Correction to: Tropical cyclone: expressions for velocity components and stability parameter

Historically, Leyte Gulf in central eastern Philippines has received catastrophic damage due to storm surges, the most recent of which was during Typhoon Haiyan in 2013. A city-level risk assessment was performed on Leyte Gulf through synthetic storm generation, high-resolution ocean modeling, and decision tree analyses. Cyclones were generated through a combination of a Poisson point process and Monte Carlo simulations. Wind and pressure fields generated from the cyclones were used in a storm surge model of Leyte Gulf developed on Delft3D. The output of these simulations was a synthetic record of extreme sea level events, which were used to estimate maximum surge heights for different return periods and to characterize surge-producing storm characteristics using decision tree analyses. The results showed that the area most prone to surges is the Tacloban–Basey area with a 2.8?±?0.3 m surge occurring at a frequency of every 50 years. Nearby Palo area will likely receive a surge of 1.9?±?0.4 m every 50 years while Giporlos–Salcedo area a surge of 1.0?±?0.1 m. The decision tree analysis performed for each of these areas showed that for surges of 3–4 m, high-velocity winds (>?30 m/s) are consistently the main determining factor. For the areas, Tacloban, Basey, and Giporlos–Salcedo, wind speed was also the main determining factor for surge?>?4 m.     

Simulation of water levels and extent of coastal inundation due to a cyclonic storm along the east coast of India

The devastation due to storm surge flooding caused by extreme wind waves generated by the cyclones is a severe apprehension along the coastal regions of India. In order to coexist with nature’s destructive forces in any vulnerable coastal areas, numerical ocean models are considered today as an essential tool to predict the sea level rise and associated inland extent of flooding that could be generated by a cyclonic storm crossing any coastal stretch. For this purpose, the advanced 2D depth-integrated (ADCIRC-2DDI) circulation model based on finite-element formulation is configured for the simulation of surges and water levels along the east coast of India. The model is integrated using wind stress forcing, representative of 1989, 1996, and 2000 cyclones, which crossed different parts of the east coast of India. Using the long-term inventory of cyclone database, synthesized tracks are deduced for vulnerable coastal districts of Tamil Nadu. Return periods are also computed for the intensity and frequency of cyclones for each coastal district. Considering the importance of Kalpakkam region, extreme water levels are computed based on a 50-year return period data, for the generation of storm surges, induced water levels, and extent of inland inundation. Based on experimental evidence, it is advocated that this region could be inundated/affected by a storm with a threshold pressure drop of 66 hpa. Also it is noticed that the horizontal extent of inland inundation ranges between 1 and 1.5 km associated with the peak surge. Another severe cyclonic storm in Tamil Nadu (November 2000 cyclone), which made landfall approximately 20 km south of Cuddalore, has been chosen to simulate surges and water levels. Two severe cyclonic storms that hit Andhra coast during 1989 and 1996, which made landfall near Kavali and Kakinada, respectively, are also considered and computed run-up heights and associated water levels. The simulations exhibit a good agreement with available observations from the different sources on storm surges and associated inundation caused by these respective storms. It is believed that this study would help the coastal authorities to develop a short- and long-term disaster management, mitigation plan, and emergency response in the event of storm surge flooding.     

Return period estimates of extreme sea level along the east coast of India from numerical simulations

Estimates of return periods of extreme sea level events along the coast are useful for impact assessment. In this study, a vertically integrated 2D model was developed for the simulation of storm surges in the Bay of Bengal. The bathymetry for the model was derived from an improved ETOPO-5 data set, which was prepared in our earlier work. The meteorological forcing for the model was obtained from the cyclone model of Holland using the data available for 136 low-pressure systems that occurred during 1974–2000 in the Bay of Bengal. The simulated total sea level and the surge component were obtained for each event. The simulated peak levels showed good agreement with the observations available at few stations. The annual maxima of sea levels, extracted from the simulations, were fitted with Gumbel distribution using r-largest annual maxima method to estimate the 5- and 50-year return periods of extreme events at 26 stations along the east coast of India. The return periods estimated from simulated sea levels showed good agreement with those obtained from observations. The 5- and 50-year return levels of total sea level along the east coast of India show a considerable increase from south to north, with the 50-year return total sea levels being as high as 6.9 and 8.7 m at stations along the north eastern coast such as Sagar Island and Chandipur, respectively. The high return levels are expected at these stations as the cyclones developed in the Bay of Bengal generally move north or north-west, producing extreme events in the northern part, and moreover, these stations are characterized by high tidal ranges. However, at some regions in the southern part such as Surya Lanka and Machilipatnam, though 50-year return levels of total sea level are not very high (2.98 and 2.97 m, respectively) because of the relatively lower tidal ranges, high return levels of surges (0.84 and 0.57 m, respectively) are found. In addition to the role of shallow depths (5.0 and 6.1 m, respectively) at the two stations, the high return levels of surges are attributed to the effect of geometrical configuration at Surya Lanka and width (100 km) and orientation of continental shelf at Machilipatnam.     

Nearshore propagation of cyclonic waves

Cyclone-generated surface waves are simulated using state-of-art SWAN (Simulating WAves Nearshore) model coupled with hydrodynamic model inputs. A severe cyclonic storm passed over the Arabian Sea during 4–9th November 1982 is selected from UNISYS track records. The cyclone lasted for nearly 6 days and subsided with a land fall at Gujarat coast, west coast of India. In this study, cyclonic wind fields are generated using a well-established relationship suggested by Jelesnianski and Taylor (1973). The associated water level variations due to storm surge and surge generated currents are simulated using POM (Princeton Ocean Model). The outputs are one-way coupled with the wave model SWAN for simulating wave parameters off Gujarat, north-east basin of Arabian Sea. An extensive literature review is carried out on the progress and methodology adopted for storm wave modelling and analysis. The results presented in this paper reveal the severity of the storm event and would be highly useful for assessing the extreme wave event/climate especially for the south coast of Gujarat.     

An analysis of beach profile changes subsequent to the Colombo Harbor Expansion Project,Sri Lanka

Man-made coastal structures directly affect sediment balance and sediment dynamics on the surrounding beaches. The Colombo Harbor Expansion Project has created about 5-km-long breakwater nearly perpendicular to the beach. The present study is focused on quantitatively and qualitatively analyzing the effect of the Colombo Harbor Expansion Project on economically important beaches in and around Colombo city area. In this study, the authors measured monthly variations of beach width, beach profile and the mean grain-size of the sediments at mean sea level for complete annual monsoon cycle. Data were analyzed to establish site-specific erosion vulnerability. Monitoring results show that cumulative beach erosion has increased after the construction of the breakwater (rate = 0.7 m/year from May 2000 to April 2011 and rate = 28.2 m/year from April 2011 to June 2012). In addition, the cumulative and site-specific sand accretion and erosion patterns have a clear relationship with the monsoon seasonality. Beaches were narrower during the stormy southwestern monsoon, whereas beaches were wider during fair weather of northeast monsoon and inter-monsoon periods. In contrast, the constructed breakwater obstructs natural longshore sediment dynamics. For example, a significant amount of sediments from the Kelani-Ganga River were buried in the Colombo Harbor due to alteration of prominent longshore sediments transportation on the western coast of Sri Lanka. Therefore, this study shows enhancement of coastal erosion in the studied southern beaches due to a lack of sediment deposition.     

Application of a fast stochastic storm surge model on estimating the high water level frequency in the Lower Rhine Delta

In the Lower Rhine Delta of the Netherlands, the high water level is driven by a joint impact of the downstream storm surge and the upstream fluvial discharge, and affected by the operation of existing man-made structures. In scenario-based risk assessment, a large number of stochastic scenarios of storm surges are required for estimating the high water level frequency. In this article, a fast computing stochastic storm surge model is applied to the gauge station of Hook of Holland in the west of the Netherlands. A fixed number of tides are considered in this model based on the information of historical storm surge events. Based on this model, a large number of stochastic storm surge scenarios are derived and forced into a one-dimensional hydrodynamic model of the Netherlands, resulting in peak water levels in Rotterdam, the most vulnerable city in the delta. These peak water levels are statistically analyzed and converted to the high water level frequency curve in Rotterdam. The high water level frequency curve in Rotterdam tends to a much lower design water level compared to the official design water level that is used to design the dikes and structures for protection of the city. Moreover, there is a significant difference in the high water level frequency curves due to the fact that the stochastic storm surge model considers different numbers of tides. This highlights the critical impact of the storm surge duration on the high water level frequency in the Lower Rhine Delta.     

Simultaneous meteorological tsunamis and storm surges at Buenos Aires coast,southeastern South America

Meteorological tsunamis are frequently observed in different tide stations at the southeastern coast of South America. They are associated with the occurrence of atmospheric gravity waves during the passages of cold fronts over the Buenos Aires Province continental shelf. On the other hand, storm surges are also frequent in the region, and they are associated with strong and persistent southerlies, which are also frequent during cold front passages. The impact of meteorological tsunamis in coastal erosion and in the statistics of storm surge trends is discussed in this paper. For this study, fifteen meteorological tsunamis (with maximum wave heights higher than 0.20 m), seven of them simultaneous to the occurrence of storm surge events (with extreme levels higher than |±0.60 m|), are selected from April 2010 to January 2013. The impact of meteorological tsunamis in the storm erosion potential index (SEPI) is evaluated. Not significant differences are obtained between SEPI calculated with and without filtering the meteorological tsunami signal from the storm surge data series. Moreover, several experiments are carried out computing SEPI from synthetic sea level data series, but very low changes (lower than 4 %) are also obtained. It is concluded that the presence of moderate meteorological tsunamis on sea level records would not enhance this index at the Buenos Aires Province coast. On the other hand, taking into account that meteorological tsunamis can reach up the 20–30 % of the storm surge height, it was concluded that the statistics of storm surge trends (and their uncertainties) should be revised for Mar del Plata data series.     

河口海岸桥隧工程设计流速推算

跨海桥隧工程设计需要推算工程位置不同重现期设计流速,由于现场缺乏长期实测流速资料,设计流速推算存在很大困难。研究提出了采用不同重现期典型风暴潮过程推算河口海岸设计流速的数值模拟方法,对河口地区考虑洪水径流与风暴潮流的耦合。在依据澳门验潮站1925—2003年实测潮位资料分析珠江口海域风暴潮过程特征的基础上,结合潮位和潮差年极值频率分析结果构建了不同重现期典型风暴潮潮型。采用平面二维水动力数学模型模拟了不同重现期风暴潮和上游一般洪水组合条件下珠江口水域的流场,得出港珠澳大桥沿线各控制点处设计流速。     

Characteristics of Extreme Meteorological Forcing and Water Levels in Mobile Bay, Alabama

The paper presents comprehensive statistical analyses of winds and water levels in Mobile Bay, Alabama, based on long-term meteorological and tidal observations at several locations. A procedure has been developed to select the most probable parent distribution function from a list of candidate distributions. The theoretical functions that fit the data best enable us to predict the extreme values of winds and water levels at different return periods. We have demonstrated the importance of dividing the winds into hurricane and nonhurricane seasons and separating astronomical tides from weather-driven water level changes. The statistical analysis suggests that the wind speed averaged over 8 min at Dauphin Island, Alabama, at the 100-year return period would be 48.9 m/s, which is equivalent to a sustained 1-min wind of 205 km/h, a very strong category 3 hurricane on the Saffir-Simpson scale. The probability distribution models predict that the 100-year maximum water level would be 3.23 m above the mean lower low water (MLLW) level at the bay entrance and 3.41 m above the MLLW level near the head of the bay, respectively. Extremely low water levels important to navigation are also found. Application of the predicted extreme winds and surges is illustrated through the development of a storm wave atlas in the estuary. It is expected that the methodology and results presented in this paper will benefit the management and preservation of the ecosystems and habitats in Mobile Bay.     

Impact of wind gusts on sea surface height in storm surge modelling, application to the North Sea

Storm surge models usually do not take into account the explicit effect of wind gusts on the sea surface height. However, as the wind speed enters quadratically into the shallow water equations, short-term fluctuations around the mean value do not average out. We investigate the impact of explicitly added gustiness on storm surge forecasts in the North Sea, using the WAQUA/DCSM model. The sensitivity of the model results to gustiness is tested with Monte Carlo simulations, and these are used to derive a parametrisation of the effect of gustiness on characteristics of storm surges. With the parametrisation and input from the ECMWF model archive, we run hindcasts for a few individual cases and also the 2007–2008 winter storm season. Although the explicit inclusion of gustiness increases the surge levels, it does not help to explain, and hence reduce, the errors in the model results. Moreover, the errors made by ignoring gustiness are small compared to other errors. We conclude that, at present, there is no need to include gustiness explicitly in storm surge calculations for the North Sea.     

Damage risk assessment of breakwaters under tsunami attack

Turkey was struck by two major events on 17 August and 12 November 1999, named Izmit (M _w = 7.4) and Düzce (M _w = 7.2) earthquakes, respectively. Rubble mound breakwaters in Izmit Bay experienced little damage, as forecasted by the new risk assessment model in which tsunami occurrence risk was included in the damage estimations. In order to determine the occurrence probability of structural damage under design conditions, including the environmental loading parameters of tsunami and storm waves, tidal range and storm surge, the Conditional Expections Monte Carlo simulation was applied in the risk assessment model developed in this study for the Esenköy Fishery Harbour, Turkey. A tsunami was not the key design parameter when compared to storm waves for the main breakwater of the harbour, however, in places with great seismic activity, the tsunami risk should be important depending on the occurrence probability and magnitude of the tsunami.     

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

Astronomical high tides and meteorological storm surges present a combined flood hazard to communities and infrastructure. There is a need to incorporate the impact of tide-surge interaction and the spatial and temporal variability of the combined flood hazard in flood risk assessments, especially in hyper-tidal estuaries where the consequences of tide and storm surge concurrence can be catastrophic. Delft3D-FLOW is used to assess up-estuary variability in extreme water levels for a range of historical events of different severity within the Severn Estuary, southwest England as an example. The influence of the following on flood hazard is investigated: (i) event severity, (ii) timing of the peak of a storm surge relative to tidal high water and (iii) the temporal distribution of the storm surge component (here in termed the surge skewness). Results show when modelling a local area event severity is most important control on flood hazard. Tide-surge concurrence increases flood hazard throughout the estuary. Positive surge skewness can result in a greater variability of extreme water levels and residual surge component, the effects of which are magnified up-estuary by estuarine geometry to exacerbate flood hazard. The concepts and methodology shown here can be applied to other estuaries worldwide.     

A modelling approach for estimating the frequency of sea level extremes and the impact of climate change in southeast Australia

An efficient approach for evaluating storm tide return levels along the southeastern coastline of Australia under present and future climate conditions is described. Storm surge height probabilities for the present climate are estimated using hydrodynamic model simulations of surges identified in recent tide gauge records. Tides are then accounted for using a joint probability method. Storm tide height return levels obtained in this way are similar to those obtained from the direct analysis of tide gauge records. The impact of climate change on extreme sea levels is explored by adding a variety of estimates of mean sea level rise and by forcing the model with modified wind data. It is shown that climate change has the potential to reduce average recurrence intervals of present climate 1 in 100 year storm tide levels along much of the northern Bass Strait coast to between 1 and 2 years by the year 2070.     

Quantification of the Attenuation of Storm Surge Components by a Coastal Wetland of the US Mid Atlantic

Coastal wetlands are receiving increased consideration as natural defenses for coastal communities from storm surge. However, there are gaps in storm surge measurements collected in marsh areas during extreme events as well as understanding of storm surge processes. The present study evaluates the importance and variation of different processes (i.e., wave, current, and water level dynamics with respect of the marsh topography and vegetation characteristics) involved in a storm surge over a marsh, assesses how these processes contribute to storm surge attenuation, and quantifies the storm surge attenuation in field conditions. During the Fall of 2015, morphology and vegetation surveys were conducted along a marsh transect in a coastal marsh located at the mouth of the Chesapeake Bay, mainly composed of Spartina alterniflora and Spartina patens. Hydrodynamic surveys were conducted during two storm events. Collected data included wave characteristics, current velocity and direction, and water levels. Data analysis focused on the understanding of the cross-shore evolution of waves, currents and water level, and their influence on the overall storm surge attenuation. Results indicate that the marsh area, despite its short length, attenuates waves and reduces current velocity and water level. Tides have a dominant influence on current direction and velocity, but the presence of vegetation and the marsh morphology contribute to a strong reduction of current velocity over the marsh platform relative to the currents at the marsh front. Wave attenuation varies across the tide cycle which implies a link between wave attenuation and water level and, consequently, storm surge height. Storm surge reduction, here assessed through high water level (HWL) attenuation, is linked to wave attenuation across the front edge of the marsh; this positive trend highlights the reduction of water level height induced by wave setup reduction during wave propagation across the marsh front edge. Water level attenuation rates observed here have a greater range than the rates observed or modeled by other authors, and our results suggest that this is linked to the strong influence of waves in storm surge attenuation over coastal areas.     

Hydrological modeling of typhoon-induced extreme storm runoffs from Shihmen watershed to reservoir, Taiwan

Typhoon-induced extreme storm runoffs often cause flood hazards. In this study, a hydrological model (HEC-HMS) was applied to Shihmen watershed located in Taiwan. Three typhoon-induced storm events, with return period ranging from 1 to 90 years, were used in case studies to characterize storm runoff. With a 5-year storm for model calibration, model parameters were carefully calibrated through the comparison between model simulated and observed flows at a stream gage station. The calibrated model was then verified for a 90-year storm and a 1-year storm event. Results indicate that the calibrated and verified HEC-HMS hydrological model is capable of providing satisfactory predictions of the typhoon-induced extreme storm runoff to support reservoir operation and flood hazard mitigation. Based on model simulations, typhoon-induced water table increases for different initial water volumes at Shihmen Reservoir was derived by adding storm-runoff volume to the reservoir’s initial elevation-volume rating curve. Water tables above the top elevation of the dam in the reservoir indicate the need for immediate water releases to avoid the risk of overflow over the dam.     

On the accuracy of atmospheric forcing for extra-tropical storm surge prediction

The ability of the SMARA storm surge numerical prediction system to reproduce local effects in estuarine and coastal winds was recently improved by considering one-way coupling of the air–sea momentum exchange through the wave stress, and best forecasting practices for downscaling. The inclusion of long period atmospheric pressure forcing in tide and tide/surge calculations corrected a systematic error in the surge, produced by the South Atlantic Ocean quasi-stationary pressure patterns. The maximum forecast range for the storm surge at Buenos Aires provided by the real-time use of water level observations is approximately 12 h. The best available water level prediction is the 6-h forecast (nowcast) based on the closest water level observations. The 24-h forecast from the numerical models slightly improves this nowcast. Although the numerical forecast accuracy degrades after the first 48 h, the improvement to the full range observation-based prediction is maintained at the inner Río de la Plata area and extends to the first 3 days at the intermediate navigation channels.     

Dynamic analysis of emergency inter-organizational communication network under public health emergency: a case study of COVID-19 in Hubei Province of China

Storm surge induced by hurricane is a major threat to the Gulf Coasts of the United States. A numerical modeling study was conducted to simulate the storm surge during Hurricane Michael, a category 5 hurricane that landed on the Florida Panhandle in 2018. A high-resolution model mesh was used in the ADCIRC hydrodynamic model to simulate storm surge and tides during the hurricane. Two parametric wind models, Holland 1980 model and Holland 2010 model, have been evaluated for their effects on the accuracy of storm surge modeling by comparing simulated and observed maximum water levels along the coast. The wind model parameters are determined by observed hurricane wind and pressure data. Results indicate that both Holland 1980 and Holland 2010 wind models produce reasonable accuracy in predicting maximum water level in Mexico Beach, with errors between 1 and 3.7%. Comparing to the observed peak water level of 4.74 m in Mexico Beach, Holland 1980 wind model with radius of 64-knot wind speed for parameter estimation results in the lowest error of 1%. For a given wind model, the wind profiles are also affected by the wind data used for parameter estimation. Away from hurricane eye wall, using radius of 64-knot wind speed for parameter estimation generally produces weaker wind than those using radius of 34-knot wind speed for parameter estimation. Comparing model simulated storm tides with 17 water marks observed along the coast, Holland 2010 wind model using radius of 34-knot wind speed for parameter estimation leads to the minimum mean absolute error. The results will provide a good reference for researchers to improve storm surge modeling. The validated model can be used to support coastal hazard mitigation planning.

     

Impact of Sea-level Rise and Storm Surges on a Coastal Community

A technique to evaluate the risk of storm tides (the combination of a storm surge and tide) under present and enhanced greenhouse conditions has been applied to Cairns on the north-eastern Australian coast. The technique combines a statistical model for cyclone occurrence with a state-of-the-art storm surge inundation model and involves the random generation of a large number of storm tide simulations. The set of simulations constitutes a synthetic record of extreme sea-level events that can be analysed to produce storm tide return periods. The use of a dynamic storm surge model with overland flooding capability means that the spatial extent of flooding is also implicitly modelled. The technique has the advantage that it can readily be modified to include projected changes to cyclone behaviour due to the enhanced greenhouse effect. Sea-level heights in the current climate for return periods of 50, 100, 500 and 1000 years have been determined to be 2.0 m, 2.3 m, 3.0 m and 3.4 m respectively. In an enhanced greenhouse climate (around 2050), projected increases in cyclone intensity and mean sea-level see these heights increase to 2.4 m, 2.8 m, 3.8 m and 4.2 m respectively. The average area inundated by events with a return period greater than 100 years is found to more than double under enhanced greenhouse conditions.     

The role of overwash in the evolution of mixing zone morphology within barrier islands

Overwash is a major controlling factor in the morphology of the mixing zone of coastal aquifers. Conceptual models of the mixing zone describe an interface controlled by tidal oscillations, wave run-up, and other factors; however, few describe the influence of large storm events. In August 1993, Hatteras Island, North Carolina, USA, experienced a 3-m storm surge due to Hurricane Emily. Sound-side flooding infiltrated a wellfield, causing a dramatic increase in TDS levels that persisted for more than 3 years. Two-dimensional simulations with SUTRA, the USGS finite-element model, are calibrated to the TDS breakthrough data of this storm to infer model dispersivity values. Simulations using the calibrated dispersivity values, predicted flooding levels, and 54 years of hurricane records to determine the influence of the overwash events suggest that it is rare for the mixing zone to approximate the conceptual morphology. Even during quiescent periods such as between 1965 and 1975, TDS levels do not return to theoretical levels before being elevated by a subsequent storm event. Thus, while tidal oscillations and other factors are important to mixing zone development, basic wind events and more severe storm events may have more influence and lasting effect on the morphology of the mixing zone.