The Impacts of Flood and Local Communities’ Coping Strategies along the River Gambia

Flood disasters as Climate change hazards are common in developing countries, particularly in communities along the river Gambia. Local communities, for instance, had their local coping strategies that enabled them to stay in their communities even amid these ordeals, and climate change disaster threats. This work strives to understand flood impacts and the local peoples’ adaptation or coping strategies along the River Gambia basin. A community-based cross-sectional research study of 422 research participants of which 294 are males (69.7%) and females 128 (30.3%), and a focus group discussion of 10 groups which comprised 5 female groups and 5 male groups respectively found that 98.6% of the households experienced floods in their community, and 70.6% experienced flood in their houses, 2.1% have impending flood information and 88.4% do not know evacuation centres. The majority of the households had some local coping strategies, but they acknowledged their insufficient effectiveness. The result also shows that the impact of floods on farmlands, roads, buildings, and livestock was greatly felt. Coping strategies such as sandbags, raised elevations, contour bonds, dikes, and buildings on highlands were all found to be common mechanisms the local people used. The study opines that floods affect communities, but the effects vary depending on individual assets.

A Participatory Assessment of the Impact of Flooding in Some Communities in Lokoja, Kogi State, Nigeria

The frequency and consequences of extreme flood events have increased in recent times, having huge impact on the socio-economic well-being of nations with the most significant impact being felt at the community level. Flooding is the most common environmental hazard in Nigeria, particularly Lokoja, with the frequency, intensity, and extent likely to increase due to the effects of global warming leading to climate change such as sea level rise, more intensive precipitation levels, and higher river discharges. While destructive impacts of flood events continue to increase, flood managers in Nigeria have continued to implement a top-down approach towards mitigating these impacts, without involving affected communities in planning and implementation of mitigation strategies. This study therefore employed a participatory approach to determine the causes and impact of flooding in the study area. Participatory research tools such as key informant interviews, focus group discussions, and questionnaire surveys using the purposive sampling method were deployed to elicit data on the perception of the communities about the causes and impact of flood events. Descriptive statistical analysis was performed to elucidate the major causes and areas of impact while qualitative analysis was carried out to corroborate the results and to make for a robust outcome. The Chi Square Test analysis was performed to empirically establish a relationship between the impacts and flooding. Results show that major causes of flooding are the release of water from dams (83% in Adankolo, 97% in Gadumo, and 100% in Ganaja), overflow of rivers, and heavy rainfall while flooding affects economic concerns, property and basic amenities. The Chi Square Test analysis determined empirically that a relationship exists between several areas of impact and flood occurrence. The research concludes that participatory flood research approach can provide flood managers and decision makers a bottom-up approach for effective and robust flood mitigation strategies.

Assessment of Socio-Economic Impacts of the December 2011 Flood Event in Dar es Salaam, Tanzania

Floods are the most devastating hazards that have significant adverse impacts on people and their livelihoods. Their impacts can be reduced by investing on: 1) improving the forecasting skills of extreme and heavy rainfall events, 2) development of Impacts Based Flood Early Warning System (IBFEWS) and 3) effective communication of impacts from anticipated extreme or heavy rainfall event. The development of IBFEWS however, requires a complete understanding of factors that relates to the formation of extreme or heavy rainfall events and their associated socio-economic impacts. This information is crucial in the development of Impacts Based Flood Forecasting Models (IBFFMs). In this study, we assess the socio-economic impacts of the December 2011 flood event in Dar es Salaam as the preliminary stage in the development of IBFFMs for the City of Dar es Salaam. Data from household survey collected using systematic random sampling techniques and structured questionnaires are used. The survey was conducted to acquire respondent’s views on the causes of floods impacts, adaptive capacity to extreme or heavy rainfall events and adaptation options to minimize flood impact. It is found that the main causes of floods were river overflow due to heavy rainfall and blocked drainage system. Poor infrastructure such as drainage and sewage systems, and ocean surge were identified to be the causes of observed impacts of the December 2011 flood event in Dar es Salaam. Death cases analysis showed that 43 people were reported dead. The flood event damaged properties worth of 7.5 million Tanzania shillings. Furthermore, the Tanzania Government spent a total amount of 1.83 billion Tanzanian shillings to rescue and relocate vulnerable communities that lived-in low-lying areas of Jagwani to high ground areas of Mabwepande in Kinondoni district.

The Impact of Urban Flooding on Surface Water Quality of Awka Town

Some physico-chemical and bacteriological parameters were analyzed for in the water samples of four different ponds located in Awka town both prior and after the rain to ascertain the impact of flood in these ponds and to establish whether the pollution was significant. Four samples were collected from each pond both before the rain and after making it a total of thirty-two samples. Twenty-seven parameters were analyzed for in each of the samples. The result revealed that twelve parameters exceeded WHO standard before the rain while fourteen exceeded after the rain. There was significant increment in the values of the analyzed parameters after the rain when compared with the value before the rain as revealed by the Anova statistical tool. It was discovered that there was a major increase in the bacteriological parameters after the rain which implied the serious health impact. It was recommended that users who utilized these ponds for squeezing bitter leaf, processing cassava and washing meats etc. should do so with the caution so as not to expose people to health problems.

Socio-Economic Impacts of Flooding on the Residents of Port Harcourt Metropolis in Rivers State, Nigeria

Floods are naturally occurring phenomena that are part of the physical and biological process which have shaped our nation’s landscape. It occurs in Nigeria environment when there is heavy rain fall for prolonged period of time. The data collection for this research was by use of primary and secondary information;questionnaire was administered by face to face interviews and key informant surveys. Analytical technique was the univariate statistical methods. The results revealed that there is clear evidence of damages to properties and that there are hazards and risks faced by these households as shown in Tables 1-4 respectively. Table 3 specifically shows the financial losses incurred annually by residents to the tune 5 million naira and above. However, the continued hazards and risks as a result of flood incidence have affected their overall income which hitherto is found within (N20000.00 - N25000.00) about 22.8% of the respondents fall in this income bracket. Furthermore, the research also revealed that about 30% say the flood has affected their income, while 29.4% say their buildings are affected. Also about 37.8% of respondents say that the flood incidence occurs all through the rainy season. The research recommends an aggressive review of the Port Harcourt Master Plan and the implementation of the development control tools in the 1992 Urban and Regional Planning Law.

Impact of Flooding on Wheel Shafts and Wheel Bearings in Abraka, and Way Forward

This study aimed at examining the impact of flooding on wheel-bearings and wheel-shaft in Abraka. The empirical and survey research designs were employed for the study. 42 checklists were dropped at the various mechanic workshops to collect data on the number of wheel-shaft and wheel-bearing changed weekly for five years and flood depths were measured for a period of five years. The simple linear regression was employed for data analysis. Findings include that: when the flood depth is at 0.10 feet in January the number of wheel-shaft and wheel-bearings changed is 396 and 220 pcs respectively. When flood depth is at 4.57 feet in August 3749 shafts and 1451 bearings were changed respectively. The regressions analysis showed that the relationship between wheel-shaft and flooding was r = 0.64, and the model was significant at p (0.00) < 0.05. Similarly, regressions analysis showed that the relationship between wheel-bearing and flooding was r = 0.62, and the model was significant at p (0.00) < 0.05. It therefore follows that impairment of wheel-shaft and wheel-bearing significantly depends on flooding events in Abraka. The following recommendations were made: construction of street side channels to drain of flood from the streets;checking the shafts and wheels hubs at regular intervals and re-grease when necessary etc.

基于FloodArea的石嘴山市暴雨山洪灾害风险影响区划

为分析评估石嘴山市暴雨山洪灾害风险及其影响,利用地形、水系、降水、人口、经济、土地等数据,采用FloodArea模型模拟与GIS空间分析相结合的方法,分析了石嘴山市极端降水变化特征,评估了不同重现期暴雨山洪灾害风险,及其对人口、社会经济的影响。结果表明:石嘴山市近20年处于极端暴雨偏多阶段,其典型暴雨过程降水分布概率具有双峰型特征。FloodArea模型能较为准确地模拟出石嘴山市的暴雨山洪过程。发生50 a、100 a一遇暴雨山洪灾害时,石嘴山市海拔1220~1310 m的山洪沟中游和海拔1095~1220 m的山洪沟下游两侧、山前海拔1300~1320 m的区域属于中高风险区,全市中风险区面积分别为170.2 km^(2)、268.3 km^(2),高风险区面积分别为159.1 km^(2)、319.3 km^(2);贺兰山下海拔1100~1300 m的村庄受暴雨山洪灾害影响最大,受影响人口数分别为3.19万、7.73万;农田、草地和建设用地三类土地受影响最大,合计受影响面积分别为3.21万hm^(2)、5.01万hm^(2);贺兰山内和沿山40%~90%的工矿企业、基础设施和农业产业会面临较大风险,受影响国内生产总值(GDP)为15.0~27.0亿元。

Rise of Urban Water Table as a Cause of Flooding: Improving Knowledge in the City of Niamey (Niger Republic)

Niamey, the capital of Niger, has experienced continuous demographic growth (+4%), accompanied by rapid urban expansion that is insufficiently controlled. This growth, combined with the effects of climate change as well as a drastic change in land use (urbanization of cultivated fields, deforestation of plateaus and erosion of slopes) disrupts the water cycle, thus leading to the superposition of three types of floods: 1) rain floods (monsoon period);2) river floods (Niger river);and 3) flooding caused by rising water table. In several neighbourhoods, the water table is now out in a sustainable manner and degrades already fragile sanitary conditions. This study aims to clarify the functioning of aquifers in the city of Niamey due to the combination of geological, geophysical and hydrogeological data. Hydrogeological investigations make it possible to identify, in areas flooded by the water table, a shallow aquifer with low capacitance (effective porosity of a few %) and low permeability (2 × 10-6 to 1 × 10-4 m/s), overlying at a level shallow clay (~10 m) and lying on the Precambrian base (schists, granites). This configuration limits flows and has led to the appearance of permanent pools created by the water table in the valley thalweg in and around the city. Thus, in Niamey, an increase of up to twenty to forty meters was observed between 1961 and 2021 with seasonal piezometric fluctuations of a pluri-metric order following the rainy season. Beyond the health impacts, this trajectory negatively impacts land and locally causes degradation or displacement of traffic axes. Containing the level of the water table appears to be essential in the long term for sustainable sanitation in the city of Niamey.

Farming Families and Climate Change Issues in Niger Delta Region of Nigeria: Extent of Impact and Adaptation Strategies

The study focused on the impacts of climate change on the farmer and the farming families in Niger Delta Region of Nigeria. The study specifically evaluated the perceived resultant situations attributed to climate change to determine the extent of impacts of climate change on the farmer and the farming families and also explored adoptable strategies for coping with the situations. The study adopted descriptive survey research design. Two research questions and two hypotheses guided the study. The population for the study was 246,909 respondents made up of farmers and extension workers who are registered with the State Ministries of Agriculture. Out of the nine Niger Delta states, Bayelsa and Delta states were randomly chosen for the study. Proportionate stratified random sampling technique was used to select a sample size of 5,038 respondents. Structured questionnaire and interview were used to collect data. The instruments were validated by three experts. Cronbach Alpha method was used to determine the internal consistency of the questionnaire items which yielded a coefficient of 0.81. The Statistical Product and Service Solutions (SPSS v 20.0) was employed for data analysis. The statistical tools used for data analysis were weighted mean to answer research questions and standard deviation to validate the closeness of the respondents from the mean and from each other in their responses while t-test was used to test the null hypotheses. The findings of the study revealed that the extent of impacts of climate change on farmers and the farming families in Niger Delta region of Nigeria are moderate. Findings further revealed that climate change has led to increased poverty level and raised cost of production (input and labour cost) as indicated by the farmers. The study recommends that farmers in the region should be encouraged by providing incentives and subsidizing inputs for them by Federal and State governments as well as other non-governmental organizations, as this will go a long way in improving production especially as most farmers agree to continue cultivation even with the observed impacts.

Assessment of the Vulnerability of the Southwestern Coast of Benin to the Risk of Coastal Erosion and Flooding

The coastal zone of Benin is inherited from the last marine oscillations of the Quaternary. A rich and very fragile environment, it presented until the 1960s, a shoreline in dynamic equilibrium over the entire 125 km of coastal line. Since the 1960s, with the construction of important development infrastructures (ports, dams, groins), the Beninese coast is now subject to risks of coastal erosion and seasonal flooding due to the overflow of lagoon water bodies. The present study, based on socio-economic surveys in the communes of Ouidah, Comè and Grand Popo, exposes the extent of coastal risks and socio-economic and environmental damage in the southwestern coastal zone of Benin. The results show that in terms of land, 2.9 ha and 5.7 ha of land have been permanently lost to coastal erosion in the communes of Ouidah and Grand Popo respectively. Similarly, 212 ha of crops of all types were affected by the flooding, including 35 ha destroyed, i.e. 6.67 ha, 11.3 ha in Comè, 4.67 ha Ouidah and 14 ha Grand Popo. Also, 6435 buildings were affected, and 4235 huts were damaged. In addition, working tools, food stocks and other items are counted among the losses recorded by coastal hazards with their corollaries of diseases. The cost of losses and damages in the 08 districts amount to 418,000,000f cfa of which 266,000,000f cfa of damage and 152,000,000f cfa of loss.

Monitoring of the Physicochemical and Bacteriological Quality of the Water of the Gounti-Yéna Basin and Assessment of the Impact on the Health of the Populations

The Gounti Yéna valley is the main watercourse that divides the left bank of the city of Niamey into two unequal parts. The area of its watershed is estimated at about 62 km2. The objective of this study is on the one hand to evaluate the current state of the physico-chemical and bacteriological quality of the water of the Gounti Yéna basin and on the other hand to define the risks of water pollution and its origin in the face of the phenomenon of the rise in the water table of this basin by defining some health risks linked to these impacts. In order to properly carry out this work, we carried out a study of the evolution of the physicochemical and bacteriological parameters of the water of the Gounti Yéna basin during the period from November 2020 to October 2021, at three sampling points chosen from upstream to downstream of the basin then entomological surveys and among the health centers of the capital. The results obtained showed that the physico-chemical quality of water in the Gounti Yéna basin is influenced by climatic factors (precipitation and temperature) and anthropogenic actions. This study also highlighted the presence of faecal contamination in the water of the Gounti Yéna basin with a greater degree during the rainy season. This contamination remains worrying and constitutes a health risk causing waterborne diseases. The stagnation of the various bodies of water is also a favorable place for the development and spread of vector-borne diseases.

The Recurrence of Natural Disasters in Jowhar, Middle Shabelle Region, Somalia: The Causes and Impacts

Natural disasters usually involve a phenomenon with consequences that exceed the response capabilities of local communities and have a significant impact on the region’s socioeconomic development. Droughts, floods, and hurricanes are all natural disasters that jeopardize the environment and the lives of Somalis. Severe floods have devastated the south and central parts of the country multiple times, destroying infrastructure and homes and killing many vulnerable people. Droughts in the south and central parts of the country, particularly in the Middle Shebelle region, have killed a number of children and mothers. It also had a negative influence on crops and cattle. Objective of this study is to know the recurrence of Natural Disasters in Jowhar, Middle Shabelle region, Somalia: The Causes and Impacts. The Somali people are completely aware of natural disasters such as droughts and floods, and they are self-sufficient in dealing with the consequences of these disasters. Furthermore, the Somali government has not fully created environmental laws to protect and conserve the environment, and the majority of laws, rules, acts, and regulations are not used or administered effectively. We also found that the Somali government is not yet financially prepared to deal with these crises, and that there are no strategic plans in the central government or even state administrations to prevent or at least control these disasters from causing extreme harm to the community and the environment.

基于马斯京根法的区间洪水推求方法

针对马斯京根法的蓄量系数K和楔蓄系数X在流域上游有水库控制时难以通过实测资料率定的问题,通过建立K、X与河道水力特征间的关系估算K、X,并采用马斯京根法将上游来水演算到下游,用下游洪水扣除上游演算到下游的洪水得到区间洪水。沭河流域青峰岭水库、小仕阳水库至莒县区间洪水的实例推求结果表明:基于马斯京根法的区间洪水推求方法与新安江模型法推求的区间洪水过程差别较小,但前者进行参数估计时可考虑不同来水河段水力特征的差异。

不同调节能力水库对洪水四要素的影响分析

本文基于26个水库工程建库前后下游洪水四个要素的变化情况,分析不同调节能力水库对下游洪水的影响程度。结果表明,多年、年、季月调节水库总体对洪水首次出现时间有滞后作用、对洪水出现次数有大幅消减作用;周日调节水库对首次洪水出现时间影响不明显,且增加了下游洪水出现频次;同调节能力、不同流域的水库对下游洪水的影响程度与水库占流域面积比无明显线性关系。

鄱阳湖水利枢纽工程施工和运行对湖区及尾闾洪水动力的影响

鄱阳湖是长江水系中的两大通江湖泊之一,在调节长江水位、涵养水源、改善当地气候和维护周围地区生态平衡等方面都起着巨大的作用。鄱阳湖水利枢纽的修建可能导致湖泊水文情势和水动力的变化。本文基于MIKE 21构建鄱阳湖二维水动力模型,选取1954年和1998年特大洪水年以及1991年长江倒灌年作为运行期的典型年,选取1995年作为施工期典型年,按照规划中的鄱阳湖水利枢纽工程施工及运行调度方案,计算水利枢纽修建前后鄱阳湖水位和流量的变化,定量分析枢纽工程对长江干流、鄱阳湖湖区及尾闾附近洪水动力的影响。结果表明:不同典型年鄱阳湖水利枢纽对长江干流、湖区及尾闾的洪水动力影响相似,其中洪水期、倒灌期及施工期一期对长江防洪、湖区及尾闾附近的影响较小,施工期二期湖区水位壅高幅度最高达0.237 m,对鄱阳湖湖区及尾闾附近防洪有一定影响;枢纽工程对星子、都昌、康山等湖区水文站水位影响幅度较为接近,且越靠近尾闾,影响越小。整体而言,鄱阳湖水利枢纽的修建会导致洪水年鄱阳湖湖区水位壅高,倒灌期湖区水位降低,湖区流速降低,但变化幅度均较小,故枢纽工程施工期和运行期对汛期行洪影响不大。

城市内涝风险影响评估关键技术研究与实践

在全球气候变化和极端降雨频发的背景下,结合城市体检工作开展排水防涝系统评估十分必要.本研究利用地理国情普查等国土空间多源数据,针对排水防涝系统中的内涝风险等级评估、积水影响评估和内涝经济损失评估等技术建立了评估分析方法和模型,并将其在北京市S地区进行了实践应用,佐证了方法的准确性和可靠性.本文的评估方法可以作为城市体检中的重要技术手段进行推广应用,其评估结果可以反馈国土空间规划,指导城市建设.

基于PSO-SVM的鹤盛溪流域山洪风险评价

为探究温州市鹤盛溪流域山洪风险空间分布,综合考虑山洪致灾因子、孕灾环境和承灾体3方面的山洪影响因子,建立基于粒子群优化-支持向量机(PSO-SVM)混合算法的山洪风险评价模型。选取准确度、灵敏度、特异性、F-score值、Kappa系数和受试者工作特征曲线等6个指标,采用学习矢量量化(LVQ)算法量化山洪影响因子对山洪灾害发生的影响程度,并将PSO-SVM混合算法模型与单一算法模型进行对比。结果表明:混合算法具有一定的迁移能力,能够更加准确地反映山洪风险的空间分布特征;验证集受试者工作特征曲线指标、Kappa系数和准确度分别为0.934、0.833、0.912,PSO-SVM混合算法模型能显著提高山洪风险评价精度。

洪水作用下高速铁路桥梁动力响应研究

为研究洪水作用对高速铁路桥梁结构动力响应的影响,以两跨不等墩高32 m高速铁路简支梁桥为研究对象,建立洪水作用下桥梁下部结构三维水动力分析模型和桥梁有限元模型,获得桥梁下部结构周围流场分布规律与流水压力荷载,探讨了洪水流速、高度和基础冲刷深度的变化对桥梁动力响应和桩基内力的影响规律。研究表明:(1)不同流速的洪水作用于桥梁下部结构时,周围流场的分布规律总体基本一致;(2)当洪水流速大于3 m/s时,下部结构所受的流水压力对桥梁结构的影响不可忽视,且该压力与洪水作用速度及高度呈正相关;(3)基础冲刷深度对下部结构受到的流水压力影响显著,但当承台裸露后,再增大基础冲刷深度时,流水压力增大不明显;(4)桥梁受到洪水冲击时,桥梁的动力响应随时间变化的总体规律基本一致,其响应具体表现为,墩顶横向加速度在冲击时间1.06 s时达到峰值,墩顶横向位移在冲击时间1.16 s时达到峰值,二者达到峰值后呈周期式迅速衰减,墩顶位移、加速度的峰值和最后稳定值以及桩基弯矩均随着洪水流速、高度的增加而增大;(5)随着基础冲刷深度的增加,桥梁动力响应和桩基弯矩均呈增大趋势,但桩基下部负弯矩区受基础冲刷深度影响更敏感。

引水式电站压力钢管爆裂洪水对厂区影响研究

为研究引水式电站压力钢管发生爆管事故后对厂区建筑物的影响,采用重力相似准则设计了大沫水电站压力钢管爆裂影响区域物理模型,对钢管爆裂事故影响情况开展了系统试验,比较了压力管道局部破裂和完全破裂后爆管水流运动过程的差异,研究了管道完全破裂后不同响应时间和前池水量下爆管水流的水力参数特征。结果表明,压力管道局部破裂与完全破裂时水流流态存在明显差异,对下游建筑物淹没过程和冲击荷载也明显不同。局部破裂时水流沿环向缺口喷出并形成大量散裂水滴覆盖厂房和水处理室,并未对建筑物产生明显冲击荷载;完全破裂后爆管水流直冲下游建筑物,并沿建筑物墙面爬升到较大高度,对建筑物底部产生较大冲击荷载。爆管水流对房屋的最大淹没深度和最大冲击荷载与爆管发生后前池通过压力钢管泄露水量密切相关。爆管事故发生后,缩短响应时间(尽快关闭钢管进口事故闸门),可有效降低各建筑物被淹没的时间。研究结果可为制定引水式水电站压力钢管爆裂事故应急抢修预案提供参考。

基于数据驱动的山区暴雨山洪水沙灾害易发区早期识别方法研究

针对山洪灾害防治研究工作中只关注暴雨-洪水的作用,忽视泥沙淤积导致的洪水-泥沙耦合致灾的问题,重建考虑松散固体物源储量空间异质性的影响因子体系,面向山区小流域复杂下垫面环境进行敏感性分析,利用地理信息空间分析、多重共线性检验计算影响因子贡献度指标,通过不同类型的贡献度-集成学习耦合算法对阿坝州5250条小流域山洪水沙灾害易发度进行识别,构建基于数据驱动的山区暴雨山洪水沙灾害早期识别方法。结果表明:山洪水沙灾害在空间上表现出一定的聚集性,影响因子特定区间对于灾害发生具有更高敏感性,部分影响因子对于灾害发生的敏感性规律具有相似性。阿坝州东部、中南部部分地区以及西北部少部分地区为高易发区,与固体物源累积高频区较为接近,洪水-泥沙耦合致灾概率相对较大,较低和低易发区主要分布在阿坝州西部和西南部地区,与固体物源累积高频区重叠度较小,洪水在致灾过程中起主导作用可能性相对较大。相对于山洪风险调查评估研究结果,基于数据驱动的山洪水沙灾害易发性早期识别结果的高易发区灾害密度更大,高风险覆盖度提高23.2—45.4个百分点。