Modeling the impact of land reclamation on storm surges in Bohai Sea,China

A nested model for the simulation of tides and storm surges in the Bohai Sea, China, has been developed based on the three-dimensional finite-volume coastal ocean model. The larger domain covers the entire Yellow Sea and Bohai Sea with a horizontal resolution of ~10 km, and the smaller domain focuses on the Bohai Sea with a fine resolution up to ~300 m. For the four representative storm surges caused by extratropical storms and typhoons, the simulated surge heights are in good agreement with observations at coastal tide gauges. A series of sensitivity experiments are carried out to assess the influence of coastline change due to land reclamation in recent decades on water levels during storm surges. Simulation results suggest that changes in coastline cause changes in the amplitude and phase of the tidal elevation, and fluctuations of surge height after the peak stage of the storm surges. Hence, for the assessment of the influence of coastline changes on the total water level during storm surges, the amplitudes and phases of both the tidal and surge heights need to be taken into account. For the three major ports in the Bohai Bay, model results suggest that land reclamation has created a coastline structure that favors increasing the maximum water level by 0.1–0.2 m. Considering that during the storm surges the total water level is close to or even exceeds the warning level for these ports, further increasing the maximum water level by 0.1–0.2 m has the potential to cause severe damages and losses in these ports.

     

Hurricane storm surge simulations for Tampa Bay

Using a high resolution, three-dimensional, primitive equation, finite volume coastal ocean model with flooding and drying capabilities, supported by a merged bathymetric-topographic data set and driven by prototypical hurricane winds and atmospheric pressure fields, we investigated the storm surge responses for the Tampa Bay, Florida, vicinity and their sensitivities to point of landfall, direction and speed of approach, and intensity. All of these factors were found to be important. Flooding potential by wind stress and atmospheric pressure induced surge is significant for a category 2 hurricane and catastrophic for a category 4 hurricane. Tide, river, and wave effects are additive, making the potential for flood-induced damage even greater. Since storm surge sets up as a slope to the sea surface, the highest surge tends to occur over the upper reaches of the bay, Old Tampa Bay and Hillsborough Bay in particular. For point of landfall sensitivity, the worst case is when the hurricane center is positioned north of the bay mouth such that the maximum winds associated with the eye wall are at the bay mouth. Northerly (southerly) approaching storms yield larger (smaller) surges since the winds initially set up (set down) water level. As a hybrid between the landfall and direction sensitivity experiments, a storm transiting up the bay axis from southwest to northeast yields the smallest surge, debunking a misconception that this is the worst Tampa Bay flooding case. Hurricanes with slow (fast) translation speeds yield larger (smaller) surges within Tampa Bay due to the time required to redistribute mass.     

A modeling study of coastal inundation induced by storm surge,sea-level rise,and subsidence in the Gulf of Mexico

The northern coasts of the Gulf of Mexico (GoM) are highly vulnerable to the direct threats of climate change, such as hurricane-induced storm surge, and such risks are exacerbated by land subsidence and global sea-level rise. This paper presents an application of a coastal storm surge model to study the coastal inundation process induced by tide and storm surge, and its response to the effects of land subsidence and sea-level rise in the northern Gulf coast. The unstructured-grid finite-volume coastal ocean model was used to simulate tides and hurricane-induced storm surges in the GoM. Simulated distributions of co-amplitude and co-phase lines for semi-diurnal and diurnal tides are in good agreement with previous modeling studies. The storm surges induced by four historical hurricanes (Rita, Katrina, Ivan, and Dolly) were simulated and compared to observed water levels at National Oceanic and Atmospheric Administration tide stations. Effects of coastal subsidence and future global sea-level rise on coastal inundation in the Louisiana coast were evaluated using a “change of inundation depth” parameter through sensitivity simulations that were based on a projected future subsidence scenario and 1-m global sea-level rise by the end of the century. Model results suggested that hurricane-induced storm surge height and coastal inundation could be exacerbated by future global sea-level rise and subsidence, and that responses of storm surge and coastal inundation to the effects of sea-level rise and subsidence are highly nonlinear and vary on temporal and spatial scales.     

地面沉降对渤海湾风暴潮灾害防治的影响研究

渤海湾沿海地区地面沉降严重、风暴潮灾害频发。本文以天津作为典型区域,对风暴潮潮位测定、风暴潮灾害和防风暴潮预案措施等方面开展研究,认为地面沉降对上述3方面均有的不同程度的影响,在风暴潮灾害防治中必须考虑地面沉降问题。     

Coastal flooding due to synoptic scale,meso-scale and remote forcings

Coastal flooding occurs due to storm surges generated by tropical and extra-tropical cyclones on the globe. The meteorological forcing fields for the generation of storm surges are the tangential surface wind stress on the ocean surface and the normal atmospheric pressure gradients associated with the weather systems. The large scale forcing from the cyclones is referred to as the synoptic scale and storm surge prediction from synoptic scale forcing is well developed and is reasonably satisfactory around the world. However, coastal flooding also occurs from weather systems, with forcing on a meso-scale and also from remote forcing. It is proposed here that the term “Storm surge” be used to only refer to coastal flooding from synoptic scale forcing and the terminology “Rissaga” be used for coastal flooding from meso-scale forcing. For flooding due to remote forcing, a new term “Kallakkadal” is proposed.     

上海复合极端风暴洪水淹没模拟

河口三角洲和沿海城市面临着台风、暴雨、高潮位和上游下泄洪水叠加的“四碰头”复合极端风暴洪水的严重威胁。构建了大气-海洋-陆地相耦合的一体化数值模拟系统,实现了上海市“风”“暴”“潮”“洪”多灾种复合情景的极端洪涝淹没模拟,并验证了耦合方法的有效性,为复合风暴洪水的一体化模拟提供了一套可行的数值模拟方法。在9711台风影响下,模拟了1998年堤防升级改造后淹没面积(水深>0.2m)比改造前减少了62%,表明沿海沿江堤防设施建设在上海市防台防汛中起着关键性的作用。复合极端风暴洪水的有效模拟可为财产保险和未来市政规划提供参考。     

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。     

Effects of Hurricane Ivan on water quality in Pensacola Bay, Florida

Pensacola Bay, Florida, was in the strong northeast quadrant of Hurricane Ivan when it made landfall on September 16, 2004 as a category 3 hurricane on the Saffir-Simpson scale. We present data describing the timeline and maximum height of the storm surge, the extent of flooding of coastal land, and the magnitude of the freshwater inflow pulse that followed the storm. We computed the magnitude of tidal flushing associated with the surge using a tidal prism model. We also evaluated hurricane effects on water quality using water quality surveys conducted 20 and 50 d after the storm, which we compared with a survey 14 d before landfall. We evaluated the scale of hurricane effects relative to normal variability using a 5-yr monthly record. Ivan's 3.5 m storm surge inundated 165 km² of land, increasing the surface area of Pensacola Bay by 50% and its volume by 230%. The model suggests that 60% of the Bay's volume was flushed, initially increasing the average salinity of Bay waters from 23 to 30 and lowering nutrient and chlorophylla concentrations. Additional computations suggest that wind forcing was sufficient to completely mix the water column during the storm. Freshwater discharge from the largest river increased twentyfold during the subsequent 4 d, stimulating a modest phytoplankton bloom (chlorophyll up to 18 μg l⁻¹) and maintaining hypoxia for several months. Although the immediate physical perturbation was extreme, the water quality effects that persisted beyond the first several days were within the normal range of variability for this system. In terms of water quality and phytoplankton productivity effects, this ecosystem appears to be quite resilient in the face of a severe hurricane effect.     

Coastal flooding: impacts of coupled wave–surge–tide models

Wind waves and elevated water levels together can cause flooding in low-lying coastal areas, where the water level may be a combination of mean sea level, tides and surges generated by storm events. In areas with a wide continental shelf a travelling external surge may combine with the locally generated surge and waves and there can be significant interaction between the propagation of the tide and surge. Wave height at the coast is controlled largely by water depth. So the effect of tides and surges on waves must also be considered, while waves contribute to the total water level by means of wave setup through radiation stress. These processes are well understood and accurately predicted by models, assuming good bathymetry and wind forcing is available. Other interactions between surges and waves include the processes of surface wind-stress and bottom friction as well as depth and current refraction of waves by surge water levels and currents, and some of the details of these processes are still not well understood. The recent coastal flooding in Myanmar (May 2008) in the Irrawaddy River Delta is an example of the severity of such events, with a surge of over 3 m exacerbated by heavy precipitation. Here, we review the existing capability for combined modelling of tides, surges and waves, their interactions and the development of coupled models.     

Multiple scenario analyses forecasting the confounding impacts of sea level rise and tides from storm induced coastal flooding in the city of Shanghai,China

Shanghai is physically and socio-economically vulnerable to accelerated sea level rise because of its low elevation, flat topography, highly developed economy and highly-dense population. In this paper, two scenarios of sea level rise and storm surge flooding along the Shanghai coast are presented by forecasting 24 (year 2030) and 44 (year 2050) years into the future and are applied to a digital elevation model to illustrate the extent to which coastal areas are susceptible to levee breach and overtopping using previously developed inflow calculating and flood routing models. Further, the socio-economic impacts are examined by combining the inundation areas with land use and land cover change simulated using GeoCA-Urban software package. This analysis shows that levee breach inundation mainly occurs in the coastal zones and minimally intrudes inland with the conservative protection of dike systems designed. However, storm surge flooding at the possible maximum tide level could cause nearly total inundation of the landscape, and put approximately 24 million people in Shanghai under direct risk resulting from consequences of flooding (e.g. contamination of potable water supplies, failure of septic systems, etc.).     

Storm surge modelling for the Bay of Bengal and Arabian Sea

Most of the countries around the North Indian Ocean are threatened by storm surges associated with severe tropical cyclones. The destruction due to the storm surge flooding is a serious concern along the coastal regions of India, Bangladesh, Myanmar, Pakistan, Sri Lanka, and Oman. Storm surges cause heavy loss of lives and property damage to the coastal structures and losses of agriculture which lead to annual economic losses in these countries. About 300,000 lives were lost in one of the most severe cyclones that hit Bangladesh (then East Pakistan) in November 1970. The Andhra Cyclone devastated part of the eastern coast of India, killing about 10,000 persons in November 1977. More recently, the Chittagong cyclone of April 1991 killed 140,000 people in Bangladesh, and the Orissa coast of India was struck by a severe cyclonic storm in October 1999, killing more than 15,000 people besides enormous loss to the property in the region. These and most of the world’s greatest natural disasters associated with the tropical cyclones have been directly attributed to storm surges. The main objective of this article is to highlight the recent developments in storm surge prediction in the Bay of Bengal and the Arabian Sea.     

Developments in storm tide modelling and risk assessment in the Australian region

An overview is provided of some of the significant storm tide modelling and risk assessment studies undertaken over the past few years within Australia and the nearby oceanic regions for government and industry. Emphasis is placed on the need for integrated planning and forecasting approaches for storm tide risk assessment. The importance of the meteorological forcing and the appropriate modelling of each of the storm tide components, namely, astronomical tide, storm surge, breaking wave setup and coastal inundation is discussed. The critical role of tropical cyclone “best track” datasets for risk assessment studies and the potential impacts on design criteria and risk assessment studies is highlighted, together with the challenge of developing credible enhanced-greenhouse climate change scenarios. It is concluded that storm tide modelling needs to be undertaken in a holistic framework that considers the relative uncertainties in each of the various elements—atmospheric, hydrodynamic and data, as well as addressing operational forecasting, design and planning needs.     

Impact of cyclonic wind field on interaction of surge–wave computations using finite-element and finite-difference models

Both finite-element and finite-difference numerical models are applied to simulate storm surges and associated currents generated by tropical cyclones that struck the coast of Andhra Pradesh, located on the east coast of India. During a cyclone, the total water level at any location on the coast is made up of the storm surge, surge–wind wave interaction and the tide. The advanced circulation two-dimensional depth-integrated (ADCIRC-2DDI) model based on finite-element formulation and the two-dimensional finite-difference model of storm surges developed at IIT Delhi, hereafter referred as IITD storm surge model, are used. These models are driven by astronomical tides at the open ocean boundary and cyclonic asymmetric winds over the surface of the computational domain. Comparison of model simulated sea-surface elevations with coarse and finer spatial resolutions suggests that the grid resolution near the coast is very crucial for accurate determination of the surges in addition to the local bathymetry. The model underpredicts surges, and the peak surge location shifts more to the right of the landfall as the spatial resolution of the model becomes coarser. The numerical experiments also demonstrate that the ADCIRC model is robust over the IITD storm surge model for surge computations as the coastline is better represented in the former.     

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.     

Extremity analysis of storm surge for fixing safe design water level

Phenomenal storm surge levels associated with cyclones are common in East Coast of India. The coastal regions of Andhra Pradesh are in rapid stride of myriad marine infrastructural developments. The safe elevations of coastal structures need a long-term assessment of storm surge conditions. Hence, past 50 years (1949–1998), tropical cyclones hit the Bay are obtained from Fleet Naval Meteorological & Oceanographic Center, USA, and analyzed to assess the storm surge experienced around Kakinada and along south Andhra Pradesh coast. In this paper, authors implemented Rankin Hydromet Vortex model and Bretschneider’s wind stress formulation to hindcast the surge levels. It is seen from the hindcast data that the November, 1977 cyclone has generated highest surge of the order of 1.98 m. Extreme value analysis is carried out using Weibull distribution for long-term prediction. The results reveal that the surge for 1 in 100-year return period is 2.0 m. Further the highest surge in 50 years generated by the severe cyclone (1977) is numerically simulated using hydrodynamic model of Mike-21. The simulation results show that the Krishnapatnam, Nizampatnam and south of Kakinada have experienced a surge of 1.0, 1.5 and 0.75 m, respectively.     

Causes of the Unusual Coastal Flooding Generated by Typhoon Winnie on the West Coast of Korea

On 19 August 1997 Typhoon Winnie brought unusually strong and extensive coastal flooding from storm surges to the west coast of Korea, which was farenough from the typhoon's center to lack significant local wind and pressure forcing.Sea levels at some tidal stations broke 36-year records and resulted in property damages of $18,000,000. This study investigated the causes of the unusual high sea levels by using an Astronomical-Meteorological Index (AMI) and a coupled ocean wave-circulation model developed by the present authors. The AMI analysis and the numerical simulation of the surge event showed that the major cause of the high sea levels was not the standard inverse barometric effect supplemented by water piling up along the coast by the wind field of the typhoon as is usual for a typical storm surge, but rather an enhanced tidal forcing from the perigean spring tide and water transported into the Yellow Sea by the currents generated by the typhoon. The numerical results also indicated that the transported water accounted for about 50% of the increased sea levels. Another cause for the coastal flooding was the resonance coupling of the Yellow Sea (with a natural normal mode period of 37.8 h) and the predominant period of the surge (36.5 h).     

Methodology and challenges of fire following earthquake analysis: an urban community study considering water and transportation networks

Typhoon Lionrock, also known as the national number 1610 in Japan, caused severe flooding in east Japan in August 28–31, 2016, leaving a death toll of 22. With a maximum sustained wind speed of ~?220 km/h from the Joint Typhoon Warning Center’s best track, Lionrock was classified as a category 4 hurricane in Saffir–Simpson Hurricane Wind Scale and as a typhoon in Japan Meteorological Agency’s scale. Lionrock was among unique typhoons as it started its landfall from north of Japan. Here, we studied the characteristics of this typhoon through tide gauge data analysis, field surveys and numerical modeling. Tide gauge analysis showed that the surges generated by Lionrock were in the ranges of 15–55 cm with surge duration of 0.8–3.1 days. Our field surveys revealed that the damage to coastal communities/structures was moderate although it caused severe flooding inland. We measured a maximum coastal wave runup of 4.3 m in Iwaisaki. Such a runup was smaller than that generated by other category 4 typhoons hitting Japan in the past. Our numerical model was able to reproduce the storm surge generated by the 2016 Typhoon Lionrock. This validated numerical model can be used in the future for typhoon-hazard studies along the coast of northeastern Japan. Despite relatively small surge/wave runups in coastal areas, Lionrock’s death toll was more than that of some other category 4 typhoons. We attribute this to various primary (e.g., flooding, surges, waves, strong winds) and secondary (e.g., landslides, coastal erosions, debris flows, wind-blown debris) mechanisms and their combinations and interactions that contribute to damage/death during a typhoon event.

     

Simulation of Storm Surges Along Myanmar Coast Using a Location Specific Numerical Model

Coastal flooding induced by storm surges associated with tropical cyclones is one of the greatest natural hazards sometimes even surpassing earthquakes. Although the frequency of tropical cyclones in the Indian seas is not high, the coastal region of India, Bangladesh and Myanmar suffer most in terms of life and property caused by the surges. Therefore, a location-specific storm surge prediction model for the coastal regions of Myanmar has been developed to carry out simulations of the 1975 Pathein, 1982 Gwa, 1992 Sandoway and 1994 Sittwe cyclones. The analysis area of the model covers from 8° N to 23° N and 90° E to 100° E. A uniform grid distance of about 9 km is taken along latitudinal and longitudinal directions. The coastal boundaries in the model are represented by orthogonal straight line segments. Using this model, numerical experiments are performed to simulate the storm surge heights associated with past severe cyclonic storms which struck the coastal regions of Myanmar. The model results are in agreement with the limited available surge estimates and observations.     

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.