Use of Systematic, Palaeoflood and Historical Data for the Improvement of Flood Risk Estimation. Review of Scientific Methods

The catastrophic floods recently occurring in Europe warn of the critical need forhydrologic data on floods over long-time scales. Palaeoflood techniques provideinformation on hydrologic variability and extreme floods over long-time intervals(100 to 10,000 yr) and may be used in combination with historical flood data (last1,000 yr) and the gauge record (last 30–50 yr). In this paper, advantages anduncertainties related to the reconstruction of palaeofloods in different geomorphologicalsettings and historical floods using different documentary sources are described.Systematic and non-systematic data can be combined in the flood frequency analysisusing different methods for the adjustment of distribution functions. Technical toolsintegrating multidisciplinary approaches (geologic, historical, hydraulic and statistical)on extreme flood risk assessment are discussed. A discussion on the potential theoreticalbases for solving the problem of dealing with non-systematic and non-stationary data ispresented. This methodology is being developed using new methodological approachesapplied to European countries as a part of a European Commission funded project (SPHERE).     

Evidence for Holocene megafloods down the Tsangpo River gorge, southeastern Tibet

Lacustrine and alluvial terraces and sediments record the extent of at least two Holocene glacially dammed lakes immediately upstream of the Tsangpo River gorge at the eastern syntaxis of the Himalaya. The larger lake covered 2835 km², with a maximum depth of 680 m and contained an estimated 832 km³ of water; the smaller lake contained an estimated 80 km³ of water. Radiocarbon dating of wood and charcoal yielded conventional radiocarbon ages of 8860 ± 40 and 9870 ± 50 ¹⁴C yr B.P. for the higher set of lake terraces, and 1220 ± 40 and 1660 ± 40 ¹⁴C yr B.P. for sediments from the lower terraces. Catastrophic failure of the glacial dams that impounded the lakes would have released outburst floods down the gorge of the Tsangpo River with estimated peak discharges of up to 1 to 5 × 10⁶ m³ s⁻¹. The erosive potential represented by the unit stream power calculated for the head of the gorge during such a catastrophic lake breakout indicates that post-glacial megafloods down the Tsangpo River were likely among the most erosive events in recent Earth history.     

概论伊吾河洪水成因及其防御对策

根据伊吾河流域洪水类型及特点,分析了伊吾河暴雨的水汽来源、环流特征以及暴雨所形成的洪水灾害,并对伊吾河洪水的防御提出了工程性措施和非工程性措施。     

热带副热带高度异常对长江流域和华北旱涝影响的数值模拟与分析

前期南亚高压的异常增强或者减弱,热带、副热带地区100 hPa高度的异常增高或者降低,热带西风的异常增强或者减弱,对长江流域和华北地区夏季的降水异常具有预示作用。文中设计了一系列的数值试验进行模拟研究,包括控制试验、敏感试验和4组合成试验。合成试验模拟结果表明,前期热带、副热带高度异常分布,能够再现长江流域、华北旱涝情况。前期南亚高压、热带、副热带高度、风异常对长江流域和华北地区夏季降水的异常均有预示作用。100 hPa叠加高度、风异常的敏感试验结果表明:前期南亚高压、热带与副热带地区100 hPa高度场和环流场的异常不仅可以预示、事实上能够引起长江流域和华北夏季降水的异常———前期南亚高压异常增强、热带、副热带地区100 hPa高度场异常增高、西风异常增强,易引起长江流域降水偏多、华北降水偏少;反之,则容易引起长江流域降水偏少、华北降水偏多。     

距平模式月际旱涝异常的诊断及预测试验

用地气耦合非定常距平模式对２４个夏季旱涝月个例进行了诊断和预测试验。结果表明,用这种动力与统计外部结合的ＭＯＳ方法进行旱涝预测比较简易可行,并且达到一定的准确率,便于在短期气候预报的业务中推广应用。     

Hydroclimatic fluctuations of the Upper Narmada catchment and its association with break-monsoon days over India

In this paper, hydroclimatic fluctuations of the Upper Narmada catchment (upto Narmadasagar damsite) have been studied by examining the time series (1901–80) of (i) 1-to 10-day annual extreme rainfall; (ii) seasonal total rainfall between May and October; (iii) the precipitation concentration index (PCI); (iv) a modified version of PCI(MPCI); and (v) parameters of the periods contributing specified percentages of rainfall to annual total. Most of these parameters followed the normal distribution and did not show any significant long-term trend. However, some dominant long period oscillations have been noticed in extreme rainfall, seasonal rainfall, PCI and MPCI series. Influence of break-monsoon days over India during July and August on the rainfall activities of the Upper Narmada catchment has also been investigated and salient findings discussed.     

我国长江、黄河两流域旱涝规律成因与预测研究的进展、成果与问题

The advances obtained by the project "Investigation on Laws, Causes and Predictions of Droughts And Floods In The Yellow River valley And The Yangtze River valley of China" for this three years are reviewed in this paper. The laws of decadal scale, interannual and Intraseasonal variations and circulation conditions of droughts and floods in these two valleys are analysed in detail. Moreover, the preliminary views of the causes of droughts and floods in these two valleys are put forward. The investigations of the project have pointed out that the thermal state in the western Pacific warm pool and the connective activities over the warm pool and the connective activities over the Tibetan Plateau may be siganificant causes of droughts and floods caused in these two valleys. Besides, the numerical simulation of occurance and circulation condition of droughts and floods resulted in these two valleys and their prediction experiments have been made by using the atmospheric general circulation model.
In this paper, the problems in research of the project are also analysed so that to obtain the investigated results in more higher level.     

Flow hydraulics and geomorphic effects of glacial‐lake outburst floods in the Mount Everest region,Nepal

Glacial‐lake outburst floods (GLOFs) on 3 September 1977 and 4 August 1985 dramatically modified channels and valleys in the Mount Everest region of Nepal by eroding, transporting, and depositing large quantities of sediment for tens of kilometres along the flood routes. The GLOF discharges were 7 to 60 times greater than normal floods derived from snowmelt runoff, glacier meltwater, and monsoonal precipitation (referred to as seasonal high flow floods, SHFFs). Specific stream power values ranged from as low as 1900 W m^?2 in wide, low‐gradient valley segments to as high as 51 700 W m^?2 in narrow, high‐gradient valley segments bounded by bedrock. Along the upper 16 km of the GLOF routes, the reach‐averaged specific stream power of the GLOFs was 3·2 to 8·0 times greater than the reach‐averaged specific stream power of the SHFFs. The greatest geomorphic change occurred along the upper 10 to 16 km of the GLOF routes, where the ratio between the GLOF specific stream power and the SHFF specific stream power was the greatest, there was an abundant supply of sediment, and channel/valley boundaries consisted primarily of unconsolidated sediment. Below 11 to 16 km from the source area, the geomorphic effects of the GLOFs were reduced because of the lower specific stream power ratio between the GLOFs and SHFFs, more resistant bedrock flow boundaries, reduced sediment supply, and the occurrence of past GLOFs. Copyright © 2003 John Wiley & Sons, Ltd.     

郁江南宁17场洪水之合成面雨量特征分析

对郁江南宁 17场洪水的合成面雨量分布特征作了较系统的分析 ,发现引发南宁洪水的主要天气系统及其配置、合成面雨量的流域值及“6 8.8”大洪水和“0 1.7”特大洪水的合成面雨量表征 ,对今后进一步做好重大洪水的气象服务具有十分积极的意义     

Example of a debris-flow risk analysis from Vancouver Island,British Columbia,Canada

In July 2005, a debris flow and a water flood occurred on two adjacent gullies in the White River area, on northern Vancouver Island in British Columbia, Canada. The 16,000 m³ debris flow buried approximately 7.5 ha of second-growth trees, buried approximately 500 m of a forestry road, and reached two fish-bearing streams. The water flood eroded approximately 240 m of the same forestry road and plugged four culverts before overtopping and inundating the road. To better plan for future events, risk analyses of debris flows, debris floods, and water floods were carried out for the two gullies involved, plus a third adjacent gully. The elements at risk that were analyzed included, in order of priority: users of the forestry road, the fish-bearing streams, the forestry road itself, and a timber bridge. Using a series of qualitative, but defined, relative-risk matrices, the following components of specific risk were estimated for each of the three types of events on each of the three gullies for each of the four elements at risk: probability of occurrence, probability that the event will reach or otherwise affect the site of the element at risk, the probability that the element at risk will be at the site when the event occurs, and the probability of loss or damage resulting from the element being at the site when the event occurs.