On the relationship between flood and contributing area     

Christopher Spence  Samson Girma Mengistu 《水文研究》2019,33(14):1980-1992

Although it is well known that the vast majority of the time only a portion of any watershed contributes run‐off to the outlet, this extent is rarely documented. Also, the power law form of the streamflow and contributing area (Q‐A_c) relationship has been known for a half century, but it is uncommon for it to be quantified, and time series of contributing area extensive enough to calculate its frequency distribution are almost non‐existent. Data from the Canadian Prairies, where there are extensive estimates of contributing area during the median annual flood, imply that the power law coefficient for any Q‐A_c curve is a function of flow magnitude and return period. These data also suggest that regional flood frequency curves are a construct of Q‐A_c curves from individual basins. This paper will discuss research that attempted to reproduce the Q‐A_c curves for the La Salle River Watershed with a semidistributed numerical hydrological model, MESH‐PDMROF. The model simulated streamflow reasonably well (Nash Sutcliffe values = 0.62) compared with published examples of comparable models applied in the region. Estimates of the coefficient and exponent of the Q‐A_c power law function ranged from 0.08–0.14 and 0.9–1.12, respectively. These exponent values were lower than those of regional flood frequency curves and support the theory that regional flood frequency curves are a construct of Q‐A_c curves. Simulations of the area contributing to the median annual flood were lower (0.3) than those derived from independent topographic analysis (0.9) described in earlier literature though there is uncertainty in both these estimates. This uncertainty was extended across the flood frequency distribution and may be too large to definitively verify the study hypothesis.  相似文献   

The 2020 Summer Floods and 2020/21 Winter Extreme Cold Surges in China and the 2020 Typhoon Season in the Western North Pacific     

Chunzai WANG  Yulong YAO  Haili WANG  Xiubao SUN  Jiayu ZHENG 《大气科学进展》2021,38(6):896-904

China experienced significant flooding in the summer of 2020 and multiple extreme cold surges during the winter of 2020/21. Additionally, the 2020 typhoon season had below average activity with especially quiet activity during the first half of the season in the western North Pacific(WNP). Sea surface temperature changes in the Pacific, Indian, and Atlantic Oceans all contributed to the heavy rainfall in China, but the Atlantic and Indian Oceans seem to have played dominant roles. Enhancement and movement of the Siberian High caused a wavier pattern in the jet stream that allowed cold polar air to reach southward, inducing cold surges in China. Large vertical wind shear and low humidity in the WNP were responsible for fewer typhoons in the first half of the typhoon season. Although it is known that global warming can increase the frequency of extreme weather and climate events, its influences on individual events still need to be quantified.Additionally, the extreme cold surge during 16–18 February 2021 in the United States shares similar mechanisms with the winter 2020/21 extreme cold surges in China.  相似文献   

2017-2019年东莞城区内涝特征及与降雨关系分析     

姜晓岑  莫伟强  尹淑娴 《广东气象》2021,43(1)

利用东莞城市内涝预报验证系统的积水和降雨数据、SWIFT自动站资料、NCEP再分析资料、广州雷达基本反射率资料,对2017年3月—2019年9月东莞城区内涝特征及内涝与降雨的关系进行分析,结果表明:东莞城区内涝发生频繁,重度内涝较多,内涝事件多发生在前汛期(4—6月),以5月最多;与长时间降雨相比,短时强降雨更易导致城区积水较深的内涝,1 h降雨量达27.6 mm以上时,城区大部可达中度内涝等级,1 h降雨量在51.2 mm以上时,城区大部将可能出现重度内涝;过程总雨量和1 h雨强都对长时间积水有影响,但过程总雨量较大更易导致积水长时间维持;积水一般滞后降雨约5~30 min出现,积水峰值滞后5和30 min才出现。  相似文献   

Toward Understanding the Extreme Floods over Yangtze River Valley in June?July 2020: Role of Tropical Oceans※     

Shaolei TANG  Jing-Jia LUO  Jiaying HE  Jiye WU  Yu ZHOU  Wushan YING 《大气科学进展》2021,38(12):2023-2039,中插8-中插11

The extreme floods in the Middle/Lower Yangtze River Valley (MLYRV) during June?July 2020 caused more than 170 billion Chinese Yuan direct economic losses. Here, we examine the key features related to this extreme event and explore relative contributions of SST anomalies in different tropical oceans. Our results reveal that the extreme floods over the MLYRV were tightly related to a strong anomalous anticyclone persisting over the western North Pacific, which brought tropical warm moisture northward that converged over the MLYRV. In addition, despite the absence of a strong El Ni?o in 2019/2020 winter, the mean SST anomaly in the tropical Indian Ocean during June?July 2020 reached its highest value over the last 40 years, and 43％ (57％) of it is attributed to the multi-decadal warming trend (interannual variability). Based on the NUIST CFS1.0 model that successfully predicted the wet conditions over the MLYRV in summer 2020 initiated from 1 March 2020 (albeit the magnitude of the predicted precipitation was only about one-seventh of the observed), sensitivity experiment results suggest that the warm SST condition in the Indian Ocean played a dominant role in generating the extreme floods, compared to the contributions of SST anomalies in the Maritime Continent, central and eastern equatorial Pacific, and North Atlantic. Furthermore, both the multi-decadal warming trend and the interannual variability of the Indian Ocean SSTs had positive impacts on the extreme floods. Our results imply that the strong multi-decadal warming trend in the Indian Ocean needs to be taken into consideration for the prediction/projection of summer extreme floods over the MLYRV in the future.  相似文献   

广州市城市内涝特征分析     

杨慧燕  李海燕  赵琴  肖柳斯  张兰  高美谭 《广东气象》2021,43(2):5-9

基于水务部门排水管理中心的内涝灾情信息,运用统计学等研究方法,分析广州市城市内涝分布特征,结果表明:广州全市内涝点最多的是中心城区天河,最少的是郊区的从化。全年发生内涝次数最多的月份是5、6月,最少的月份是2、12月;全天最容易发生内涝的时间是08:00、13:00和19:00。内涝发生时对应的最大小时雨量主要集中在50~80mm,占55%;过程累计雨量在120mm以上占41.76%。内涝过程的最大小时雨量和累计雨量空间分布和内涝点的空间分布特征大致吻合,内涝过程平均小时雨量集中在30~50mm,占61%。从与致涝相关的天气系统来看,主要是东路或者西路冷空气配合中层的线槽及低层切变线的过程;另外副高边缘的摆动加上低层偏南风加大和台风过程也容易致涝。  相似文献   

Flow Behavior of Clay-Silt to Sand-Silt Water-Rich Suspensions at Low to High Shear Rates: Implications for Slurries, Transitional Flows, and Submarine Debris-Flows     

Pierdomenico DEL GAUDIO  Guido VENTURA 《《地质学报》英文版》2018,92(6):2395-2404

Water-rich clay to sand suspensions show a shear rate dependent flow behavior and knowledge of the appropriate rheological model is relevant for sedimentological, industrial and hydraulic studies. We present experimental rheological measurements of water-rich (40 to 60 wt%) clay to silt (population A) and silt to sand (population B) suspensions mixed in different proportions. The data evidence a shear rate dependent shear thinning-shear thickening transition. At lower shear rates, the suspensions organize in chains of particles, whereas at higher shear rates, these chains disrupt so increasing the viscosity. The viscosity, consistency and yield stress decrease as the A+B fraction decreases as the content of B particles increases. This behavior reflects the competing effects of the lubrication and frictional processes as a function of particle size and water content. Transitional flows form by the incorporation of small amounts of the finer fraction while ‘oceanic floods’ form at the estuary of rivers and the submarine debris-flows increase their velocity by incorporating water. The critical Reynolds number of the studied suspensions is ~2000±100 suggesting that the grainsize plays a major role in the laminar to turbulent transition. Our results have implications for the modeling of sediment flows and the hazard related to floods.  相似文献   

A Multiple Criteria Decision Modelling approach to selection of estimation techniques for fitting extreme floods     

L. Duckstein  B. Bobée  F. Ashkar 《Stochastic Hydrology and Hydraulics》1991,5(3):227-238

The problem of fitting a probability distribution, here log-Pearson Type III distribution, to extreme floods is considered from the point of view of two numerical and three non-numerical criteria. The six techniques of fitting considered include classical techniques (maximum likelihood, moments of logarithms of flows) and new methods such as mixed moments and the generalized method of moments developed by two of the co-authors. The latter method consists of fitting the distribution using moments of different order, in particular the SAM method (Sundry Averages Method) uses the moments of order 0 (geometric mean), 1 (arithmetic mean), –1 (harmonic mean) and leads to a smaller variance of the parameters. The criteria used to select the method of parameter estimation are:

–	- the two statistical criteria of mean square error and bias;
–	- the two computational criteria of program availability and ease of use;
–	- the user-related criterion of acceptability.

These criteria are transformed into value functions or fuzzy set membership functions and then three Multiple Criteria Decision Modelling (MCDM) techniques, namely, composite programming, ELECTRE, and MCQA, are applied to rank the estimation techniques.  相似文献   

山洪视角下社区韧性影响因素及其定量分析     

钟鸣  肖璐  张倩  温家洪 《地理科学进展》2022,41(3):423-436

山洪灾害具有广泛性、突发性、破坏性等特征,开展山洪易发区的社区韧性评估,从而提高灾害应对能力是当前防灾减灾的前沿热点和难点。论文提出了一套多学科的综合方法：① 利用中介效应明晰了山洪视角下社区韧性评价体系各指标间的定量化传递关系;② 构建了基于决策实验室分析和解释结构模型的耦合数学模型,确定社区韧性影响因素的多级递阶解释结构模型,分析社区韧性的差异化影响因素;③ 采用信息扩散方法,定量分析山洪灾害社区韧性的变化趋势并排序。以粤北山洪易发区为例,从城镇、村落、城乡结合部3种类型社区进行灾害韧性分析。结果表明：山洪视角下的社区韧性指标体系是一个多维度多层次的复杂网络系统,包括环境、社会、心理、制度和信息沟通5个方面;不同类型社区灾害韧性的直接影响因素呈差异化特征,而供排水设施建设和洪灾应急演练为社区韧性的根本影响因素,对增强山洪视角下社区韧性发挥本质性作用;由于调研村落多位于山洪频发区,居民防范灾害、减轻灾害影响的意识较强,村落较城镇和城乡结合社区呈现出更高的韧性。研究可为提升粤北山洪易发区社区韧性及社区防灾减灾能力提供科学参考,该综合分析方法亦可为其他类型灾害的精细化防灾减灾提供支持。  相似文献   

Sedimentation of overbank floods in the confined complex channel–floodplain system of the Lower Yellow River,China          下载免费PDF全文

Min Zhang  He Qing Huang  Paul A. Carling  Mingwu Zhang 《水文研究》2017,31(20):3472-3488

The channel boundary conditions along the Lower Yellow River (LYR) have been altered significantly since the 1950s with the continual reinforcement and construction of both main and secondary dykes and river training works. To evaluate how the confined complex channel–floodplain system of the LYR responds to floods, this study presents a detailed investigation of the relationship between the tempo‐spatial distribution of sedimentation/erosion and overbank floods occurred in the LYR. For large overbank floods, we found that when the sediment transport coefficient (ratio of sediment concentration of flow to flow discharge) is less than 0.034, the bankfull channel is subject to significant erosion, whereas the main and secondary floodplains both accumulate sediment. The amount of sediment deposited on the main and secondary floodplains is closely related to the ratio of peak discharge to bankfull discharge, volume of water flowing over the floodplains, and sediment concentration of overbank flow, whereas the degree of erosion in the bankfull channel is related to the amount of sediment deposited on the main and secondary floodplains, water volume, and sediment load in flood season. The significant increase in erosion in the bankfull channel is due to the construction of the main and secondary dykes and river training works, which are largely in a wide and narrow alternated pattern along the LYR such that the water flowing over wider floodplains returns to the channel downstream after it drops sediment. For small overbank floods, the bankfull channel is subject to erosion when the sediment transport coefficient is less than 0.028, whereas the amount of sediment deposited on the secondary floodplain is associated closely with the sediment concentration of flow. Over the entire length of the LYR, the situation of erosion in the bankfull channel and sediment deposition on the main and secondary floodplains occurred mainly in the upper reach of the LYR, in which a channel wandering in planform has been well developed.  相似文献   

Detailed spatio‐temporal sediment supply reconstruction using tree roots data          下载免费PDF全文

Karel Šilhán  Tomáš Galia  Václav Škarpich 《水文研究》2016,30(22):4139-4153

Floods are an important geomorphic agent that accelerate sediment supply from bank failures. The quantitative proportions supplied by lateral inputs and the transport conditions of the channel can create local or extended accumulation zones within the channel reaches. These accumulation zones play an important role in the geomorphic regime of the stream. Knowledge of long‐term history of sediment supply is necessary to determine how these input and deposition forms developed. This study introduces a new approach for the quantification of past sediment supply via lateral erosion (incised banks and individual bank failures), using a case study of the confluence of three partial tributaries in the accumulation zone in the Outer Western Carpathians. For each tributary, as well as the channel reach downstream of the confluence zone, we calculated the mean of the largest bed particles and the unit stream power as indicators of transport capacity. We found that two of the tributaries supply significant amounts of sediment to the accumulation zone because of their higher unit stream power related to their higher transport potential, and observed coarser bed sediment. Seventy‐three bank failures with a total volume 395.5 m³ were mapped, and the sediment supply volume was dated using dendrogeomorphic analysis of 114 scarred tree roots (246 samples). The total volume of the dated sediment supply in the individual tributaries was 193.9 m³, whereas the volume of erosion in the accumulation zone was only 4.9 m³ for a period of approximately 30 years. The period represented by the dated tree roots included 12 years in which erosion events occurred and impacted the total sediment budget in the study area. Although sediment supply was greater than erosion in the accumulation zone, there are no present‐day signs of accretion. The rupture of a dam in an old pond (which is situated approximately 50 m below the accumulation zone) probably increased the transport conditions in the accumulation zone so that it balanced the high sediment supply from individual tributaries. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献