Estimation of time-varying discharge and cumulative volume in individual overtopping waves

Hughes, Steven A.; Thornton, Chris

doi:10.1016/j.coastaleng.2016.08.006

Cited by 20 publications

(31 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Experiments [7,28] have shown that the flow velocity and layer thickness instantaneously increase to their maximum followed by a slower decrease to zero as the wavefront passes ( Figure 1b). The time difference between the moment the wavefront arrives and the flow velocity or layer thickness becomes zero is called the overtopping period T 0 (s).…”

Section: Model Input Variablesmentioning

confidence: 99%

Modelling the Wave Overtopping Flow over the Crest and the Landward Slope of Grass-Covered Flood Defences

Bergeijk

Warmink

Hulscher

2020

JMSE

View full text Add to dashboard Cite

The wave overtopping flow can exert high hydraulic loads on the grass cover of dikes leading to failure of the cover layer on the crest and the landward slope. Hydraulic variables such as the near bed velocity, pressure, shear stress and normal stress are important to describe the forces that may lead to cover erosion. This paper presents a numerical model in the open source software OpenFOAM® to simulate the overtopping flow on the grass-covered crest and slope of individual overtopping waves for a range of landward slope angles. The model provides insights on how the hydraulic forces change along the profile and how irregularities in the profile affect these forces. The effect of irregularities in the grass cover on the overtopping flow are captured in the Nikuradse roughness height calibrated in this study. The model was validated with two datasets of overtopping tests on existing grass-covered dikes in the Netherlands. The model results show good agreement with measurements of the flow velocity in the top layer of the wave, as well as the near bed velocity. The model application shows that the pressure, shear stress and normal stress are maximal at the wave front. High pressures occur at geometrical transitions such as the start and end of the dike crest and at the inner toe. The shear stress is maximal on the lower slope, and the normal stress is maximal halfway of the slope, making these locations vulnerable to cover failure due to high loads. The exact location of the maximum forces depends on the overtopping volume. Furthermore, the model shows that the maximum pressure and maximum normal stress are largely affected by the steepness of the landward slope, but the slope steepness only has a small effect on the maximum flow velocity and maximum shear stress compared to the overtopping volume. This new numerical model is a useful tool to determine the hydraulic forces along the profile to find vulnerable points for cover failure and improve the design of grass-covered flood defences.

show abstract

Section: Model Input Variablesmentioning

confidence: 99%

Modelling the Wave Overtopping Flow over the Crest and the Landward Slope of Grass-Covered Flood Defences

Bergeijk

Warmink

Hulscher

2020

JMSE

View full text Add to dashboard Cite

show abstract

“…Hughes and Nadal (2009) presented results from model levees that include distributions of overtopping discharge, individual volumes, and flow depths, of interest in this paper. More recently Hughes and Thornton (2016) scrutinized 5799 individual overtopping events to derive a two-parameter Weibull probability density function for wave discharge that they used to assess the resiliency of sea dike protection.…”

Section: Literaturementioning

confidence: 99%

“…Burcharth & Hughes, 2006;EurOtop, 2016). There are other approaches that use a deterministic, physics-based approach but these are limited to gentle slopes up to a steepness of 1:3 (Hughes & Nadal, 2009;Hughes & Thornton, 2016).…”

Section: Introductionmentioning

confidence: 99%

Individual violent wave-overtopping events: behaviour and estimation

Raby

Jayaratne

Bredmose³

et al. 2019

Journal of Hydraulic Research

View full text Add to dashboard Cite

To better understand individual violent wave overtopping, of significance for coastal defence design, three breaking wave types (steep-fronted, plunging and broken) based on focused wave groups, were generated in laboratory and numerical models. High-speed video captured overtopping events and produced velocity vector maps by means of bubble image velocimetry (BIV). Results were compared with a numerical model based on a linear wave detection procedure and a two-phase incompressible Navier-Stokes-based solver. This novel approach revealed that the overtopping waves comprised an initial jet of 0.2 s duration, but dominated by quasi-steady flow. Whilst laboratory surface-elevation time-histories were highly repeatable, overtopping volume repeats were sensitive to the breaker type. Measured volumes were compared with: the numerical model (which over-predicted, but was reasonably accurate for steep-fronted waves); estimations based on BIV results (which provided very close agreement for the steep-fronted waves); and a weir-based analogy (which provided reasonable agreement, but always under-predicted).

show abstract

“…The more recent automatic procedures for the reconstruction of the individual overtopping volumes are based on the zero up-crossing or down-crossing analysis of the sea surface elevation signals at weigh cells (Victor, 2012, later modified by Platteeuw, 2015Molines et al 2019) or at resistant gauges (Nørgaard et al, 2014;Hughes, 2015;Hughes and Thornton, 2016). Many of these procedures seem to be affected by unaffordable inaccuracy in comparison with the manually supervised analysis of the discharge time series (Hughes, 2015).…”

Section: Introductionmentioning

confidence: 99%

“…This contribution describes a new, advanced and versatile procedure for the identification of the overtopping waves specifically developed to overcome the problems of the automatic detection, in order to reproduce the number of the overtopping waves as they would have been recognized by a manual analysis of the wave signal (see Hughes et al, 2015;2016). The procedure has been recently presented in Formentin and Zanuttigh (2018, b) through a preliminary application to a numerical database consisting of wave overtopping at smooth dikes.…”

Section: Introductionmentioning

confidence: 99%

Semi-automatic detection of the overtopping waves and reconstruction of the overtopping flow characteristics at coastal structures

Formentin

Zanuttigh

2019

Coastal Engineering

View full text Add to dashboard Cite

This paper proposes a semi-automatic and customizable procedure for the identification of the overtopping waves based on a threshold-down-crossing analysis of the sea surface elevation signals. The procedure can be applied to 2D experimental and numerical signals, to emerged and submerged structures, with the same accuracy of a human-supervised analysis. The procedure includes an original and innovative algorithm to compare the water level signals at consecutive gauges and couple the waves propagating in between. The coupling algorithm implies a series of original applications of practical relevance, such as: i) the computation of the wave celerity, which is a crucial parameter for the assessment of the structural stability and the hydraulic vulnerability of the landward area; ii) the estimation of the wave overtopping discharge, which can be obtained by integrating the wave celerities with the surface elevations; iii) the description of the wave overtopping characteristics and their evolution over the structure crest; iv) the evaluation of the volumes lost for percolation in permeable structures. The application to new and literature data and the comparison with well-established formulae prove that the results obtained from the identification and coupling procedures are accurate and reliable.

show abstract

Estimation of time-varying discharge and cumulative volume in individual overtopping waves

Cited by 20 publications

References 13 publications

Modelling the Wave Overtopping Flow over the Crest and the Landward Slope of Grass-Covered Flood Defences

Modelling the Wave Overtopping Flow over the Crest and the Landward Slope of Grass-Covered Flood Defences

Individual violent wave-overtopping events: behaviour and estimation

Semi-automatic detection of the overtopping waves and reconstruction of the overtopping flow characteristics at coastal structures

Contact Info

Product

Resources

About