Flood Hazard Assessment for a Hyper-Tidal Estuary as a Function of Tide-Surge-Morphology Interaction

Lyddon, Charlotte; Brown, Jennifer M.; Leonardi, Nicoletta; Plater, Andrew J.

doi:10.1007/s12237-018-0384-9

Cited by 46 publications

(39 citation statements)

References 80 publications

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“…This study considers conditions typical of winter, where stratification is weak with little near-bed effect (Holt et al, 2001). Consequently, depth-averaged hydrodynamics were considered adequate in line with previous modeling approaches in the region (Bricheno et al, 2015;Holt et al, 2001;Lyddon et al, 2018;Pingree & Griffiths, 1980;Pingree & Le Cann, 1989;Uncles, 1982Uncles, , 2010Xia et al, 2010). The effect of secondary flow generation due to a rotating current field on the depth-averaged flow is included by addition of a correction term to the depth-averaged momentum equations, assuming a logarithmic velocity profile, where spiral motion intensity is described by a depth-averaged advection-diffusion equation (Deltares, 2014;Kalkwijk & Booij, 1986).…”

Section: Numerical Modelmentioning

confidence: 95%

The Impact of Waves and Tides on Residual Sand Transport on a Sediment‐Poor, Energetic, and Macrotidal Continental Shelf

et al. 2019

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The energetic, macrotidal shelf off South West England was used to investigate the influence of different tide and wave conditions and their interactions on regional sand transport patterns using a coupled hydrodynamic, wave, and sediment transport model. Residual currents and sediment transport patterns are important for the transport and distribution of littoral and shelf‐sea sediments, morphological evolution of the coastal and inner continental shelf zones, and coastal planning. Waves heavily influence sand transport across this macrotidal environment. Median (50% exceedance) waves enhance transport in the tidal direction. Extreme (1% exceedance) waves can reverse the dominant transport path, shift the dominant transport phase from flood to ebb, and activate sand transport below 120‐m depth. Wave‐tide interactions (encompassing radiation stresses, Stoke's drift, enhanced bottom‐friction and bed shear stress, refraction, current‐induced Doppler shift, and wave blocking) significantly and nonlinearly enhance sand transport, determined by differencing transport between coupled, wave‐only, and tide‐only simulations. A new continental shelf classification scheme is presented based on sand transport magnitude due to wave‐forcing, tide‐forcing, and nonlinear wave‐tide interactions. Classification changes between different wave/tide conditions have implications for sand transport direction and distribution across the shelf. Nonlinear interactions dominate sand transport during extreme waves at springs across most of this macrotidal shelf. At neaps, nonlinear interactions drive a significant proportion of sand transport under median and extreme waves despite negligible tide‐induced transport. This emphasizes the critical need to consider wave‐tide interactions when considering sand transport in energetic environments globally, where previously tides alone or uncoupled waves have been considered.

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Section: Numerical Modelmentioning

confidence: 95%

The Impact of Waves and Tides on Residual Sand Transport on a Sediment‐Poor, Energetic, and Macrotidal Continental Shelf

et al. 2019

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“…At the same time, the storm surge modifies the hydrodynamic processes with which it interacts, for example, shifting the phase (Horsburgh & Wilson, 2007) and altering the amplitude (Arns et al, 2017) of the tide wave. Quantifying such effects, however, remains challenging and is typically assessed by simulating storm surge in a numerical model that is run with and without tides (e.g., Lyddon et al, 2018; Shen et al, 2006). The difference between the modeled storm surge waves is then attributed to nonlinear tide‐surge interaction.…”

Section: Introductionmentioning

confidence: 99%

Tide‐Storm Surge Interactions in Highly Altered Estuaries: How Channel Deepening Increases Surge Vulnerability

2020

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We develop idealized analytical and numerical models to study how storm surge amplitudes vary within frictional, weakly convergent, nonreflective estuaries. Friction is treated using Chebyshev polynomials. Storm surge is represented as the sum of two sinusoidal components, and a third constituent represents the semidiurnal tide (D 2 ). An empirical fit of storm surge shows that two sinusoidal components adequately represent storm surge above a baseline value (R 2 = 0.97). We find that the spatial transformation of surge amplitudes depends on the depth of the estuary, and characteristics of the surge wave including time scale, amplitude, asymmetry, and surge-tide relative phase. Analytical model results indicate that surge amplitude decays more slowly (larger e-folding) in a deeper channel for all surge time scales (12-72 hr). Deepening of an estuary results in larger surge amplitudes. Sensitivity studies show that surges with larger primary amplitudes (or shorter time scales) damp faster than those with smaller amplitudes (or larger time scales). Moreover, results imply that there is a location with maximum sensitivity to altered depth, offshore surge amplitude, and time scale and that the location of observed maximum change in surge amplitude along an estuary of simple form moves upstream when depth is increased. Further, the relative phase of surge to tide and surge asymmetry can change the spatial location of maximum change in surge. The largest change due to increased depth occurs for a large surge with a short time scale. The results suggest that both sea level rise and channel deepening may also alter surge amplitudes.Plain Language Summary Many estuaries around the world are heavily altered from their natural state. Wetlands have been reclaimed, and shipping channels widened and deepened to accommodate large container ships. The effects on storm surge and flood risk are just beginning to be explored. In this paper we employ a theoretical approach to understand how the characteristics of a storm surge-such as how fast it is moving, how big it is, and whether it happens on flood or ebb tide-change how it behaves in an estuary. Our results show that storm surge generally gets larger when channels are dredged and deepened; the largest amplification is observed for fast-moving storms with a short time scale, within estuaries that are highly frictional. Other characteristics-such as the timing relative to the tide and the shape of the estuary-also impact the amplitude and the amount of sensitivity to changing conditions. We find that channel deepening effects are negligible at the coast and far upstream. In between, a region of maximum sensitivity to dredging occurs. Thus, changes in flood risk due to channel deepening and sea level rise can be spatially variable, even within a single estuary.

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“…Delft3D-FLOW simulates hydrodynamic flow under the shallow water assumption, and Delft3D-WAVE simulates the generation and propagation of waves, based on the third-generation spectral wave model Simulating WAves Nearshore, which solves the spectral action balance (Booij et al, 1999). A -2-D horizontal, curvilinear grid of the Severn Estuary extends from Woolacombe, Devon and Rhossili, South Wales in the west, with a maximum resolution of 5 km, to Gloucester in the east with a minimum resolution of 25 m at the coast, to resolve fine-scale processes in shallow water ( Figure 1a) and has been validated in Lyddon et al, 2018aLyddon et al, , 2018bLyddon et al, , 2019 Gridded bathymetry data at 50-m resolution (SeaZone Solutions Ltd., 2013) was interpolated over the 2DH curvilinear grid. Delft3D-FLOW has two open boundaries forced by time varying, spatially uniform water level, representing the Atlantic Ocean to the west and the River Severn to the east.…”

Section: Delft3d Hindcast Of Select Historic Eventsmentioning

confidence: 99%

Quantification of the Uncertainty in Coastal Storm Hazard Predictions Due to Wave‐Current Interaction and Wind Forcing

Lyddon

Brown

Leonardi

et al. 2019

Geophysical Research Letters

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Coastal flood warning and design of coastal protection schemes rely on accurate estimations of water level and waves during hurricanes and violent storms. These estimations frequently use numerical models, which, for computational reasons, neglect the interaction between the hydrodynamic and wave fields. Here, we show that neglecting such interactions, or local effects of atmospheric forcing, causes large uncertainties, which could have financial and operational consequences because flood warnings are potentially missed or protection schemes underdesigned. Using the Severn Estuary, SW England, we show that exclusion of locally generated winds underestimates high water significant wave height by up to 90.1%, high water level by 1.5%, and hazard proxy (water level + 1/2 significant wave height) by 9.1%. The uncertainty in water level and waves is quantified using a system to model tide-surge-wave conditions, Delft3D-FLOW-WAVE in a series of eight model simulations for four historic storm events.Plain Language Summary Coastal zones worldwide are subject to combined effects of astronomical tides, meteorological storms surges, waves, and wind during storms and hurricanes, which can lead to flooding, property damage, and casualties. Coastal communities and critical infrastructure rely on accurate water level and wave forecasts to mitigate these combined hazards. Forecasts utilize hydrodynamic numerical models, which need to accurately represent these hazards and how they interact with, and feedback to, each other. This study uses a model, Delft3D-FLOW-WAVE, to calculate how tides and waves from four historic storm events combine to contribute to water level, wave height, and hazard proxy (water level + 1/2 wave height) in the Severn Estuary, southwest England. Additional simulations are run to show how local winds can further contribute to the hazard. Results show that including locally generating winds in simulations of water level, wave height, and hazard proxy is most important for accurate representation of physical processes that contribute to coastal hazards. Excluding locally generated winds from numerical model predictions could mean that flood alerts, warnings, and evacuation orders are missed, or coastal protection schemes are underdesigned, potentially leading to more flooding.

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Flood Hazard Assessment for a Hyper-Tidal Estuary as a Function of Tide-Surge-Morphology Interaction

Cited by 46 publications

References 80 publications

The Impact of Waves and Tides on Residual Sand Transport on a Sediment‐Poor, Energetic, and Macrotidal Continental Shelf

The Impact of Waves and Tides on Residual Sand Transport on a Sediment‐Poor, Energetic, and Macrotidal Continental Shelf

Tide‐Storm Surge Interactions in Highly Altered Estuaries: How Channel Deepening Increases Surge Vulnerability

Quantification of the Uncertainty in Coastal Storm Hazard Predictions Due to Wave‐Current Interaction and Wind Forcing

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