277 D62. Clastics - Floodplains as Repositories of Information on Climate, Hydrology, Ecology, and Human Activities

Wednesday, 7 November 2018
1:30 PM - 5:30 PM
Room 234

NO STONE UNTURNED, LITERALLY: HUNTING FOR PALEOFLOOD DEPOSITS IN THE TENNESSEE RIVER GORGE

Paper number: 277-7
Program: Technical Sessions
Time: 2:55 PM – 3:10 PM

Authors

Abstract

The geomorphology of the Tennessee River Gorge and adjacent floodplain preserves deposits from large late-Holocene Tennessee River floods that can be used to improve flood frequency analyses. Large colluvial sandstone boulders, which tumbled from the surrounding cliffs, dot the slopes of the gorge and provide flow obstructions during large floods. Flow separation around many of these boulders promotes sediment deposition and preservation if appropriately oriented. The stable bedrock boundary and narrow valley of the gorge allow for sensitive stage-discharge relationships so that reliable flow magnitudes can be estimated from the elevation of the flood deposits. Preliminary stratigraphic analysis and geochronology show evidence of 3-4 floods in the last 3,000 years similar in magnitude to the 1867 peak of record (460,000 ft3/s at nearby Chattanooga, Tennessee) that inundated much of the city. Evidence of the largest late-Holocene flood on the Tennessee River indicates it may have an estimated discharge about twice the 1867 flood and probably occurred in the last 400 years. Flood sediment preserved in caves and small alcoves in limestone bedrock immediately upstream from the gorge constriction provide additional evidence of large late-Holocene floods.

The USGS in cooperation with the Nuclear Regulatory Agency are using the paleoflood data developed for the Tennessee River to improve procedures for flood-risk assessments for nuclear power plants in the United States. The magnitude, timing and number of floods can be directly incorporated into flood frequency analyses using the recently released Guidelines for Determining Flood Flow Frequency - Bulletin 17C. This study is one of the first studies in the eastern U.S. to use paleoflood data to improve flood frequency estimates for rare, low annual exceedance probability floods.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-319512

© Copyright 2018 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.