Basin characteristics in support of generalized least-squares (GLS) regression for 136 USGS streamgages in urban areas in Tennessee and parts of Alabama, Georgia, Mississippi, North Carolina, and South Carolina (ver. 3.0, June 2026)

This data release contains a dataset of geospatial and tabular data used in support of a flood-frequency study of urban streams in Tennessee and parts of Alabama, Georgia, Mississippi, North Carolina, and South Carolina (Wagner and Ladd, 2026). The dataset includes data used in the development of generalized least-squares (GLS) regression equations for predicting streamflows at ungaged locations in the study area corresponding to 50-, 20-, 10-, 4-, 2-, 1-, 0.5-, and 0.2-percent annual exceedance probabilities. Included in the dataset are shapefiles of the streamgage basins and outlets used in the study packaged in a zip file (TNurbanFFreq_Basins and TNurbanFFreq_Outlets feature classes in TNurbanFFreq_Basins_and_Outlets.zip), four rasters in tiff format developed for calculation of basin characteristics packaged in a zip file (nlcd2011_imperviousness_percent.tif, nlcd2011_developed_percent.tif, piedmont_eco_lvl3_percent.tif, and ridge_and_valley_eco_lvl3_percent.tif in Basin_Characteristic_Rasters.zip), and a table in csv format listing the basin characteristics that were tested as explanatory variables for development of the regression equations (BasinCharsTested.csv). The data contained in the shapefiles of basin polygons and outlet locations for streamgages used in the flood-frequency analysis were derived from various sources (Falcone, 2011; U.S. Environmental Protection Agency and U.S. Geological Survey, 2012; U.S. Geological Survey, 2019) further described in the Entity and Attribute section information in this metadata document related to the TNurbanFFreq_Basins.shp shapefile. The table from this data release listing the basin characteristics tested as explanatory variables predominately includes characteristics that were not used in the final GLS regression equations. The variables used in the final equations were drainage area, the percentage of developed land from the 2011 National Land Cover Database (NLCD; Homer and others, 2015; Dewitz and U.S. Geological Survey, 2021), and the percentages of land within the Piedmont level 3 ecoregion and the Ridge and Valley level 3 ecoregion (U.S. Environmental Protection Agency, 2013). The rasters included in this data release represent the percentages of imperviousness and developed land derived from the 2011 NLCD and the percentages of land within the Piedmont level 3 ecoregion and the Ridge and Valley level 3 ecoregion. As part of a data release revision in September 2025, a child item containing alternate versions of basin-characteristic rasters for use in the StreamStats application (U.S. Geological Survey, 2019) for Tennessee was added to the data release. Alternate versions of three of the rasters mentioned above were added to the child item in a zip file: nlcd2011_developed_percent_ss.tif, piedmont_eco_lvl3_percent_ss.tif, and ridge_and_valley_lvl3_eco_percent_ss.tif in Basin_Characteristic_Rasters_ss.zip. While the rasters created for use in StreamStats represent the same information as the basin characteristic rasters generated for the flood-frequency analysis, they have a different spatial reference, spatial extent, cell size, and range of values. Therefore, the information pertaining to the rasters generated for use in StreamStats is included in a separate metadata document associated with the child item. The data release revision also included addressing errors in the ancillary raster attribute tables associated with the original basin-characteristic rasters (nlcd2011_developed_percent.tif, piedmont_eco_lvl3_percent.tif, and ridge_and_valley_eco_lvl3_percent.tif in Basin_Characteristic_Rasters.zip). The tables associated with the rasters in the zip file were replaced, and the values described in the Entity and Attribute Information section of this metadata document were updated to reflect the corrected values in the raster attribute tables. As part of a second data release revision in June 2026, two versions of a raster representing the percentage of surface imperviousness from the 2011 NLCD (Homer and others, 2015; Dewitz and U.S. Geological Survey, 2021) were added to the data release. The imperviousness raster was used to screen streamgages for use in the flood-frequency analysis conducted as part of this study; streamgages with basins that had at least 10-percent impervious area based on calculations using the 2011 NLCD imperviousness raster were considered urban stations that could be used in the analysis. One version of the raster (nlcd2011_imperviousness_percent.tif) was clipped to the study area for the flood-frequency analysis covering Tennessee and parts of Alabama, Georgia, Mississippi, North Carolina, and South Carolina and is included in the Basin_Characteristic_Rasters.zip file served in this data release. The other version of the raster (nlcd2011_imperviousness_percent_ss.tif), generated for use in the StreamStats application (U.S. Geological Survey, 2019) for Tennessee, is included in the Basin_Characteristic_Rasters_ss.zip file associated with the child item in this data release. This version of the raster is used to determine if urban or rural equations should be applied to predict streamflows corresponding to annual exceedance probabilities for basins delineated using the application.

[
  "010:12"
]

{
  "fn": "David E Ladd",
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  "hasEmail": "mailto:deladd@usgs.gov"
}

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[
  "Alabama",
  "Georgia",
  "Mississippi",
  "North Carolina",
  "South Carolina",
  "Tennessee",
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  "Virginia",
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  "southeastern U.S.",
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  "streamgage"
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{
  "name": "U.S. Geological Survey",
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[
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