Step 1
StreamStats application
Delineate a basin, calculate the required basin characteristics, and run the applicable USGS regression scenarios for a selected site.
Open official USGS resource : StreamStats application (opens in a new tab)Use the equation selected by USGS for the site—not a generalized national coefficient set
This page intentionally does not generate a peak-flow number. There is no single national USGS regional regression equation: methods are tied to a jurisdiction or hydrologic region and have publication-specific predictor definitions, limits, and uncertainty. Use the official tools and source report below for an estimate you can trace and review.
Official USGS tools and documentation
Step 2
Regression publications by state or territory
Use the USGS National Streamflow Statistics directory to find the reports and limitations for the jurisdiction and statistic you need.
Open official USGS resource : Regression publications by state or territory (opens in a new tab)Step 3
How StreamStats reports ungaged-site results
Read how parameter ranges, extrapolation warnings, hydrologic regions, uncertainty indicators, and cross-boundary estimates are reported.
Open official USGS resource : How StreamStats reports ungaged-site results (opens in a new tab)DrainageCalculators.com is not affiliated with or endorsed by the U.S. Geological Survey. Links above go to official USGS services and documentation.
Safe workflow for an ungaged site
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Choose the correct jurisdiction
In StreamStats, select the state or regional application containing the outlet. Use the national publication directory to identify the source report and check whether a newer report supersedes it.
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Delineate and inspect the basin
Confirm the outlet, drainage divide, contributing area, stream network, and any edits. A plausible flow estimate cannot rescue an incorrect watershed boundary.
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Check applicability before the number
Read how the report defines each predictor and verify its calibration range. Check exclusions for regulation, diversion, urbanization, karst, tidal influence, and other special basin conditions described by the study.
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Review uncertainty and corroborate
Retain the prediction interval or other error indicators reported for the selected equation. Compare the estimate with nearby gages and an independent applicable method, and document the reviewing agency's criteria.
Examples of official peak-flow regression reports
These examples show why the source report matters: study areas and valid basin conditions differ. This is not a complete catalog. Use the official state-or-territory directory above to find the report applicable to your project.
Georgia · North Carolina · South Carolina
Magnitude and frequency of floods for rural streams
Scientific Investigations Report 2023-5006 · published 2023
Rural ungaged sites with no or minor regulation; equations are organized by applicable regression region.
Read the official USGS publication (opens in a new tab)Virginia · West Virginia
Estimation of magnitude and frequency of floods for rural, unregulated streams
Scientific Investigations Report 2025-5110 · published 2026
Rural, unregulated streams within the report's development, regulation-index, drainage-area, and regional limits.
Read the official USGS publication (opens in a new tab)Texas
Regression equations for estimation of annual peak-streamflow frequency for undeveloped watersheds
Scientific Investigations Report 2009-5087 · published 2009
Undeveloped, ungaged Texas watersheds; use the report's regional definitions and predictor limits.
Read the official USGS publication (opens in a new tab)Washington
Flood peak-discharge regression equations and associated statistics
USGS Fact Sheet 016-01 · published 2001
Ungaged, substantially unregulated and nonurbanized Washington basins within the published regional limits.
Read the official USGS publication (opens in a new tab)South Dakota
Techniques for estimating peak-flow magnitude and frequency relations
Water-Resources Investigations Report 98-4055 · published 1998
Natural-flow streams in the report's seven hydrologic subregions and stated drainage-area ranges.
Read the official USGS publication (opens in a new tab)Why equations cannot be interchanged
A published regional equation commonly has a power-law form such as the schematic expression below:
Qp = a · Ab · Bc · Cd · …
This expression is conceptual only. In an official report, a and every exponent are fitted for one annual exceedance probability and region; A, B, and C have exact definitions, units, data sources, and valid ranges. Some equations also require bias corrections, region weighting, or special procedures near a streamgage or jurisdiction boundary. Coefficients and even similarly named predictors are therefore not portable between reports.
StreamStats helps select and solve the implemented equations, but its own guidance still calls for checking the basin delineation, parameter limits, warnings, uncertainty, and source publication. Values outside published ranges are extrapolations with unknown and potentially substantial error.
What to save in the project record
- Outlet coordinates, delineated-basin map, and StreamStats workspace or report date
- State application, hydrologic region, scenario, AEP, and exact USGS publication
- Basin-characteristic values, units, published ranges, and any edits or warnings
- Flow estimate, uncertainty indicators, independent checks, and agency concurrence
Frequently asked questions
Why does this page not provide one national USGS regression calculator?
USGS regression equations are developed for a specific state, metropolitan area, or hydrologic region. The predictors, coefficients, transformations, calibration ranges, applicable flow conditions, and uncertainty measures differ by publication. A single generalized coefficient set would not be an official USGS method and could produce a misleading design value.
Where should I calculate a USGS ungaged-site flow estimate?
Start with the official USGS StreamStats application. Select the correct state or regional application, delineate and inspect the basin, compute the required basin characteristics, choose the applicable flow-statistics scenario, and read the cited publication before using the result.
What should I check before accepting a StreamStats estimate?
Verify the outlet and watershed boundary, confirm the site meets the report’s assumptions about regulation and development, compare every predictor with its published minimum and maximum, review extrapolation warnings, and retain the reported uncertainty indicators. Also confirm local agency requirements and whether a newer study supersedes the cited report.
Can a regional regression estimate be used as the final design discharge?
That depends on the applicable publication and the reviewing authority. Regional regression can be an accepted design method when used inside its documented scope, but it does not replace site-specific judgment, nearby streamgage analysis, flood records, agency criteria, or an independent hydrologic check where those are required.