{cc8c85ea-1944-40f8-8513-ce7ad82fe4a7} eng; USA utf8 dataset EnviroAtlas Coordinator U.S. Environmental Protection Agency, Office of Research and Development-Sustainable and Healthy Communities Research Program, EnviroAtlas Geospatial Data Owner (919) 541-3832 109 T.W. Alexander Drive Research Triangle Park NC 27709 EnviroAtlas@epa.gov https://www.epa.gov/enviroatlas pointOfContact 2025-07-10 ISO 19115 Geographic Information - Metadata ISO 19115:2003/Cor.1:2006(E) EnviroAtlas - Watershed Index Online Hydrologically Connected Zone Mask for the Conterminous United States 2022-06-01 publication U.S. EPA Office of Research & Development (ORD) - National Exposure Research Laboratory (NERL) Research Triangle Park NC publisher US Environmental Protection Agency (US EPA) originator The Hydrologically Connected Zone (HCZ) Mask was determined using grid analysis to combine surface water features in the United States from three datasets: First, the surface water features were extracted from the 2019 National Land Cover Database (NLCD) produced by the Multi-Resolution Land Characteristics Consortium. Features included are 'Open Water' (code 11), 'Woody Wetlands' (code 90) and 'Emergent Herbaceous Wetlands' (code 95). Second, the flowline and waterbody features as represented in the catseed grid from the National Hydrography Dataset (NHD) Plus version 2.1. Third, all areas contiguous to surface water that also have a wetness index value of 550 or greater. The wetness index, also known as the compound topographic index (CTI), is a steady state wetness index. It is commonly used to quantify topographic control on hydrological processes. The combination of these three datasets represents the Hydrologically Connected Zone. This dataset was produced by the US EPA to support research and online mapping activities related to the Watershed Index Online (WSIO) and EnviroAtlas. EnviroAtlas (https://www.epa.gov/enviroatlas) allows the user to interact with a web-based, easy-to-use, mapping application to view and analyze multiple ecosystem services for the contiguous United States. The dataset is available as downloadable data (https://edg.epa.gov/data/Public/ORD/EnviroAtlas) or as an EnviroAtlas map service. Additional descriptive information about each attribute in this dataset can be found in its associated EnviroAtlas Fact Sheet (https://www.epa.gov/enviroatlas/enviroatlas-fact-sheets). This data was produced for the Watershed Index Online and Recovery Potential Screening Tools. It was used to summarize landscape information within hydrologically connected zones and create indicators of water quality. This data could be used in conjunction with other data to identify areas in the landscape that have a connectivity to water or to summarize data within this zone. The overall goal of EnviroAtlas is to employ and develop the best available science to map indicators of ecosystem services production, demand, and drivers for the nation. completed EnviroAtlas Coordinator U.S. Environmental Protection Agency, Office of Research and Development-Sustainable and Healthy Communities Research Program, EnviroAtlas Geospatial Data Owner (919) 541-3832 109 T.W. Alexander Drive Research Triangle Park NC 27709 EnviroAtlas@epa.gov https://www.epa.gov/enviroatlas pointOfContact asNeeded Ecosystem Environment theme EPA GIS Keyword Thesaurus Ecosystem Services EnviroAtlas Environment Environmental Atlas Land Cover Management Riparian Surface Water Water Wetlands theme EnviroAtlas Alabama Arizona Arkansas California Colorado Connecticut Delaware Florida Georgia Idaho Illinois Indiana Iowa Kansas Kentucky Louisiana Maine Maryland Massachusetts Michigan Minnesota Mississippi Missouri Montana Nebraska Nevada New Hampshire New Jersey New Mexico New York North Carolina North Dakota Ohio Oklahoma Oregon Pennsylvania Rhode Island South Carolina South Dakota Tennessee Texas United States Utah Vermont Virginia Washington Washington DC West Virginia Wisconsin Wyoming place None https://edg.epa.gov/EPA_Data_License.html otherRestrictions Use Constraints: None. Please check sources, scale, accuracy, currency and other available information. Please confirm that you are using the most recent copy of both data and metadata. Acknowledgement of the EPA would be appreciated. otherRestrictions Access Constraints: None PUBLIC https://project-open-data.github.io/schema/#accessLevel Standard Technical Controls eng; USA environment -128.02839229 -65.20336449 22.7348894 51.6773602 2019-01-01 true Entity and Attribute Information Entity and Attribute Overview: A comprehensive list of metric creation steps is included in the Processing Steps metadata element. Notes on the wetness index: The wetness index was derived from the NHDPlus flow accumulation (usa_fac) and the slope of the DEM (usademslope) using the following equation: grid wet_ndx = 100*(ln (flow accumulation/tan(slope)) + 3x3 mean of ln (flow accumulation/tan(slope))/2 The values were not scaled by an area factor and were smoothed by ½ to make up for some inconsistencies across the national DEM, because of differences in the resolution of the DEM by USGS quad sheet. The data were then compared to the 2001 NLCD wetland classes, Region 4 FEMA flood zone classes, and Georgia National Wetlands classes. The threshold for value of 800, of the wetness index, represents areas which are usually wet. This was primarily based on the 2001 NLCD comparison, but also supported by the other analyses. (Moore,1991, Wollock, 1993) Moore, I. D., Grayson, R. B., and Ladson, A. R., 1991, Digital terrain modelling: A review of hydrological, geomorphological and biological applications. Hydrological Processes, 5, 3-30. Wolock, D.M., 1993, Simulating the variable-source-area concept of streamflow generation with the watershed model TOPMODEL: U.S. Geological Survey Water-Resources Investigations Report 93-4124, 33 p. Notes: This raster dataset was calculated from NHDPlusV2.1 source data by Dr. John Richardson. There were no spatial changes to the NHD FD and FAC raster datasets after the original download on June 18, 2013. Therefore, the wetness index raster dataset from WSIO version 2 is used for calculations for the version 3 updates. Confirmed no change by running NHD version tool, CheckNHDPlusV21Currentness. Entity and Attribute Detail Citation: https://www.epa.gov/enviroatlas/enviroatlas-fact-sheets EnviroAtlas Coordinator U.S. Environmental Protection Agency, Office of Research and Development-Sustainable and Healthy Communities Research Program, EnviroAtlas Geospatial Data Owner (919) 541-3832 109 T.W. Alexander Drive Research Triangle Park NC 27709 EnviroAtlas@epa.gov https://www.epa.gov/enviroatlas distributor https://gispub.epa.gov/arcgis/rest/services/r4/HCZ/MapServer download Download The URL providing direct access to the downloadable dataset. download https://www.epa.gov/enviroatlas/enviroatlas-data ESRI:ArcGIS API The endpoint of a web service to access the dataset (REST endpoint, WMS GetCapabilities URL, or a SOAP WSDL endpoint). webMapService https://www.epa.gov/enviroatlas information Documentation URL for accessing related documents such as data dictionary, technical information about a dataset, developer documentation, etc. information dataset Horizontal Positional Accuracy Report Data were collected using methods that have unknown accuracy (EPA National Geospatial Data Policy [NGDP] Accuracy Tier 10). For more information, please see EPA's NGDP at http://epa.gov/geospatial/policies.html Features represented have not been tested for completeness Features represented have not been tested for completeness Tests for integrity have not been performed. This lineage was generated by the FGDC CSDGM to 19139 transformation Acquired NHDPlusV2.1 catseed grid. 2022-06-01T00:00:00 Acquired 2019 NLCD raster. 2022-06-01T00:00:00 Reclassify NLCD water and wetland classes (11, 90, 95) to a value of 1, and all other classes to 0. 2022-06-01T00:00:00 Reclassify NHDPlusV2.1 catseed grid so that all NHD flowline cells have a value of 1 all other values are 0. 2022-06-01T00:00:00 Add the NHDPlus catseed grid and the reclassified NLCD grid using the Plus function in ArcGIS. 2022-06-01T00:00:00 In the new raster output by the Plus function, reclassify values 1 and 2 to 1, all other values to 0; name this raster h2o_01. 2022-06-01T00:00:00 In h2o_01, reclassify values 1 to 0, and all other values to nodata to produce a raster with values of 0 for water and NoData for all other cells; name this raster h2o_src. This is the Water Mask layer. 2022-06-01T00:00:00 Create the Wetness Index layer using the NHDPlusV2.1 flow accumulation (usa_fac) and the slope of the DEM (usademslope) using the following equation: grid wet_ndx = 100*(ln (flow accumulation/tan(slope)) + 3x3 mean of ln (flow accumulation/tan(slope))/2. See Overview section for additional details. 2022-06-01T00:00:00 All cells with a value greater than 550 were reclassified as a 1 in the Wetness Index layer, all other values were reclassified as 0. 2022-06-01T00:00:00 Add layer of all surface water (h2o_01) and the Wetness Index > 550 Layer using the Plus function in ArcGIS. 2022-06-01T00:00:00 Create layer by reclassifying values of 1&2 to 1 and all other values to nodata; this layer shows all surface water from the NLCD or the NHDPlusV2 catseed grid, plus land with Wetness Index > 550. 2022-06-01T00:00:00 Using a raster dataset with all water cells having a value of 0 and all others values as no data (h2o_src), run the Cost Distance function with a maximum distance of 45,000. 2022-06-01T00:00:00 Reclassify values 0-45,000 to 1 and nodata values to nodata to create the HCZ Mask. 2022-06-01T00:00:00 unknown 2029-02-11 This metadata was automatically generated from the FGDC Content Standard for Digital Geospatial Metadata standard (version FGDC-STD-001-1998) using the 2024-02-09T11:11:00 version of the FGDC CSDGM to ISO 19139 transform. EnviroAtlas Coordinator U.S. Environmental Protection Agency, Office of Research and Development-Sustainable and Healthy Communities Research Program, EnviroAtlas Geospatial Data Owner (919) 541-3832 109 T.W. Alexander Drive Research Triangle Park NC 27709 EnviroAtlas@epa.gov https://www.epa.gov/enviroatlas pointOfContact