雨水口堵塞程度对其泄流能力影响的试验研究

雨水口是下泄地表径流的关键设施,一旦堵塞将导致市政排水系统的泄流能力无法充分发挥,这是引发城市洪涝灾害的主要原因之一。为定量分析雨水口堵塞对其泄流能力的影响,本研究分别考虑进水篦及连接管不同堵塞程度的情况,开展了较大来流水深下的概化水槽试验,共计进行了608组试验。试验结果表明:①进水篦及连接管堵塞均会显著影响雨水口的泄流能力,且后者对雨水口泄流能力的影响更大。②利用试验数据率定了各堵塞情况下水流以堰流或管嘴流形式从雨水口下泄时的流量系数;基于量纲分析及回归分析,给出了各堵塞情况下雨水口泄流能力的幂函数表达式,并利用试验数据对参数进行了率定,率定效果优于堰流或管嘴流公式。③通过与未堵塞情况进行比较,基于幂指数均值假定及非线性拟合方法,建立堵塞系数与堵塞程度之间的经验关系,并最终提出了一个可以分别考虑进水篦与连接管堵塞影响的雨水口泄流能力公式;该公式可以考虑雨水口堰流及管嘴流等不同泄流形式,能够反映进水篦、连接管不同堵塞程度的影响,适用于来流水深较大的情况。     

区域气候模式水平分辨率对黄淮海流域当代气候模拟的影响

区域气候模式是进行流域尺度气候变化研究的重要工具,其中水平分辨率对流域模拟结果的影响亟待评估。本文使用区域气候模式RegCM4,在ERA-Interim再分析资料驱动下,进行2种水平分辨率（50 km和25 km）1990-2010年东亚区域的长时间连续积分模拟。通过与观测资料的对比,评估RegCM4对黄淮海流域的模拟性能,同时分析水平分辨率对模拟结果的影响。结果表明:① 2组模拟均可以较好地再现黄淮海流域冬季、夏季平均气温和降水的空间分布,以及气温和降水的年循环变化;对极端气候事件指数的分布模拟效果也较好,且对与气温有关的极端气候事件指数模拟效果优于与降水有关的极端气候事件指数。②与观测相比,也存在一定的偏差,如模拟的冬季气温存在冷偏差,夏季气温存在暖偏差,冬季、夏季降水在大部分地区偏多等。③ 2组模拟对比来看,对冬季、夏季平均气温的量级和空间分布,25 km模拟与观测更加接近;对冬季、夏季平均降水,50 km模拟与观测的空间相关系数分别为0.86和0.44,较25 km模拟有较大提高;对极端事件,2组模拟差别不大。模拟结果可为后续此版本模式在黄淮海流域气候变化研究中的应用提供参考。     

堰槽组合设施测流机制试验研究

山区季节性溪流流量变化大,已有灌溉渠道量水设施难以在较大流量范围内均达到测流精度要求,本文以克伦普堰和排淤量水槽组合而成的堰槽组合量水设施为试验对象,通过试验探究其测流机制。根据流量在5~79 L/s范围内的概化水槽水力性能试验,分析不同流量下的水面线、弗劳德数、垂线纵向时均流速、薄水层特征长度和特征宽度的变化,建立不同流量阈值范围内的测流公式。结果表明:①随流量的增大,堰槽组合设施流动形态从槽内流变为堰流,流量阈值对应的阈值相对水深为0.885,拟合得到组合设施槽内流和堰流的测流公式,与实测流量对比,相对误差小于3%。②组合设施槽内流和堰流水力特性不同,槽内流时槽内各测点纵向时均流速、薄水层的特征长度和特征宽度以及综合流量系数均随着流量增大而增大;堰流时,排淤量水槽槽内前段各测点纵向时均流速随着流量增大而减小,后段各测点纵向时均流速随着流量增大而增大,槽内收缩扭面段中部附近断面平均流速大小一致。③堰槽组合流量系数随着流量增大而减小。④堰槽设施下游薄水层的特征长度和特征宽度随着流量增大有下降趋势,最大值均出现在流量阈值情况下。本研究有效解决了流量变幅较大的明渠测流设施匮乏问题,可为山区季节性溪流测流设施应用提供参考。     

城市洪涝中雨水口泄流能力的试验研究

近年来中国城市洪涝灾害频发,对人民群众的生命财产安全造成了严重威胁,其中雨水口泄流能力的大小对于计算受淹区的积水程度或路面雨水的排除效率至关重要。为此本研究专门修建了具有上下两层结构的城市洪涝过程综合试验平台,考虑雨篦子、雨水井及侧支管等完整的雨水口结构,开展了76组不同来流水深及流速下的雨水口泄流能力试验。试验结果表明:雨水口的下泄流量在井身充满前后表现出不同的变化规律,即在雨水井充满前,路面雨水以堰流形式下泄;在雨水井充满后,以管嘴出流形式下泄。基于试验数据率定出雨水口堰流及管嘴出流时的流量系数,并进一步采用量纲分析法,建立雨水口的泄流能力与雨篦子尺寸、篦前水流的弗劳德数等因素之间的经验关系,具有较高的相关系数。采用本文公式计算原型尺寸雨水口的泄流能力,并与中国现行雨水口泄流能力的参考值进行对比,发现当水深较大时现行参考值偏大较多。本研究成果能为精细化的城市洪涝管理提供计算依据。     

植被发育斜坡土体大孔隙三维重构模型渗流场的LBM数值模拟

以云南昭通头寨植被发育斜坡土体为研究对象,结合CT扫描试验与数字图像处理技术实现了其三维大孔隙空间结构模型的重构。然后基于格子Boltzmann方法（LBM）的D3Q19模型,将固体土骨架视为渗流场边界,并设置反弹格式的边界条件模拟土骨架与水分间的相互作用,从细观角度研究了水在植被发育斜坡土体大孔隙中的渗流特性。研究结果表明：土体渗流过程中,在大孔隙纵向连通的通道内形成了优先流,且通道中的流速远超其他部位;而在封闭或者连通性差的大孔隙中导水率极小,流速几乎为0。土体中大孔隙通道内的流速由孔壁至通道中心逐渐增大,且流速与至通道中心的距离近似呈二次抛物线的分布特征。沿深度方向土体切片大孔隙率大的截面平均渗流流速Uz也较大,从整体变化趋势来看,截面大孔隙率与平均渗流流速有相似的变化规律,这充分说明植被发育斜坡土体内的大孔隙分布对土壤沿深度方向的渗流特性有重要影响。     

基于旋转水槽试验的泥石流阻力坡降速率效应研究

使用自主研发的旋转水槽制作稳定循环流动的泥石流,通过实测泥石流阻力坡降和流动速度,探索泥石流阻力坡降的速率效应。在旋转水槽试验中,通过控制线速度v,制作出稳定循环运动的泥石流,其阻力坡降J等于槽底坡降tanθ,可以实测。试验再现了野外的泥石流运动特性,观察到“龙头”、颗粒弹跳、低阻力坡降、固液相分离、剪切速率效应等现象。试验结果表明,在一定的流动速度范围内（例如试验中1.88m·s-1≥v>0.47m·s-1）,泥石流的流动速度越高,阻力坡降越大;如果泥石流运动速率过低（例如试验中v<0.47m·s-1）,泥石流会出现固液两相分离现象,砾石（粒径>2mm）运动明显落后于液相运动。本项目的试验研究成果为泥石流制作和阻力坡降测量提供新途径,为泥石流阻力坡降的速率效应理论研究提供实验支持。     

弯道水流对下游回水响应特征试验研究

弯道水面横比降及断面环流是弯道水流的显著特性。通过U形弯道水流壅水试验,对弯道水面横向比降、横向流速分布、环流强度、紊动能及纵向流速沿程的变化进行了试验研究。结果显示,随着下游回水的抬高,弯道水面横比降、横向流速分布、环流强度、紊动能及纵向流速将发生明显的改变。为深入探讨下游回水对弯道水流结构的影响提供了科学依据。     

明渠湍流涡运动尺度分布特性

为了解明渠湍流涡运动尺度沿水深的分布特征,使用高精度粒子图像测速法水槽试验系统测量充分发展的明渠湍流,利用改进后的功率谱分析方法,对明渠湍流涡运动尺度沿水深分布、上升流、下扫流和平均涡量等进行了分析。结果表明:明渠湍流涡运动尺度大小沿水深增加呈先增大后减小;沿水深增加下扫流比上升流更容易发生;各自水深的顺向涡涡量大于逆向涡涡量,在近壁区平均涡量最大;明渠湍流近壁区产生涡量大、尺度小的涡结构,沿水深增加,涡尺度发展变大,但受水面区下扫流抑制,涡尺度又变小。     

内陆河三角洲堆积体形成发展过程

通过概化水槽试验对水流泥沙从内陆河进入浅水湖泊后的三角洲堆积体形成发展过程进行研究。试验结果表明,在平面形态上,三角洲堆积体的形成发展过程可分3个阶段:第一阶段,水流泥沙在初期依次按小沙波体、带状沙波体、扇形三角洲堆积体和舌状三角洲堆积体形态形成发展,堆积体表面无明显主河槽且两侧区域无串沟;第二阶段,水流泥沙沿堆积体表面河槽在左侧区域和右侧区域之间交替推进;第三阶段,水流泥沙沿新河槽在摆动中同步推进。在纵向推进中,第一阶段初始较大,受横向展宽影响逐渐减弱;第二阶段以相对稳定的速率交替推进;第三阶段呈减弱趋势,最终保持同步推进速率。在垂向上,堆积体以稳定的速率淤积抬高发展;在横向上,水流泥沙在河槽主流摆动中不断横向输移泥沙。     

An analysis of the supply process of loose materials to mountainous rivers and gullies as a result of dry debris avalanches

A dry debris avalanche will produce different volumes of colluviums or depositions (loose materials), which can have a significant impact on mountainous rivers or gullies. The loose material supply process caused by a debris avalanche is an important issue for understanding secondary disasters that form via the coupling of water flow and loose materials. Two flumes were designed for laboratory tests of the loose materials supply process to rivers/gullies, and the related impact factors were analyzed. Experimental results show that the supply of loose materials is a continuous process that directly relates to the avalanche’s mass movement processes. The sliding masses with smaller particle sizes are more sensitive to the flume slope and exhibited a longer supply time. The time-consuming for the debris avalanche travel in the flume decreased with the increasing particle size (such as flume B, time-consuming is decreased 0.2 s when the particle size increased from <1.0 to 20–60 mm), landslide volume and flume slope (flume A, consuming 1.6–2.1 s when flume slope is 29° decreased to consuming 1.3–1.5 s when flume slope is 41°), which means the increasing mobility of loose materials. The total supply time increased with the increasing landslide volume or decreasing particle size and flume slope. An empirical model for the process is presented based on numerous laboratory tests and numerical simulations, which can successfully describe the supply process for loose materials to a river/gully. The supply process of loose materials to mountainous gully from a dry debris avalanche is controlled by the material compositions of sliding masses, topographical conditions, landslide volume and bed friction, where large-volume debris avalanches that occur in mountainous river regions are more likely to obstruct the river flow and form a landslide-dammed lake.     

泥石流堆积形态与坡降的相关性分析

本文以密云县石城镇贾峪东沟为实验模拟原型,通过小型水槽实验,对沟床纵坡降与泥石流堆积形态的关系进行实验研究。通过实验,获取了不同沟床纵坡降泥石流的堆积长度、宽度、厚度、堆积面积以及堆积形态比方面的数据。通过对实验数据分析,得出沟床纵坡降分别与堆积长度、宽度、厚度、面积与堆积形态比的回归方程及相关系数,为泥石流危险性或危害性评价提供参考。     

Erosion Resistance of HPTRM Strengthened Levee from Combined Wave and Surge Overtopping

Post-Katrina investigations revealed that most earthen levee damage occurred on the levee crest and land-side slope as a result of either wave overtopping, storm surge overflow, or a combination of both. This study addresses erosion resistance performance of a levee strengthening technique—high performance turf reinforcement mat under combined wave and surge overtopping conditions using full-scale flume tests as well as erosion function apparatus (EFA) tests. Based on the results of full-scale flume tests, an “upper limit” of soil loss is observed for certain flow conditions. Erosion rate was presented as a function of velocity and freeboard. The effect of duration of overtopping on the erosion depth is also determined. The results of EFA tests indicate that the presence of grass roots substantially improve the critical velocity and soil erodibility.     

An experimental study on controlling post-earthquake debris flows using slit dams

Post-earthquake debris flows often break out in groups frequently, which are usually caused by the abundant loose solid materials that produced by earthquake. Slit dams represent a practical and effective kind of countermeasure for controlling the post-earthquake debris flow. Flume experiments were carried out to study the interaction mechanism and the effect of slit dams on the post-earthquake debris flows. The results showed that affected by the slit dams, some certain types of deposits formed on the upstream. The steeper the flume slope, as well as the greater the width and the density of slits, the easier the lateral deposit became “V” shaped. Otherwise, the lateral deposit was more likely to be “–?” shaped. When the flume slopes were 12°, 16° and 20°, the profiles of the deposits would be long-shallow type, short-thick type and short-shallow type, respectively. The slope of the deposition first decreases and then increases with the flume slope increasing within a certain range. The slit dam can trap the coarse sand and discharge the fine sand. The maximum attenuation rate can reach 44.4%. The effect of this capacity gradually weakens as the flume slope is increased. When the width or the density of slits is smaller, the greater the rate of decrease in peak sand discharge and the greater the effect of peak cutting will be. The reduction in the sediment storage rate is likely due to the increase in the width and the density of the slits. With the increase in flume slope, the sediment storage rate first increases, then decreases, which reaches a maximum value when the flume slope is 16°.     

Experimental study on the formation and development law of delta deposition in shallow and narrow water basins

This study conducted a generalized experiment of non-uniform sediment, in order to examine the formation and development laws of delta deposition in shallow and narrow water basins caused by constant water and sediment flow. A test of 425 h in duration is presented in this paper, and the results obtained from the experiment are as follows. First, the evolution process can be divided into two stages before the front of the sediment deposition reaches the outlet of the flume. In stage one, the front advancing of the deposition follows a certain cycle, and the front of the delta has an alternative development between the longitudinal advancing and lateral widening along the flume. The sediment first occurs longitudinally advancing along the water flow direction to make the front of the delta spread in the shape of a fan and lift through the constant deposition. Then, after the front deposition has been lifted, the topographical gradient along the way decelerates, which leads to the diversion water flowing toward the areas at both sides and constant lateral widening development. Next, after the lateral transport is blocked on the two side walls, the flow sediment turns back, inclines toward the central area, undergoing inclined spreading in a fan shape, and deposition lifting and development constantly occur during this process of spreading. With the increase of the test duration, the delta deposits in the area of both sides constantly undergo deposition and lifting, the water flow is centered and returned to the flume, then turns to the central area to further lift the deposition in the front of the delta through longitudinal advancing, and the above process is repeated. In stage two, the front of the delta deposition develops progressively without stagnation. Sediment constantly advances along the swinging flume, which causes the delta deposit to undergo deposition and lifting development in the swinging. Second, the paper analyzes the changes of the longitudinal advancing rate, lateral widening, and vertical deposition lifting rate shown in the two development stages of the delta. Finally, the paper analyzes the factors influencing the two development stages of the delta. The transportation of water flow and sediment is mainly controlled by three factors: the inertia of the inflow from the inlet, topography of the bed, and the side walls of the flume. In the evolution of the delta sediment deposition, the first influencing factor only acts in the initial stage, while the second and third factors are the dominating factor altering periodically in stage one, which results in the cycling of the front advancing. Meanwhile, in stage two, the evolution of the delta deposition is dominated by the other two factors.     

Formation conditions of outburst debris flow triggered by overtopped natural dam failure

Natural dams formed by landslides may produce disastrous debris flows after dam outburst. However, studies on the critical conditions required for the formation of outburst debris flow resulting from natural dam failure are still at an early stage. In this paper, we present the results of a series of laboratory tests that assessed three different materials, five different flume bed slope angles (2°, 7°, 9°, 10°, and 13°), two in-flow rates, and four types of dam geometric shapes. The results showed that the unit weight of downstream fluid increased with increasing bed channel slope. Additionally, a critical flume bed angle was found for debris flow formation. Furthermore, the combination of lake volume and flume bed angle was found to influence the formation of debris flow. A nonlinear trend was observed between the unit weights of debris flow and the uniformity coefficients of solid material. Based on the theory of stream power, a critical condition for debris flow formation from natural dam failure was established. Based on two case studies, the results indicate that the condition that was established for debris flow formation following natural dam failure agrees well with reality.     

阶梯-深潭结构对沟道稳定性的作用机制

阶梯-深潭结构是山区河流中典型的高效消能结构,以消耗水能、增加阻力的方式提升沟道稳定性。通过水槽试验模拟沟道冲刷,探究阶梯-深潭结构稳定沟道的机制及效果,为山区河流消能减灾和稳定河床提供科学和技术参考。结果表明：阶梯-深潭结构能有效消耗水流能量、抑制泥沙输移和提升水流阻力,从而有效控制河床下切和边坡破坏;在阶梯-深潭结构的作用下,沟道的Darcy-Weisbach系数约增加为无结构条件下的4倍,时均输沙率降低20%～66%,但随着流量的增大,阶梯-深潭稳定沟道的效果降低;阶梯高度与长度比(0.1)相同时,结构提升沟道稳定性的效果接近。阶梯-深潭结构自身的稳定是其稳定沟道的关键条件,实际应用过程中需防止结构发生逐级破坏。     

Energy relations of density-current flows: an experimental investigation*

Three series of density-current experiments were performed in a 5.76 m flume. In the first series, the flume was horizontal, and in the second and third, it was inclined with a positive slope and negative slope, respectively. Energy relations during successive stages of density-current movement were computed from observed data, which showed an appreciable frictional energy dissipation. The computed friction factors of our experimental density-flows were compared to the friction factors for pipe flows (Moody diagram), and while the calculated friction factor increases with increasing Reynold's number within the range of our experiments (Re 2 × 10³?2 × 10⁴), it is concluded that with increasing Reynold's number above about 5 × 10⁴ the friction factor decreases. For natural turbidity currents, the Moody diagram gives a reasonable estimate of the friction factor between the current and sediment bed. The value of the friction factor for the interface between the current and overlying water was found to be about 0.2 times the friction factor for the current and flume. However, due to errors inherent in measuring the depth of the current, a value of 0.4 would be more reasonable for density-currents in our range of Reynold's number. Friction tends to decrease the value of the dimensionless coefficient in Keulegan's law of saline front and to decrease the thickness of the flow. In contrast, the presence of a slope in the direction of flow tends to compensate the effect of friction. The angle θ^c that provides the potential energy to exactly offset the energy losses incurred during movement by the density-currents in our experiments has a calculated value of 31′. An empirical formula φ= 0.935θ—0·57 relating friction, in terms of the hydraulic gradient φ, to the slope angle θ was obtained. Since the thickness of the current can be computed from the relationship between φ and θ, we estimated the thickness of naturally occurring density-currents in Swiss lakes. The results suggest the applicability of our experimental results to small turbidity currents in nature. Our analysis further indicates that large turbidity currents have a small φ and can be expected to flow very long distances on a flat abyssal plain.     

考虑河床坡度和泄流槽横断面影响的堰塞坝溃决过程试验研究

针对缺乏地形条件和工程处置措施对堰塞坝溃决过程影响研究的现状,采用4种河床坡度(0°、1°、2°、3°)和3种泄流槽横断面型式(三角形、梯形、复合型),开展了堰塞坝溃决的模型试验。通过分析堰塞坝的溃决流量、溃决历时、溃口发展和坝体纵截面演变过程,研究了不同河床坡度和泄流槽横断面对堰塞坝溃决过程的影响规律。试验结果表明:(1)堰塞坝溃决过程可分为3个阶段。阶段Ⅰ:溃口形成阶段,溃决流量较小;阶段Ⅱ:溃口发展阶段,水流下蚀及侧蚀强烈,溃决流量到达峰值;阶段Ⅲ:衰减-平衡阶段,粗化层形成,溃口停止发展。(2)河床坡度增加意味着下游坝坡、坝顶及泄流槽的坡度增加,导致水流侵蚀能力增强,溃口下切迅猛,因此在0°～3°范围内河床坡度越大,峰值流量越大,峰现时间越早,溃决流量过程曲线越趋于“高瘦型”,且残留坝高越小。(3)泄流槽横断面型式不同导致其槽深、槽宽和侧坡坡度不同,进而影响溃口发展和溃决流量。三角形槽的水土作用面积小,溃口下切及展宽速率最高,峰值流量最大,峰现时间最早;梯形槽的槽底高程最高,水土作用面积最大,溃口下切速率最低,峰现时间最晚;而复合槽介于前两者之间。试验成果将为堰塞坝应急抢险和工...     

Variational Laws of Debris Flow Impact Force on the Check Dam Surface Based on Orthogonal Experiment Design

Debris flow impact force is an important factor for controlling structural damage, and it is the key factor for engineering design and risk assessment. Variation laws of debris flow impact force play an important role in preventing check dam impact damage and providing technology, data and support for check dam construction. Many influencing factors exist in debris flow impact force with different influencing magnitudes. The three main factors, i.e. the debris flow bulk density, the drainage channel slope and the upstream surface gradient of the check dam, were selected to be analyzed. The purpose of the study was to analyze the influencing degree of the three factors. Three levels were set for each factor and nine text schemes were established based on the theory of orthogonal experimental design. What is more, the related miniaturized flume experiment was carried out to measure impact force of debris flow. Finally, taking the impact force mean values of key point as the evaluation index, the flume experiment results were analyzed in detail by extreme difference analysis and variance analysis. Research results indicate: among the three factors, the drainage channel slope has the most significant influence, the upstream surface gradient of the check dam is in the second place and the debris flow slurry density is the third. The form of impact force mean with the maximum value: the drainage channel slope is 15°, the debris flow bulk density is 18.1 kN/m³ and the upstream surface gradient of the check dam is 1:0.     

Influence of Two Tropical Storms on the Residual Flow in a Subtropical Tidal Inlet

The mechanisms responsible for the modulation of laterally sheared non-tidal (residual) exchange flow in a subtropical inlet, with special emphasis on tropical storm influence, are studied using a combination of current velocity profiles and hydrographic and meteorological data. The mouth of the inlet, St. Augustine Inlet in northeast Florida, is characterized by a 15-m-deep channel flanked by shoals (<6 m deep). Residual flows across the inlet mouth were laterally sheared with inflow in the channel and outflow over the shoals. This pattern persisted during four separate semi-diurnal tidal cycle surveys effected over 3 years. During spring tides, residual exchange flows intensified relative to neap tides. Residual inflow in the channel only reversed immediately after tropical storms because of their extreme winds and major temporal changes in water level. After the residual flow reversed in the channel, along-channel baroclinicity drove gravitational circulation that persisted for 4.5 days and was enhanced by offshore winds. A depth-averaged along-basin momentum budget highlighted the importance of bottom friction to help balance the barotropic pressure gradient. The rest of the momentum budget was likely provided by advective terms. During and after tropical storms, accelerations from wind stress and baroclinic pressure gradients also became influential in the along-basin momentum budget.