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Flooding implications of Beach Groundwater and Swash Interactions��

Timu Gallien

M-P. Delisle, Y. Kim, M. Maple, M. Angelis

Civil and Environmental Engineering, UCLA

UCLA Coastal Flood Lab

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Quiz!

Wave overtopping flooding is likely to occur during:

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  1. high tide
  2. big waves
  3. a and b
  4. when Timu leaves the beach to go get a coffee
  5. none of the above

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Quiz!

Wave overtopping flooding is likely to occur during:

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  1. high tide
  2. big waves
  3. a and b
  4. when Timu leaves the beach to go get a coffee
  5. none of the above

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Wave Overtopping Flooding

Thompson et al., 2017

Le Roy et al., 2015

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Swash Groundwater Interactions

Gourlay, 1992

Bakhtyar et al., 2011

Turner and Masselink et al., 1998

Low beach groundwater levels promote infiltration processes, reducing wave runup (Bakhtyar et al., 2011, Pintado-Patino et al., 2015).

Pintado-Patino et al., 2015

Water table over height increases with decreased permeability (Gourlay, 1992)

R2% maximum after tidal peak (Turner and Masselink et al., 1998)

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Observations

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December 12, 2015

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December 24, 2015

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Wave Overtopping & Tide

out of phase with tide, in phase with groundwater

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SedOlaFlow – novel numerical model

  • CFD numerical model; includes air, water, and sediment phases
  • Validated with bore-driven swash event (Kikkert et al., 2013) on permeable, fixed beaches made of either sand or gravel

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Sand

d50 = 1.3 mm

Gravel

d50 = 8.4 mm

Delisle et al., 2023, JGR: Oceans

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Impacts of groundwater on swash (gravel beach)

Delisle et al., 2023, JGR: Oceans

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hg = 0 m

hg = 0.3 m

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Impacts of groundwater on swash (gravel beach)

Delisle et al., 2023, JGR: Oceans

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hg = 0 m

hg = 0.3 m

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Impacts of groundwater on swash (gravel beach)

Delisle et al., 2023, JGR: Oceans

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Δx ~ 0.8 m

hg = 0 m

hg = 0.3 m

Δz ~ 0.08 m

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1) Elevated groundwater levels increase swash extent and duration

2) Maximum flood vulnerability controlled by tides, waves, and groundwater

Delisle et al., 2023, JGR: Oceans

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m = 2:15

m = 1:10

m = 1:15

Sand

Gravel

hg = 0 m

hg = 0.3 m

hg = 0 m

hg = 0.3 m

Δrz

te

Impacts of groundwater on swash

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Impacts of multiple waves on runup

Delisle et al., JGR: Oceans, in review 

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Sand

Gravel

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Impacts of multiple waves on runup (sand)

Delisle et al., JGR: Oceans, in review

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hg = 20 cm, hg = 0.1 cm, hg = 0 cm

hg = 0

hg = 0.1

hg = 0.2

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Impacts of multiple waves (gravel)

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Impacts of multiple waves on runup

Delisle et al., JGR: Oceans, in review

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Runup distance

Beachface turbulence

1) Saturation reduces turbulence 🡪 increases runup extent

2) Runup interactions depend on more than just wave characteristics (H/D)

→ Sediment and beach characteristics are important

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Flooding Implications

  • SLR will raise beach groundwater promoting higher runup on some beaches
  • Higher runup increases beach groundwater which reduces TKE, in turn promoting higher runup
  • Intense (or longer duration) precipitation may raise beach groundwater and exacerbate wave runup
  • Job security!!!

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Acknowledgements

  • US Army Corps of Engineers & USCRP
  • Department of Navy
  • California Parks and Recreation DBW
  • California Coastal Conservancy
  • Cities
    • Newport Beach, Imperial Beach, Encinitas, Seal Beach
    • Students and P-docs
      • B-X. Tang, J. Lucey, M-P. Delisle, M. Winters, M. Maple, Y. Kim, N. Kalligeris
    • Guza, Okihiro, Ritzman and the field crew

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Thank you!