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USGS-derived 1-percent Annual Exceedance Probability Flood-Flow Estimates at Flood Insurance Study Locations Across Pennsylvania

March 31, 2022

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).