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1.
In order to study historical flood-frequency records we plot the log of the number of floods on a river per unit time in which the peak discharge exceeds a specified value against the log of that value. For ten benchmark stations we find good correlations with scale-invariant (fractal) statistics. We suggest that the underlying physical processes associated with the generation of floods are sufficiently scale invariant over time scales from one to one hundred years that they provide a rational basis for the application of scale-invariant statistics. Our results fall within the range of flood-frequency estimates made by other statistical techniques. We propose that the ratio of the ten-year peak discharge to the one-year peak discharge is a quantitative measure of flood potential. With scale invariance is also the ratio of the one-hundred year flood to the ten-year flood. We find that the values of for ten stations on rivers throughout the country range from 2.04 to 8.11 and find strong regional variations that can be correlated in terms of climate. Our results are consistent with the observed fractal statistics in sedimentary sections. We have also carried out R/S analyses for the ten stations and have obtained values of the Hurst exponent. We find that the Hurst exponent cannot be used for flood-frequency forecasting. 相似文献
2.
D. L. Turcotte L. Greene 《Stochastic Environmental Research and Risk Assessment (SERRA)》1993,7(1):33-40
In order to study historical flood-frequency records we plot the log of the number of floods on a river per unit time in which the peak discharge exceeds a specified value against the log of that value. For ten benchmark stations we find good correlations with scale-invariant (fractal) statistics. We suggest that the underlying physical processes associated with the generation of floods are sufficiently scale invariant over time scales from one to one hundred years that they provide a rational basis for the application of scale-invariant statistics. Our results fall within the range of flood-frequency estimates made by other statistical techniques. We propose that the ratio of the ten-year peak discharge to the one-year peak discharge is a quantitative measure of flood potential. With scale invariance is also the ratio of the one-hundred year flood to the ten-year flood. We find that the values of for ten stations on rivers throughout the country range from 2.04 to 8.11 and find strong regional variations that can be correlated in terms of climate. Our results are consistent with the observed fractal statistics in sedimentary sections. We have also carried out R/S analyses for the ten stations and have obtained values of the Hurst exponent. We find that the Hurst exponent cannot be used for flood-frequency forecasting. 相似文献
3.
High‐magnitude floods across Europe within the last decade have resulted in the widespread reassessment of flood risk; this coupled with the introduction of the Water Framework Directive (2000) has increased the need for a detailed understanding of seasonal variability in flood magnitude and frequency. Mean day of flood (MDF) and flood seasonality were calculated for Wales using 30 years of gauged river‐flow records (1973–2002). Noticeable regional variations in timing and length of flood season are evident, with flooding occurring earlier in small catchments draining higher elevations in north and mid‐west Wales. Low‐altitude regions in West Wales exposed to westerly winds experience flooding during October–January, while large eastern draining catchments experience later flooding (January–February). In the northeast and mid‐east regions December–January months experience the greatest number of floods, while the southeast has a slightly longer flood season (December–February), with a noticeable increase in January floods. Patterns obtained from MDF data demonstrate their effectiveness and use in analysing regional patterns in flood seasonality, but catchment‐specific determinants, e.g. catchment wetness, size and precipitation regime are important factors in flood seasonality. Relatively strong correlations between precipitation and flood activity are evident in Wales, with a poorer relationship between flooding and weather types and the North Atlantic Oscillation (NAO). Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
4.
The homogeneity of the flood frequency regime for a given pooling-group of sites is a fundamental assumption for many regional flood frequency analysis techniques. Assessing regional homogeneity is a critical step, which may be complicated by the presence of cross-correlation among flood sequences. The scientific literature proposes a number of statistical homogeneity tests and documents that inter-site correlation of floods is normally not negligible, but does not specifically address the impact of cross-correlation on such statistical tests. This paper analyzes the effectiveness of a well-known homogeneity test proposed in the scientific literature in the presence of inter-site cross-correlation through a series of Monte Carlo experiments. The numerical experiments enable us to comment on a possible theoretical correction for the test and to identify an empirical tool that accounts for the impact of inter-site cross-correlation of floods. 相似文献
5.
Abstract The Pearl River Delta (PRD) is a complicated criss-cross river network. The booming economy and intensifying human activity have greatly altered the natural water levels, which threatens regional sustainable development. The Mann-Kendall trend test and the kriging interpolation method were used to detect the spatial and temporal patterns in the trends of extreme high/low water levels related to different magnitudes of streamflow, in order to explore the impacts of hydrological processes on the water-level changes throughout the PRD. The results indicate that: (a) streamflow changes at the Sanshui and Makou stations exhibit different characteristics. No significant trend can be identified in the streamflow changes at Makou station; however, the streamflow at Sanshui station shows a significant increasing trend, especially in low-flow periods. The decreasing Makou/Sanshui streamflow ratio exerts tremendous impacts on the water-level changes in the hinterland of the PRD region. (b) Extreme high/low water levels exhibit similar changing patterns. The extreme high/low water levels in the high/normal flow periods are decreasing in both the upper PRD and the hinterland of the PRD region. Increasing extreme high/low water levels in low-flow periods can be identified in the hinterland of the PRD region. The coastal regions are characterized by increasing extreme high/low water levels. (c) Extreme high/low water levels for high/normal flow periods in the hinterland of the PRD are heavily impacted by topographic changes due to in-channel dredging. Increasing extreme high/low water levels along the coastal regions are mainly backwater effects caused by serious siltation and rising sea level. This study has scientific and practical merits in regional fluvial management and mitigation of natural hazards. Citation Zhang, Q., Xu, C.-Y. & Chen, Y. D. (2010) Variability of water levels and impacts from streamflow changes and human activity within the Pearl River Delta, China. Hydrol. Sci. J. 55(4), 512–525. 相似文献
6.
Traditional flood‐frequency analysis involves the assumption of homogeneity of the flood distribution. However, floods are often generated by heterogeneous distributions composed of a mixture of two or more populations. Differences between the populations may be the result of a number of factors, including seasonal variations in the flood‐producing mechanisms, changes in weather patterns resulting from low‐frequency climate shifts and/or El Niño/La Nina oscillations, changes in channel routing owing to the dominance of within‐channel or floodplain flow, and basin variability resulting from changes in antecedent soil moisture. Not recognizing these physical processes in conventional flood‐frequency analysis probably is the main reason that many frequency distributions do not provide an acceptable fit to flood data. In this paper, we use long‐term hydroclimatic records from the Gila River basin of south‐east and central Arizona in the USA to explore the extent and significance of mixed populations. First, we discuss the probable causes of heterogeneity in the frequency distribution of annual flood and present evidence of its occurrence. Second, we investigate the implications of using various popular homogeneous distributions for predicting peak flows for basins that exhibit mixed population characteristics. Third, we demonstrate how alternative frequency models that explicitly account for floods generated by a mixture of two or more populations are both hydrologically and statistically more appropriate. We illustrate how the selection of the most plausible distribution for flood‐frequency analysis also should be based on hydrological reasoning as opposed to the sole application of the traditional statistical goodness‐of‐fit tests. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
7.
To what extent have changes in channel capacity contributed to flood hazard trends in England and Wales? 
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下载免费PDF全文 Louise J. Slater 《地球表面变化过程与地形》2016,41(8):1115-1128
The frequency of floods has been projected to increase across Europe in the coming decades due to extreme weather events. However, our understanding of how flood frequency is affected by geomorphic changes in river channel capacity remains limited. This paper seeks to quantify the influence of trends in channel capacity on flood hazards. Measuring and predicting the effect of geomorphic changes on freshwater flooding is essential to mitigate the potential effects of major floods through informed planning and response. Hydrometric records from 41 stream gauging stations were used to measure trends in the flood stage (i.e. water surface elevation) frequency above the 1% annual exceedance threshold. The hydrologic and geomorphic components of flood hazard were quantified separately to determine their contribution to the total trend in flood stage frequency. Trends in cross‐sectional flow area and mean flow velocity were also investigated at the same flood stage threshold. Results showed that a 10% decrease (or increase) in the channel capacity would result in an increase (or decrease) in the flood frequency of approximately 1.5 days per year on average across these 41 sites. Widespread increases in the flood hazard frequency were amplified through both hydrologic and geomorphic effects. These findings suggest that overlooking the potential influence of changing channel capacity on flooding may be hazardous. Better understanding and quantifying the influence of geomorphic trends on flood hazard will provide key insight for managers and engineers into the driving mechanisms of fluvial flooding over relatively short timescales. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
8.
Water level variability and trends in Lake Constance in the light of the 1999 centennial flood 总被引：1，自引：0，他引：1
The extreme flood of Lake Constance in 1999 focused attention on the variability of annual lake levels. The year 1999 not only brought one of the highest floods of the last 180 years but also one of the earliest in the season. The 1999 extreme event was caused by heavy rainfall in the alpine and pre-alpine regions. The influence of precipitation in the two distinct regional catchments on lake level variations can be quantified by correlation analysis. The long-term variations in lake level and precipitation show similar patterns. This is seen through the use of spectral analysis, which gives similar bands of spectral densities for precipitation and lake level time series. It can be concluded from the comparison of these results with the analysis of climate change patterns in northern Europe, i.e. the index of the North Atlantic Oscillation, that the regional effects on lake level variations are more pronounced than those of global climate change. 相似文献
9.
A large amount of the total sediment load in the Chinese Yellow River is transported during hyperconcentrated floods. These floods are characterized by very high suspended sediment concentrations and rapid morphological changes with alternating sedimentation and erosion in the main channel, and persistent sedimentation on the floodplain. However, the physical mechanisms driving these hyperconcentrated floods are still poorly understood. Numerical modelling experiments of these floods reveal that sedimentation is largely caused by large vertical concentration gradients, both in the channel during the rising stage of the flood, as well as on the floodplains, during a later stage of the flood. These vertical concentration gradients are large because the turbulent mixing rates are reduced by the increased sediment‐induced density gradients, resulting in a positive feedback mechanism that produces high deposition rates. Erosion prevails when the sediment is largely held in suspension due to hindered settling, and is strengthened by the reduced wetted cross‐section caused by massive sedimentation on the floodplain. Observed patterns of erosion and sedimentation during these floods can be qualitatively reproduced with a numerical model in which sediment‐induced density effects and hindered settling are included. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
10.
During the 20th century many floods of different intensity and extent have occurred on the Odra River and its tributaries. On the basis of long-term water level observations five major floods, that affected the entire upper and middle Odra River basin, were chosen for further analysis: June 1902, July 1903, August 1977, August 1985 and July 1997. However, hazardous floods were not only those that covered the whole upper and middle Odra River basin, so several local floods were also studied. Detailed historical analysis was made of meteorological conditions, with special emphasis on precipitation patterns and amounts. Then, on the basis of flood peak time occurrence, the stages of flood wave formation were formulated. The natural flood wave of the Odra River is often modified by hydro-technical infrastructure, the development and improvement of which is briefly described in this paper. In conclusion, a comparison of flood wave characteristics such as rising time, falling time, duration, peak flow and volume is presented. 相似文献
11.
变化环境下珠江流域洪水频率变化特征、成因及影响(1951-2010年) 总被引：4，自引：0，他引：4
气候变化和人类活动导致珠江流域水文变化,变化前后洪水频率分布显著不同.运用滑动秩和(Mann-Whitney U test)结合Brown-Forsythe、滑动T、有序聚类和Mann-Kendall检验法,并用累积距平曲线法获取年最大流量序列详细信息,综合确定样本最佳变化节点,并对水文变化成因做了系统分析.在此基础上,对整体序列、变化前后序列用线性矩法推求广义极值分布参数以及不同重现期设计流量.结果表明:(1)西江大部以及北江流域最佳变化节点在1991年左右;东江流域最佳变化节点与该流域内3大控制性水库建成时间基本吻合;(2)变化后,西江、北江年最大流量持续增加,洪峰强度增大,尤其是西江干流年最大流量显著增加;东江流域年最大流量显著减小,洪峰强度降低;(3)变化后,西江与北江洪水风险增加,尤其是下游珠三角地区本身受人类活动显著影响,加之西江与北江持续增加的洪水强度,珠三角地区发生洪水的强度及频次加剧,而东江洪水风险减小.此研究对于珠江流域在变化环境下的洪水风险评估与防洪抗灾具有重要意义. 相似文献
12.
The flood seasonality of catchments in Switzerland is likely to change under climate change because of anticipated alterations of precipitation as well as snow accumulation and melt. Information on this change is crucial for flood protection policies, for example, or regional flood frequency analysis. We analysed projected changes in mean annual and maximum floods of a 22‐year period for 189 catchments in Switzerland and two scenario periods in the 21st century based on an ensemble of climate scenarios. The flood seasonality was analysed with directional statistics that allow assessing both changes in the mean date a flood occurs as well as changes in the strength of the seasonality. We found that the simulated change in flood seasonality is a function of the change in flow regime type. If snow accumulation and melt is important in a catchment during the control period, then the anticipated change in flood seasonality is most pronounced. Decreasing summer precipitation in the scenarios additionally affects the flood seasonality (mean date of flood occurrence) and leads to a decreasing strength of seasonality, that is a higher temporal variability in most cases. The magnitudes of mean annual floods and more clearly of maximum floods (in a 22‐year period) are expected to increase in the future because of changes in flood‐generating processes and scaled extreme precipitation. Southern alpine catchments show a different signal, though: the simulated mean annual floods decrease in the far future, that is at the end of the 21st century. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
13.
14.
长江流域历史水旱灾害分析 总被引：2，自引：1，他引：1
长江流域有丰富和长期的水旱灾害史料,最早的水灾和旱灾记载有2000余年的历史,经过系统整理和分析的历史水旱灾害资料有1000余年的旱涝型年表和500余年的旱涝分布图集.在以上资料基础上,对长江流域历史水旱灾害的地域分布特性和时间变化规律进行了初步分析:500余年历史水旱灾害的地域分布显示,流域水旱灾害总体特征是水灾重于旱灾,各级水旱灾害频率的地域分布极不均匀,存在着显著的灾害多发和少发地带,它们与自然地理环境、水系特征、气候条件和社会经济条件等因素有关;1000余年旱涝型年表分析表明,长江流域洪涝和干旱频次在时间上的非均匀分布并非完全随机,表现出多种时间尺度的年际变化特征,其中主要表现为约100a上下的大干湿气候期变化及40a左右的小旱涝期振动. 相似文献
15.
1840年以来长江大洪水演变与气候变化关系初探 总被引：25，自引：3，他引：22
长江洪水灾害是我国频率高、为患严重的自然灾害之一.本文依据可靠资料,选择1840年至2000年间32次大洪水记录,探讨其演变与气候变化的关系.认知1910s前的19世纪冷期出现大洪水13次(包括1870年的极值大洪水事件)频率为1.9次／10a.1921-2000年间出现了大洪水19次,频率为2.4次／10a.20世纪暖期又分出两个变暖时段,前一变暖时段的峰值期1920s-1940s出现大洪水9次,包含1931年全流域大洪水.后一变暖时段,即1980s与1990s出现大洪水8次.实测记录到的最大洪水1954年位于前一变暖时段结束阶段.1990s是全球,也是我国近百年中最暖年代,受东南季风影响大的中下游地区夏季降水量是近百年最多的,大暴雨频率也是有较多记录的40年来最高的.以此出现了10年5次大洪水高频率现象,包含1998年全流域型大洪水,表明了全球变暖的显著影响.也指示30-40年问周期性振荡中多雨年代.如此可预期21世纪初期降水会有小幅度下降与大洪水频率在短期内降低的可能性.长江上游受西南季风影响较大,19世纪下半期与20世纪上半期为多降水期,大洪水频率较高.20世纪下半期为少降水期,大洪水频率较低.关于气候变化研究有待深入,前景不易预估. 相似文献
16.
Changes to flood peaks of a mountain river: implications for analysis of the 2013 flood in the Upper Bow River,Canada 下载免费PDF全文
下载免费PDF全文 The mountain headwater Bow River at Banff, Alberta, Canada, was subject to a large flood in June 2013, over which considerable debate has ensued regarding its probability of occurrence. It is therefore instructive to consider what information long‐term streamflow discharge records provide about environmental change in the Upper Bow River basin above Banff. Though protected as part of Banff National Park, since 1885, the basin has experienced considerable climate and land cover changes, each of which has the potential to impact observations, and hence the interpretations of flood probability. The Bow River at Banff hydrometric station is one of Canada's longest‐operating reference hydrological basin network stations and so has great value for assessing changes in flow regime over time. Furthermore, the station measures a river that provides an extremely important water supply for Calgary and irrigation district downstream and so is of great interest for assessing regional water security. These records were examined for changes in several flood attributes and to determine whether flow changes may have been related to landscape change within the basin as caused by forest fires, conversion from grasslands to forest with fire suppression, and regional climate variations and/or trends. Floods in the Upper Bow River are generated by both snowmelt and rain‐on‐snow (ROS) events, the latter type which include flood events generated by spatially and temporally large storms such as occurred in 2013. The two types of floods also have different frequency characteristics. Snowmelt and ROS flood attributes were not correlated significantly with any climate index or with burned area except that snowmelt event duration correlated negatively to the Pacific Decadal Oscillation. While there is a significant negative trend in all floods over the past 100 years, when separated based on generating process, neither snowmelt floods nor large ROS floods associated with mesoscale storms show any trends over time. Despite extensive changes to the landscape of the basin and in within the climate system, the flood regime remains unchanged, something identified at smaller scales in the region but never at larger scales. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
17.
As a supplementary method to the conventional flood frequency analysis based on annual peak flows, we propose an approach in this paper to infer the flood frequency distribution on quarterly and semi-annual time scale, which are then converted to annual time scale to obtain the floods corresponding to return periods in unit of year. Two criteria for test of data independence, namely, minimum 7 and 15-day interval between two consecutive peak flows, are tested. The proposed approach was applied to Des Moines River at Fort Dodge, Iowa, USA using its 62 years of observation daily flows. The results show that the estimated floods for given return periods from quarter-annual data series are in general higher than the corresponding estimated floods from semi-annual data series, which is further larger than estimated floods from annual peak flows. The floods estimated from semi-annual data series agree well with the results of previous US Geological Survey study. 相似文献
18.
Spatial and seasonal patterns of flood change across Brazil 总被引：1，自引：1，他引：0
Brazil has some of the largest rivers in the world and has the second greatest flood loss potential among the emergent countries. Despite that, flood studies in this area are still scarce. In this paper, we used flood seasonality and trend analysis at the annual and seasonal scales in order to describe flood regimes and changes across the whole of Brazil in the period 1976–2015. We identified a strong seasonality of floods and a well-defined spatio-temporal pattern for flood occurrence. There are positive trends in the frequency and magnitude of floods in the North, South and parts of Southeast Brazil; and negative trends in the North-east and the remainder of Southeast Brazil. Trends in the magnitude (frequency) were predominant in the winter (summer). Overall, floods are becoming more frequent and intense in Brazilian regions characterized by wet conditions, and less frequent and intense in drier regions. 相似文献
19.
Real data on wadi flood flows from Saudi Arabia, Yemen, Oman, Kuwait, UAE, Bahrain and Qatar were used to develop methodologies for the prediction of annual maximum flows and average monthly flows in the Arabian Gulf states. For the prediction of annual maximum floods, three methods have been investigated. In the first method, regional curves were developed and used together with the mean annual flood flow, estimated from the characteristics of the drainage basin, to estimate flood flows at a location in the basin. The second method fits data to various probability distribution functions, with a developed methodology introduced to account for floods generated by more than one system of climate, and the best fitted function was used for flood estimates. In the third method, only floods over a threshold, which depends on characteristics of the drainage basin, were considered and modelled. For the prediction of average monthly flows, stochastic simulation approaches of flood frequency analysis were used. Each of the prediction methods was verified by being applied in 40 different drainage basins. Based on the results obtained, recommendations were made on the best method to be applied (at present) by design engineers in the Arabian Gulf states. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
20.
Mathias J. Collins 《水文研究》2019,33(5):687-698
The New England and Mid‐Atlantic regions of the Northeast United States have experienced climate‐induced increases in both the magnitude and frequency of floods. However, a detailed understanding of flood seasonality across these regions, and how flood seasonality may have changed over the instrumental record, has not been established. The annual timing of river floods reflects the flood‐generating mechanisms operating in a basin, and many aquatic and riparian organisms are adapted to flood seasonality, as are human uses of river channels and flood plains. Changes in flood seasonality may indicate changes in flood‐generating mechanisms, and their interactions, with important implications for habitats, flood plain infrastructure, and human communities. I applied a probabilistic method for identifying flood seasons at a monthly resolution for 90 Northeast U.S. watersheds with natural, or near‐natural, flood‐generating conditions. Historical trends in flood seasonality were also investigated. Analyses were based on peaks‐over‐threshold flood records that have, on average, 85 years of data and three peaks per year—thus providing more information about flood seasonality than annual maximums. The results show rich detail about annual flood timing across the region with each site having a unique pattern of monthly flood occurrence. However, a much smaller number of dominant seasonal patterns emerged when contiguous flood‐rich months were classified into commonly recognized seasons (e.g., Mar–May, spring). The dominant seasonal patterns identified by manual classification were corroborated by unsupervised classification methods (i.e., cluster analyses). Trend analyses indicated that the annual timing of flood‐rich seasons has generally not shifted over the period of record, but 65 sites with data from 1941 to 2013 revealed increased numbers of June–October floods—a trend driving previously documented increases in Northeast U.S. flood counts per year. These months have been historically flood‐poor at the sites examined, so warm‐season flood potential has increased with possible implications for aquatic and riparian organisms. 相似文献