Development of regression equations for the estimation of flood flows at ungaged streams in Pennsylvania

Estimation and comparison of 1-percent annual exceedance probability flood flows at Federal Emergency Management Agency flood insurance study flow locations across Pennsylvania

“…As FEMA Region 3 periodically assesses the modernity and accuracy of FISs across Pennsylvania, the USGS is periodically analyzing its long-term records (10 to 100 or more years) of streamflow at gaging stations. This was most recently done in 2019 for Pennsylvania (Roland and Stuckey, 2019) using streamflow records through 2015 where flood-flow estimates of various frequencies were computed for 356 streamflow gaging stations not subject to substantial flow regulation, diversion, or mining activity (fig. 1).…”

“…Beyond assessing flood risk to communities, information regarding the magnitude and frequency of floods is critical to floodplain managers and engineers for designing and building bridges, culverts, and other structures near streams and rivers. In 2019, the USGS, in cooperation with FEMA and the Pennsylvania Department of Transportation (PennDOT) developed updated regression equations to estimate flood flows associated with various annual exceedance probabilities (AEPs) for ungaged streams in Pennsylvania not subject to substantial regulation, diversion, or mining activity (Roland and Stuckey, 2019).…”

“…Thousands of miles of streams and rivers need attention across the State, according to data that are available from FEMA's coordinated needs management strategy (CNMS) (FEMA, 2023). To aid in the prioritization of FEMA's FIS restudy process, the USGS computed 1-percent AEP flood flows at 5,258 FIS flow locations in Pennsylvania using updated regression equations and methods presented by Roland and Stuckey (2019). To utilize the USGS's extensive network of streamgages across Pennsylvania, methods were developed to incorporate streamgage data at FIS flow locations within qualifying proximity to a USGS streamgage.…”

“…To utilize the USGS's extensive network of streamgages across Pennsylvania, methods were developed to incorporate streamgage data at FIS flow locations within qualifying proximity to a USGS streamgage. One-percent AEP flood-flow estimates for FIS flow locations at or near a streamgage were computed using weighting and transferring techniques suggested by Roland and Stuckey (2019); 1-percent AEP flood-flow estimates for FIS flow locations not at or near a streamgage were computed using the updated regression equations in Roland and Stuckey (2019). The USGS 1-percent AEP flood-flow estimates at each FIS flow location in Pennsylvania were then compared to the FEMA FIS 1-percent AEP flood-flow estimates.…”

Magnitude and frequency of floods for rural streams in Georgia, South Carolina, and North Carolina, 2017—Results

“…Although maintaining the moments-based approach of the Bulletin 17B procedures, the method outlined in Bulletin 17C introduces the expected moments algorithm (EMA) (Cohn and others, 1997;Roland and Stuckey, 2019), an improved method-of-moments approach for fitting the LPIII distribution to the flood peaks that was used for this study. Application of this new method can accommodate interval estimates of peak flow, censored estimates of peak flow, and multiple thresholds of observation.…”