Estimating the Magnitude and Frequency of Floods at Ungaged Locations on Urban Streams in Tennessee and Parts of Alabama, Georgia, Mississippi, North Carolina, and South Carolina, Using Data Through the 2022 Water Year
Links
- Document: Report (4.03 MB pdf) , HTML , XML
- Data Releases:
- USGS Data Release - 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)
- USGS Data Release - At-site flood frequency for 139 urban streamgages in Tennessee and parts of Alabama, Georgia, Mississippi, North Carolina, and South Carolina using data through water year 2022
- USGS Data Release - Results 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. 1.1, January 2026)
- NGMDB Index Page: National Geologic Map Database Index Page (html)
- Download citation as: RIS | Dublin Core
Abstract
In 2024, the U.S. Geological Survey, in cooperation with the Tennessee Department of Transportation, updated the methods for predicting the magnitude and frequency of floods at ungaged locations on streams in urban areas in Tennessee. The study area included 136 streamgages in urban areas in Tennessee, Mississippi, Alabama, Georgia, South Carolina, and North Carolina that had at least 10 percent developed imperviousness in their basins as indicated by data from the 2011 National Land Cover Database. Regression equations were developed to predict streamflows corresponding to the 50-, 20-, 10-, 4-, 2-, 1-, 0.5-, and 0.2-percent annual exceedance probabilities (AEPs) and were incorporated into the StreamStats application. In generalized least-squares regression, the base-10 logarithm of drainage area, the percentages of the streamgage basins in developed land use, and the percentages of the streamgage basins in the Piedmont and Ridge and Valley Level 3 ecoregions were statistically significant in explaining the variability in annual peak streamflows in the study area. Drainage areas ranged from 0.164 to 93.4 square miles, the percentage of the streamgage basins in developed land use ranged from 26 to 100 percent, and the percentage of the streamgage basins in Piedmont and Ridge and Valley Level 3 ecoregions ranged from 0 to 100 percent. Pseudo R-squared values for the regression equations ranged from 0.86, or 86 percent, for the 50- and 20-percent AEPs (2- and 5-year floods) to 0.71, or 71 percent, for the 0.2-percent AEP (500-year flood). The average variance of prediction (in log base-10 units) ranged from 0.023 for the 20- and 10-percent AEPs to 0.05 for the 0.2-percent AEP. The average variance of prediction can be reported as a percentage of the predicted value, known as the standard error of prediction, which ranged from 35.8 percent for the 20-percent AEP (5-year flood) to 55.4 percent for the 0.2-percent AEP (500-year flood). Methods are presented for estimating annual peak streamflows for gaged locations, ungaged locations on gaged streams, and locations on ungaged streams.
Suggested Citation
Wagner, D.M., and Ladd, D.E., 2026, Estimating the magnitude and frequency of floods at ungaged locations on urban streams in Tennessee and parts of Alabama, Georgia, Mississippi, North Carolina, and South Carolina, using data through the 2022 water year: U.S. Geological Survey Scientific Investigations Report 2025–5104, 17 p., https://doi.org/10.3133/sir20255104.
ISSN: 2328-0328 (online)
Study Area
Table of Contents
- Abstract
- Introduction
- At-Site Flood-Frequency Analysis
- Basin Characteristics
- Regression Equations
- Applications of Regression Equations
- Summary
- Acknowledgments
- References Cited
| Publication type | Report |
|---|---|
| Publication Subtype | USGS Numbered Series |
| Title | Estimating the magnitude and frequency of floods at ungaged locations on urban streams in Tennessee and parts of Alabama, Georgia, Mississippi, North Carolina, and South Carolina, using data through the 2022 water year |
| Series title | Scientific Investigations Report |
| Series number | 2025-5104 |
| DOI | 10.3133/sir20255104 |
| Publication Date | February 05, 2026 |
| Year Published | 2026 |
| Language | English |
| Publisher | U.S. Geological Survey |
| Publisher location | Reston, VA |
| Contributing office(s) | Lower Mississippi-Gulf Water Science Center |
| Description | Report: vi, 17 p.; 3 Data Releases |
| Country | United States |
| State | Alabama, Georgia, Mississippi, North Carolina, South Carolina, Tennessee |
| Online Only (Y/N) | Y |