Preprints
https://doi.org/10.5194/hess-2022-251
https://doi.org/10.5194/hess-2022-251
 
25 Jul 2022
25 Jul 2022
Status: this preprint is currently under review for the journal HESS.

Investigating coastal backwater effects and flooding in the coastal zone using a global river transport model on an unstructured mesh

Dongyu Feng1, Zeli Tan1, Darren Engwirda2, Chang Liao1, Donghui Xu1, Gautam Bisht1, Tian Zhou1, Hong-Yi Li3, and Ruby Leung1 Dongyu Feng et al.
  • 1Pacific Northwest National Laboratory, Richland, WA, 99354, USA
  • 2T-3 Fluid Dynamics and Solid Mechanics Group, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA
  • 3Department of Civil and Environmental Engineering, University of Houston, TX, 77204, US

Abstract. Coastal backwater effects are caused by the downstream water level increase as the result of elevated sea level, high river discharge and their compounding influence. Such effects have crucial impacts on floods in densely populated regions but have not been well represented in large-scale river models used in Earth System Models (ESMs), partly due to model mesh deficiency and oversimplifications of river hydrodynamics. Using two mid-Atlantic river basins as a testbed, we perform the first attempt to simulate the backwater effects comprehensively over a coastal region using the MOSART river transport model under an Earth system model framework i.e., Energy Exascale Earth System Model (E3SM) configured on a regionally-refined unstructured mesh, with a focus on understanding the backwater drivers and their long-term variations. By including sea level variations at the river downstream boundary, the model performance in capturing backwaters is greatly improved. We also propose a new flood event selection scheme to facilitate the decomposition of backwater drivers into different components. Our results show that while storm surge is a key driver, the influence of extreme discharge cannot be neglected, particularly when the river drains to a narrow river-like estuary. Compound flooding, while not necessarily increasing the flood peaks, exacerbates the flood risk by extending the duration of multiple coastal and fluvial processes. Furthermore, our simulations and analysis highlight the increasing strength of backwater effects due to sea level rise and more frequent storm surge during 1990–2019. Thus, backwaters need to be properly represented in ESMs for improving predictive understanding of coastal flooding.

Dongyu Feng et al.

Status: open (until 19 Sep 2022)

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  • RC1: 'Comment on hess-2022-251', Anonymous Referee #1, 08 Aug 2022 reply

Dongyu Feng et al.

Dongyu Feng et al.

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Short summary
Sea level rise, storm surge and river discharge can cause coastal backwater effects in river’s downstream sections, creating critical flood risks. This study simulates the backwater effects using a large-scale river model on a coastal-refined computational mesh. By decomposing the backwater drivers, we revealed their relative importance and long-term variations. Our analysis highlights the increasing strength of backwater effects due to sea level rise and more frequent storm surge.