30 May 2022
30 May 2022
Status: this preprint is open for discussion.

Hydrogeological controls on the spatio-temporal variability of surge-induced hydraulic gradients along coastlines: implications for beach surface stability

Anner Paldor1, Nina Stark2, Matthew Florence2, Britt Raubenheimer3, Steve Elgar3, Rachel Housego3,4, Ryan S. Frederiks1, and Holly A. Michael1,5 Anner Paldor et al.
  • 1Department of Earth Sciences, University of Delaware, Newark, DE, USA
  • 2Department of Civil and Environmental Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA
  • 3Department of Applied Ocean Physics and Engineering, Woods Hole Oceanographic Institution, Woods Hole, MA, USA
  • 4MIT-WHOI Joint Program in Oceanography, 86 Water St., Woods Hole, MA, USA
  • 5Department of Civil and Environmental Engineering, University of Delaware, Newark, DE, USA

Abstract. Ocean surges pose a global threat for coastal stability. These hazardous events alter flow conditions and pore pressures in flooded beach areas during both inundation and subsequent retreat stages, which can mobilize beach material, potentially enhancing erosion significantly. In this study, the evolution of surge-induced pore-pressure gradients is studied through numerical hydrologic simulations of storm surges. The spatiotemporal variability of critically high gradients is analyzed in 3D. The analysis is based on a threshold value obtained for momentary liquefaction of beach materials under groundwater seepage. Simulations of surge events show that during the run-up stage, head gradients can rise to the calculated critical level landward of the advancing inundation line. During the receding stage, critical gradients were simulated seaward of the retreating inundation line. These gradients reach maximum magnitudes just as sea level returns to pre-surge level, and are most accentuated beneath the still-water shoreline, where the model surface changes slope. The gradients vary along the shore owing to variable beach morphology, with the largest gradients seaward of intermediate-scale (1–3 m elevation) topographic elements (dunes) in the flood zone. These findings suggest that the common practices in monitoring and mitigating surge-induced failures and erosion, which typically focus on the flattest areas of beaches, might need to be revised.

Anner Paldor et al.

Status: open (until 25 Jul 2022)

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Anner Paldor et al.

Anner Paldor et al.


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Short summary
Ocean surges can impact the stability of beaches by changing the hydraulic regime. These surge-induced changes in the hydraulic regime have important implications for coastal engineering and for beach morphology. This work uses 3D computer simulations to study how these alterations vary in space and time. We find that certain areas along and across the beach are potentially more vulnerable than others, and that previous assumptions regarding the most dangerous places may need to be revised.