Uncertainty in estuarine extreme water level predictions due to surge-tide interaction

Pagliara

2019

Water

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The emerging shift of extreme events, combined with an aging infrastructure and bridges, highlights the potential increase in the risk of damage and catastrophic failure of bridges with climate change. This article analyzes the behavior of the flow and turbulence features in proximity to bridge piers, at two different moments of the scour temporal evolution in free-surface and pressure-flow conditions. Bridge pressure-flow conditions occur when the water depth submerges a bridge deck during extreme events. A circular pier and two rectangular decks of different lengths were used for this research. All tests were carried out in clear water conditions at the sediment critical velocity. This paper studied first the rate of scour temporal evolution and scour morphologies. Second, velocity measurements were taken using a Nortek acoustic Velocimeter at 25 Hz sampling rate in both free-surface and pressure-flow conditions. The average three-dimensional flow velocities, turbulence intensities, Reynolds stress, and turbulent kinetic energy were studies for the cross section corresponding to the center of the pier. The results show that pressure flow conditions accelerate the scour rate. This rate approximately reaches twice the scour in free-surface conditions with a vertical contraction of about 17%. Flow and turbulence measurements clearly exhibit how, under pressure-flow conditions, the additional turbulence and accelerated velocity modifies the flow pattern and circulation, accelerating the scour evolution around the bridge base. While numerous studies exist for pier scour and turbulence in free-surface conditions, pressure flow conditions received limited attention in the past. These results provide essential information for understanding scour mechanisms and for facilitating the design of future structures to increase bridge safety and resilience.

Section: Introductionmentioning

confidence: 99%

Characteristics of Flow Structure around Cylindrical Bridge Piers in Pressure-Flow Conditions

Carnacina

Pagliara

2019

Water

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“…Given the same morphology, increasing sea levels cause an increase in residual currents and net transport near the coastline. Similar to other coastal systems, this can be explained by considering that an increase in water depth causes the tidal wave to propagate more easily, yielding higher discharge and increased velocity values [27,73,74]. A decrease in sea level causes a large dampening of residual currents and residual transport within the Thames region, and especially in the northern portion of the domain; a reduction in sea level also generally causes a large decrease in net sediment transport.…”

Section: Discussionmentioning

confidence: 82%

A Numerical Investigation on Tidally Induced Sediment Transport and Morphological Changes with Changing Sea Level in South-East England

Carnacina

2019

Geosciences

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The impact of tide-induced morphological changes and water level variations on the sediment transport in a tidally dominated system has been investigated using the numerical model Delft3D and South-East England as a test case. The goal of this manuscript is to explore the long-term changes in morphology due to sea level rise and the large-scale morphodynamic equilibrium of the South-East England. Our results suggest that the long term (century scale) tidally-induced morphological evolution of the seabed slows down in time and promotes a vanishing net transport across the large scale system. Century-scale morphologically updated simulations show that both morphological changes and net transport values tend to decrease in time as the system attains a dynamic equilibrium configuration. Results further suggest that the presence of a gradual increase in mean sea level accelerates the initial morphological evolution of the system whose morphological rate of change gradually attains, however, same plateau values as in the absence of sea level rise. Given the same base morphology, increasing water levels enhance residual currents and the net transport near the coastline; and vice-versa, decreasing sea levels minimize both residuals and net transport near the coastline. The areas that are more affected by, water level and morphological changes, are the ones where the net transport is the highest. This manuscript explores and allows extending the idea of morphodynamic equilibrium at a regional scale, larger than the one for which this concept has been generally explored i.e., estuarine scale.

“…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

Geophysical Research Letters

et al. 2019

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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.