Nearshore Vertical Pore Pressure Gradients and Onshore Sediment Transport under Tropical Storm Forcing

Florence, Matthew; Stark, Nina; Raubenheimer, Britt; Elgar, Steve

doi:10.1061/(asce)ww.1943-5460.0000723

Cited by 5 publications

(34 citation statements)

References 29 publications

(87 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…(2022), analyzing pore pressures on a beach consisting of medium/coarse sand, and Florence et al. (2022), measuring pore pressures under storm conditions, confirm that phase‐shifting plays a crucial role in explaining large pore‐pressures. This is in line with our conclusion that the pressure measurements clearly display rapid attenuation and phase shifts.…”

Section: Discussionmentioning

confidence: 81%

“…This could partially be explained by the fact that their study sampled the pressure at 2 Hz, which is considerably lower than in our study (100 Hz), and they analyzed components with frequencies of around 0.2 Hz and lower. However, the recent studies of Stark et al (2022), analyzing pore pressures on a beach consisting of medium/coarse sand, and Florence et al (2022), measuring pore pressures under storm conditions, confirm that phase-shifting plays a crucial role in explaining large pore-pressures. This is in line with our conclusion that the pressure measurements clearly display rapid attenuation and phase shifts.…”

Section: Comparison With Other Studiesmentioning

confidence: 99%

See 1 more Smart Citation

Measurements and Modeling of Pore‐Pressure Gradients in the Swash Zone Under Large‐Scale Laboratory Bichromatic Waves

Kranenborg,

Pauli,

Jacobsen

et al. 2023

JGR Oceans

View full text Add to dashboard Cite

The present work presents physical laboratory measurements of surface elevation and pore water pressures in a fine sand bed under bichromatic waves in a large‐scale laboratory experiment. This was done at three cross‐shore locations in the swash zone, with pressures being measured at different depths in the bed. The measurements show that the pore pressure signal decays and shifts with increased depth. These measurements are used to validate a practical model, based on the theory of Yamamoto et al. (1978, https://doi.org/10.1017/S0022112078003006) and Guest and Hay (2017, https://doi.org/10.1002/2016JC012257). The model corresponds well with the measurements (nRMSE < 0.2 and R2 > 0.95 for most probes) and shows that a frequency‐based model can reproduce the pressures in the bed, despite the bed being exposed during dry periods. Furthermore, the model provides the opportunity to calculate pressure gradients, both throughout the bed and at the bed surface. These modeled pressure gradients at the bed surface show that the vertical pressure gradient can have an important impact on the Shields parameter, thereby influencing sediment transport.

show abstract

Section: Discussionmentioning

confidence: 81%

Section: Comparison With Other Studiesmentioning

confidence: 99%

Measurements and Modeling of Pore‐Pressure Gradients in the Swash Zone Under Large‐Scale Laboratory Bichromatic Waves

Kranenborg,

Pauli,

Jacobsen

et al. 2023

JGR Oceans

View full text Add to dashboard Cite

show abstract

“…Mory et al (2007) and Michallet et al (2009) both give a low estimate of the liquefaction threshold for loose sediment conditions and high gas content (ρ s = 2,600, ϵ = 0.5, C gas = 0.06) and a high estimate of the liquefaction threshold for compact sediment conditions and low gas content (ρ s = 2,750, ϵ = 0.4, C gas = 0.01). A theoretical minimum for the liquefaction threshold was also calculated using the loose sediment conditions with C gas = 0.30 based on measurements of void ratio and saturation in the intertidal zone (Florence et al, 2022). During the period of observation in Figure 8, six events exceed the theoretical minimum threshold, and two events reach the range in which momentary liquefaction may occur depending on soil conditions as described above.…”

Section: Momentary Liquefactionmentioning

confidence: 99%

“…Empirical evidence shows that sandy beaches with a grain size less than 0.3 mm are more sensitive to the effect of effective weight alteration than altered boundary layers (Bujan et al, 2019;Butt et al, 2001;Nielsen, 2001). Additionally, while many studies have observed the reduction of effective weight due to upward-directed pressure gradients during backwash (Michallet et al, 2009;Mory et al, 2007;Stark et al, 2022;Tonkin et al, 2003;Yeh & Mason, 2014), several studies have also observed a similar reduction of effective weight under wave crests after a rapid reduction in pressure (Florence et al, 2022;Pujara et al, 2015).…”

Section: Swash Dynamics Effective Weight and Bed Fluidizationmentioning

confidence: 99%

“…Liquefaction is defined to occur when the effective stress within a sediment matrix equals zero (Holtz & Kovacs, 1981; Terzaghi, 1943). Momentary liquefaction can occur within coastal sediments under forcing like tsunamis (Yeh & Mason, 2014) and waves (Florence et al., 2022; Michallet et al., 2009; Mory et al., 2007). In coastal applications, momentary liquefaction is often studied by examining the flow velocity (Turner & Nielsen, 1997) or by examining pressure gradients (Florence et al., 2022; Michallet et al., 2009; Mory et al., 2007; Stark et al., 2022; Tonkin et al., 2003; Turner & Masselink, 1998; Yeh & Mason, 2014).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Beach and Dune Subsurface Hydrodynamics and Their Influence on the Formation of Dune Scarps

Bond,

Wengrove,

Puleo

et al. 2023

JGR Earth Surface

View full text Add to dashboard Cite

Erosive beach scarps influence beach vulnerability, yet their formation remains challenging to predict. In this study, a 1:2.5 scale laboratory experiment was used to study the subsurface hydrodynamics of a beach dune during an erosive event. Pressure and moisture sensors buried within the dune were used both to monitor the water table and to examine vertical pressure gradients in the upper 0.3 m of sand as the slope of the upper beach developed into a scarp. Concurrently, a line‐scan lidar tracked swash bores and monitored erosion and accretion patterns along a single cross‐shore transect throughout the experiment. As wave conditions intensified, a discontinuity in the slope of the dune formed; the discontinuity grew steeper and progressed landward at the same rate as the R2% runup extent until it was a fully formed scarp with a vertical face. Within the upper 0.15 m of the partially saturated sand, upward pore pressure gradients were detected during backwash, influencing the effective weight of sand and potentially contributing to beachface erosion. The magnitude and frequency of the upward pressure gradients increased with deeper swash depths and with frequency of wave interaction, and decreased with depth into the sand. A simple conceptual model for scarp formation is proposed that incorporates observations of upward‐directed pressure gradients from this study while providing a reference for future studies seeking to integrate additional swash zone sediment transport processes that may impact scarp development.

show abstract

Field Observations of Hydrostatic Pressure Deviations in a Nearshore Sediment Bed

Marry,

Foster

2024

JGR Oceans

View full text Add to dashboard Cite

Momentary liquefaction (ML), an instantaneous loss of effective stress between individual sand grains, is caused by the upward vertical pressure gradient of the excess pore‐water pressure in the sediment during the passage of a wave. Few field experiments have provided detailed observations of vertical pressure gradients within a sediment bed. Here, a novel autonomous pressure‐profiling instrument, the Pressure Stick, was deployed in the surf zone of an ocean beach in Rye, New Hampshire. The Pressure Stick has eight time‐synced absolute pressure sensors distributed over a 70 cm distance to measure absolute pressure in the water column and in the sediment bed. The absence of direct measurements of the sediment‐water interface location and sediment porosity limit direct observations of ML but allow for an examination of the hydrostatic pressure deviations. Observed upward vertical pressure head gradients within the sediment exceed the assumed effective weight of the sediment. Exceedances of two ML thresholds are observed within 16 cm of the sediment‐water interface and consistently occur at the onset of steeper and larger wave crests. Individual waves are characterized with an approximation of the Sleath parameter and the depth normalized wave height. The ML thresholds are exceeded 1%–40% of the time when the Sleath parameter is greater than 0.1 and 1%–33% of the time when the depth normalized wave height is greater than 0.4. These results suggest that wave steepness and nonlinearity may be necessary to induce large vertical pressure gradients that substantially deviate from hydrostatic pressure.

show abstract

Nearshore Vertical Pore Pressure Gradients and Onshore Sediment Transport under Tropical Storm Forcing

Cited by 5 publications

References 29 publications

Measurements and Modeling of Pore‐Pressure Gradients in the Swash Zone Under Large‐Scale Laboratory Bichromatic Waves

Measurements and Modeling of Pore‐Pressure Gradients in the Swash Zone Under Large‐Scale Laboratory Bichromatic Waves

Beach and Dune Subsurface Hydrodynamics and Their Influence on the Formation of Dune Scarps

Field Observations of Hydrostatic Pressure Deviations in a Nearshore Sediment Bed

Contact Info

Product

Resources

About