet locations. References cited: U.S. Environmental Protection Agency and U.S. Geological Survey, 2012, National Hydrography Dataset Plus - NHDPlus, version 2.1, accessed August 2020 at https://nhdplus.com/NHDPlus/NHDPlusV2_data.php. U.S. Geological Survey, U.S. Department of Agriculture - Natural Resource Conservation Service, U.S. Environmental Protection Agency, and other Federal, State, and local partners, 2020, Watershed Boundary Dataset - WBD, accessed August 2020 at https://apps.nationalmap.gov/viewer/.

This data set is a complete digital hydrologic unit boundary layer to the Subwatershed (12-digit) 6th level for the entire United States. This data set consists of geo-referenced digital data and associated attributes created in accordance with the "Federal Guidelines, Requirements, and Procedures for the National Watershed Boundary Dataset; Chapter 3 of Section A, Federal Standards, Book 11, Collection and Delineation of Spatial Data; Techniques and Methods 11-A3" (04/01/2009). http://www.ncgc.nrcs.usda.gov/products/datasets/watershed/index.html . Polygons are attributed with hydrologic unit codes for 4th level sub-basins, 5th level watersheds, 6th level subwatersheds, name, size, downstream hydrologic unit, type of watershed, non-contributing areas and flow modification.

In 2013, the Regional Stream Quality Assessment (RSQA) study was started as part of the U.S. Geological Survey (USGS) National Water Quality Assessment (NAWQA) project. One of the objectives of the RSQA is to characterize the relationships between water-quality stressors and stream ecology and subsequently determine the relative effects of these stressors on aquatic biota within the streams (Garrett and others, 2017; Journey and others, 2015; Coles and others, 2019; Sheibley and others, 2017; May and others, 2020). The study was implemented in five regions across the United States (U.S.); the Midwest (MSQA) in 2013, the Southeast (SESQA) in 2014, the Pacific Northwest (PNSQA) in 2015, the Northeast (NESQA) in 2016, and California (CSQA) in 2017. To meet this objective, a framework of fundamental geospatial data was required to develop physical and anthropogenic characteristics of each study region, sampled sites, and corresponding watersheds and riparian zones. This dataset represents the riparian-zone boundaries for 476 water-quality sites sampled for the RSQA and is one of the four fundamental geospatial data layers that were developed for the RSQA study.

This dataset provides numerical and categorical descriptions of 48 basin characteristics for 9,314 ungaged basins coinciding with 12-digit hydrologic unit code (HUC12) pour points that drain to the Gulf of Mexico. Characteristics are indexed by National Hydrography Dataset (NHD) version 2 COMID (integer that uniquely identifies each feature in the NHD) and HUC12 identifying number. The variables represent mutable and immutable basin characteristics and are organized by characteristic type: physical (5), hydrologic (6), categorical (12), climate (6), landscape alteration (7), and land cover (12). Mutable characteristics such as climate, land cover, and landscape alteration variables are reported in decadal increments (for example, average percent forest for the decade 1950-1959, 1960-1969, etc). The majority of basin characteristics in this dataset were calculated using divergence-routing methods and are often referred to as “network-accumulated”. This method uses a modified routing database to navigate the NHDPlus reach network to aggregate (accumulate) the values derived from the reach catchment scale (Schwarz, G.E., and Wieczorek, M.E., 2018, Database of modified routing for NHDPlus version 2.1 flowlines: ENHDPlusV2_us: U.S. Geological Survey data release, https://doi.org/10.5066/P9PA63SM ). In four instances, values are also provided for the entire catchment above a site and area designated using the “CAT_” prefix.

Two methods of calculating hydrologic alteration were applied to modeled daily streamflow data for 9,201 12-digit hydrologic unit code (HUC12) pour points draining to the Gulf of Mexico (Robinson and others, 2020). The first method is a new modified method of calculating ecosurplus and ecodeficit called hydro change. For this project, ecosurplus and ecodeficit have been combined to assess overall hydrologic regime change. The second method is the confidence interval hypothesis test (Kroll and others, 2015). The first method is a means of quantifying hydrologic alteration while the second is a hypothesis test to simply determine if statistically significant alteration has occurred. Both methods are employed to determine which is best at analyzing alteration of the hydrologic regime in the Gulf Coast Ecosystem Restoration Council (RESTORE) study area. Statistical analysis was done in RStudio (2020). The data release includes four attached files: (1) metadata .xml file, (2) csv with the p-values for each HUC12, (3) csv with results from the hydrologic change analysis, and (4) the shapefile of the pour point locations for the HUC12s used in the analyses.

In 2013, the Regional Stream Quality Assessment (RSQA) study was started as part of the U.S. Geological Survey (USGS) National Water Quality Assessment (NAWQA) project. One of the objectives of the RSQA is to characterize the relationships between water-quality stressors and stream ecology and subsequently determine the relative effects of these stressors on aquatic biota within the streams (Garrett and others, 2017; Journey and others, 2015; Coles and others, 2019; Sheibley and others, 2017; May and others, 2020). The study was implemented in five regions across the United States (U.S.); the Midwest (MSQA) in 2013, the Southeast (SESQA) in 2014, the Pacific Northwest (PNSQA) in 2015, the Northeast (NESQA) in 2016, and California (CSQA) in 2017. To meet this objective, a framework of fundamental geospatial data was required to develop physical and anthropogenic characteristics of each study region, sampled sites, and corresponding watersheds and riparian zones. This dataset represents the five study region boundaries for the RSQA and is one of the four fundamental geospatial data layers that were developed for the RSQA study.

A crosswalk table between NHDPlus version 2.1 flowlines (using the unique field COMID) and the Watershed Boundary Dataset (WBD) 12-digit-hydrologic units (HU-12) is provided for the 48 contiguous United States. The crosswalk table provides a WBD HU-12 assignment for every networked flowline in the NHDPlus. In this way, the network developed for navigation and modeling, NHDPlus, is aligned with accounting units of the WBD HU-12s to the extent possible given the assumptions that were made in creating each. A crosswalk table for NHDPlus isolated sinks was produced by a simple overlay process where the sinks were assigned HU-12 values based on their position relative to the WBD snapshot HU-12s. This table was integrated with the flowline associations into one crosswalk table for both feature types. There is good alignment between aggregated NHDPlus catchments and WBD HU-12 units in many locations. These are areas where the flows and chemical or nutrient loads that are accumulated leave the HU-12 at a single outlet and are passed down to the next HU-12 downstream (or to the coast) as is assumed in the WBD model. A second pass through the data was made to account for any secondary outlet from each HU-12. The location of a secondary outlet with a significant drainage from that HU was identified in the alignment with NHDPlus. This resulted in a reduction in areas of mismatch as well as an improved crosswalk table. The crosswalk table should be used with caution in areas where efforts could be made to improve the data. For example, with medium-resolution NHD, a better definition of flow direction of the flowlines in Southern Florida would result in more flowlines being included in the “networked” flowlines with catchments, and that, in turn, would result in better alignment between NHDPlus catchments and HU-12s. Correcting errors in either the medium-resolution NHD or WBD would improve the alignment between the two datasets.