One-percent annual exceedance probability (AEP) flood-flow estimates were computed at flood insurance study (FIS) locations across Pennsylvania using methods identified in Scientific Investigation Report (SIR) 2019-5094. Following guidance outlined in SIR 2016-5149, valid statistical reaches (VSRs) were identified for streamgages, which were used to assist with the determination of the applicable method used to compute a USGS-derived 1-percent AEP flood-flow estimate at an FIS location. Methods included: weighting, weighting and transferring, and regression equations. The USGS-derived 1-percent AEP flood-flow estimates were then compared to 1-percent AEP flood-flow estimates published in FIS's and furnished by the Federal Emergency Management Agency (FEMA).

Flood Insurance Studies (FISs) published by the Federal Emergency Management Agency (FEMA) provide 10-, 2-, 1-, and 0.2-percent annual exceedance probability (AEP) streamflows and water-surface elevations for many stream reaches that were affected by the July 2023 flood in Vermont. After a flood, it is useful to compare observed streamflows and water-surface elevations to flood flow-frequency and water-surface elevations published in a FIS report (Federal Emergency Management Agency, 1980–2014). Theoretically, the AEP for the peak water-surface elevation and the AEP for the peak streamflow from the same event at the same location should be the same. Reaches for which the AEPs do not align show where existing FISs could be updated with new hydrologic data and hydraulic models. Flood streamflows for 10-, 2-, 1- and 0.2-percent frequencies using annual peak-flow data through water year 2023 were compared to peak streamflows in FEMA FIS reports and pending (2024) FIS studies. The proposed peak streamflows from pending FIS studies are based on statistical analyses of annual peak flow data prior to water year 2023. Although flood-frequency estimates were updated for 80 streamgages after the July 2023 flood, only a fraction of the streamgages have detailed hydrologic analysis in FIS reports (or pending FIS reports) and can be used in the streamflow comparison. Peak-water surface elevations from the July 2023 flood were also documented at surveyed high-water marks (HWMs) along selected river reaches impacted by the July 2023 flood in Vermont. Reaches that had HWMs, a streamgage on the same river with a drainage area within fifty percent of the reach drainage area, and an effective FIS were selected for evaluation. Streamflows and HWMs from the July flood event are presented alongside statistical streamflows and elevations for the 10- to 0.2-percent AEPs from the applicable FIS.

Flood Insurance Studies (FISs) published by the Federal Emergency Management Agency (FEMA) provide 10-, 2-, 1-, and 0.2-percent annual exceedance probability (AEP) streamflows and water-surface elevations for many stream reaches that were affected by the July 2023 flood in Vermont. After a flood, it is useful to compare observed streamflows and water-surface elevations to flood flow-frequency and water-surface elevations published in a FIS report (Federal Emergency Management Agency, 1980–2014). Theoretically, the AEP for the peak water-surface elevation and the AEP for the peak streamflow from the same event at the same location should be the same. Reaches for which the AEPs do not align show where existing FISs could be updated with new hydrologic data and hydraulic models. Flood streamflows for 10-, 2-, 1- and 0.2-percent frequencies using annual peak-flow data through water year 2023 were compared to peak streamflows in FEMA FIS reports and pending (2024) FIS studies. The proposed peak streamflows from pending FIS studies are based on statistical analyses of annual peak flow data prior to water year 2023. Although flood-frequency estimates were updated for 80 streamgages after the July 2023 flood, only a fraction of the streamgages have detailed hydrologic analysis in FIS reports (or pending FIS reports) and can be used in the streamflow comparison. Peak-water surface elevations from the July 2023 flood were also documented at surveyed high-water marks (HWMs) along selected river reaches impacted by the July 2023 flood in Vermont. Reaches that had HWMs, a streamgage on the same river with a drainage area within fifty percent of the reach drainage area, and an effective FIS were selected for evaluation. Streamflows and HWMs from the July flood event are presented alongside statistical streamflows and elevations for the 10- to 0.2-percent AEPs from the applicable FIS.

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.

The Flood Risk Database (FRD) contains risk information and supporting data used to depict risk data on a project level. The primary risk data developed are the Changes Since Last FIRM, Risk Assessment Results, Areas of Mitigation Interest, and Depth and Annual Chance grids. The FRD is derived from Flood Insurance Studies (FISs), previously published Flood Insurance Rate Maps (FIRMs), flood hazard analyses performed in support of the FISs and FIRMs, new mapping data, where available, and Hazus risk analysis. The Flood Risk Database and any accompanying products (e.g., Flood Risk Report, Flood Risk Map, and the average annualized loss) are published by the Federal Emergency Management Agency (FEMA).

Flood Models of the Woodend (Vic) area showing how far flood waters will reach in 1% Annual Exceedance Probability (AEP), 1% AEP Climate Change and 5% AEP events.

Volume 1 Report This flood study has been undertaken to determine the flood behaviour in the catchment due to local storm runoff for the 0.5% Annual Exceedance Probability (AEP), 1% AEP, 2% AEP, 5% AEP, 10% AEP, 20% AEP, 50% AEP and 100% AEP flood events and the Probable Maximum Flood (PMF). In accordance with its objectives, the study has determined the nature and extent of flooding through the estimation of design flood flows, levels and velocities. Flood impacts due to storm events in the Brisbane Water estuary are detailed in the Brisbane Water Foreshore Flood Study (2009). In undertaking the flood study, a hydrologic-hydraulic computer model of the major channels and floodplain within the catchment was established and verified against historical flood event observations. The hydraulic model was then used with design rainfall conditions to simulate design flood behaviour in the catchment. The study has defined Provisional Flood Hazard and Hydraulic Categories for the flood affected areas. The objective of this Study is to define the nature of the existing flood behaviour due to local runoff only in the Davistown catchment. To achieve the objectives, the following tasks were undertaken:,