Tennessee StreamStats

Tennessee StreamStats incorporates regression equations for estimating instantaneous annual peak flows corresponding to annual exceedance probabilities (AEPs) of 50, 20, 10, 4, 2, 1, 0.5 and 0.2 percent (recurrence intervals of 2, 5, 10, 25, 50, 100, 200 and 500 years, respectively) at locations on both rural and urban streams (Ladd and Ensminger, 2025; Wagner and Ladd, 2025) and regression equations for estimating low flows, flow duration statistics, seasonal flows, and annual flows (Law and others, 2009).  Basin characteristics available in Tennessee StreamStats include drainage area and contributing drainage area, 10-85 channel slope, percentage of drainage area underlain by soils having permeability greater than or equal to 2 inches per hour, average soil permeability, percentages of basins in various Level III Ecoregions, percentages of basins in selected land-use classes based on the 2011 National Land Cover Database, two-year climate factor, and streamflow recession index.  Estimates of bankfull width, depth, and channel cross-sectional area (Bieger and others, 2015) and the maximum probable flood (Crippen and Bue, 1977) are also provided. 

In addition to equations that can be used to estimate low flows, mean annual flows, seasonal flows and selected flow-duration statistics, Law and others (2009) also provided Region-Of-Influence (ROI) methods for estimating the same statistics. The ROI methods are not implemented in StreamStats; however, a stand-alone computer program is available to estimate the flow statistics from the report using both the conventional regression equations and the ROI method. This computer program requires manual entry of the basin characteristics for ungaged locations to obtain estimates of the flow statistics; the basin characteristics can be obtained using StreamStats. An advantage of using the stand-alone ROI program is that it computes the probability of zero flow for the low-flow equations and then outputs zero if the probability is greater than a threshold. The low-flow report and associated stand-alone program can be downloaded by clicking on the embedded link in the citation above. Users should note that there are some differences in the naming of the basin characteristics between StreamStats and the stand-alone program.  For example, the “geology factor” required in the stand-alone program is named the “streamflow-recession index” in StreamStats and the “soil factor” needed in the stand-alone program is named the “percent area underlain by soil permeability of at least 2 in/hr” in StreamStats.

The reports and data releases listed below document the regression equations, the methods used to develop them and the basin characteristics used in the equations, the errors associated with the estimates obtained from the equations, and the methods used to develop the bankfull and maximum probably flood statistics.  Users should familiarize themselves with these reports before using StreamStats to obtain estimates of flows for ungaged locations on streams in Tennessee.

• Wagner, D.M. and Ladd, D.E., 2025, 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.
• Ladd, D.E., and Ensminger, P.A., 2025, Estimating the magnitude and frequency of floods at ungaged locations on streams in Tennessee through the 2013 water year: U.S. Geological Survey Scientific Investigations Report 2024–5130, 19 p.
• Heal, E.N., Ladd, D.E., and Ensminger, P.A., 2025, Tabular and geospatial data for the magnitude and frequency of floods at ungaged locations on streams in Tennessee, through the 2013 water year: U.S. Geological Survey data release, https://doi.org/10.5066/P9IEJQB7.
• Wagner, D.M., and Ladd, D.E., 2024, 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: U.S. Geological Survey data release, https://doi.org/10.5066/P9VMP56R.
• Ladd, D.E., and Wagner, D.M., 2024, 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): U.S. Geological Survey data release, https://doi.org/10.5066/P1JTPBQY.
• Wagner, D.M., and Ladd, D.E., 2024, 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): U.S. Geological Survey data release, https://doi.org/10.5066/P1TE9KTH.
• Law, G.S., Tasker, G.D., and Ladd, D.E., 2009, Streamflow-characteristic estimation methods for unregulated streams of Tennessee: U.S. Geological Survey Scientific Investigations Report 2009–5159, 212 p., 1 pl.
• Bieger, Katrin; Rathjens, Hendrik; Allen, Peter M.; and Arnold, Jeffrey G., 2015, Development and Evaluation of Bankfull Hydraulic Geometry Relationships for the Physiographic Regions of the United States, Publications from USDA-ARS / UNL Faculty, 17p.
• Crippen, J.R. and Bue, Conrad D., 1977, Maximum Floodflows in the Conterminous United States, Geological Survey Water-Supply Paper 1887, 52p.

Click on this link to obtain general information on the Tennessee application, as well as specific sources and computation methods for basin characteristics.