18 Feb 2022
18 Feb 2022
Status: this preprint is currently under review for the journal OS.

Compound Flooding in Convergent Estuaries: Insights from an Analytical Model

Ramin Familkhalili1, Stefan Talke2, and David Jay3 Ramin Familkhalili et al.
  • 1Department of Civil and Environmental Engineering, Old Dominion University, Norfolk, VA, USA
  • 2Department of Civil and Environmental Engineering, California Polytechnic State University, San Luis Obispo, CA, USA
  • 3Department of Civil and Environmental Engineering, Portland State University, Portland, OR, USA

Abstract. We investigate here the effects of geometric properties (channel depth and cross-sectional convergence length), storm surge characteristics, friction, and river flow on the spatial and temporal variability of compound flooding along an idealized, meso-tidal coastal-plain estuary. An analytical model is developed that includes exponentially convergent geometry, tidal forcing, constant river flow, and a representation of storm surge as a combination of two sinusoidal waves. Non-linear bed friction is treated using Chebyshev polynomials and trigonometric functions, and a multi-segment approach is used to increase accuracy. Model results show that river discharge increases the damping of surge amplitudes in an estuary, while increasing channel depth has the opposite effect. Sensitivity studies indicate that the impact of river flow on peak water level decreases as channel depth increases, while the influence of tide and surge increases in the landward portion of an estuary. Moreover, model results show less surge damping in deeper configurations and even amplification in some cases, while increased convergence length scale damps surge waves with time scales of 12 h–72 h along an estuary. For every modeled scenario, there is a point where river discharge effects on water level outweigh tide/surge effects. As a channel is deepened, this cross-over point moves progressively upstream. Thus, channel deepening may alter flood risk spatially along an estuary and reduce the length of a river-estuary, within which fluvial flooding is dominant.

Ramin Familkhalili et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on os-2022-9', Anonymous Referee #1, 21 Mar 2022
  • RC2: 'Comment on os-2022-9', Anonymous Referee #2, 22 Apr 2022

Ramin Familkhalili et al.

Ramin Familkhalili et al.


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Short summary
In this study we investigate these factors and how changes to estuary and river geometry influence peak water levels. Our results show that surge waves become larger when the depth of a shipping channel is increased, for example due to dredging or sea-level rise. The same deepening, however, reduces the effect of river flow on peak water level. The result is that the region over which river influence dominates the peak water level moves upstream as a system becomes deeper.