This data release provides the source data and results of a flood frequency analysis and annual exceedance probability estimation for a flood that occurred on July 11, 2022 in the Delta River Basin, Alaska. Data are provided for two streamgages that had at least 10 years of peak-flow record. The data include streamgage information, PeakFQ input (.txt and .PSF files) PeakFQ output (.PRT, .EXP, and .JPEG files), flood frequency parameters, flood frequency estimates for the 50-, 20-, 10-, 4-, 2-, 1-, 0.5-, and 0.2-percent annual exceedance probabilities, and annual exceedance probability estimates for the flood of interest. These data were intended to support investigations of streamflow in the Delta River Basin.

This data release provides the source data and results of a flood frequency analysis and annual exceedance probability estimation for a flood that occurred on June 22, 2020 in the Fortymile River Basin, Alaska. Data are provided for two streamgages that had at least 10 years of peak-flow record. The data include streamgage information, PeakFQ input (.txt and .PSF files) PeakFQ output (.PRT, .EXP, and .JPEG files), flood frequency parameters, flood frequency estimates for the 50-, 20-, 10-, 4-, 2-, 1-, 0.5-, and 0.2-percent annual exceedance probabilities, and annual exceedance probability estimates for the flood of interest. These data were intended to support investigations of streamflow in the Fortymile River Basin.

This data release provides the source data and results of a flood frequency analysis and annual exceedance probability estimation for a flood that occurred on June 22, 2020 in the Fortymile River Basin, Alaska. Data are provided for two streamgages that had at least 10 years of peak-flow record. The data include streamgage information, PeakFQ input (.txt and .PSF files) PeakFQ output (.PRT, .EXP, and .JPEG files), flood frequency parameters, flood frequency estimates for the 50-, 20-, 10-, 4-, 2-, 1-, 0.5-, and 0.2-percent annual exceedance probabilities, and annual exceedance probability estimates for the flood of interest. These data were intended to support investigations of streamflow in the Fortymile River Basin.

This data collection of U.S. Geological Survey data releases provides the source data and results of flood frequency analyses and annual exceedance probability estimation for selected observed floods in Alaska and conterminous basins in Canada. The data include streamgage information, PeakFQ input and output, flood frequency parameters, flood frequency estimates for selected annual exceedance probabilities, and annual exceedance probability estimates for selected observed flood events.

This data collection of U.S. Geological Survey data releases provides the source data and results of flood frequency analyses and annual exceedance probability estimation for selected observed floods in Alaska and conterminous basins in Canada. The data include streamgage information, PeakFQ input and output, flood frequency parameters, flood frequency estimates for selected annual exceedance probabilities, and annual exceedance probability estimates for selected observed flood events.

This data release provides the source data and results of a flood frequency analysis for a streamgage in the Hulahula River Basin, Alaska. Data are provided for one streamgage that had at least 10 years of peak-flow record. The data include streamgage information, PeakFQ input (.txt and .PSF files) PeakFQ output (.PRT, .EXP, and .JPEG files), flood frequency parameters, flood frequency estimates for the 50-, 20-, 10-, 4-, 2-, 1-, 0.5-, and 0.2-percent annual exceedance probabilities. These data were intended to support investigations of streamflow in the Hulahula River Basin.

This data release provides the source data and results of a flood frequency analysis for a streamgage in the Hulahula River Basin, Alaska. Data are provided for one streamgage that had at least 10 years of peak-flow record. The data include streamgage information, PeakFQ input (.txt and .PSF files) PeakFQ output (.PRT, .EXP, and .JPEG files), flood frequency parameters, flood frequency estimates for the 50-, 20-, 10-, 4-, 2-, 1-, 0.5-, and 0.2-percent annual exceedance probabilities. These data were intended to support investigations of streamflow in the Hulahula River Basin.

The U.S. Geological Survey (USGS), in cooperation with Connecticut Department of Transportation, completed a study to improve flood-frequency estimates in Connecticut. This companion data release is a Microsoft Excel workbook for: (1) computing flood discharges for the 50- to 0.2-percent annual exceedance probabilities from peak-flow regression equations, and (2) computing additional prediction intervals, not available through the USGS StreamStats web application. The current StreamStats application (version 4) only computes the 90-percent prediction interval for stream sites in Connecticut. The Excel workbook can be used to compute the 70-, 80-, 90-, 95-, and 99-percent prediction intervals. The prediction interval provides upper and lower limits of the estimated flood discharge with a certain probability, or level of confidence in the accuracy of the estimate. The standard error of prediction for the Connecticut peak-flow regression equations ranged from 26.3 to 45.0 percent (Ahearn and Hodgkins, 2020). The Excel workbook consists of four worksheets. The worksheets provide an overview of how the application works; input and output tables of the explanatory variables and flood discharges, and graphical display of the results; and the computational formulas used to estimate the flood discharges and prediction intervals.

The U.S. Geological Survey (USGS), in cooperation with Connecticut Department of Transportation, completed a study to improve flood-frequency estimates in Connecticut. This companion data release is a Microsoft Excel workbook for: (1) computing flood discharges for the 50- to 0.2-percent annual exceedance probabilities from peak-flow regression equations, and (2) computing additional prediction intervals, not available through the USGS StreamStats web application. The current StreamStats application (version 4) only computes the 90-percent prediction interval for stream sites in Connecticut. The Excel workbook can be used to compute the 70-, 80-, 90-, 95-, and 99-percent prediction intervals. The prediction interval provides upper and lower limits of the estimated flood discharge with a certain probability, or level of confidence in the accuracy of the estimate. The standard error of prediction for the Connecticut peak-flow regression equations ranged from 26.3 to 45.0 percent (Ahearn and Hodgkins, 2020). The Excel workbook consists of four worksheets. The worksheets provide an overview of how the application works; input and output tables of the explanatory variables and flood discharges, and graphical display of the results; and the computational formulas used to estimate the flood discharges and prediction intervals.

Flood-frequency analyses were conducted for three streamgages operated by the U.S. Geological Survey (USGS) in the Black River basin of southeastern Missouri (MO) and northeastern Arkansas (AR): 07064000, Black River near Corning, AR; 07068000, Current River at Doniphan, MO; and 07069000, Black River at Pocahontas, AR. Results from the analyses will be used for design purposes by the Arkansas Department of Transportation in the future Interstate 57 alignment from Walnut Ridge, AR to the MO state line. Annual peak-flow data through the 2023 water year (a water year is defined as the period October 1 - September 30, named for the year in which it ends) were downloaded from the USGS National Water Information System (NWIS) website at https://nwis.waterdata.usgs.gov/nwis/peak. Flood-frequency analyses using the Expected Moments Algorithm (EMA) were conducted in version 7.5.1 of USGS PeakFQ software (Veilleux and others, 2014; Flynn and others, 2006) following federal guidelines (England and others, 2019) and the techniques outlined in the most recent USGS flood-frequency report for Arkansas (Wagner and others, 2016). Peak-flow (.pkf), specification (.psf), output (.PRT) and export (.EXP) files from PeakFQ are provided, in addition to a plot of the frequency curve for each streamgage in .PNG format. Results from the flood-frequency analyses, including estimates of the magnitudes of floods corresponding to the 0.5, 0.2, 0.1, 0.04, 0.02, 0.01, 0.005, and 0.002 annual exceedance probabilities (AEPs; the equivalent of the 2-, 5-, 10-, 25-, 50-, 100-, 200-, and 500-year recurrence intervals, respectively) and their associated variances and confidence intervals were retrieved from the .PRT file and are provided in .csv format.