Influence of inflow discharge and bed erodibility on outburst flood of landslide dam

Accurate prediction of the hydrographs of outburst floods induced by landslide dam overtopping failure is necessary for hazard prevention and mitigation. In this study, flume model tests on the breaching of landslide dams were conducted. Unconsolidated soil materials with wide grain size distributions were used to construct the dam. The effects of different upstream inflow discharges and downstream bed soil erosion on the outburst peak discharge were investigated. Experimental results reveal that the whole hydrodynamic process of landslide dam breaching can be divided into three stages as defined by clear inflection points and peak discharges. The larger the inflow discharge, the shorter the time it takes to reach the peak discharge, and the larger the outburst flood peak discharge. The scale of the outburst floods was found to be amplified by the presence of an erodible bed located downstream of the landslide dam. This amplification decreases with the increase of upstream inflow. In addition, the results show that the existence of an erodible bed increases the density of the outburst flow, increasing its probability of transforming from a sediment flow to a debris flow.

Prototype observation and influencing factors of environmental vibrationinduced by flood discharge

Due to a wide range of field vibration problems caused by flood discharge at the Xiangjiaba Hydropower Station, vibration characteristics and influencing factors were investigated based on prototype observation. The results indicate that field vibrations caused by flood discharge have distinctive characteristics of constancy, low frequency, small amplitude, and randomness with impact, which significantly differ from the common high-frequency vibration characteristics. Field vibrations have a main frequency of about 0.5-3.0 Hz and the characteristics of long propagation distance and large-scale impact. The vibration of a stilling basin slab runs mainly in the vertical direction. The vibration response of the guide wall perpendicular to the flow is significantly stronger than it is in other directions and decreases linearly downstream along the guide wall. The vibration response of the underground turbine floor is mainly caused by the load of unit operation. Urban environmental vibration has particular distribution characteristics and change patterns, and is greatly affected by discharge, scheduling modes, and geological conditions. Along with the increase of the height of residential buildings, vibration responses show a significant amplification effect. The horizontal and vertical vibrations of the 7th floor are, respectively, about 6 times and 1.5 times stronger than the corresponding vibrations of the 1st floor. The vibration of a large-scale chemical plant presents the combined action of flood discharge and working machines. Meanwhile, it is very difficult to reduce the low-frequency environmental vibrations. Optimization of the discharge scheduling mode is one of the effective measures of reducing the flow impact loads at present. Choosing reasonable dam sites is crucial.

Similarity criterion of flood discharge atomization

By combining the results of prototype observation of flood discharge atomization at the Wujiangdu Hydropower Station, and by adopting the serial model test method, the model scale effect was examined, the influences of the Reynolds and Weber numbers of water flow on the rain intensity of flood discharge atomization were analyzed and a rain intensity conversion relation was established. It is demonstrated that the level of atomization follows the geometric similarity relations and it is possible to ignore the influence of the surface tension of the flow when the Weber number is greater than 500. Despite limitations such as incomplete data sets, it is undoubtedly helpful to study the scale effect of atomization flow, and it is beneficial to identify the rules of the model test results in order to extrapolate to prototype prediction.

Climate change drives flooding risk increases in the Yellow River Basin

The Yellow River Basin(YRB)has experienced severe floods and continuous riverbed elevation throughout history.Global climate change has been suggested to be driving a worldwide increase in flooding risk.However,owing to insufficient evidence,the quantitative correlation between flooding and climate change remains illdefined.We present a long time series of maximum flood discharge in the YRB dating back to 1843 compiled from historical documents and instrument measurements.Variations in yearly maximum flood discharge show distinct periods:a dramatic decreasing period from 1843 to 1950,and an oscillating gentle decreasing from 1950 to 2021,with the latter period also showing increasing more extreme floods.A Mann-Kendall test analysis suggests that the latter period can be further split into two distinct sub-periods:an oscillating gentle decreasing period from 1950 to 2000,and a clear recent increasing period from 2000 to 2021.We further predict that climate change will cause an ongoing remarkable increase in future flooding risk and an∼44.4 billion US dollars loss of floods in the YRB in 2100.

Flood Discharge Changes by Urbanization from Farmland Based on the Unit Flood Concept at the Kurabe River, Japan

Flood runoff models of urbanization from farmland based on the physical characteristics of a basin have been minimally used in previous research until today. Consequently, the runoff analysis has not been performed that is based on physical basis. Therefore, this research undertook flood discharge analysis from urbanization using the unit flood discharge concept that is enhanced the previous research. The study area was selected at the Kurabe River basin, which is 17.5 km2 in area having a very steep landscape. Twenty-one rainfall events at 10-minute intervals were selected, and five urbanized years were tested. From 1976 to 2009 during 35 years, the flood discharge increased approximately 2.0 times, in which residential areas increased from 23% to 48%;the maximum specific discharge was 21.7 m3·s-1·km-2 in a some block, which is a remarkably large amount. Furthermore, following issues investigated: changes in the hydrograph were associated with urbanization, the effect of a small reservoir aiming to cut down the peak discharge and the relationship between the unit discharge, and the relationship between our method and the discharge estimated by a “Rational Formula”. In particular, the effect of the small reservoir for flood control was found to be remarkably efficient. Finally, the validity of our method was confirmed at the study area in the observed discharge. This result is very useful for estimating runoff discharge changes by urbanization from farmland.

Probabilistic analysis for the response of nonlinear base isolation system under the ground excitation induced by high dam flood discharge

According to theoretical analysis, a general characteristic of the ground vibration induced by high dam flood discharge is that the dominant frequency ranges over several narrow frequency bands, which is verified by observations from the Xiangjiaba Hydropower Station. Nonlinear base isolation is used to reduce the structure vibration under ground excitation and the advantage of the isolation application is that the low-frequency resonance problem does not need to be considered due to its excitation characteristics, which significantly facilitate the isolation design. In order to obtain the response probabilistic distribution of a nonlinear system, the state space split technique is modified. As only a few degrees of freedom are subjected to the random noise, the probabilistic distribution of the response without involving stochastic excitation is represented by the δ function. Then, the sampling property of the δ function is employed to reduce the dimension of the Fokker-Planck-Kolmogorov （FPK） equation and the low-dimensional FPK equation is solvable with existing methods. Numerical results indicate that the proposed approach is effective and accurate. Moreover, the response probabilistic distributions are more reasonable and scientific than the peak responses calculated by conventional time and frequency domain methods.

An improved numerical model of ski-jump flood discharge atomization

Atomizing rainfall caused by flood discharge of high dams poses a great threat to the safety of powerhouse and ecological environment.As an indispensable means,numerical calculation is widely used in the safety design of discharge structures.The distribution of rainfall intensity is closely related to the trajectory nappe shape,jet trajectory distances,the splashed water droplet diameter and its velocity,and the spatial distribution of downstream nappe wind.In this paper,an experimental result is used to verify the improved stochastic splash mathematical model under different bucket types and discharge conditions,and the sensitivity of downstream rainfall intensity distribution to the shape of trajectory nappe,discharge flow,spatial distribution of downstream nappe wind,and the corresponding relationship between the droplet diameter and its splashing velocity is analyzed.The results show that the calculation accuracy of downstream rainfall intensity distribution is significantly improved when the above factors are taken into consideration.It is found that the bucket type and flood discharge rate play the greatest role in the rainfall intensity distribution,followed by the downstream nappe wind distribution,and finally the corresponding relationship between the diameter and velocity of splash droplets.Therefore,these factors should be considered comprehensively when the rainfall intensity distribution of flood discharge atomization is calculated.This study can help us to understand the influence factors of flood discharge atomization more deeply and predict the distribution of flood discharge atomization rainfall intensity more accurately.

INFLUENCE OF SEA－AIR INTERACTION ON THEDISCHARGE OF FLOOD SEASON IN THEUPPER REACHES OF THE CHANGJIANG RIVER

On the method of correlation analysis the poper begins with searching theSST (Sea Surface Temperature) and circulation features of some regions with close correlation to the discharge of the flood season (from June to September) in the upperreaches of the Changjiang (Yangtze) River, then discusses the characteristics of sea-airinteraction and the relations between the sea-air interaction and the discharge of theflood season,after that analyzes the possible mechanisms through which the main searegions affect atmospheric circulation, and of the influence of the circulation changes onthe discharge of the flood season.

Estimation of Unit Flood Discharge for Various Land Use Types with a Focus on Urbanization

We proposed unit flood discharge model that defined as the discharge into end-order (smallest) drainage canals. The discharge acts an important role for estimating regional flooding by big rainfall events which leading roughly estimation of flood discharge associated with land use changes as urbanization. In some areas of Japan, increased urbanization with insufficient drainage canal capacity has led to increasingly frequent flooding and flood damage. The aim of this study was to investigate the effect of urbanization on unit flood discharge using a runoff model for the Tedori River alluvial fan area, Japan. The discharge was studied as collecting runoff from paddy fields, upland crop fields, and residential lots. A runoff model for various land use types in the study area was developed using actual and physical properties of the runoff sites, and parameters for paddy fields. The model was tested using 54 big events and inputted those. The maximum total runoff ratio among different land use types was observed for residential lots, and the ratio remained relatively constant across different flood events. The minimum total runoff ratio was observed for irrigated paddy fields. There was a positive relationship between the total runoff ratio and total precipitation for all land use types. Whereas, the relationship between the peak runoff ratio and peak precipitation was variable. The runoff analysis was carried out using 60-min and 10-min precipitation data. For agricultural land, data for both intervals produced similar results.

Effect of Flood Peak Discharge Control by a Small Reservoir in an Urbanized Area—Case Study in the Kurabe River Basin, Japan

Recently severe damage of flooding by urbanization was frequently occurred. To prevent this damage, small reservoir was constructed in the urbanized residential area. This paper describes an effect of flood peak discharge control by a small reservoir (control reservoir) caused by rapidly developed urbanization. Although work for this purpose was conducted, research on the effects of the control reservoir was not conducted until now. This research, conducted by simulation, was a case study in the Kurabe River Basin in the Tedori River Alluvial Fan Area, Japan, based on the precise investigation of the reservoir in the actual field. The study was conducted to determine not only the actual control reservoir capacity for the newly developed residential area but also the ideal capacity for all present residential areas and the largest capacity allowable for a maximum rainfall event that recently occurred. The control reservoir effects between individual blocks and the entire basin area were compared by dividing the test basin into 15 blocks (sub-basins). The results showed that the effects on the capacity per unit area of the residential area in blocks have close relationship with the decreasing ratio of peak discharge in blocks. Consequently, the effects of control reservoir capacity and the limitation were clarified. In the future, control reservoirs should be constructed for all of the already developed residential areas, for example, by utilizing underground car parking lot. The results of this research can contribute to the design of the control reservoir for protection against flooding damage in urbanized areas.

Numerical Investigation on Downstream Increase in Peak Discharge of Hyperconcentrated Floods in the Lower Yellow River

Hyperconcentrated floods in the Yellow River usually accompanied with some peculiar phenomena that cannot be explained by general conceptions of ordinary sediment-laden flow (e.g., downstream increase in peak discharge, instability flow, ripping up the bottom). Up to date, the mechanisms for the abnormal phenomena are not well understood. The aim of this paper is to facilitate a new insight into the abnormal downstream increase in peak discharge of hyperconcentrated floods in the lower Yellow River. Numerical model experiments have been conducted on a typical flood occurred in August 1992 in the Lower Yellow River during which the peak discharge at Huayuankou station was 1690 m3/s larger than the value at Xiaolangdi station at upstream. It is found that a fully coupled model that incorporates the contribution of bed evolution to the mass conservation of the water-sediment mixture, can reasonably well capture the characteristics of peak discharge rise and severe bed scour, while separate numerical experiment using a decoupled model, which ignores the feedback effects of bed evolution, shows no rise in the peak discharge. This leads us to comment, if only briefly, that the entrainment of sediment due to bed erosion is the main reason for causing peak discharge increase along downstream course.

Ecological Design of Flood Discharging Canals in Shijiazhuang City

From the perspective of ecological conservation and satisfaction of people's visual and psychological demands,existing problems in the urban revetment were analyzed,and the connotation of ecological revetment as well as the selection of different ecological revetments according to different types of river ways was discussed.

EXPERIMENTS OF INFLUENCE OF DISCHARGE PROCESS ON CHANNEL PATTERN

Based on experimental data and theory, by means of simplified discharge durations in a small flume, the influence of discharge process on channel morphology and channel pattern was analyzed in this paper. It was concluded that on the same original channel, different discharge and channel conditions would end with different river morphology, including thalwegs and radius of bends. Different discharge process resulted in two kinds of change: tiny change in the process of "big-small-big" and distinct change in the process of "small-big-small". Flood discharge duration was verified to be the main cause in the discharge process. Proper discharge process will change the morphologies of river, even can led to channel pattern transformation. The influences based on the relationship between the flow and the channel itself, including slope and riverbed constitution. Although not be a main cause, original channel morphology may influence its final channel pattern. Neglecting the influence of channel itself will hamper the understanding of channel patterns.

山洪灾害雨量预警指标分析方法评述与展望

山洪灾害预警指标是山洪灾害预报预警的核心,我国现阶段主要采用经验法和水位流量反推法确定雨量预警指标,并逐步推广应用复合预警指标法和动态临界雨量法。在系统阐述国内外常用雨量预警指标分析方法及其特点基础上,针对山洪灾害预警指标分析中需考虑的降雨时空分布变化、高含砂水流、泥石流及其他不确定因素影响问题,提出今后雨量预警指标研究方向。

滦河口退养还滩工程引起的径潮相互作用变化分析

围垦养殖对河口海岸的水动力和水环境带来了潜在危害,因此,在围垦区逐渐开始实施退养还滩工程以修复河口的水动力环境。但是,目前对于退养还滩工程引起的水动力变化还缺少完善的评价和研究。以滦河口退养还滩工程为研究对象,构建二维水动力数值模型,从水动力场、纳潮能力和行洪能力三个方面研究还滩工程对滦河口径潮作用特征的影响。结果表明:滦河口退养还滩工程区域面积约300 hm^(2),河口断面扩宽造成了河口内水动力条件的变化。径流动力明显减弱,洪季河道内下泄流速最大降幅约为61.82%;潮流动力显著增强,枯季时潮流上溯流速增加0.25 m/s;径潮作用平衡位置向上游移动。河口纳潮能力显著增强,枯季大潮期间涨潮历时延长了12.5%,涨潮周期纳潮通量增长了219.8%。河口行洪能力明显提高,河道内洪季最大水面降幅达45.8%,水力坡度逐渐减缓,主动力轴线流速明显降低。退养还滩工程有利于河口的防洪御潮及生态环境改善,建议进一步加大实施力度。

三峡大坝运行20年泄洪安全评价

近年来国内外高坝泄水建筑物破坏事故时有发生,三峡大坝泄洪流量和落差大,泄洪功率居世界第一,其泄洪安全备受关注。结合三峡大坝自2003年蓄水以来的历次水力学原型观测和以往水工模型试验结果,围绕泄水建筑物布置、泄流能力、动水压强、水流空化、水流掺气与通气风速、空蚀磨损、消能防冲7个要素指标,依据有关技术标准和工程经验建立了一套完整的高坝泄洪安全评价方法,提出了定性标准和量化阈值,并据此对三峡大坝深孔、表孔、排沙孔和排漂孔进行泄洪安全评价。结果表明:大坝泄水建筑物布置是合理的;大坝实际泄流量与设计值符合良好;大坝泄洪流道未见空蚀磨损破坏;三峡大坝运行20 a,泄水建筑物和坝下消能区运行性态正常,泄洪安全可靠。

丘陵-平原复合小流域多致灾因子洪涝减灾分析

我国东南沿海地区常因复杂的洪涝致灾因子和复合的地形特征,导致流域行洪不畅而引发洪涝灾害,建立适合此流域特征的洪涝模拟模型,并通过洪涝减灾分析制定有效的防洪减灾手段十分必要。利用流域数字高程数据、河网数据、土地利用数据等资料,建立模拟沿海丘陵-平原复合流域洪涝过程的水文-水动力耦合模型,探讨基于工程调度的降低洪涝风险的方法。选择浙江省沿海城市—临海市的大田港流域作为研究区域,充分考虑研究区丘陵汇流、水库下泄、潮位涨落、河道初始水位、闸门泄洪等流域特征要素,设计模型边界条件,模拟不同设计洪水以及工程调度影响下研究区的洪水演进过程和洪水淹没情况。结果表明,所建立的模型能够较好地模拟丘陵-平原复合小流域的河道洪水演进过程。对于极易造成洪水淹没的重点防洪区域,通过调节内河初始水位和控制流域内的防洪挡潮闸门有效的缓解了大田港下游主城区和灵湖景区的洪水淹没情况。大田港流域东北侧区域与山丘接壤,下游工程调度对该区域洪水淹没的缓解效果延时。情景模拟结果为研究区洪涝灾害的预演、预报、预警以及预案提供了数据支撑,为城市防洪工程和平原排涝工程的进一步推进提供依据,为沿海丘陵-平原复合型小流域多致灾因子导致的洪涝灾害提供了解决思路。

四川金阳县2023年“8·21”山洪泥石流灾害成因分析

2023年8月21日凌晨,四川金阳县芦稿林河流域受短时强降雨影响暴发山洪,位于下游的沿江高速JN1(金宁一)标段项目部钢筋加工场民工驻地板房被冲毁,造成52人死亡失联。灾害发生后,四川省委、省政府高度重视,派出专家对灾害过程进行调查评估。结合现场调查情况,通过水文气象分析计算、河道行洪能力计算等,分析了灾害形成过程及致灾原因,可供类似项目山洪灾害防御工作参考。

黄河下游花园口以上河道滞沙指标研究

水沙搭配关系是影响黄河下游河道冲淤调整的重要因素,局部河段滞沙则是改善下游水沙关系的有效手段之一。小浪底水库运用后,河槽沿程冲刷不均衡,河床粗化,细沙补给不足,输沙效率明显降低。分析黄河下游河道冲淤特性及水沙演进规律,建立不同类型洪水滞沙河段(花园口以上河段)与排洪瓶颈河段(高村—艾山河段)的冲淤关系。基于滞沙对河道行洪和稳定性的影响,以排洪瓶颈河段不淤积为约束,提出洪水滞沙的水沙优化配置指标。中泥沙洪水滞沙指标为:洪水平均流量为1800~3700 m^(3)/s,平均含沙量为66~235 kg/m^(3)。

挑流喷溅水滴的数论分档随机喷溅数学模型

挑流泄洪雾化时,水舌与下游水垫塘的碰撞会喷溅大量随机运动的水滴,它构成了喷溅水滴运动的初值问题,基于数论方法在选点较少的情况下仍然有较好的均匀性的思想。本文提出了数论分档水滴的概念,通过数论方法对水滴进行分档,并将高维相空间降维到一维相空间来计算,建立了水滴数论分档随机喷溅数学模型。对比其数值解和高精度解的结果表明:在计算水滴数相同时,本文数学模型的误差最小,随着水滴数的增加,其误差减小的也最快并迅速接近高精度解。因此,水滴数论分档随机喷溅数学模型不仅能够用更少的水滴获得更高的计算精度,而且能够实现高维初值相空间降维到一维相空间的简洁表达。