Daily Bank Erosion Rates in the Lower Yellow River Before and After Dam Construction

During the period of water impoundment and sediment detention of the Sanmenxia Reservoir, riverbank erosion processes played a key role in the channel evolution of the Lower Yellow River (LYR). However, research into bank erosion rates of the LYR has been neglected due to the lack of direct field monitoring. In this study, an indirect method is proposed to determine bank erosion rates at daily time scales by outlining a detailed calculation procedure using measured hydrological data. A total of 810 data points of daily bank erosion rates before and after the construction of Sanmenxia Dam was calculated at seven hydrometric sections along the LYR, with the corresponding values of the bank stability coefficient and the width‐to‐depth ratio also being calculated. Empirical relations were then developed to estimate the daily bank erosion rates, using these parameters at the sections. Temporal and spatial variability in daily bank erosion rates in the LYR before and after dam construction were also investigated, revealing that: (1) the bank erosion rates had a mean value of 16.7‐29.1 m/day in the braided reach, with a maximum value of 290.0 m/day, while they were relatively low in the meandering reach, with a mean value of 2.5 m/day; (2) the erosion rates before dam construction were slightly greater than those after dam construction, with the difference reaching 5‐10 m/day in the braided reach, decreasing in the transitional reach gradually, and being slight in the meandering reach.     

辽宁省白石水库环境工程地质问题综述

白石水库位于辽宁省北票市上园乡附近的大凌河干流上,是大凌河流域第一期开发的控制性骨干工程，水库建成后，将产生许多环境工程地质问题。从库坝区的地质背景出发，对水库渗漏、库岸再造与泥沙淤积、淹没与浸没、水库诱发地震、坝下冲刷坑稳定性等主要环境工程地质问题进行了综合评述。     

仓面浇筑立体空间冲突致灾过程建模与伤害评价*

为定量评价大坝浇筑过程空间冲突致灾事故后果,通过对缆机运输典型情景进行危害能量运动分解,确定在水平和竖直方向运动方式,阐述危害能量在流动路径相互转化形式;根据能量守恒定律,分析危害能量在吊罐与承灾体碰撞接触之间转移规律,将吊罐与人头部接触过程抽象为带强阻尼的弹簧振子系统,建立危害能量与碰撞冲量相等的动量方程,量化空间冲突致灾后果。结果表明:吊罐坠落危害能量极大,产生的碰撞冲击力与吊罐的运输速度、高度呈正相关,与阻力系数呈负相关,风速、载重对其影响较大。对比2种不同碰撞情景发现,机械碰撞因顶部承载力缓冲,对人头部产生伤害远小于直接碰撞,并对碰撞结果分级评价,研究结果可为大坝浇筑交叉作业空间冲突致灾风险评价提供参考。     

Minimizing disruptions caused by damming and ensuring the health of downstream ecosystems

In view of the Brazilian Ten‐Year Energy Expansion Plan 2021, this article presents a discussion on environmental flow (e‐flow). The authors analyze the literature to show the evolution of publications concerning e‐flow releases from the perspective of ecosystems services preservation considering results from different case studies from throughout the world. Finally, two main recommendations are drawn regarding e‐flow are: (1) performing a holistic approach to e‐flow planning, including hydrological, hydraulic, water quality, habitat, and riparian zone considerations; and (2) installing in new structures adequate bottom outlets to allow a range of adjustable e‐flow from reservoir dams to reproduce natural flow variations.     

Upstream Sediment‐Control Dams: Five Decades of Experience in the Rapidly Eroding Dahan River Basin,Taiwan

Sedimentation is emerging as a key issue in sustainable reservoir management. One approach to controlling reservoir sedimentation is to trap sediment in hydraulic structures upstream of the reservoir. In the 1,163‐km² catchment of the Dahan River (Taiwan) over 120 “sabo” dams were built to reduce sediment yield to Shihmen Reservoir. Built in 1963 for water supply, Shihmen has lost over 40% of its 290‐Mm³ storage capacity to sedimentation. Most of these upstream structures were small, but three had capacities >9 Mm³. Field measurements and historical data from the Water Resources Agency show most smaller dams had filled with sediment by 1976. The three largest were full or nearly so by 2007, when one (Barlin Dam) failed, releasing a pulse of 7.5 Mm³, most of its 10.4 Mm³ stored sediment downstream. The Central Range of Taiwan is rapidly eroding (denudation rates 3‐6 mm/yr), so geologically high loads make sediment problems manifest sooner. Even in other environments, however, eventually small dams built upstream of large reservoirs are likely to fill themselves, creating multiple small sediment‐filled reservoirs, some located in sites inaccessible to mechanical removal. Our analysis suggests sabo dams do not offer a long‐term basis for controlling reservoir sedimentation in such a high‐sediment yield environment. Sustainable solutions must somehow pass sediment downstream, as would be accomplished by a sediment bypass around Shihmen Reservoir, as now being studied.     

ASSESSING THE THREAT TO LIFE FROM DAM FAILURE1

ABSTRACT: To facilitate decisions regarding the need for modification of potentially unsafe dams, the U.S. Bureau of Reclamation developed procedures for assessing the threat to human lives posed by the failure of individual dams. The procedures provide a conceptual model of the variables influencing the loss of life from dam failure and a method for predicting loss of life based on the size of the population at risk from failure and the amount of warning time available for that population. The prediction equations are based on an analysis of 24 dam failures and major flash floods occurring since 1950. Adjustments to the predictions to reflect special local conditions are also discussed.     

某热电厂灰坝工程坝坡稳定性分析

某热电厂灰坝由粘聚力较小的石渣填筑,而粘聚力较小的砂粘土、砂土、砾石、碎石等筑成的土坡、大坝,边坡破坏时其破裂面近似平面,在横断面上近似直线.利用此理论,在有渗水和无渗水作用时对该灰坝外侧坝坡进行稳定性分析.     

无定河流域浮游动物群落结构特征及水质生物评价

为探究无定河流域浮游动物群落结构特征及其水质状况,于2021年春秋季对无定河干流、6条支流及3个淤地坝水体展开生态调查。共鉴定出浮游动物125种,其中原生动物40种、轮虫54种、枝角类15种、桡足类16种,秋季物种数(103种)高于春季(76种),均以小型浮游动物为主。浮游动物优势种共31种,以臂尾轮虫和龟甲轮虫等富营养型水体指示生物居多,春季优势种优势度整体高于秋季。春季浮游动物平均密度(360.9个/L)和平均生物量(0.600 mg/L)均高于秋季(83.6个/L、0.298 mg/L),且春秋季淤地坝水体中浮游动物平均密度和生物量均高于河流。非度量多维尺度分析也表明:河流与淤地坝2种水体中的浮游动物群落分布存在差异,采用冗余分析进一步探明,主要差异为河流和淤地坝2种水体中影响浮游动物群落分布的环境因子不同,其中化学指标(溶解氧、盐度、亚硝氮、硝态氮、溶解磷、叶绿素a)和物理指标(水深、透明度、浊度)分别是影响河流和淤地坝水体中浮游动物群落结构的主要环境因子。水质生物评价结果显示,春秋季水质均为无定河干流最优,支流次之,淤地坝水质最差,且干流中下游水质优于上游。     

跨境河流环境应急拦污坝及配套纳污湿地建设探讨

我国跨境河流较多,为保证跨境断面水质达标,需加强对跨境河流水环境污染风险的防范。探讨了跨境河流环境应急拦污设施的解决方案及其设计思路与原则,提出环境应急拦污设施包括应急拦污坝及配套纳污湿地,并从拦污坝设计、配套纳污湿地设计、配套应急措施、环境影响最小要求及运行工况等方面阐述了设计要求。以我国西北地区某跨境河流为例,进行环境应急拦污设施的案例设计,在该跨境河流特点和水环境风险源分析的基础上,从工程地址比选、拦污坝坝型选择及坝高设计、配套纳污湿地主要设计参数等方面进行设计,并对该环境应急拦污设施处理效率进行模拟。结果表明,环境应急拦污设施的建设将会极大地提高该河流的环境风险防范能力,且在未发生水污染事故时该设施可起到引流和促使沿岸其他湿地修复的作用。     

长荡湖围堰干法环保清淤工程实施效果评价

内源污染是造成湖泊富营养化和水体重金属风险的重要来源。以长荡湖围堰干法清淤工程为例,探讨了清淤工程实施前后的底泥营养盐和重金属质量分数及上覆水体水质变化,开展了清淤工程实施效果评价,提出了围堰干法清淤工艺适用性思考。结果表明,围堰干法清淤工程对底泥的部分营养盐去除效果良好,底泥中有机质含量的平均降低幅度为27.09%,14个采样点位中,有11个点位清淤后底泥有机质平均含量低于清淤前;清淤后的底泥TN质量分数比清淤前平均降低76.95%,底泥TN质量分数得到有效削减;清淤后底泥TP质量分数比清淤前提高了35.16%,原因可能与采样季节、采样方法、磷素沉积及清淤过程中的机械干扰有关。清淤工程有效降低了底泥重金属风险,对底泥镉的平均去除率为76.00%,清淤后没有点位底泥生态风险等级超过“中风险”,底泥生态风险显著降低。清淤工程实施前后上覆水体水质无明显变化,清淤后水质仍处于Ⅳ类―V类水,超标因子为TN和TP。围堰干法施工有效降低了长荡湖底泥中部分营养盐和重金属赋存量,但是软弱地基区域施工机械难以实施,机械操作可能造成下层底泥的翻动,部分区域难以完全实现预期清淤目标。该研究结果表明,应综合考虑清淤目标和施工机械、场地条件等影响因素合理选择清淤工艺和确定清淤深度。