Data in support of estimation of magnitude and frequency of floods for rural, unregulated streams in and near Virginia and West Virginia

This data release contains the supporting datasets, tables, and geospatial information generated and analyzed in the 2025 flood-frequency study for Virginia and West Virginia. In this study, the magnitude and frequency of annual peak streamflows were estimated using the Expected Moments Algorithm for 813 streamgages on rural, unregulated streams in and near Virginia and West Virginia with a minimum of 10 years of uncensored, systematic peaks through the 2021 water year. A subset containing 565 of these streamgages were further analyzed in a process called regionalization to characterize homogeneous flood characteristics, resulting in the development of twelve hydrologic regions. Generalized least squares regression equations between logarithmic-transformed drainage area and peak streamflow were then developed for the 0.5, 0.2, 0.1, 0.04, 0.02, 0.01, 0.005, and 0.002 annual exceedance probabilities for each of these hydrologic regions. These regional regression equations can be applied to estimate the magnitude and frequency of a flood at an ungaged stream location.

A regulation index was developed for Virginia and West Virginia that accounts for dam storage, drainage area of the dams, and drainage area at the streamgage and was used to identify regulation status of streamgages used in the flood-frequency study. Frequency analyses were computed for 86 streamgages on regulated streams, who's regulation status was identified or confirmed though the regulation index analysis.

This data release is grouped into six child items, each representing a component of the study:

1) Computed basin characteristics and geospatial shapefiles containing streamgage points and drainage basins: Basin characteristics considered for multiple regression analysis for 1050 selected streamgages in and near Virginia and West Virginia, 2025

2) Streamgages considered and other miscellaneous information: Streamgages considered for analysis, results of redundancy screen, and comparison of computed frequency results for streamgages in and near Virginia and West Virginia, 2025

3) Regulated streamgage flood-frequency statistics and regulation index development information: Flood-frequency statistics for regulated streamgages and supporting documentation for regulation index development for Virginia and West Virginias, 2025

4) Unregulated streamgage flood-frequency statistics: At-site flood-frequency statistics for unregulated streams in and near Virginia and West Virginia, 2025

5) A geospatial shapefile containing regression regions: Regression Regions for Estimating Magnitude and Frequency of Floods in Virginia and West Virginia, 2025

6) Regression equation statistics: Results of generalized least-squares regression for 565 streamgages on rural, unregulated streams in and near Virginia and West Virginia, 2025

A copy of selected datasets referenced as tables in the manuscript were aggregated and included on this landing page in MS Excel Worksheet format (*.xlsx). Additionally, a plot containing an array of scatterplots showing selected streamgage drainage basin characteristics is included on this landing page in Portable Document Format (*.pdf). Details on where to find these original datasets within this data release are included in the Entity and Attribute section of this metadata record.