Preventing flooding or regulating flood levels?: Case studies on perception of flood alleviation in Bangladesh

Based on a systematic sample survey among the residents of two contrasting floodplain environments - the Tista floodplain (a shallow flood area) and the Ganges-Brahmaputra floodplain (a deep flood area) - this study tests a central hypothesis that the floodplain residents of Bangladesh preferred regulation of flood levels as the main flood alleviation measure. The study found that, despite significant differences in property setting, flood hazard experience and the nature of indigenous adjustments to floods between the two sample areas, an overwhelming 95% of the respondents from each area preferred regulation of flood levels within a range of 0.3 to 2.0 m. The study attempts to provide an explanation for the popularity of regulated flood levels in the context of indigenous adjustments of floodplain crops and infrastructures tonormal flood levels in Bangladesh, which coincided with the respondents' preferred range of flood levels. The study points out that the objective of the UNDP/World Bank-sponsored embankment compartmentalization projects also coincides with this goal of regulating flood levels. However, to test the physical limitations of regulating water levels between neighbouring compartments and to assess the environmental impacts of the proposed projects, the study stresses the need for initiating environmental baseline surveys on the pilot compartmentalization project, which is located on the left bank of the Brahmaputra.     

Analysis of flood causes and associated socio-economic damages in the Hindukush region

Pakistan is exposed to numerous hazards, but the problem of recurrent floods has been causing massive losses to lives and other properties. Swat valley is no exception to it. In this paper, an attempt has been made to analyse the causes and associated socio-economic impacts of floods on the Swat valley, Pakistan. Swat valley falls in the Hindukush region, North-west-Pakistan. The valley has been studied with special reference to its physical and socio-economic environment. Similarly, three-sample villages were also randomly selected from the active floodplain for micro-level analysis. The sample villages include Ningolai, Delay and Ghureijo. All the three-sample communities are located on the right bank of river Swat. This area is located in the active flood zone of Swat valley. The analysis revealed that in the study area, floods occur during summer season, which is mainly caused by heavy rainfall as well as rapid melting of snow and glacier. Besides these, there are some floods intensifying factors, which accelerate intensity of floods and enhance resultant damages in the valley. It was found that during flood season, water overflows the natural levees and trigger tremendous loses to housing, agricultural land, standing crops and other properties. The flood-related Government Departments have only implemented limited structural mitigation measures. However, in addition to structural measure, land-use zoning and flood abatement strategies would largely help in reducing the adverse consequences of this recurrent phenomenon.     

Bankline change and the facets of riverine hazards in the floodplain of Subansiri–Ranganadi Doab, Brahmaputra Valley, India

Subansiri?CRanganadi Doab (confluence country), located in Lakhimpur district, Assam, is one of the worst flood-affected areas in Brahmaputra valley. The Doab is well populated, and land around these rivers is extensively used for cultivation. As means of flood protection, embankments were constructed in the 1950s along the banks of both the rivers. On the other hand, these rivers are dynamic in terms of banklines and other forms of channel changes. Progressive migration of bankline, due to erosion, results in loss of cultivable land. Moreover, it causes breaches in the embankments increasing the severity of flood in the Doab. This paper attempts to study the changes in the banklines of two major rivers in the floodplains of the Subansiri?CRanganadi Doab during 1997?C2009 in the context of the riverine hazards it brings to the floodplain dwellers. The shift of the banklines in Subansiri?CRanganadi Doab, downstream of North Lakhimpur, has been estimated using IRS LISS imageries of 1997 and 2009 in GIS environment. The river Subansiri during the study period has migrated westward and has widened substantially resulting in erosion of an area of ~19.137?km². For Ranganadi, the total area that has been eroded due to channel changes is ~0.897?km². The channel changes are mainly due to concave bank erosion associated with high stages of flow. Channel widening in Subansiri and Ranganadi in the study area during the decades of 1990s and 2000 has led to frequent breaches in the embankments. Lateral erosion and inundation due to embankment failure are the most dominant facets of riverine hazards in the study area as these lead to loss of livelihood. Therefore, it is necessary to incorporate geomorphic changes in formulating flood management programmes.     

Floodplain Residents' Preferences for Water Level Management Options in Flood Control Projects in Bangladesh

A maximum difference conjoint (MDC) model was part of a questionnaire toassess floodplain residents' preferences for the outcomes of water level managementinside an enclosed embankment system on the left bank of the Dhaleswari River, calledthe Compartmentalization Pilot Project (CPP)-Tangail. The outcomes were described as(a) varied flood depths in the rice field, (b) incidence of flooding on the courtyard andinside homes, (c) changes in floodplain and culture fisheries, and (d) varied conditionsof drainage congestion. Following a standard survey, the respondents from inside andoutside a completed section of the compartment (Cluster 1b) were shown profiles of these flood management outcomes and were asked to indicate for each profile the one most preferred and the one least preferred item. The results of the study indicated that the respondents had a clear preference for preventing flooding of their homes and courtyards and for an ideal water depth of 2 ft in the aman rice fields. At the same time, they also showed a strong concern about malfunctioning of sluices and to a lesser extent about the changes in the fish habitat. The successful application of the MDC as an approach to model tradeoffs among rural residents of Bangladesh shows that a relatively complex quantitative survey method, incorporating choice cards as pictograms, can be applied successfully even in a developing country.     

Geo-hydrological database modeling for integrated multiple hazards and risk assessment in Lesser Himalaya: a GIS-based case study

The main objective of the study was to assess the integrated multiple hydrological hazards and their environmental and socio-economic risks in Himalaya through geographical information system (GIS) and database management system (DBMS). The Dabka Watershed constitutes a part of the Kosi Basin in the Kumaun Lesser Himalaya has been selected for the case illustration. The Dabka DBMS is constituted of three GIS modules, that is, geo-informatics, hydro-informatics and hazard-informatics. Through the integration and superimposing of these modules prepared Hydrological Hazard Index to identify the level of vulnerability for existing hydrological hazards and their socio-economic and environmental risks. The results suggested that geo-environmentally most stressed barren land areas have high rate of runoff, flood magnitude, erosion sediment load and denudation during rainy season particularly in the month of August (i.e., respectively, 84.56 l/s/km², 871.80 l/s/km², 78.60 t/km² and 1.21 mm/year), which accelerates high hazards and their socio-economic and environmental risks, whereas geo-environmentally least stressed dense forest areas experience low rate of stream runoff, flood magnitude, erosion sediment load and denudation in the same season and month (i.e., respectively, 20.67 l/s/km², 58.12 l/s/km², 19.50 t/km² and 0.20 mm/year) comparatively have low hazards and their socio-economic and environmental risks. The other frazzled geo-environment that also found highly vulnerable for natural hazards and their risks is agricultural land due to high stream runoff, flood magnitude, erosion sediment load and denudation rates (i.e., respectively, 53.15 l/s/km², 217.95 l/s/km², 90.00 t/km² and .92 mm/year). This makes it necessary to take up an integrated and comprehensive sustainable land use policy for the entire Himalaya region based on the scientific interpretation of the crucial linkages between land use and hydrological hazards, that is, floods, erosion, landslides during rainy season and drought due to dry-up of natural springs and streams during summer season. The study would help the village, district and state development authority to formulate decision support system for alternate planning and management for the Himalaya region.     

Rhine flood deposits recorded in the Gallo-Roman site of Oedenburg (Haut-Rhin, France)

From the first to the fourth century AD, the Gallo-Roman town of Oedenburg developed in the alluvial landscape of the southern Upper Rhine Graben. Throughout this period, the landscape mosaic, composed of palaeochannels, stable palaeoislands and river terraces, continued to evolve. A district of this town, situated on a lateral Rhine channel system, was archaeologically excavated. Large-scale excavation and cross-section analysis provide evidence of changing fluvial conditions during the period under study. At about AD 20 or earlier, this lateral part of the floodplain, affected by very fine sedimentation, was occupied by moribund marshy palaeochannels. When the first Gallo-Roman settlers occupied the site, they filled parts of the channels with woven brushwood in order to create an efficient circulation surface. The sedimentary infill of this palaeochannel records four different flood deposits interlayered with dated anthropogenic units (pavements, road embankments, and other structures). Archaeological analysis and dendrochronological dating indicate that these four flooding events occurred during a short time period between AD 20 and AD 145/146. These geoarchaeological observations focus on floods that do not seem to have significantly affected human occupation in this part of the Rhine floodplain. These results are set in the broader context of the Rhine catchment and the Alps.     

煤层覆岩与地下水在采动损害中的互馈效应探讨

地下水的存在可以改变岩体的力学性质及覆岩应力状态,从而加剧由地下采煤诱发的地表变形、塌陷、地裂缝及水资源流失等采动损害现象;在采动损害过程中产生的覆岩中隔水层破断,又反过来改变地下水系统,引起井下突水事故和地面环境恶化。两者相互影响、相互制约,形成有利于采动损害发生、发展的互馈效应。在研究采动损害时,地下水是一个不可忽略的重要因素。      

People at Risk of Flooding: Why Some Residents Take Precautionary Action While Others Do Not

Self-protective behavior by residents of flood-prone urban areas can reduce monetary flood damage by 80%, and reduce the need for public risk management. But, research on the determinants of private households’ prevention of damage by natural hazards is rare, especially in Germany. To answer the question of why some people take precautionary action while others do not, a socio-psychological model based on Protection Motivation Theory (PMT) is developed, explaining private precautionary damage prevention by residents’ perceptions of previous flood experience, risk of future floods, reliability of public flood protection, the efficacy and costs of self-protective behavior, their perceived ability to perform these actions, and non-protective responses like wishful thinking. The validity of the proposed model is explored by means of representative quantitative telephone surveys and regression analyses, and compared with a socio-economic model (including residents’ age, gender, income, school degree and being owner or tenant). Participants were 157 residents of flood-prone homes in Cologne, Germany, a city that has traditionally been subject to minor and major flood events. Results of the study show the explanatory power of the socio-psychological model, with important implications for public risk communication efforts. To motivate residents in flood-prone areas to take their share in damage prevention, it is essential to communicate not only the risk of flooding and its potential consequences, but also the possibility, effectiveness and cost of private precautionary measures.     

Risk Assessment,Emergency Preparedness and Response to Hazards: The Case of the 1997 Red River Valley Flood,Canada

The prevention and/or mitigation offlood disasters requires continual research, numerouscapital investment decisions, and high-qualitymaintenance and modifications of flood-controlstructures. In addition, institutional and privatepreparedness is needed. The experience offlood-control in North America has shown mixedoutcomes: while flood frequency has declined duringthe last few decades, the economic losses havecontinued to rise. Recent catastrophic floods havealso been linked to major structural interventions inthe region. The flood diversions may cause harmfuleffects upon the floodplain inhabitants by influencingflood levels in areas which are not normallyflood-prone. The increasing vulnerability of thefloodplain inhabitants poses new challenges and raisesquestions concerning the existing risk assessmentmethods, institutional preparedness and responses todisaster-related public emergencies, and local-levelpublic involvement in flood mitigation efforts.In the context of the catastrophic 1997 floods of theRed River Valley, Manitoba, Canada, this researchfocuses on two aspects of flood-related emergencygovernance and management: (i) the functions andeffectiveness of control structures, and (ii) theroles, responsibilities and effectiveness oflegislative and other operational measures. The studyconcludes that the flood-loss mitigation measures,both in terms of effects of control structures andinstitutional interventions for emergency evacuation,were not fully effective for ensuring the well-beingand satisfaction of floodplain inhabitants. Althoughorganizational preparedness and mobilization to copewith the 1997 flood emergency was considerable, theirsuccess during the onset of the flood event waslimited. Lack of communication and understandingbetween institutions, a reluctance to implementup-to-date regulations, and minimal publicparticipation in the emergency decision-making processall contributed to the difficulties experienced byfloodplain inhabitants.     

Emerging grassroots resilience and flood responses in informal settlements in Accra,Ghana

In the last five decades, many informal communities in Accra, Ghana have suffered from annual flood hazards. Residents of these communities appear to have successfully resisted evictions by city authorities; survived flood hazards and poor environmental health conditions. These flood affected households continue to survive with increasing housing and population densities in the face of these annual floods. Are they becoming resilient? Have residents built adaptive capacities through learning experiences from previous flood occurrences and evictions attempts? What has produced and continued to shape their responses to flooding? What can be learned from this supposed grassroots resilience to inform flood management in urban Africa? Using case studies of three informal communities of Glefe, Agbogbloshie and Old Fadama, this paper explores the gradual and evolving adaptive capacities and social resilience to flood hazards among poor urban dwellers. The paper reveals the depth of understanding and embodied nature of flood experiences among affected slum dwellers and how these are gradually being transformed into adaptive capacities and shaping their responses. In the absence of efficient state flood interventions, there are emerging and enduring flood responses and adaptation practices shaped by residents’ social networks, political alliances and sense of place. These responses translates into continuous re-structuring of housing units, construction of communal drains, creation of local evacuation teams and safe havens. Urban policy contributions that can be learned from these emerging grassroots capacities for flood vulnerability management have been proposed.     

河漫滩沉积体系对洪水事件的指示——以修河为例

河漫滩是洪水漫溢过自然堤而在河流两岸水流流速降低的地貌环境下所塑造的河流地貌单元,是洪水过程所形成的独特沉积体系,蕴含着大量的河流水文信息,但由于河流侧向摆动、河漫滩沉积速度较快等原因,造成河漫滩沉积环境变化较快,河漫滩沉积体系长期以来没有得到足够的重视。以鄱阳湖修河下游永修三角乡修河右岸的近现代河漫滩沉积序列为例,基于¹³⁷Cs比活度测试和事件性沉积建立时间标尺,依据粒度组份等指标,结合气象和水文观测数据,探究了器测以来河漫滩沉积体系对洪水事件的记录及记录特点。研究结果表明:较大洪水期间水动力不稳定、粒度较粗、分选差(或者好)、粒度跨度宽;该剖面揭示了1953年来16次较大洪水年份的14次,检出率高;平均粒径(μm)和SS(分选系数×粒径跨度)等指标对洪水事件的检出最好。这样揭示出来的洪水,可称为异常洪水,有别于基于滞水沉积所反演的极端洪水事件。研究在一定程度上能拓宽古洪水的研究内容与研究内涵。     

Assessment of flood hazard,vulnerability and risk of mid-eastern Dhaka using DEM and 1D hydrodynamic model

Floods are regular feature in rapidly urbanizing Dhaka, the capital city of Bangladesh. It is observed that about 60% of the eastern Dhaka regularly goes under water every year in monsoon due to lack of flood protection. Experience gathered from past devastating floods shows that, besides structural approach, non-structural approach such as flood hazard map and risk map is effective tools for reducing flood damages. In this paper, assessment of flood hazard by developing a flood hazard map for mid-eastern Dhaka (37.16 km²) was carried out by 1D hydrodynamic simulation on the basis of digital elevation model (DEM) data from Shuttle Radar Topography Mission and the hydrologic field-observed data for 32 years (1972–2004). As the topography of the area has been considerably changed due to rapid land-filling by land developers which was observed in recent satellite image (DigitalGlobe image; Date of imagery: 7th March 2007), the acquired DEM data were modified to represent the current topography. The inundation simulation was conducted using hydrodynamic program HEC-RAS for flood of 100-year return period. The simulation has revealed that the maximum depth is 7.55 m at the southeastern part of that area and affected area is more than 50%. A flood hazard map was prepared according to the simulation result using the software ArcGIS. Finally, to assess the flood risk of that area, a risk map was prepared where risk was defined as the product of hazard (i.e., depth of inundation) and vulnerability (i.e., the exposure of people or assets to flood). These two maps should be helpful in raising awareness of inhabitants and in assigning priority for land development and for emergency preparedness including aid and relief operations in high-risk areas in the future.     

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.     

Assessing flood hazard using flood marks and analytic hierarchy process approach: a case study for the 2013 flood event in Quang Nam,Vietnam

The production of flood hazard assessment maps is an important component of flood risk assessment. This study analyses flood hazard using flood mark data. The chosen case study is the 2013 flood event in Quang Nam, Vietnam. The impacts of this event included 17 deaths, 230 injuries, 91,739 flooded properties, 11,530 ha of submerged and damaged agricultural land, 85,080 animals killed and widespread damage to roads, canals, dykes and embankments. The flood mark data include flood depth and flood duration. Analytic hierarchy process method is used to assess the criteria and sub-criteria of the flood hazard. The weights of criteria and sub-criteria are generated based on the judgements of decision-makers using this method. This assessment is combined into a single map using weighted linear combination, integrated with GIS to produce a flood hazard map. Previous research has usually not considered flood duration in flood hazard assessment maps. This factor has a rather strong influence on the livelihood of local communities in Quang Nam, with most agricultural land within the floodplain. A more comprehensive flood hazard assessment mapping process, with the additional consideration of flood duration, can make a significant contribution to flood risk management activities in Vietnam.     

Flood hazard in Ratnapura, Sri Lanka: Individual attitudes vs collective action

In Ratnapura monsoonal flooding is a chronic problem of which the residents are acutely aware. Responses to structured interviews indicated that a wide range of actions are employed to reduce flood impact, although these actions are not perceived as specific adjustments to flooding. The only widely acknowledged means of mitigating the flood threat is government action. Dependency on government action reflects the government's role in dispensing aid to flood victims. While relief programmes do reduce personal, short-term losses, they simultaneously encourage resettlement in high-risk areas. In seeking a viable, long-term management policy, the Sri Lankan government recently adopted a plan to move the municipality of Ratnapura to invulnerable high ground. In making the decision to relocate, however, the attitudes of the residents were not evaluated, and government officials seemed unconcerned that residents viewed relocation as an unacceptable solution to the problem. Although individual attitudes concerning residential satisfaction in the context of the flood hazard varied with factors such as income, length of residency and land tenure, an overwhelming number of residents adamantly maintained that they would not move to the new town.     

Geoarchaeological research in the coastal plain portion of the Savannah River valley

Selected archaeological, stratigraphical, sedimentological, hydrological, sea level, and ¹⁴C data are considered in order to ascertain the times and rates of saltmarsh, floodplain, river swamp, and alluvial terrace development in the lower Savannah River valley. Archaeological data are emphasized in the elucidation of these developmental trends and their environmental correlates. It is concluded that the modern environments associated with the categories of archaeological sites examined (estuarine shell middens, river swamp point bar sites, raised terrace/point bar sites) are not representative of local conditions during occupation(s). Accordingly, a mid-Holocene development of lower energy depositional environments is documented, along with a corresponding shift in subsistence-settlement patterning that suggests more diffuse, or broad spectrum, socio-economic strategies. A base level (sea level) dominance on river sedimentation, even far inland from the coast, may also be indicated.     

Cross-border conservation in East Central Europe: The Danube-Carpathian complex and the contribution of the World Wide Fund for Nature

Cross-border cooperation in environmental matters has become much more evident since 1989 because open frontiers facilitate contact while common tasks emerge as protected areas in frontier zones lose their isolation. Pollution hazards have been discussed more openly since 1989 while further stimuli arise from the harmonisation process in the run-up to EU enlargement and the finance available from Brussels and other international donors to solve pollution problems and create international ecological networks. The paper examines the progress made in the Danube Valley and the Carpathians which together constitute the core of East Central Europe. Particular attention is paid to the role of environmental non-governmental organisations (ENGOs) – and especially the World Wide Fund for Nature (WWF) – in the progress of conservation. Along with the World Conservation Union (IUCN), WWF has demonstrated the value of floodplain wetlands and ensured that wetland restoration is an important part of the Strategic Action Plan for the Danube. And by involving local ENGOs in specific projects the role of the non-governmental sector in environment matters is enhanced. Also, with momentum growing for a pan-European ecological network ('Natura 2000'), WWF has attracted the support of international donors for a ecoregion-based conservation (ERBC) in the Carpathians where priority areas have now been identified. Ecological and diplomatic capacities are thus deployed to maximise the scope for biodiversity conservation commensurate with sustainable socio-economic development. This revised version was published online in July 2006 with corrections to the Cover Date.     

What do people think about the flood risk? An experience with the residents of Talcahuano city,Chile

In the province of Concepción (Chile), floods are considered one of the main natural hazards. One of the most important cities of this area is Talcahuano. During the last years, Talcahuano has been affected by a number of flood episodes, as a consequence of an increase in the frequency of extraordinary atmospheric events, along with a higher exposure to the flood risk caused by an intense urban development. On 27 February 2010, an 8.8° earthquake (Richter scale) occurred in central southern Chile and originated the tsunami which flooded a large percentage of the residential area and military base of the Talcahuano city. This flood event affected a population higher than 180,000 people (including 23 casualties and invaluable economic and environmental losses). The objective of this study is to investigate the social perception and knowledge of Talcahuano residents affected by different types of flood, including tsunami, emphasizing which are their risks, vulnerability, resilience and coping capacity concepts. In addition, the kind of measures that have been proposed to improve their capacity to face floods after having suffered the natural disaster will be determined. This social assessment has been carried out based on a survey to permanent residents. Research results reveal that their endogenous and exogenous characteristics have resulted determinant to explain their perception.     

Integrated application of the analytic hierarchy process and the geographic information system for flood risk assessment and flood plain management in Taiwan

Flooding is one of the major natural hazards in Taiwan, and most of the low-lying areas in Taiwan are flood-prone areas. In order to minimize loss of life and economic losses, a detailed and comprehensive decision-making tool is necessary for both flood control planning and emergency service operations. The objectives of this research were (i) to develop a hierarchical structure through the analytic hierarchy process (AHP) to provide preferred options for flood risk analysis, (ii) to map the relative flood risk using the geographic information system (GIS), and (iii) to integrate these two methodologies and apply them to one urban and one semi-rural area in central Taiwan. Fushin Township and the floodplain of Fazih River (1 km on either side of the channel) in Taichung City were selected for this study. In this paper, the flood risk is defined as the relative flood risk due to broken dikes or the failure of stormwater drainage systems. Seven factors were considered in relation to the failure of stormwater drainage, and five to that of broken dikes. Following well-defined procedures, flood maps were drawn based on the data collected from expert responses to a questionnaire, the field survey, satellite images, and documents from flood management agencies. The relative values of flood risk are presented using a 200-m grid for the two study areas. It is concluded that integration of AHP and GIS in flood risk assessment can provide useful detailed information for flood risk management, and the method can be easily applied to most areas in Taiwan where required data sets are readily available.