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. 2.0, September 2025)

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. 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), three rasters in tiff format developed for calculation of basin characteristics packaged in a zip file (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).

As part of a data release revision in September 2025 (see file "versionhistory.txt"), a child item containing alternate versions of the basin characteristic rasters mentioned above for use in the StreamStats application for Tennessee was added to the data release. While the rasters created for use in StreamStats represent the same information as the basin characteristic rasters generated for the flood frequency study, they have a different spatial reference, spatial extent, cell size, and range of values than the rasters used for the flood-frequency analysis. 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.

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 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), and the percentages of land within the Piedmont level 3 ecoregion and the Ridge and Valley level 3 ecoregion. The rasters included in this data release represent the percentage of 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.

For more information about the sources used for basin delineation and basin characteristic calculations, see the metadata documents associated with this data release.

First release: 2024

Revised: September 2025 (ver. 2.0)d with this data release.