Assessment of Storm Surge and Flood Inundation in Chittagong City of Bangladesh Based on ADCIRC and GIS

Coastal flooding caused by tropical cyclones has long been a major threat to life,property,and infrastructure in coastal zones.This study assessed the risk of flooding in Chittagong,southeastern Bangladesh,under extreme sea level scenarios caused by high astronomical tides and storm surges.The Jelesnianski typhoon model and the ADvanced CIRCulation hydrodynamic model were used to simulate 91 typhoons that occurred in the Bay of Bengal between 1981 and 2017,and observational data were used for model validation.The inundation model was based on a digital elevation model and a seed spread algorithm,and a geographical information system was used to visualize the flood risk.Under four scenarios,the changes in flood levels caused by sea level rise had no signifi-cant influence on the extent of flooding in Chittagong.At flood levels of 8.82m(50-year storm surge without sea level rise)and 8.89 m(50-year storm surge with sea level rise),the maximum estimated area of inundation was 11.35 km^(2).The western coastal and southeastern river coastal plain areas of Chittagong have the highest risk of inundation due to their low-lying terrain.At flood levels of 9.83m(100-year storm surge without sea level rise)and 9.97m(100-year storm surge with sea level rise),the maximum simulated flood extent was 36.44km^(2).Simulated floodwaters propagated in a south–north direction,and most of the northern areas of the city are at risk of inundation under these scenarios.

Identification of Inundation Hazard Zones in Manas Basin, China, Using Hydrodynamic Modeling and Remote Sensing

A two-dimensional hydrodynamic model, Floodarea was applied to simulate the flood inundation area and flood depth in Manas basin, China. Two scenes of Landsat TM images were also used in this research. One image was used to produce the spatial distributed manning roughness to feed the model, the other one was used to delineate the actual inundated area by a modified NDWI method. The model and the manning roughness were validated by the comparison of simulated flood inundation extent and the corresponding actual inundated area obtained from Landsat image. The results show that the actual inundation extent obtained from Landsat image was 240.45 km2, and the modeled inundation area was276.15 km2. It indicates that manning roughness ranging from 0.025 to 0.833 is appropriate in the basin. In addition, the modeled flood depth varied from 0 to7.77 m. Taking land use into account, five hazard zones were identified in the study area. This study would be beneficial to flood control and disaster reduction.

Numerical Study of Storm Surge Inundation in the Southwestern Hangzhou Bay Region During Typhoon Chan-Hom in 2015

Storm surge inundation is a major concern in marine hazard risk assessment during extreme weather conditions.In this study,a high-resolution coupled model(the ADVanced CIRCulation model+the Simulating WAves Nearshore model)was used to investigate the storm surge inundation in the southwestern Hangzhou Bay region during Typhoon Chan-hom in 2015.The simulated hydrodynamic processes(sea surface wave and storm tide)were validated with measured data from wave buoys and tide gauges,indicating that the overall performance of the model was satisfactory.The storm surge inundation in the coastal area was simulated for several idealized control experiments,including different wave effects(wave-enhanced wind stress,wave-enhanced bottom stress,and wave radiation stress).Dike overflowing cases with different dike heights and dike breaking cases with different dike breach lengths were considered in the simulation.The results highlight the necessity of incorporating wave effects in the accurate simulation of storm surge inundation.Dike height significantly influences the magnitude and phase of the maximum inundation area in the dike overflowing cases,and dike breach length is an important factor impacting the magnitude of the maximum inundation area in the dike breaking cases.This study may serve as a useful reference for accurate coastal inundation simulation and risk assessment.

An experimental study on tsunami inundation over complex coastal topography

In recent studies, the effects of complex costal topography on tsunami run-up has sparked heated discussion. This study mainly aims at investigating the effects of complex costal topography on the tsunami inundation distance and the effectiveness of sand dunes in dissipating tsunami wave energy. The experiments were carried out in a wave flume to investigate the potential reduction effects of wave run-up by non erodible sand dune like features. The results show that increasing dunes spacing could not significantly affect inundation distance. However, if the height of sand dunes is of the same order of magnitude as the incoming tsunami wave and the gaps between the dunes are large enough, successful tsunami mitigation could also be possible.

Inundation Studies Along the East Coast of India due to Tsunamigenic Earthquakes in North-Andaman and Car Nicobar Subduction zone

The Sumatra-Andaman arc is an active subduction zone and had generated several destructive Tsunamis in the past.In this paper we have analyzed two historical Tsunamigenic earthquakes from this region. One of the historical earthquake is the earthquake of 26th June 1941 in the North Andaman region,which was one of the strongest in the Andaman Sea and Bay of Bengal of magnitude M_w=7.7.This earthquake had triggered tsunami which affected the east coast of India.The other is the earthquake in Car Nicobar region on 31 st December 1881 of magnitude M_w=7.9. This submarine earthquake beneath the

Numerical Simulation and Risk Analysis of Coastal Inundation in Land Reclamation Areas:A Case Study of the Pearl River Estuary

Coastal inundation results in many human casualties and significant economic losses.In this study,an inundation model with an unstructured mesh was developed using the ADvanced CIRCulation(ADCIRC)and Simulating WAves Nearshore(SWAN)models to simulate 43 inundation events from 1998 to 2018.A combined wind-pressure field derived from the assimilation windpressure model was used to drive the coupled ADCIRC-SWAN model.On the basis of the model results,a sensitivity study of the influence of land reclamation on coastal inundation was conducted.The results of the study showed that coastline changes caused by reclamation significantly influence the distribution of coastal inundation,particularly in areas where narrow waterways,bays,and peninsulas are newly formed.Combining the extreme inundation events calculated using the Gumbel and Weibull distributions,the 10-year,50-year,100-year,and 200-year return coastal inundations were obtained for the Pearl River Estuary in China.The risk of coastal inundation was analyzed according to the probability of the inundation depth exceeding 1 m.A hazard grade zoning map was drawn to guide disaster relief and mitigation in the reclamation area.

Saco-Casco Bays Inundation Modeling of Five Winter Storms

Coastal inundation along the northeast coast of the United States is usually caused by strong winter storms(WS).However,the accurate prediction of coastal inundation due to the WS is challenging.Therefore,our study aims to develop a unique high-resolution modeling system to accurately predict the coastal inundation in the ungauged coastal areas of Saco-Casco Bays and map the flood risk zones to potential sea level rise due to these storms.Hindcasts of five classic WS in 2014-2015 were studied.The inundation models are based on FVCOM that uses unstructured grid to capture the minor to significant flooding near the shallow areas of the bays,harbor entrance and river banks.In this study,topography has been generated from the NOAA’s integrated dataset of Portland,ME 1/3 arc-second MHW digital elevation model.The model runs were driven by two different sets of meteorological(NECOFS WRF and NOAA’s NAM WRF)forcing to examine the effect of spatial resolution on the predicted inundation.The study reveals that among the five storm surge cases,WS-III produces a maximum surge of 0.7 m and WS-II cause a minimum surge of 0.3 m.In all scenarios,southward wind-driven coastal current flowing towards Biddeford Pool,Pine Point and Camp Ellis forms a small-scale eddy which causes significant inundation however strength of the current varies accordingly.Sensitivity experiments have been carried out using NECOFS WRF simulation products with varying parameters of marshland elevation and bottom friction to understand the influence of intertidal storage on the predicted flooding.

Inundation Maps for Extreme Flood Events at the Mouth of the Danube River

Hydrodynamic modeling is used to analyse the inundation behavior of St. George village during extreme flood events, in particular for a flood happened in spring 2006. The study reach, 4 km in length, is situated in the Danube Delta, at the mouth of St. George distributary and includes St. George village. Land and bathymetric surveys were used to create a digital terrain model (DTM) of the river channel and the village. By coupling the geometry with hydrologic data, a 2D hydrodynamic model was built up with the help of the CCHE2D code (University of Mississippi). The model is based on integrating Saint-Venant shallow waters (depth averaged) equations through finite-difference implicit numerical scheme. It was calibrated in terms of roughness coefficients on measured values of water surface elevation registered in the St. George port. Flood maps obtained from computations were compared to satellite images from the same days of the spring 2006 extreme event. Inundation behaviour of the St. George village was analysed for different scenarios of river hydrological and sea level (variable because of wind waves) conditions. Findings were compared with high water marks and inhabitants testimonials. The model proved that sea level has a higher influence upon the inundability of the area than the river flood events.

Modelling and validation of flash flood inundation in drylands

In the context of climate change and human activities,flood disasters in arid mountainous areas have become increasingly frequent,and seriously threatened the safety of people's lives and property.Rapid and accurate flash flood inundation modelling is an essential foundational research area,which can aid in the reduction of casualties and the minimization of disaster losses;however,this modelling is also very difficult,and models need to be urgently developed to address flash flood forecasting and warnings.The objective of this study is to construct a numerical modelling method for flash floods in drylands.Based on a 2D high-resolution flood numerical model(Flood Map-Hydro Inundation2D),we hindcasted the dynamic process of flash flooding and show the spatio-temporal characteristics of flash flood inundation for the“8·18”flash flood disaster that occurred in Datong county,Qinghai province.The results showed that the model output effectively agreed with the observed inundation after the event in terms of both spatial extent and temporal process.Extensive flooding mainly occurred between 00:00 and 01:00 on August 18,2022.Qingshan,Hejiazhuang and Longwo villages were affected most heavily.We further conducted model sensitivity analysis and found that the model was highly sensitive to both roughness and hydraulic conductivity in drylands,and the effect of hydraulic conductivity was more pronounced.Our study confirmed the good performance of our model for the simulation of flash flooding in arid areas and provides a potential method for flash flood assessment and management in arid areas.

Reflections on coastal inundation,climate change impact,and adaptation in built environment:progresses and constraints

Coastal inundation causes considerable impacts on communities and economies.Sea level rise due to climate change increases the occurrence of coastal flood events,creating more challenges to coastal societies.Here we intend to draw the understanding of coastal inundation from our early studies,and provide a silhouette of our approaches in assessing climate change impacts as well as developing risk-based climate adaptation.As a result,we impart a distinctive view of the adaption towards the integration of asset design,coastal planning and policy development,which reflect multiscale approaches crossing individual systems to regions and then nation.Having the approaches,we also discussed the constraints that would be faced in adaptation implementation.In this regard,we initially follow the risk approach by illustrating hazards,exposure and vulnerability in relation to coastal inundation,and manifest the impact and risk assessment by considering an urban environment pertinent to built,natural,and socioeconomic systems.We then extend the scope and recommend the general approaches in developing adaptation to coastal inundation under climate change towards ameliorating overall risks,practically,by the reduction in exposure and vulnerability in virtue of the integration of design,planning and polices.In more details,a resilience design is introduced,to effectively enhance the capacity of built assets to resist coastal inundation impact.We then emphasize on the cost-effective adaptation for coastal planning,which delineates the problem of under-adaptation that leaves some potential benefits unrealized or over-adaptation that potentially consumes an excessive amount of resources.Finally,we specifically explore the issues in planning and policies in mitigating climate change risks,and put forward some emerging constraints in adaptation implementation.It suggests further requirements of harmonizing while transforming national policies into the contents aligned with provincial and local governments,communities,and households.

A Rapid Prediction Model of Urban Flood Inundation in a High-Risk Area Coupling Machine Learning and Numerical Simulation Approaches

Climate change has led to increasing frequency of sudden extreme heavy rainfall events in cities,resulting in great disaster losses.Therefore,in emergency management,we need to be timely in predicting urban floods.Although the existing machine learning models can quickly predict the depth of stagnant water,these models only target single points and require large amounts of measured data,which are currently lacking.Although numerical models can accurately simulate and predict such events,it takes a long time to perform the associated calculations,especially two-dimensional large-scale calculations,which cannot meet the needs of emergency management.Therefore,this article proposes a method of coupling neural networks and numerical models that can simulate and identify areas at high risk from urban floods and quickly predict the depth of water accumulation in these areas.Taking a drainage area in Tianjin Municipality,China,as an example,the results show that the simulation accuracy of this method is high,the Nash coefficient is 0.876,and the calculation time is 20 seconds.This method can quickly and accurately simulate the depth of water accumulation in high-risk areas in cities and provide technical support for urban flood emergency management.

Extreme storm surge induced coastal inundation in Yangtze Estuary regions

Coastal inundation induced by the storm surge belongs to one of the major natural hazards in Shanghai and other regions around the Yangtze Estuary.The worst scenarios of coupling the extreme storm and the sea level rise are presented to assess the storm surge hazard in the Yangtze Estuary.The numerical model MIKE 21 FM is adopted to implement the numerical study,which includes wind,current,tide and wave.The storm surge induced by typhoon 9711 is simulated,and the measurements of six tide gauges are used to validate the numerical model.To identify the worst case scenario of severe typhoon(9711)and super typhoon(5612),we propose seven typhoon tracks through the Yangtze Estuary and fourteen scenarios of landfall time for each typhoon track,which generates 196 cases.Finally,based on the worst case scenario and the relative sea level rise in the range of 0 m to 0.7 m,the coastal inundation maps of Pudong New District and Changxing Island are provided and discussed.

SCENARIO-BASED URBAN FLOOD FORECAST WITH FLOOD INUNDATION MAP

The objective of this study is to introduce how to apply the urban flood forecast with numerous flood inundation map scenario in Korea. In modeling of urban flood, drainage networks 1D model like SWMM(Storm Water Management Model) used to analysis stormwater runoff within drainage pipe system and 2D surface model used to simulate inundation area and depth. This 1D-2D model(drainage network 1D coupled to 2D surface model) is used to make the inundation map of urban flood. The accuracy of the 2D model is highly dependent of the input data resolution. The cell by cell running on these high surface resolution need to be required more computation time. Thus, the 1D-2D models have some limitations in using operational real-time forecast. In this sense, the scenario-based approach can be a good alternative method to forecast urban flood. The flood inundation maps would be completed with 320 rainfall scenarios which are finely divided according to rainfall intensity and duration on the basis of design rainfall. The forecast process is very simple if we use pre-existing scenarios. We use a predicted radar rainfall as input for simulated scenario selection, and then selected inundation map would be serviced to people. In this study, the current results for the scenario-based urban flood forecast with flood inundation map are demonstrated.

Rapid flood inundation mapping by differencing water indices from pre-and post-flood Landsat images

Following flooding disasters,satellite images provide valuable information required for generating flood inundation maps.Multispectral or optical imagery can be used for generating flood maps when the inundated areas are not covered by clouds.We propose a rapid mapping method for identifying inundated areas based on the increase in the water index value between the pre-and post-flood satellite images.Values of the Normalized Difference Water Index(NDWI)and Modified NDWI(MNDWI)will be higher in the post-flood image for flooded areas compared to the pre-flood image.Based on a threshold value,pixels corresponding to the flooded areas can be separated from non-flooded areas.Inundation maps derived from differencing MNDWI values accurately captured the flooded areas.However the output image will be influenced by the choice of the pre-flood image,hence analysts have to avoid selecting pre-flood images acquired in drought or earlier flood years.Also the inundation maps generated using this method have to be overlaid on the post-flood satellite image in order to orient personnel to landscape features.Advantages of the proposed technique are that flood impacted areas can be identified rapidly,and that the pre-existing water bodies can be excluded from the inundation maps.Using pairs of other satellite data,several maps can be generated within a single flood which would enable emergency response agencies to focus on newly flooded areas.

Assessment of the potential storm tide inundation hazard under climate change:case studies of Southeast China coast

Four typical cases of storm tide inundation at one of the typical storm surge prone areas in China and worldwide,i.e.Southeast China coast,are presented to demostrate the impact of climate change.It is relied on the statistical trend analysis of tropical cyclone intensification(TCI)and sea level rise(SLR)considering temporally non-stationary and spatially non-uniform effects,numerical analysis taking into account the tide-surge-wave coupling effect and GIS-based analysis for inundation evaluation.The results show that the high sea surface elevation tends to occur in the bays and around the estuaries.The maximal sea surface elevations of the worst situation at present without considering TCI and SLR(i.e.scenario S2)are 6.06 m,5.82 m and 5.67 m around Aojiang,Feiyunjiang and Oujiang river estuaries,respectively.Whereas,the maximal sea surface elevations for the three estuaries would increase to 7.02 m,6.67 m and 6.44 m,respectively,when the non-stationary extreme wind speed of 100-year recurrence period and SLR equivalent to the situation of 2100s(i.e.scenario S4)are taking into account.The potential inundation area of scenario S4 would expand by 108%to about 798 km^(2) compared with scenario S2.In addition,the remotely sensed maps and inundation durations of the hardest hit regions are provided,which will aid the prevention and mitigation of storm tide inundation hazard and future coastal management there.

Flood risk assessment of check dams in the Wangmaogou watershed on the Loess Plateau of China

Check dams have been widely used in China’s Loess Plateau region due to their effectiveness in erosion and flood control.However,the safety and stability of the check dam decrease with the operation process,which increases the probability of dam failure during flood events and threatens local residents’ life and property.Thus,this study simulated flood process of the check dam failure in the Wangmaogou watershed in Yulin City,Shaanxi Province,China,calculated different types of inundation losses based on the flood inundation area within the watershed,and determined the number of key flood protection check dams by classifying the flood risk levels of the check dams.The results showed that 5 dams in the watershed were subject to overtopping during different rainfall return periods,which was related to their flood discharge capacity.Dam failure flood process showed a rapid growth trend followed by slow decrease,and the time of flood peak advanced with increase in the return period.After harmonization of evaluation scales,the magnitude of flood inundation losses can be ranked as:economic losses(212.409 million yuan) > life losses(10.368 million yuan) > ecological losses(6.433 million yuan).The risk value for both individual dams and the whole dam system decreases as the return period increases.The number of key flood protection check dams in the Wangmaogou watershed was 2,3,3,3,4,and 5 for floods with return periods of 10,20,30,50,100,and 200 years,respectively.The results provided a theoretical basis for the safe operation and risk evaluation of check dams in the Loess Plateau Hills watershed.

基于多项式逼近的固定式平台响应谱理论研究

依据波浪力成因和作用效果的不同,将波浪力分为两部分(Morisson波浪力和Inundation波浪力)讨论。对于两种波浪力中的非线性拖曳力项,采用高次多项式逼近,结合高斯型统计量高阶矩计算原理、相关函数、变换法和单输入多输出系统的互谱关系,预测海流海浪联合作用下的海洋平台响应谱的理论形式,求得总波浪力谱以及平台响应谱。在Inundation模态力的相关函数推导过程中,考虑海流影响时,惯性力项PI与拖曳力项PD的相关函数总和为0,这一结果与不考虑海流影响时的结果相同。

Possibilities of urban flood reduction through distributed-scale rainwater harvesting

Urban flooding in Chittagong City usually occurs during the monsoon season and a rainwater harvesting(RWH)system can be used as a remedial measure.This study examines the feasibility of rain barrel RWH system at a distributed scale within an urbanized area located in the northwestern part of Chittagong City that experiences flash flooding on a regular basis.For flood modeling,the storm water management model(SWMM)was employed with rain barrel low-impact development(LID)as a flood reduction measure.The Hydrologic Engineering Center's River Analysis System(HEC-RAS)inundation model was coupled with SWMM to observe the detailed and spatial extent of flood reduction.Compared to SWMM simulated floods,the simulated inundation depth using remote sensing data and the HEC-RAS showed a reasonable match,i.e.,the correlation coefficients were found to be 0.70 and 0.98,respectively.Finally,using LID,i.e.,RWH,a reduction of 28.66%could be achieved for reducing flood extent.Moreover,the study showed that 10%e60%imperviousness of the subcatchment area can yield a monthly RWH potential of 0.04e0.45 m3 from a square meter of rooftop area.The model can be used for necessary decision making for flood reduction and to establish a distributed RWH system in the study area.

The Physico-Chemical Water Quality of the Obafemi Awolowo University Teaching and Research Farm Lake, O.A.U. Campus, Ile-Ife, Southwest, Nigeria

The physico-chemical water quality of the Obafemi Awolowo University Teaching and Research Farm Lake, Ile-Ife, Nigeria, was studied over an annual cycle (September 2006 to August 2007) almost 40 years after its impoundment in 1967. This was with a view to obtaining the then current state of physico-chemical water quality parameters with their variations in time and space as well as using some of the data obtained to evaluate the aging process of the lake for the 40 years of its existence. There was no significant (p > 0.05) horizontal variation (i.e. upstream-dowstream) in the physico-chemical characteristics of the lake whereas, Apparent-color, True color, Turbidity, Total Suspended Solids (TSS), Total Solids (TS) and Total Acidity increased significantly (p < 0.05) from the lake surface towards the bottom of the lake. On the other hand, water pH, Dissolved Oxygen (DO);Dissolved Oxygen Saturation (DO% Sat.) and Biochemical Oxygen Demand (BOD5) decreased significantly (p < 0.05) from the lake surface towards the bottom of the lake. Dissolved Oxygen (DO), Dissolved Oxygen Saturation (DO% Sat.) and Nitrate ion (NO-3) were significantly higher (p < 0.05) in the dry season than in the rainy season while, True colour, pH, Conductivity, Total Hardness, Calcium ion (Ca2+), Magnesium ion (Mg2+), Potassium ion (K+) and Sulphate ion (SO2-4) were significantly higher (p < 0.05) in the rainy season than in the dry season. The lake water could be regarded as shallow, coloured, turbid, less transparent, slightly acidic, soft and well-buffered fresh-waterbodies with evidence of aging (i.e. transforming the lake from an oligotrophic status to a eutrophic waterbody). The results indicated that the lake is suitable for most of its applications with little or no adjustments as the case may be;except probably for drinking purposes where some microbial analysis may be necessary.

Evaluation of Impacts of Sea Level Rise on the Coast of Mohammedia(Morocco):Land at Risk of Flooding and Socioeconomic Impacts

One of the significant consequences of the climate change predicted for the next decades is the sea and ocean level rise.The coastal zone of Mohammedia (Morocco),a site of significant socio-economic activeties largely open to the Atlantic Ocean,is thus confronted with hydrodynamic agents and a possible sea level rise,whose impacts will result in an immersion of the low topography areas。