Quantifying the failure probability of a canal levee

Polders in the Netherlands are protected from flooding by flood defence systems along main water bodies such as rivers, lakes or the sea. Inside polders, canal levees provide protection from smaller water bodies. Canal levees are mainly earthen levees along drainage canals that drain excess water from polders to the main water bodies. The water levels in these canals are regulated. During the last decades, probabilistic approaches have been developed to quantify the probability of failure of flood defences along the main water bodies. This paper proposes several extensions to this method to quantify the probability of failure of canal levees. These extensions include a method to account for (i) water-level regulation in canals, (ii) the effect of maintenance dredging on the geohydrological response of the canal levee and (iii) survival of loads in the past. The results of a case study demonstrate that the proposed approach is capable of quantifying the probability of failure of canal levees and is useful for exploring the relative benefit of risk mitigating measures for canal levees.     

A decadal historical satellite data analysis for flood hazard evaluation: A case study of Bihar (North India)

Flood is one of the major recurrent natural disasters faced by the state of Bihar in north India. In the present study the authors assess the severity of flood hazard in Bihar, using 128 decadal historical satellite datasets acquired during different flood magnitudes during 1998 to 2010. The satellite‐based observations have been analysed in conjunction with the hydrological data, for assessing the frequency of inundation, severity of flood hazard and cropped land under flood hazard. This study assesses the spatial distribution of flooding and creation of systematic flood hazard database, which can be analysed from a spatial dimension in GIS. It is observed that about 24.56 lakh ha of the state's area and about 15.85 lakh ha of the cropped area are vulnerable to flood hazard. North Bihar is more vulnerable to flooding; 8 of the 10 areas identified as worst flood‐affected districts lie in this region.     

2001-2012年新疆融雪型洪水时空分布特征

利用2001-2012年新疆区域内发生的融雪型洪水资料,分析研究了近12 a新疆融雪型洪水时空分布特征.结果表明:新疆融雪型洪水与前一年10月至当年3月新疆全站总累计降水量大小相关,降水量大的年份,对应的融雪型洪水发生次数也多;冬末至夏季融雪型洪水在北疆地区基本上是从西向东、从南向北的先后顺序出现,而在南疆地区的融雪洪水基本上是从西向东、从北向南先后顺序出现.新疆融雪型洪水主要集中出现在春夏季,其中,北疆地区在3月,南疆地区在7月发生较多;伊犁河谷、昌吉、阿勒泰、和田等地区及青河、乌鲁木齐、阿克陶、民丰等市县是新疆融雪型洪水的高发区.     

四川省山洪地质灾害气象预警系统的设计与实现

四川省是一个山区较多的省份,尤其是环绕四川盆地的山脉和川西高原,海拔高、坡度陡;并且四川省降雨不均匀,这些因素导致四川省是一个饱受山洪地质灾害侵害的省份。因此,为了对四川省山洪地质灾害的发生环境和影响因素进行量化分析,提高防灾减灾水平,降低人身财产损失,建立四川省山洪地质灾害气象预警系统是非常有必要的。本研究基于SuperMap GIS平台和Web技术建立山洪地质灾害气象预警系统,使用SuperMapGIS平台对山洪地质灾害等相关地理信息数据进行管理和分析,利用Web技术对山洪地质灾害信息进行发布,将GIS技术的空间分析能力与Web技术的易用性、高扩展性、交互性和广泛用户群体性相结合。本文首先对四川省的降雨量、地表地形、地质构造、土地利用等各种可能引发山洪地质灾害的因素进行了综合分析,然后建立了山洪地质灾害预警模型,最后在预警模型的基础上构建了四川省山洪地质灾害气象预警系统。在系统可视化的界面中,客户端可以通过选择日期作为输入参数传送到服务器端,服务器端通过模型分析得到所指定日期的山洪地质灾害危险等级信息,为地质灾害的预警与防治提供一定的参考。     

Flood prediction and assessment of vulnerability risk in the southern coasts of the Caspian Sea

Abstract

The southern part of the Caspian Sea shoreline in Iran with a length of 813 km has different topographic conditions. Owing to sea fluctuation, these zones have various dimensions in different times. During the last years, the Caspian Sea experienced enormous destructive rises. The historical information and tidal gauge measurements showed different ranges of sea rise from ?30 m to ?22 m from the mean sea level. On the other hand, the probable flooding zone is related to slope gradient of coasts. To help the determination of the probable flooding area owing to sea level rises, the coastal zones can be modelled using geographic information system (GIS) environment as vulnerability risk rates. These rates would be useful for making decisions in coastal management programs. This study examined different scenarios of sea rise to determine hazard-flooding rates in the coastal cities of the Mazandaran province and classified them based on vulnerability risk rates. The 1:2000 scale topographic maps of the coastal zones were prepared to extract topographic information and construct the coastal digital elevation model. With the presumption of half-metre sea rise scenarios, the digital elevation models classified eight scenarios from ?26 to ?22 m. The flooding areas in each scenario computed for 11 cities respectively. The vulnerability risk rate in each rise scenario was computed by dividing the flooded area of each scenario to city area. The results showed that in the first four scenarios, from ?26 to ?24 m, the Behshahr, Joibar, Neka and Babolsar cites would be more vulnerable than other cites. Moreover, for the second four scenarios from ?24 to ?22 m sea level rise scenario, only the coastal area of Chalous city would be vulnerable. It was also observed that the coastal region of Behshahr would be critical in total scenarios. Further studies would be necessary to complete this assessment by considering social-economic and land use information to estimate the exact hazardous and vulnerable zones.     

Hydrological considerations for dam siting in arid regions: a Saudi Arabian study

Abstract

In any dam siting study in arid regions, rainfall records, runoff measurements and their greatest magnitudes are very important. Unfortunately, the data are scarce and, therefore, empirical approaches and charts obtained from similar regions in other parts of the world are necessary for complete applications. The lack of observed data presents the major problem for runoff modelling in arid regions. These regions have characteristically high rainfall intensity and consequent flash floods with large amounts of sediments. Occurrence of rainfall is sporadic, both temporally and spatially, which makes the interpretation of the rainfall-runoff relationship quite difficult. Flood estimations play a significant role in dam siting from the point of view of water availability. This paper presents the basic calculations of floods and sediment amounts that are necessary in dam siting and construction in an arid area by considering the southwestern part of the Kingdom of Saudi Arabia.     

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Abstract

A reliable flood warning system depends on efficient and accurate forecasting technology. A systematic investigation of three common types of artificial neural networks (ANNs) for multi-step-ahead (MSA) flood forecasting is presented. The operating mechanisms and principles of the three types of MSA neural networks are explored: multi-input multi-output (MIMO), multi-input single-output (MISO) and serial-propagated structure. The most commonly used multi-layer feed-forward networks with conjugate gradient algorithm are adopted for application. Rainfall—runoff data sets from two watersheds in Taiwan are used separately to investigate the effectiveness and stability of the neural networks for MSA flood forecasting. The results indicate consistently that, even though the MIMO is the most common architecture presented in ANNs, it is less accurate because its multi-objectives (predicted many time steps) must be optimized simultaneously. Both MISO and serial-propagated neural networks are capable of performing accurate short-term (one- or two-step-ahead) forecasting. For long-term (more than two steps) forecasts, only the serial-propagated neural network could provide satisfactory results in both watersheds. The results suggest that the serial-propagated structure can help in improving the accuracy of MSA flood forecasts.     

气象水文耦合的洪水预报研究进展

从洪水预报中定量降水预报应用进展、面向洪水预报的流域水文模型研究进展、气象水文耦合预报不确定性研究进展三个方面系统介绍气象水文耦合的洪水预报研究进展。研究指出,融合预报员预报的格点化定量降水预报技术是提高面向洪水预报的流域降水预报精度的重要方法,中尺度集合预报技术是提升流域局地性强降水预报能力的主要途径;概念性与物理性相结合的分布式水文模型是面向洪水预报的流域水文模型发展方向;水文集合预报是考虑气象水文单向耦合预报不确定性有效解决技术,贝叶斯系列模型可为分析气象水文预报不确定性提供重要的借鉴意义。     

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。     

Petrology and geochemistry of the ultramafic–mafic Mawpyut complex,Meghalaya: a Sylhet trap differentiation centre in northeastern India

The present article describes, for the first time, petrological and geochemical details of the Mawpyut differentiated complex which is related to the Sylhet trap located at Jaintia Hills district, Meghalaya, northeastern India. The Mawpyut complex occurs as an arcuate body that intrudes into the surrounding Shillong Group rocks. The complex in general contains ‘ultramafic’ and ‘mafic’ rocks, as well as minor syenitic veins that postdate the main units. The lithotypes correspond to cumulate and noncumulate units. The cumulate unit is represented by olivine clinopyroxenite, clinopyroxenite, plagioclase‐bearing ultramafic, olivine gabbronorite, mela‐gabbronorite, melagabbro, orthopyroxene gabbro, and gabbro, all with a pronounced cumulus texture. The noncumulate unit is marked by gabbro, monzonite, monzodiorite, and quartzsyenite. The use of several major and trace element variation diagrams suggests that magmatic differentiation led to the formation of cumulate and noncumulate units. In chondrite‐normalized REE diagrams the cumulate rocks show flat LREE and MREE patterns and a moderate positive Eu anomaly (in plagioclase‐bearing ultramafics) due to plagioclase cumulation. The rocks of the noncumulate unit show a strongly fractionated REE pattern and no Eu anomaly. The noncumulate mafic rocks are geochemically comparable to high‐phosphorous/high‐titanium basalts (HPT) indicative of low pressure fractional crystallization. In a primitive mantle‐normalized multielement diagram some of the cumulate rocks show pronounced negative anomalies for K and P, indicating anorogenic mafic magmatism in a within‐plate setting. The rocks of the noncumulate unit show a slight negative anomaly for Yb and a Nb–Ta trough, indicating a subduction‐related signature that perhaps is inherited from subducted sedimentary rocks incorporated during crustal contamination of the derived magma (left after crystal cumulation) with country rocks. Various trace element ratios for the cumulate mafic rocks indicate parent EMI/EMII/HIMU sources with a very limited crustal signature. The noncumulate mafic rocks (corresponding to the derived evolved magma) indicate EMI/EMII/HIMU sources with a pronounced crustal contamination. The Sr–Nd isotopic compositions of the Mawpyut samples typically plot in the continental flood basalt field, with an affinity to the EMII source. The isotopic compositions of the noncumulate rocks also clearly indicate crustal contamination. We suggest that partial melting (involving garnet in the residue) of the enriched mantle source EMI/EMII/HIMU could have derived the parental melt; this melt, in turn, underwent assimilation and fractional crystallization to produce the variety of cumulate‐noncumulate lithologies of the Mawpyut complex. Copyright © 2013 John Wiley & Sons, Ltd.