A paleoflood chronology and updated flood frequency analysis for the French Broad River, Tennessee (USA)

Keywords: Paleofloods, Flood Frequency, Flood Hazard
Session Type: Virtual Paper Abstract
Day: Friday
Session Start / End Time: 2/25/2022 08:00 AM (Eastern Time (US & Canada)) - 2/25/2022 09:20 AM (Eastern Time (US & Canada))
Room: Virtual 19

Abstract

Instrumented gauge records in the southeastern United States rarely extend beyond 100 years, which produces error in flood frequency models developed to estimate the risk of extreme floods (floods with recurrence intervals of 100 years or more). The accuracy of flood frequency models can be improved by including paleoflood hydrologic data, i.e. reconstructed floods derived from sedimentary and tree ring records. A paleoflood chronology was developed for the French Broad River, based on sampling and analyses conducted at an upstream floodplain (DT3A) site and a downstream rock shelter (DRS1) site. A sediment core taken from DT3A (floodplain) was analyzed using laser granulometry to determine particle size of each centimeter of the core. Using several statistical analysis tools, large flood events were identified based on the volume of medium or greater sand (>0.25 mm). Estimates of paleoflood discharges were made using a linear regression model of paleoflood peaks and a 150+ year-long peak flow record taken from a USGS stream gauge located within 100 m of the sediment coring site. Stratigraphic descriptions and radiocarbon dating were used to identify 4 paleoflood events preserved at two different topographic levels at DRS1. The paleoflood discharge and age information was combined with the modern gauge record and a new flood frequency analysis was developed. The new extreme flood information provided by these analyses have the potential to change the way hazard mitigation strategies are developed and applied.