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Abstract Catastrophic drainage of glacial Lake Missoula through the Columbia River Gorge, USA, produced some of the largest floods ever known. However, erosion of the gorge during flooding has not been quantified, hindering discharge reconstructions and our understanding of landscape change by megafloods. Using a neural network and geomorphic observations, we reconstructed the gorge topography and found ∼7.4 km3of rock was eroded from gorge walls. Accounting for a narrower canyon and matching flood high‐water marks resulted in peak‐flood discharge reconstructions of 6 × 106–7 × 106 m3 s−1, which are 30%–40% lower than prior estimates based on the present‐day topography. Sediment transport modeling indicated that more frequent intermediate‐sized floods transported most of the eroded rock. Thus, similar to alluvial rivers, discharge magnitude‐frequency tradeoffs may also govern canyon formation by repeated megafloods.
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Cold Region River Flood Mapping and Scour Potential Prediction: Insights from Hydraulic Model Using Advanced Autonomous Surface Vehicles
Abstract This study aimed to map the 2022 flood with a 16.5-year return period near a bridge on the Red River, close to Grafton City, North Dakota, and evaluate the scour potential around the bridge. The Red River Basin (RRB) near Grand Forks, ND, and Emerson, ND, is a cold region river vulnerable to floods. Local scouring around bridge piers during floods can lead to hydraulic structure failure. An Autonomous Surface Vehicle (ASV) equipped with LiDAR DEM data from the ND DWR’s LiDAR dataset was used to collect comprehensive bathymetry and discharge data, including the 2022 flood. The HEC-RAS model was used to create flood maps, and the Colorado State University (CSU) methodology was employed to assess local scour around the bridge pier. The study area recorded maximum velocities of 1.71 m/s, 1.87 m/s, and 1.56 m/s for discharge values of 368 m3/s, 784 m3/s, and 1335 m3/s, respectively, with higher velocities recorded upstream of the bridge. The maximum water depth reached 13.14 m during the peak discharge of 1335 m3/s. Higher discharge resulted in increased Froude number and contraction scour depth, with the latter continuing to increase even when the Froude number decreased as water reached the bridge deck. The study highlights the effectiveness of integrating ASVs, bathymetry, and LiDAR data to comprehensively understand flood dynamics and bridge scour in cold region rivers, offering the way for the development of effective flood control measures and strategies to safeguard critical infrastructure.
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- Award ID(s):
- 2146078
- PAR ID:
- 10587424
- Publisher / Repository:
- Springer
- Date Published:
- Journal Name:
- Environmental Processes
- Volume:
- 11
- Issue:
- 3
- ISSN:
- 2198-7491
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Bedrock erosion and canyon formation during extreme floods have dramatically altered landscapes on Earth and Mars. Grand Coulee was carved by outburst floods from Pleistocene glacial Lake Missoula and is the largest canyon in the Channeled Scabland, a megaflood‐scoured landscape in the northwestern USA. Quantifying paleo‐discharge is required to understand how landscapes evolve in response to extreme events, but there are few constraints on the magnitude of the floods that incised Grand Coulee; hence, we used hydraulic modeling and geologic evidence to quantify paleo‐flood discharges during different phases of canyon incision. When upper Grand Coulee was incising by headward waterfall retreat, the paleo‐discharge was 2.6 × 106 m3s−1, which produced shear stresses great enough to cause the waterfall to retreat via toppling of basalt columns. The largest possible flood through upper Grand Coulee, a Missoula flood which raised glacial Lake Columbia to a stage of 750 m, produced a modeled discharge of 7.6 × 106 m3s−1. The discharges associated with waterfall retreat and drainage of glacial Lake Columbia are >80% and ∼50% lower, respectively, than the 14–17 × 106 m3s−1discharge predicted by assuming the present‐day topography was inundated to the elevation of high‐water marks. Due to bedrock incision, high‐water marks may overestimate paleo‐flow depth in canyons carved by floods, hence bedrock erosion should be considered when estimating paleo‐discharge in flood‐carved canyons. Our results indicate that outburst floods with discharges and flow depths much lower than those required to inundate high‐water marks are capable of carving deep canyons.more » « less
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1007/s40710-024-00721-7
