Storm Surge Propagation Research Articles

Application of an unstructured mesh model to storm surge propagation in the Mersey estuary region of the Irish Sea

The storm surge period of 13–16 November 1977 when there was a major positive surge followed by a negative surge in the Irish Sea is investigated using a two-dimensional unstructured mesh model of the west coast of Britain. The model accounts for tidal and external surge forcing across its open boundaries which are situated in the Celtic Sea and off the west coast of Scotland. Although this period has been examined previously using a uniform finite-difference model, and a finite element model, neither of these could resolve the Mersey estuary which is the focus of the present study. By using a finite element model with very high mesh resolution within the Mersey, the spatial variability of surge elevations and currents within the Mersey to rapidly changing surge dynamics can be examined. The mesh in the model varies from about 7 km in deep water, to the order of 100 m in the Mersey, with the largest mesh length reaching 17 km in deep offshore regions, and smallest of order 26 m occurring in shallow coastal regions of the Mersey estuary. The model accounts for wetting/drying which occurs in shallow water coastal areas. Calculations showed that during the positive surge period, the amplitude and speed of propagation of the surge was largest in the deep water channels. This gave rise to significant spatial variability of surge elevations and currents within the estuary. As wind stresses decreased over the Irish Sea, a negative surge occurred over Liverpool Bay and at the entrance to the Mersey. However, within the Mersey there was a local positive surge which continued to propagate down the estuary. This clearly showed that although the large scale response of the Irish Sea to changing wind fields occurred rapidly, the response in the Mersey was much slower. These calculations with a west coast variable mesh model that included a high-resolution representation of the Mersey revealed for the first time how elevations and currents within the Mersey responded to Irish Sea surges that rapidly changed from positive to negative.

THE NUMERICAL SIMULATION OF STORM-SURGE AND COASTAL INUNDATION OF 2007 TYPHOON SEPAT

A comprehensive numerical model for simulating storm surge has been aimed at the middle-east Taiwan Strait, in which contains the Penghu Channel (PHC) and Changyun Rise (CYR). The simulation results can be used to understand the direct impact of storm surge on the interest area during typhoon invades. The case in this study is Typhoon SEPAT, which passed through central Taiwan in 2007. The transport characteristics through the Taiwan Strait under the influence of Typhoon SEPAT were analyzed using both field observations and numerical simulations during the typhoon period. The results show that storm surge did not respond to the southerly winds but the northerly winds, in contrast to the wind waves. According to the influence of dynamical forces on the storm surge in the Taiwan Strait, the atmospheric pressure gradient is found to be the dominant force of the coastal inundation during the typhoon event. By comparing with the numerical experiment, the Coriolis force is found to have a negative contribution to the storm surge generation in the Taiwan Strait.

Storm surge propagation in Galveston Bay during Hurricane Ike

We studied Hurricane Ike's storm surge along the Texas–Louisiana coast using the fully nonlinear Finite-Volume Coastal Ocean Model (FVCOM, by Chen et al., 2003) with a high-resolution unstructured mesh. The model was validated with USGS surge data collected during Hurricane Ike. This study focused on 1) how the surge wave propagates into and within Galveston Bay and 2) the importance of the bay's barrier system. Ike's coastal surge propagated alongshore due east towards Louisiana, partly because of Bolivar Peninsula, which, together with Galveston Island, provided a barrier protecting the bay. In the upper bay, a west–east oscillation of water surface gradient of about 0.08 m/km was found and studied. We then varied Bolivar Peninsula's topography for different simulations, examining the role of barrier islands on surge propagation into the bay. Results suggest that when the Peninsula's height (or volume) was reduced to about 45% of the original, with two breaches, the bay was exposed to dangerously high water levels almost as much as those if the Peninsula was leveled to just 0.05 m above the Mean Sea Level, underlining the nonlinear nature of this bay-barrier system.

Storm surge computations in estuarine and near-coastal regions: the Mersey estuary and Irish Sea area

An unstructured grid storm surge model of the west coast of Britain, incorporating a high-resolution representation of the Mersey estuary is used to examine storm surge dynamics in the region. The focus of the study is the major surge that occurred during the period 11–14 November 1977, which has been investigated previously using uniform grid finite difference models and a finite element model of the west coast of Britain. However, none of these models included the Mersey estuary. Comparison of solutions in the eastern Irish Sea with those computed with these earlier models showed that, away from the Liverpool Bay region, the inclusion of the Mersey estuary had little effect. However, at the entrance to the Mersey, its inclusion did influence the solution. By including a detailed representation of the Mersey estuary within the model, it was possible to conduct a detailed study of storm surge propagation in the Mersey, which had never previously been performed. This detailed study showed for the first time that the surge’s temporal variability within the estuary is influenced by surge elevation at its entrance. This varies with time as a function of spatial and temporal variations of wind stress over the west coast of Britain. Within the Mersey, calculations show that the spatial variability is mainly determined by changes in bottom topography, which had not been included in earlier finite difference models. However, since water depth is influenced by variations in tidal elevation, this, together with tide surge interaction through bottom friction and momentum advection, influences the surge. The ability of the finite element model to vary the mesh in near-shore regions to such an extent that it can resolve the Mersey and hence the impact of the Mersey estuary upon the Liverpool Bay circulation shows that it has distinct advantages over earlier finite difference models. In the absence of detailed measurements within the Mersey at the time of the surge, it was not possible to validate predicted surge elevations within the Mersey. However, significant insight into physical processes influencing the surge propagation down the estuary, its reflection and spatial/temporal variability could be gained.

Storm Surge Simulations for Hurricane Hugo (1989): On the Significance of Inundation Areas

The storm surge generated by Hurricane Hugo (1989) is reproduced for the purposes of (1) evaluating the significance of including inland flooding areas and corresponding levels of spatial resolution and (2) assessing the spatial variability of near-inlet boundary forcings with respect to storm surge hydrographs. The study focuses on the coastal regions of South Carolina, incorporating inundation areas between Charleston and Shallotte Inlet and including Winyah Bay and the Waccamaw River. The region of interest is modeled with five variations of an unstructured, finite-element mesh, including a localized coarse grid with and without floodplains, a localized fine grid with and without floodplains, and a large-domain approach that includes floodplains and the continental shelf and deep ocean. Simulation results demonstrate that the inclusion of inland flooding areas significantly improves the description of storm surge generation within coastal regions. While the large-domain approach is shown to be beneficial, it is determined that the coarse mesh resolution of the floodplains is sufficient. Computed water surface elevations at specific locations surrounding Winyah Bay Inlet indicate that storm surge hydrographs are highly spatially dependent near inlets, as opposed to the astronomical tides, which exhibit minimal variance in space around the inlet environment.

Grid convergence studies for the prediction of hurricane storm surge

SUMMARY The focus of this paper is a systematic determination of the relationship between grid resolution and errors associated with computations of hurricane storm surge. A grid structure is sought that provides the spatial resolution necessary to capture pertinent storm surge physics and does not overdiscretize. A set of numerical experiments simulating storm surge generation over 14 grid discretizations of idealized domains examines the influence of grid spacing, shoreline detail, coastline resolution and characteristics of the meteorological forcing on storm surge computations. Errors associated with a given grid are estimated using a Richardson-based error estimator. Analysis of the magnitude and location of estimated errors indicates that underresolution on the continental shelf leads to significant overprediction of the primary storm surge. In deeper waters, underresolution causes smearing or damping of the inverted barometer forcing function, which in turn results in underprediction of the surge elevation. In order to maintain a specified error level throughout the duration of the storm, the highest grid resolution is required on the continental shelf and particularly in nearshore areas. The disparity of discretization requirements between deep waters and coastal regions is best met using a graded grid. Application of the graded gridding strategy to the hindcast of Hurricane Camille reinforces the necessity of using a grid that has high levels of resolution in nearshore regions and areas of complex coastal geometry. # 1998 John Wiley & Sons, Ltd. Int. J. Numer. Meth. Fluids, 26: 369‐401 (1998).

The influence of domain size on the response characteristics of a hurricane storm surge model

The influence of domain size on boundary condition specification and on computed storm surge response is investigated. Storm surge response along the Florida shelf in the Gulf of Mexico due to Hurricane Kate is examined over three domains using two different open ocean boundary forcing functions, a still water (or zero elevation) condition and an inverted barometer condition which accounts for the atmospheric pressure component of the meteorological forcing. The first domain is relatively small and is situated primarily on the continental shelf in the region of intense storm surge generation. A second domain includes the entire Gulf of Mexico basin. The final domain covers the Gulf of Mexico, contiguous basins, and extends out into the deep Atlantic Ocean. The computed storm surge response indicates that the small domain is inadequate, since cross‐shelf boundaries are in regions of significant storm surge generation where surge and therefore boundary conditions are not known a priori. Also, the behavior of resonant modes that are physically excited within the Gulf of Mexico due to the passage of the hurricane is unknown at the boundaries of this small domain. The domain that includes the entire Gulf of Mexico captures the primary storm surge well but may not correctly model resonant modes. In general, these resonant modes are difficult to accurately set up by boundary condition specification, since they may be dependent on interactions between the Gulf and contiguous basins. The primary storm surge response as well as resonant modes excited by the storm are best represented using a domain which encompasses the western North Atlantic Ocean, the Caribbean Sea, and the Gulf of Mexico. This domain with deep Atlantic Ocean boundaries facilitates simple boundary condition specification and minimizes the influence of boundary conditions on storm surge generation in coastal regions. Basin resonant modes and basin to basin interactions are also captured.

Modeling of storm surges in the Bering Sea and Norton Sound

Sea level, currents, and ice distribution are studied in the Bering Sea during storm events. The ice and ice edge are incorporated into storm surge model. The interaction of wind, ice, and water is expressed by the normal and tangential stresses. A numerical grid is established for the Bering Sea, and a second refined grid is constructed for Norton Sound. Construction of open boundary conditions for the water and ice motion and numerical questions related to the application of a large frictional coefficient for ice are also discussed. Storm events from February and March 1982 are analyzed and compared with observations of bottom pressure and ice motion made by NOAA Pacific Marine Environmental Laboratory in the Bering Sea and sea level observations at Stebbins, Alaska. The influence of the ice on the storm surge propagation is shown, particularly that of the fast ice in Norton Sound. The model reproduces several observed features of the ice distribution in the Bering Sea, including the “race track” region off Nome, the polynya south of Saint Lawrence Island, and the movement of the ice edge.

STUDY ON CHARACTERISTICS OF CONCURRENCE OF RAINFALL AND STORM SURGE ASSOCIATED WITH TYPHOON

The characteristics of concurrence of rainfall and storm surge at Osaka are made clear by analyzing the available data of typhoons for the period 1900-1980; Distributions of typhoon positions when maximum storm surge ηmax or peak rainfall intensity γp occurred, a histogram of time-lag between ηmax and γp, and relationships between ηmax and γp, and between ηmax and total rainfall RT, are shown. Predictors of rainfall and storm surge are selected by using the stepwise regression analysis, and the probability distributions of the residuals are revealed. It is probable that the flood wave following the rainfall moves downstream in a river and the storm surge invades the river, with a considerably short time-lag. On these occasions, the high water levels along the river change, depending on the length of the time-lag. Such features of high water levels are examined in terms of the behavior of storm surge propagation in the lower reach with mild slope.

Two‐step explicit finite element method for storm surge propagation analysis

Two‐step explicit finite element method for storm surge propagation analysis

A NUMERICAL CALCULATION OF STORM TIDES INDUCED BY A TROPICAL STORM IMPINGING ON A CONTINENTAL SHELF

The transient phase of a storm surge generated by an idealized tropical storm in a coastal area is investigated by numerical means. Linearized forms of the storm surge equations of motion are used without bottom friction. Open water boundaries are considered in a basin with varying depth. The basin is separated into regions of differing grid sizes that give a greater density of points in shallow water. It is found that inflow of wind across the isobars is significant in storm surge generation, whereas the motion of the storm plays a smaller role. The pressure gradient gives only static heights in deep water with three times the static height at the coast on passage of a moderately moving storm.

The identification of weather conditions associated with the generation of major storm surges along the west coast of the British Isles

AbstractThe complex mechanism of storm surge generation in the Eastern Atlantic has introduced severe difficulties in attempts to establish the basis of a flood‐warning system for the west coast of the British Isles. As an interim measure, while coastal defences are being assessed in the light of the estimated probability of abnormal levels (Lennon 1963) and while research proceeds so that any consequent contingency may eventually be met, a qualitative technique has been devised which aims at an identification of weather situations which are potentially dangerous particularly for the British Channel area and for Liverpool Bay.Major surges are found to be generated as a result of the passage, over the sea approaches to the region, of a certain type of depression which, moving at a critical speed over shallow water, can establish conditions of near‐resonance. The relevant meteorological conditions are found to be remarkably uniform and capable of definition.

Meteorological Aspects of Strom Surge Generation

Facts concerning hurricanes and their effects on sea level as they relate to prevention of future disasters; meteorological aspects of storm surge generation by hurricanes; assuming probable errors in forecast, area several times as large as that actually affected must be alerted; how with improved instrumentation and forecasting techniques, number of evacuations will be reduced.