Regional Cooperation in Flood Management in the Ganges-Brahmaputra-Meghna Region: Bangladesh Perspective

Bangladesh is known to behighly vulnerable to floods. Frequent floods have put enormous constraints on its development potential. Unfortunately, the frequency of high intensity floods is on the rise. So far the country has struggled to put a sizeable infrastructure in place to prevent flooding in may parts of the country with limited success. In recent times, it was found that losses of lives and valuable assets could be significantly minimized by implementing non-structural measures including the improvement of flood forecasting and warning system. The existing flood forecasting and warning capacity of Bangladesh could be more effective if real-timedata could be acquired from upstreamareas within the Ganges-Brahmaputra-Meghna (GBM) catchment, where runoff is generated. In order to do so, Bangladesh needs to foster an effective regional cooperationwith the other GBM regional countries of India, Nepal, and Bhutan. This article examines how GBM regional cooperation could be useful towards managing floods in Bangladesh in particularand the region in general.     

Analysis of flood vulnerability and assessment of the impacts in coastal zones of Bangladesh due to potential sea-level rise

The 4th IPCC report highlights the increased vulnerability of the coastal areas from floods due to sea-level rise (SLR). The existing coastal flood control structures in Bangladesh are not adequate to adapt these changes and new measures are urgently necessary. It is important to determine the impacts of SLR on flooding to analyse the performance of the existing structures and corresponding impact to plan for suitable adaptation and mitigation measures to reduce the impacts of floods on coastal zone. The study aims to develop a comprehensive understanding of the possible effects of SLR on floods in the coastal zone of Bangladesh. A hydrodynamic model, which is a combination of surface and river parts, was utilized for flood simulation. The tool was applied under a range of future scenarios, and results indicate both spatial variability of risk and changes in flood characteristics between now and under SLR. Estimated impact on population, infrastructure and transportation is also exposed. These types of impact estimation would be of value to flood plain management authorities to minimize the socio-economic impact.     

Flood Forecasting and Flood Warning in the Firth of Clyde, UK

Coastal flooding has caused significant damage to a number of communities around the Firth of Clyde in south-west Scotland, UK. The Firth of Clyde is an enclosed embayment affected by storm surge generated in the Northern Atlantic and propagated through the Irish Channel. In recent years, the worst flooding occurred on 5th January 1991 with the estimated damage of approximately £7M. On average, some £0.5M damage is caused each year by coastal flooding. With the latest climate change predictions suggesting increased storm activity and the expected increase in mean sea levels, these damages are likely to increase. In line with the expansion of flood warning provision in Scotland, the Scottish Environment Protection Agency (SEPA) has developed a flood warning system to provide local authorities and emergency services with up to 24 h warning of coastal flooding within the Firth of Clyde and River Clyde Estuary up to Glasgow City Centre. The Firth of Clyde flood warning system consists of linked 1-D and 2-D mathematical models of the Firth of Clyde and Clyde Estuary, and other software tools for data processing, viewing and generating warning messages. The general methodology adopted in its implementation was developed following extensive consultation with the relevant authorities, including local councils and police. The warning system was launched in October 1999 and has performed well during four winter flood seasons. The system currently makes forecasts four times a day and is the only operational coastal flood warning system in Scotland.This paper summarises the development of the warning system, gives a review of its operation since its launch in 1999 and discusses future developments in flood warning in Scotland.     

Flood hazard in Hunan province of China: an economic loss analysis

Natural and man-made disasters have been increasing and affecting millions of people throughout the world. Floods are the most common natural disasters affecting more people across the globe than all other natural or technological disasters and also are the most costly in terms of human hardship and economic loss. In order to explore the total economic loss, components of economic loss, and factors influencing economic loss during flooding, a retrospective study was carried out in year 2000 in areas that suffered floods in 1998 in Hunan province, China. A total of 10,722 families were investigated using a multistage sampling method. We found that the total economic loss to the 10,722 families investigated was US$ 8.925 million; translating into an average economic loss of US$ 832.45 per family and US$ 216.75 per person. Economic loss related to property loss, income loss, and increased medical cost accounted for 57.38%, 40.00%, and 2.62% of the total economic loss, respectively. Economic loss was significantly related to a family’s pre-flood income; duration of the flood; severity of flood; and type of flood. River floods yielded the highest economic loss and drainage problem floods yielded the lowest loss. We recommended that flood-related preventive measures should focus on the prevention of river floods and shortening the duration of floods with the view of significantly minimizing economic losses associated with floods.     

Flood susceptibility modelling using advanced ensemble machine learning models

Floods are one of nature's most destructive disasters because of the immense damage to land, buildings, and human fatalities.It is difficult to forecast the areas that are vulnerable to flash flooding due to the dynamic and complex nature of the flash floods.Therefore, earlier identification of flash flood susceptible sites can be performed using advanced machine learning models for managing flood disasters.In this study, we applied and assessed two new hybrid ensemble models, namely Dagging and Random Subspace(RS) coupled with Artificial Neural Network(ANN), Random Forest(RF), and Support Vector Machine(SVM) which are the other three state-of-the-art machine learning models for modelling flood susceptibility maps at the Teesta River basin, the northern region of Bangladesh.The application of these models includes twelve flood influencing factors with 413 current and former flooding points, which were transferred in a GIS environment.The information gain ratio, the multicollinearity diagnostics tests were employed to determine the association between the occurrences and flood influential factors.For the validation and the comparison of these models, for the ability to predict the statistical appraisal measures such as Freidman, Wilcoxon signed-rank, and t-paired tests and Receiver Operating Characteristic Curve(ROC) were employed.The value of the Area Under the Curve(AUC) of ROC was above 0.80 for all models.For flood susceptibility modelling, the Dagging model performs superior, followed by RF,the ANN, the SVM, and the RS, then the several benchmark models.The approach and solution-oriented outcomes outlined in this paper will assist state and local authorities as well as policy makers in reducing flood-related threats and will also assist in the implementation of effective mitigation strategies to mitigate future damage.     

Settlement relocations in the char-lands of Padma River basin in Ganges delta, Bangladesh

Bangladesh has a unique hydro-geological setting and deltaic floodplain which is jointly formed by the deposition of the Ganges (Padma), Brahmaputra (Jamuna) and Meghna River. The physical characteristics of the geographic location, river morphology and the monsoon climate render Bangladesh highly vulnerable to natural disasters, primarily, floods and cyclones. River flooding has exerted a great impact on the culture and socioeconomic activities. The char people and their settlements in the Padma River channel are under threat due to floods and associated river bank erosion. The excess of water happens during the monsoon season because of widespread flooding that damages char-land settlements, agricultural crops, infrastructure and communication networks. Purba Khas Bandarkhola Mouza of Char-Janajat is largely affected by annual floods, and as a result the char people are displaced frequently from one place to another within and/or outside the char. The dwellers can return to the native char when new land emerges in the river channel after floods. This study has revealed that the displacement of char settlement takes place in almost every 3–5a at Purba Khas Bandarkhola Mouza of Char-Janajat. Our findings shed light on the char flood disaster management and social adaptation plan for settlement development of char livelihood in the Padma River basin in the Ganges delta of Bangladesh.     

从2020年长江上游洪水看流域防洪对策

2020年长江上游和中下游先后发生特大洪水,其中干流编号洪水全部发生在上游,构成了长江流域洪水的主要部分。首先回顾2020年洪水及洪灾情况,然后根据历史上几次特大洪水过程和历年实测资料,分析长江上游洪水特征、洪灾类型及特点,最后提出新时代长江流域洪水整体防御战略及山洪灾害防治战术。研究表明:金沙江洪水是长江上游洪水基础部分,岷江、嘉陵江和干流区间是洪峰的主要来源,三者洪水遭遇是产生上游特大洪水的主因,上游洪水又是全流域特大洪水的基础和重要组成部分。目前造成洪灾死亡人数最多的是山洪以及山洪引起的地质灾害,财产损失最大的是中下游及湖泊地区。未来堤防仍然是防洪的基础,提高沿江城市防洪标准主要手段是控制性水库的联合优化调度,而减少洪涝灾害损失最有效的途径是给洪水以空间的自然解决方案等非工程措施。     

Reconstruction and post-event analysis of a flash flood in a small ungauged basin: a case study in Slovak territory

Flash floods are one of the major natural hazards occurring in small streams with a negative effect on the country as well as on human lives. Heavy rainfall occurred on July 20, 2014 and July 21, 2014 and caused severe surface water flooding and a flash flood in the Malá Fatra National Park (Slovakia). The most affected was Vrátna Valley with the Varínka stream. This study presents a reconstruction and post-event analysis of a flash flood on small ungauged basin located in this protected area of Slovakia. The reconstruction included hydraulic terrain measurements on estimating the flood’s culmination and documenting the flood’s development. The measurements were taken at three cross sections of the Varínka stream. This paper is focused mainly on post-event analysis of the Varínka stream in two profiles: Strá?a (gauged profile) and Tiesňavy (ungauged cross section). Subsequently, the extremeness of the flash flood was preliminary evaluated. Results of the post-event analysis showed that the July 2014 flood was not the highest flood in this area despite its catastrophic consequences. By studying historical materials, we came to the conclusion that in the past (e.g. in 1848 or 1939) some devastating floods in this area had occurred, which had disastrous consequences for the population. The second part of the study is focused on comparing this flash flood with three major floods which have occurred in Slovak territory since 1998. The first flood occurred on the 20th of July, 1998 on the Malá Svinka stream, and the two others are floods which occurred on the 7th of June, 2011 in the Small Carpathian Mountains: on the Gidra stream in Píla village and on the Parná stream in Horné Ore?any village. Such comparison of flash floods from different geographical regions and different rainfall events can provide comprehensive information about their regimes, threats and disastrous effects.     

Flood Management in India

In this paper, flood problems in India, regional variabilityof the problem, present status of the ongoing management measures, their effectiveness and futureneeds in flood management are covered. Flood problems in India are presented by four zonesof flooding, viz. (a) Brahmaputra River Basin, (b) Ganga River Basin, (c) North-WestRivers Basin, and (d) Central India and Deccan Rivers Basin. Some special problems,related to floods like dam break flow, and water logging in Tal areas, are also mentioned.Progress of various flood management measures, both structural and non-structural, arediscussed. In addition, future needs to achieve efficient and successful flood managementmeasures in India are also pointed out.     

Flooding and its relationship with land cover change,population growth,and road density

Bangladesh experiences frequent hydro-climatic disasters such as flooding.These disasters are believed to be associated with land use changes and climate variability.However,identifying the factors that lead to flooding is challenging.This study mapped flood susceptibility in the northeast region of Bangladesh using Bayesian regularization back propagation(BRBP)neural network,classification and regression trees(CART),a statistical model(STM)using the evidence belief function(EBF),and their ensemble models(EMs)for three time periods(2000,2014,and 2017).The accuracy of machine learning algorithms(MLAs),STM,and EMs were assessed by considering the area under the curve-receiver operating char-acteristic(AUC-ROC).Evaluation of the accuracy levels of the aforementioned algorithms revealed that EM4(BRBP-CART-EBF)outperformed(AUC＞90％)standalone and other ensemble models for the three time periods analyzed.Furthermore,this study investigated the relationships among land cover change(LCC),population growth(PG),road density(RD),and relative change of flooding(RCF)areas for the per-iod between 2000 and 2017.The results showed that areas with very high susceptibility to flooding increased by 19.72％between 2000 and 2017,while the PG rate increased by 51.68％over the same period.The Pearson correlation coefficient for RCF and RD was calculated to be 0.496.These findings highlight the significant association between floods and causative factors.The study findings could be valuable to policymakers and resource managers as they can lead to improvements in flood management and reduction in flood damage and risks.     

Damaging flood severity assessment in Northern Portugal over more than 150 years (1865–2016)

Floods are a major natural hazard, with vast implications over a wide range of socio-economic activities. A harmonized post-flood classification is critical for a better understanding of this hazard, by providing homogeneous flood catalogues for future research on triggering mechanisms. We apply a flood severity index (FSI) to damaging floods in Northern Portugal over a 152-year period (1865–2016) and identify the most critical areas to flood occurrences. The index is a damage-based post-event assessment tool, which includes five categories ranging from minor flooding (1) to catastrophic flooding (5). FSI is applied to a historical damaging flood database with 2318 occurrences. In Northern Portugal, serious floods (3) are the most frequent typology, while catastrophic floods are typically river floods occurring in the Douro basin. Overall, damaging flood occurrences are favoured by the positive phase of the East Atlantic pattern and by the negative phase of the North Atlantic Oscillation. Furthermore, the north-western areas reveal higher concentrations of damaging flood occurrences, mainly due to higher population density, higher precipitation values and more flood plain areas. In particular, 48% of all occurrences are concentrated in the Porto Metropolitan Area, mainly the Porto city centre and nearby riverside areas of the Douro River. High-population density and heavily urbanized areas lead to greater exposure to flood risk, whereas the most peripheral municipalities, with large agricultural/forested areas, show much lower numbers of damaging floods. FSI is tool to communicate the magnitude of the flood risk and is, therefore, of foremost relevance to civil protection and risk management.     

动态实时洪水风险分析及管理系统

当前洪水风险分析按照典型设计标准洪水进行计算的模式难以满足实际防洪管理需要,为了提高洪水风险分析的实时性以及适应洪水演进的动态性,设计了动态实时洪水风险分析框架。在本框架中,先采用一维和二维动态耦合水动力学数值方法耦合溃堤模型,然后在樵桑联围防洪保护区建立洪水演进模拟模型,通过灵活处理模型计算边界条件以及动态设置溃堤功能,计算不同设计标准洪水发生时,堤防出现单一溃口或者组合溃口后保护区内洪水演进过程。按照上述框架开发了樵桑联围动态实时洪水风险图编制与管理应用系统,并利用历史洪水资料开展模型验证,验证结果表明,2008-06洪水马口站、三水站、大熬站、甘竹（一）站的实测最高水位和模型计算最高水位的绝对误差分别为-0.10、0.10、0.09、0.04 m,均满足洪水模拟精度要求。利用模型计算了西江发生200年一遇的洪水情况下,江根堤防出现溃口后的洪水流量及溃口内外洪水水位变化过程,模拟溃口宽度168 m,最大溃口洪水流量达到5 190 m³,分析了堤防溃决后3、6和24 h洪水漫延导致村落淹没情况,结果表明其满足合理性分析。     

The Flood Risk in Cairns

The Cairns region, on the north tropical coast of Queensland, forms part of the wettestarea in Australia, with mean annual rainfalls of 2,000 to 4,000 mm. During the summerand early autumn months, intense rainfalls associated with cyclones and other tropicalweather influences persist for several days, and can produce severe flooding in theBarron, Mulgrave and Russell Rivers and smaller drainage systems. There is oftensome loss of life and the damage to buildings, transport infrastructure, sugar cane andother agricultural crops can easily exceed 100 million. Very high intensity rainfallsover shorter periods, only a few hours, also present a significant urban flash flood risk,as happened at Townsville City, some 300 km to the south of Cairns, in January 1998.Despite the use of good floodplain management practices in recent decades, the combinedrisk of severe river floods and urban drainage floods is relatively high when comparedwith the other more damaging, but less frequent, natural hazards.     

三峡水库建成后长江中下游防洪战略思考

三峡水库建成后,长江中下游防洪形势显著改善,但由于经济社会发展,防洪要求的提高和江湖关系的变化,长江防洪形势发生了一些新的变化。以1954年和1998年典型大洪水为例,分析了三峡水库建成后长江中下游防洪形势出现的新变化,讨论了长江中下游蓄滞洪空间格局调整及江湖关系变化对于防洪的影响。根据长江水沙变化、河道演变、水库群调控和分蓄洪区使用几率变化等出现的新问题,提出未来防洪战略及对策。结果表明:三峡建成后,百年一遇以下洪水防御形势明显好转,而百年一遇以上特大防洪的防洪形势仍然严峻,洪水风险主要转移到水库群上;今后需要在加强蓄滞洪区建设的基础上,重点推动防洪非工程措施建设,以减轻特大洪水带来的灾害损失。     

The Disastrous Flood of 1998 and Long Term Mitigation Strategies for Dhaka City

The disastrous flood of 1998 was a result of excessiverainfall all over the catchment areas of the major rivers of Bangladesh. Dhaka City, which is surroundedby rivers on all sides, was seriously affected despite the completion of Phase I of the Dhaka IntegratedFlood Protection Project (DIFPP). Water entered into the protected part of the city throughhydraulic leakage such as buried sewerage pipes, breached and incomplete floodwalls, ungated culverts andinoperative regulators. The drainage network and retention ponds of the city were found to be in poorconditions and capacities of the pumping stations were found inadequate. There was a serious lack of coordinationbetween the agencies responsible for flood protection and drainage of the city. These issues must beaddressed to achieve long-term flood mitigation. In addition, feedback from both the experts andgeneral public indicated that completion of Phase II of DIFPP was essential to bring the eastern part ofthe city under flood protection. Other structural measures suggested in this paper include installing andmaintaining adequate drainage and pumping capacity and timely operation of regulators. This studyalso suggests a set of non-structural measures for flood mitigation that include protectingthe retention ponds, raising public awareness on maintaining the city drains, introducing landzoning and flood proofing in the eastern part of Dhaka, and stream lining institutional bottlenecks.     

Computer-based Model for Flood Evacuation Emergency Planning

A computerized simulation model for capturing human behavior during flood emergency evacuation is developed using a system dynamics approach. It simulates the acceptance of evacuation orders by the residents of the area under threat; number of families in the process of evacuation; and time required for all evacuees to reach safety. The model is conceptualized around the flooding conditions (physical and management) and the main set of social and mental factors that determine human behavior before and during the flood evacuation. The number of families under the flood threat, population in the process of evacuation, inundation of refuge routes, flood conditions (precipitation, river elevation, etc.), and different flood warnings and evacuation orders related variables are among the large set of variables included in the model. They are linked to the concern that leads to the danger recognition, which triggers evacuation decisions that determine the number of people being evacuated. The main purpose of the model is to assess the effectiveness of different flood emergency management procedures. Each procedure consists of the choice of flood warning method, warning consistency, timing of evacuation order, coherence of the community, upstream flooding conditions, and set of weights assigned to different warning distribution methods. Model use and effectiveness are tested through the evaluation of the effectiveness of different flood evacuation emergency options in the Red River Basin, Canada.     

淮河干流洪水预报系统及其在1991年大洪水的应用

综述了淮河流域概况，淮河干流洪水预报系统物采用的预报方法。１９９１年淮河干流洪水预报采用了降雨径流预报与上，下游站相应流量预防方法相配合，并注重实时水情分析；在行洪区多，行洪后水面宽广而比降又极小的河段的汇流计算，采用了以实测洪水资料绘制的经验蓄曲线为充分发挥的湖泊洪水演算方法。     

Hydroclimatological Perspective of the Kerala Flood of 2018

Flood is among the deadliest disasters in India, and the frequency of floods and extreme precipitation events is projected to increase under the warming climate. The frequency of floods in India varies geographically as some regions are more prone to floods than the others. The Kerala flood of 2018 caused enormous economic damage, affected millions of people, and resulted in the death of more than 400 people. Here we provide a hydroclimatological perspective on the Kerala flood of 2018. Using the observations and model simulations from the Variable Infiltration Capacity (VIC) model, we show that the 2018 extreme precipitation and runoff conditions that caused flooding were unprecedented in the record of the past 66 years (1951–2017). Our results show that mean monsoon precipitation has significantly declined while air temperature has significantly increased during 1951–2017 in Kerala. The drying and warming trends during the monsoon season resulted in a declined total runoff in large part of the state in the last 66 years. Apart from the mean hydroclimatic conditions, extreme precipitation, and extreme total runoff have also declined from 1951 to 2017. However, 1 and 2-day extreme precipitation and extreme runoff conditions in August 2018 exceeded substantially from the long-term 95^th percentiles recorded during 1951–2017. Since there is no increase in mean and extreme precipitation in Kerala over the last six decades, the extreme event during August 2018 is likely to be driven by anomalous atmospheric conditions due to climate variability rather anthropogenic climate warming. The severity of the Kerala flood of 2018 and the damage caused might be affected by several factors including land use/land cover change, antecedent hydrologic conditions, reservoir storage and operations, encroachment of flood plains, and other natural factors. The impacts of key drivers (anthropogenic and natural) on flood severity need to be established to improve our understanding of floods and associated damage.     

Towards Formulation of a Space-borne System for Early Warning of Floods: Can Cost-Effectiveness Outweigh Prediction Uncertainty?

The three most important components necessary for functioning of an operational flood warning system are: (1) a rainfall measuring system; (2) a soil moisture updating system; and, (3) a surface discharge measuring system. Although surface based networks for these systems can be largely inadequate in many parts of the world, this inadequacy particularly affects the tropics, which are most vulnerable to flooding hazards. Furthermore, the tropical regions comprise developing countries lacking the financial resources for such surface-based monitoring. The heritage of research conducted on evaluating the potential for measuring discharge from space has now morphed into an agenda for a mission dedicated to space-based surface discharge measurements. This mission juxtaposed with two other upcoming space-based missions: (1) for rainfall measurement (Global Precipitation Measurement, GPM), and (2) soil moisture measurement (Hydrosphere State, HYDROS), bears promise for designing a fully space-borne system for early warning of floods. Such a system, if operational, stands to offer tremendous socio-economic benefit to many flood-prone developing nations of the tropical world. However, there are two competing aspects that need careful assessment to justify the viability of such a system: (1) cost-effectiveness due to surface data scarcity; and (2) flood prediction uncertainty due to uncertainty in the remote sensing measurements. This paper presents the flood hazard mitigation opportunities offered by the assimilation of the three proposed space missions within the context of these two competing aspects. The discussion is cast from the perspective of current understanding of the prediction uncertainties associated with space-based flood prediction. A conceptual framework for a fully space-borne system for early-warning of floods is proposed. The need for retrospective validation of such a system on historical data comprising floods and its associated socio-economic impact is stressed. This proposal for a fully space-borne system, if pursued through wide interdisciplinary effort as recommended herein, promises to enhance the utility of the three space missions more than what their individual agenda can be expected to offer.     

Flood risk management in Central Viet Nam: challenges and potentials

This article explores the impacts of floods on the economy, environment, and society and tries to clarify the rural community’s coping mechanism to flood disasters in Central Viet Nam. It focuses on the social aspects of flood risk perception that shapes the responses to floods. The research findings revealed that flooding is an essential element for a coastal population, whose livelihood depend on productive functions of cyclical floods. The findings also revealed that floods, causing losses and damages, often inhibited economic development. The surveyed communities appeared to have evolved coping mechanisms to reduce the negative impacts of the floods, yet these coping mechanisms are under pressure due to environmental degradation. Integrated flood risk management is considered as a suitable paradigm for coping with flood disasters.