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.     

Numerical simulation of storm surges in Lake Winnipeg

A high-resolution unstructured grid two-dimensional finite-element model was applied to simulate the storm surge associated with the October 2010 extratropical storm in Lake Winnipeg. The wind and pressure fields from two high-resolution weather forecast models were used to drive the hydrodynamic model. The model results were compared with the observed water levels at several stations during the storm event. The model-predicted storm surge in the range of 0.6–1.5 m is comparable with observations in the southern basin of Lake Winnipeg. Model results are further analyzed to assess the transport of water between north and south basins of Lake Winnipeg during the event. Computed water surface elevations at specific locations at the outlet of the rivers and embayments indicate that the model needs some improvements in terms of grid resolution in those areas.     

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.

     

Numerical simulation and prediction of storm surges and water levels in Shanghai harbour and its vicinity

A water level model incorporating the nonlinear interactions between tides and storm surges for numerical simulation and prediction use is developed in this paper. Using a conventional two-dimensional nonlinear storm surge model and tide model and associated semi-momentum finite-difference scheme, both the storm surges caused by the tropical cyclones hitting Shanghai and the tides in related regions during the period 1949–1990, are numerically simulated. In simulating storm surges, 16 tropical cyclones with different kinds of tracks are chosen. Meanwhile, to simulate tides, the governing equations for tides, along with 63 prescribed tidal constituents at open sea boundaries are numerically computed. Sixteen associated cases of total water-level simulations comprising joint effects linking surges and tides and one case of real-time prediction have been carried out in 1990 on the basis of computed surges and tides. The total water levels thus obtained in this way give better results than those obtained by the traditional method, i.e. without taking into account, in the model, nonlinear coupling between storm surges and tides.Comparison of the predictions of storm surges and the total water level with the hindcast ones in 1990 showed that a relatively larger error of prediction mainly results from the incorrect forecasting of tropical cyclones but not from the prediction method itself.     

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.     

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.     

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).     

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.     

Simulation of the Hurricane Dennis storm surge and considerations for vertical resolution

A high-resolution storm surge model of Apalachee Bay in the northeastern Gulf of Mexico is developed using an unstructured grid finite-volume coastal ocean model (FVCOM). The model is applied to the case of Hurricane Dennis (July 2005). This storm caused underpredicted severe flooding of the Apalachee Bay coastal area and upriver inland communities. Accurate resolution of complicated geometry of the coastal region and waterways in the model reveals processes responsible for the unanticipated high storm tide in the area. Model results are validated with available observations of the storm tide. Model experiments suggest that during Dennis, excessive flooding in the coastal zone and the town of St. Marks, located up the St. Marks River, was caused by additive effects of coincident high tides (~10–15% of the total sea-level rise) and a propagating shelf wave (~30%) that added to the locally wind-generated surge. Wave setup, the biggest uncertainty, is estimated on the basis of empirical and analytical relations. The Dennis case is then used to test the sensitivity of the model solution to vertical discretization. A suite of model experiments is performed with varying numbers of vertical sigma (σ) levels, with different distribution of σ-levels within the water column and a varying bottom drag coefficient. The major finding is that the storm surge solution is more sensitive to resolution within the velocity shear zone at mid-depths compared to resolution of the upper and bottom layer or values of the bottom drag coefficient.     

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。     

Storm surges in the Arabian Gulf

The storm surge phenomenon in the Arabian Gulf, including the Strait of Hormuz, is discussed with particular emphasis on the development of mathematical models for prediction purposes. The Gulf is mainly influenced by extra-tropical weather systems, whereas the region south of the Strait of Hormuz is affected by tropical cyclones. The west-to-east directed extra-tropical cyclone tracks and the generally east-to-west directed tropical cyclone tracks converge near the Strait of Hormuz. A meso-scale weather system that deserves special attention in prescribing the meteorological forcing functions is the so-called winter Shamal. A two-dimensional numerical model is developed to study the storm surges in the Arabian Gulf. The results show that the Gulf is subject to major negative and positive storm surges. Strong winds associated with the Shamal system, coupled with atmospheric pressure gradients, topography and tidal effects, can give rise to water level deviations of several meters. Storm surges observed during the period 17–19 January 1973 show that negative values in the 0.5 to 1.0m range were widespread in the Gulf.     

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.

     

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.     

钱塘江河口杭州湾风暴潮溢流计算方法研究

建立钱塘江河口杭州湾风暴潮模型,探讨风暴潮出现溢流的计算方法。将可能出现溢流的沿海堤防以及海水侵入的陆地均依照高程概化为计算区域,采用糙率控制潮水的溢流流量,以模型的堤顶单宽流量和根据计算潮位采用宽顶堰公式换算流量的一致性来率定糙率值。在此基础上模拟了风暴潮漫溢堤防的过程,结果表明风暴潮出现溢流后,钱塘江河口杭州湾之间两岸大片的陆地存在淹没风险,沿程潮位由于溢流出现不同程度的降低响应。     

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.     

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.

     

Records of palaeo‐sea level and eruption duration in a coastal tuff ring,Jeju Island,Korea

Phreatomagmatic volcanoes and their sedimentary products can preserve high‐resolution records of earth surface processes because of their high deposition rate. Songaksan, Jeju Island, Korea, is a phreatomagmatic volcano, which erupted c. 3.7 ka BP in a coastal setting. Its tuff ring preserves a record of intertidal to supratidal facies transition in the basal part, which reveals the position of palaeo‐high‐tide level for at least 13 high‐tide events, and a record of a storm‐surge event in the middle part of the tuff ring, which lasted approximately three tidal cycles. Based on these features, the phreatomagmatic eruption of Songaksan is estimated to have taken place over a month. The sea level at the time was almost identical to that at present. This study shows that coastal phreatomagmatic volcanoes can preserve high‐resolution records of eruption duration and palaeo‐sea level, and can provide accurately levelled and dated data points to the Quaternary sea‐level curve.     

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.