Structural,dynamic and anthropic conditions that trigger the emergence of the levee effect: insight from a simplified risk-based framework

ABSTRACT

Levees are the most common structural solution to prevent flooding, reduce damage and generate benefits through more investment/economic activity in floodplain areas. While being relatively easy to build, levee effectiveness can be compromised by poor design and substandard construction methods and maintenance, thus increasing failure probability. Further, levees might increase societal vulnerability by instilling a sense of safety, the so-called “levee effect”. To cope with these phenomena, we develop a risk-based framework that quantifies residual risk under levee breaching and the levee effect, by disentangling its structural, dynamic and anthropic components, thus contributing to a better understanding of the phenomena at different spatial scales and the definition of flood risk policies. Through an illustrative example, we show how residual risk might become larger than under natural conditions, as function of the scale of interest, e.g. an area, a line at a given distance from the river, or a point within the floodplain.     

Using historical source data to understand urban flood risk: a socio-hydrological modelling application at Gregório Creek,Brazil

ABSTRACT

The city of São Carlos, state of São Paulo, Brazil, has a historical coexistence between society and floods. Unplanned urbanization in this area is a representative feature of how Brazilian cities have developed, undermining the impact of natural hazards. The Gregório Creek catchment is an enigma of complex dynamics concerning the relationship between humans and water in Brazilian cities. Our hypothesis is that social memory of floods can improve future resilience. In this paper we analyse flood risk dynamics in a small urban catchment, identify the impacts of social memory on building resilience and propose measures to reduce the risk of floods. We applied a socio-hydrological model using data collected from newspapers from 1940 to 2018. The model was able to elucidate human–water processes in the catchment and the historical source data proved to be a useful tool to fill gaps in the data in small urban basins.     

1991年江淮特大洪涝灾害的剖析与研究

1991年气候异常,入春以后雨量偏多,5月中旬起,高空低槽不断东移,北方冷空气频频南下,北太平洋副热带高压增强很快,高压脊线西伸北抬,梅雨提早发生,雨期连绵两三个月,范围广、强度大、持续时间长,加上长江和淮河的洪水夹击,使江淮流域和太湖地区遭受了历史上罕见的特大暴雨洪涝灾害.本文从江淮地区的地理气候特点出发,分析了导致这场灾害的大气环流异常和下垫面水文水利状况,研究了形成这场灾害的雨情特征、水情特征和灾情特征,并与1954年的特大洪涝灾害相对比,揭示了这次暴雨洪涝灾害的气象水文特征与机理.     

蒙古五十年来旱涝变化和降水趋势的研究

本文利用蒙古２５个台站的５２年逐月降水量资料，研究了蒙古旱变化和降水趋势。结果表明：蒙古平均年降水量为２１６．１ｍｍ，分布由南向北增加，东西部少，中部多，南部和西部为干旱区，中部和东部为半干旱区，与我国干旱半干旱区是一个整体，降水主要集中在夏季；年降水量变率为１５．６％－３８．０％。蒙古旱涝都很频繁，旱的频率高于涝的频率，而大涝的频率是大旱的两倍。年降水量服从正态分布，并有准３年和１１－１４年周期     

CHARACTERISTICS OF SEDIMENT TRANSPORT AND CHANNEL FORMATION BY FLOODS AT HYPERCONCENTRATIONS OF SEDIMENT IN THE YELLOW RIVER

1. INTRODUCTIONThe Yellow River is a heavily sediment--laden river. Floods at Hyperconcentrationso f sediment (hereinafter simply referred to as hyperconcentrated flood) frequently occurring in the main river and its tributaries possess different characteristics of sedimenttransport. Sometimes they cause severe deposition whereas at other times they are capable of carrying substantial amount of sediment over long distances. The study on the lawof sediment transport is of significance to …     

Studies of Cainozoic environmental change in Tasmania and coastal East Antarctica: a review

Observational studies on Cainozoic environmental changes in both Tasmania and East Antarctica have led to important modifications in the accepted interpretation of the history of glaciation for each area. Many contributors have played an important role in the processes of investigation leading to the present state of knowledge. A crucial role has been played by the integration of the methods of glacial geomorphology, stratigraphy, sedimentology and dating methods. From studies based on combinations of these approaches, a model of multiple glaciations has been developed to explain observed features in Tasmania. This model is complemented by studies of vegetation history, largely through pollen analysis. A less complete picture of the history of ice‐sheet fluctuations in East Antarctica is beginning to emerge from similar applications of cross‐disciplinary studies.     

1991年初夏江淮大水的天文因素──太阳质子耀斑爆发

研究了1991年初夏江淮大水前,北半球环流的异常与太阳上的一系列质子耀斑之间的关系.研究结果表明:太阳上连续不断的质于耀斑爆发是1991年初夏江淮大水的重要天文因素.太阳质子耀斑可能触发或加剧了极涡的冷空气南下,低空西南急流的东移和西太平洋副热带高压的西伸北移过程.由于冷热气流多次在长江中下游和淮河地区相遇.因而形成了频繁的暴雨和特大暴雨过程,造成了江淮地区的特大洪涝灾害.     

洪水影响的综述

洪水影响涉及到自然和社会系统的诸多方面.本文将洪水影响纳入洪水环境系统进行统一考虑,综述了洪水对自然生态、社会经济及国家政策的可能影响,提出了对特定洪水事件应通过多学科的合作,探求技术、经济和环境综合效应,为洪水灾害的防治提供科学依据.     

岳城水库汛期调度方案的改进

通过对岳城水库现行调度方案的分析,提出了“峰量控制法”调度方案.采用“峰量控制法”调度,1000年一遇水位较现状低1.1m,使水库设计防洪标准从1000年一遇提高到1600年一遇非常运用标准从2000年一遇提高到2600年一遇.在保持保持现有防洪前提准前提下,可使设计汛限水位从13lm抬高到135m.论经证,该方案具有良好的可操作性,对下游河道及水库自身的防洪是安全的.