简讯

湖南省水文总站的研究人员经过10年努力,顺利完成了河、渠糙率的研究工作。此项目从1978年开始,省水文总站先后在常德、石门等县31条人工渠道中,进行了170多次控制放水试验,收集了各种断面和衬砌材料的顺直渠道糙率和部分弯道附加糙率实测资料。1981年开始对全省河流进行糙率分析试验。现已完成了湖南省河渠糙率的研究工作。     

跃进总干渠(下段)防渗改建工程渠道横断面设计

从跃进总干渠(下段)防渗改建工程的工程地质概况、地基土的渗透特性、渠线地下水位等实际情况出发,计算确定了渠道复合断面糙率、渠顶宽度等。根据横断面设计比较,最终确定本次跃进总干渠防渗改造工程渠道横断面采用梯形断面。     

骨干渠道糙率取值合理性测试研究

在满足试验段选取原则的基础上,选取了不同断面形式与砌护材料形式的7个典型渠段进行渠道断面几何参数与水力要素原型监测试验,利用曼宁公式对实测数据进行计算得出渠道实测糙率,将单一衬砌材料糙率结合复合渠道设计与实测数据进行加权平均,计算得出两组糙率数值,并与实测、设计糙率进行对比,结合试验段具体情况对率定糙率值偏大的原因进行了分析。结果表明:率定糙率值偏大的主要原因为断面几何尺寸不标准、渠底比降不连续和渠道淤积。最终得出宁夏引黄灌区不同衬砌材料渠道的糙率,并结合国家及地方规范给出了各种砌护材料糙率的设计取值范围,为宁夏引黄灌区渠道设计糙率选取提供了依据。     

引黄干渠清临渠段输水能力分析

清临渠段为河北省引黄总干渠首段,其输水能力决定着计划制订和输水调度.根据近年引黄济津输水实测资料,基于稳定输水阶段渠道水流特性,选用能量平衡的水面线计算方法反演糙率、渗漏综合系数等参数,分析计算出该渠段的输水能力,以期为输水管理调度提供参考.     

跨流域调水工程输水建筑物糙率研究

对于长距离输水工程,合理选取糙率值意义重大。本文分析了引洮供水一期总干渠隧洞的具体运行状况、工程特点等,结合与其类似的引大入秦总干渠原型观测及研究,综合考虑引洮供水工程总干渠实际能达到的二次衬砌浇筑水平,提出了各类建筑物糙率值优化建议,有效减少了开挖断面,节约了工程投资,对国内水工隧洞的设计有一定借鉴作用。     

不同断面形状对人工渠道糙率影响的试验研究

为探究不同断面对渠道糙率的影响,采用2种不同断面的人工渠道,在2种底坡及5种不同流量的条件下研究糙率随流量、底坡的变化规律。试验结果表明:在明渠均匀流条件下,在相同底坡、不同断面的人工渠道中,糙率的变化与流态有关,当Fr<1时,糙率值随着流量的增大逐渐减小;当Fr>1时,糙率值随着流量的增大逐渐增大。人工渠道断面形状发生变化时,糙率与各水力要素之间关系的变化规律基本相同,渠道的断面形状并不是影响渠道糙率变化的因素之一。     

韩墩引黄灌区总干渠糙率实测成果浅析

以韩墩引黄灌区总干渠实测糙率资料为基础，分析了糙度与流量及含沙量的关系。分析结果表明：糙度随流量的增大而减小，与含沙量没有明显的关系。渠道的尺寸取决于过渠的最大流量，而在大流量情况下，糙度较小，这是在选择设计糙率时应特别注意的。通过验证，韩墩总干渠的设计糙率较实际值偏大。     

引洮供水一期工程总干渠糙率原型观测 (1)——研究方法与水位、流量监测

 大型长距离输水工程的糙率是工程设计中的关键参数,随着工程施工技术的进步,工程建成后的实际糙率小于规范值,但设计中如何减小糙率取值则无选择的依据。为了给引洮供水工程优化设计提供依据,甘肃省引洮水利水电有限责任公司于 2006 年立项进行糙率原型观测研究,原型试验工程选择 1995 年建成的甘肃引大灌区总干渠和东二干渠,原型观测隧洞试验段分别在 30 A 隧洞出口与盘道岭隧洞进口修建机翼形量水槽,采用自动监测系统实时监测流量,隧洞水位各设 6 个观测断面,并采用水位自动监测系统实时监测。两处明渠段糙率原型观测试验水位流量采用人工方式进行。本文为该项研究的第一部分。     

南水北调中线工程渠道糙率计算方法研究

为了明确南水北调中线工程渠道糙率的合理取值,分别选取杨开林公式、美国垦务局公式、美国陆军工程兵团公式,以及优化方法来计算糙率,并构建南水北调中线总干渠水力学模型进行检验。将模型方法应用到刁河节制闸-湍河节制闸渠段的10组稳定工况时,4种方法计算出的糙率值分别为0.01538、0.0156、0.01389和0.0169,代入水力学模型计算的刁河节制闸各工况闸后水位与实测值的相对误差总和分别为0.1744%、0.1586%、0.3028%和0.0947%。4种方法得到的糙率值代入水力学模型的模拟精度中,优化方法最好,建议作为中线渠道糙率计算的方法。     

仰山三级电站引水隧洞糙率原型观测

仰山三级电站引水隧洞为不衬砌隧洞,只在弯道段和岩体破碎段进行了全断面衬砌。文中介绍了不衬砌隧洞糙率的计算方法,并根据原型观测资料得到仰山三级电站引水隧洞不衬砌段的实际糙率。     

人工渠道糙率系数影响因素的试验研究

通过物理模型试验资料分析,探讨了矩形渠道的糙率与渠道水深、弗汝德数的变化规律。分析得出:当底坡不变时,随着弗汝德数Fr的增大,糙率n值逐渐减小。在缓流渠道中,渠道糙率n随弗汝德数Fr变化的速率很快;在急流渠道中,渠道糙率n值随弗汝德数Fr的速率较慢。糙率系数n随水深h的变化关系与流态有关。缓流中,随着水深h的增大,糙率n值减小;急流中,当弗汝德数11.51时,糙率系数n随水深h的增大而增大。     

黄河乌兰布和沙漠段不同区域入黄沙物质粒度特征及其来源分析

土壤是具有自相似结构及一定分形特征的不规则复杂多孔介质,为更好地对黄河乌兰布和沙漠段不同区域入黄沙物质粒度特征进行定量表征并解析其来源,利用传统统计学和多重分形理论,研究了黄河乌兰布和沙漠不同地段土壤的粒度特征及粒径分布。结果表明:研究区土壤颗粒组成具有明显的多重分形特征,沙头对岸D_0值为0.821、D_1值为4.386,即粒径分布范围最宽且最不均匀,荒漠草原D_1值为2.970、D_1/D_0值为4.595,即粒径分布最均匀且离散程度最大;不同地段土壤粒径分布范围间存在差异,但相近地段颗粒组成类似;河道左岸由于受乌兰布和沙漠的影响,使得河道左侧的沉积物粒度变粗,其来源于沙漠的沙物质,而右侧河道几乎不受乌兰布和沙漠的影响。     

Discharge Coefficient for Trapezoidal Labyrinth Side Weir in Subcritical Flow

The discharge coefficient of a trapezoidal labyrinth side weir is a function of the Froude number F ₁, the dimensionless effective crest length L/ℓ, the dimensionless weir length L/B, the dimensionless weir height p/h ₁, and the sidewall angle α. A labyrinth weir is an overflow weir, folded in plan view to provide a longer total effective length for a given overall weir width. These weirs have advantages compared to the straight overflow weir and the standard ogee crest. Previous studies on the subject have generally focused on rectangular side weirs located on a straight channel. The present study investigates the hydraulic behavior of a trapezoidal labyrinth side weir. The results show that the discharge coefficient of labyrinth side weirs gives a significantly higher coefficient value compare to that of conventional straight side weirs. Discharge coefficient of the trapezoidal labyrinth side weir is 1.5 to 5.0 times higher than the conventional straight side weir. Consequently, an equation for the coefficient of discharge is introduced. The results predicted by the equation were shown to be very satisfactory using root mean square error (RMSE), mean absolute error (MAE) and correlation coefficient (R) statistics.     

Lateral stability of sandbed canals

The lateral stability of unlined sandbed irrigation canals is a problem in the operation and maintenance of gravity irrigation systems. This problem has been studied from the aspect of meandering thalwegs that develop in otherwise straight channels.Hydrodynamic stability analysis of two-dimensional flow in sandbed channels has been used to predice the conditions under which meandering thalwegs will develop and lead to lateral instability. The analytical study shows that, with realistic functions for hydraulic resistance and bedload transport used herein, the two parameters which determine if meandering thalwegs will develop are the discharge intensity, q and channel width W.Results of analysis are confirmed by extensive data, especially collected for this purpose from straight irrigation canals in Pakistan. This study leads to criteria for stable channel width.Notation A _* coefficient, Equation (32) - B _* coefficient, Equation (32) - a, b dimensionless constants, Equation (5) - C _* dimensionless Chezy's coefficient - CC} dimensionless equilibrium bed material load, Equation (27) - D ₅₀ median bed material size - d flow depth - d ₀ equilibrium value of d - d perturbation in d - dd} a dimensionless dimensionless function of y - E _* coefficient, Equation (32) - G _* coefficient, Equation (32) - F Froude number of equilibrium flow - g acceleration of gravity - g _b bed material transport rate - g _b0 equilibrium value of g _b - g _bx,g _by values of g _balong x and y, respectively - H _y first partial derivative of hh} with respect to y - H _yy second partial derivative of hh} with respect to y - h water surface level, with reference to an arbitrary datum - h ₀ equilibrium value of h     

Testing and improving predictions of scour and fill depths in a northern California coastal stream

Seasonal scour and fill from bankfull flows were measured in Freshwater Creek, a gravel‐bed coastal stream of northern California, to test a previously developed approach predicting the reach‐average and distribution of scour or fill depths based on Shields stress and the exponential function. Predictions of reach‐average scour and fill depths were within 4–60% of measured depths. Three of the four predicted distributions of scour and fill depths were statistically different (p < 0.05) from measured distributions. Differences between predicted and measured values were likely due to scour and fill patterns in Freshwater Creek that were influenced by sediment supply and location within the channel network, channel form roughness, and possibly multiple peak flows. Consequently, the predictive approach may be better suited for individual peak flows on straight reaches that are in equilibrium between sediment supply and transport, and with form roughness similar to the creeks where the approach was developed. Improved predictions of scour and fill are possible with adjustments for aggrading reaches and form roughness. Copyright © 2005 John Wiley & Sons, Ltd.     

Design of earthen vegetated open channels

Modified formulas for Manning's equation are developed for use in the design of earthen open channels with submerged aquatic weeds. The proposed relations have their basis in field and experimental data. A multiple regression analysis was used to develop a relationship between the mean velocity, hydraulic radius, and water surface slope. The new formulas are dependent on the distribution of weeds along the channel's wetted perimeter and the percentage of vegetation density with respect to the cross-section area of the waterway.Notation A cross-section area - A _w area of weeds - B ₁ top width of channel flow - g acceleration of gravity - h height of roughness element - n Manning's coefficient - Q discharge of flow - R hydraulic radius - S water surface slope - S ₀ bed surface slope - V mean flow velocity     

Sediment transport in a curved channel

Conclusions Bed-load discharge in a curved channel (with curvature of the channel line and preservation of parallelism of the banks) considerably increases compared with a straight channel, and the more so, the greater the ratio v/v₀.The hydraulic resistances in the experiments with a curved channel increase insignificantly compared with a straight channel ('the Chezy coefficients C in the experiments with the curved channel line decrease by 5–12%).Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 5, pp. 37–40, May, 1987.     

Fundamental differential equation of flow of a fluid with a variable mass in the case of bilateral water diversion

Conclusions 1.The relationships (26) and (27) obtained indicate that at the site of division of the flow there occurs a change in the depths h_o and h_cr related to the law of variation of discharge. Hence the line of the normal and the line of the critical depths will have a curvilinear outline. 2.For bilateral symmetric diversion of water the specific energy of the basic flow in section I-I is greater than the half-sum of the specific energies of the dividing flows.If we assume that E _l.d = E_r.d = E_d, then E_b1>E_d.Actually, the piezometric head in section I-I in the case of passage of part of the discharge into the diversions is partially expended on overcoming the losses and is partially transformed into kinetic energy of the diverted flows. 3.The fundamental differential equation of steady fluid flow obtained in the case of bilateral water diversion in open channels can be used only in the case when the distance between axes of the diversions is taken within limits from 0 tol.If the diversions are spaced at a distance greater thanl or symmetric pairs of diversions are located at a distance at which the interaction of these symmetric pairs of diversions with each other is not observed, then a system of fundamental differential equations of steady flow of a fluid with a variable mass obtained for each pair of diversions separately is set up. 4.Design engineers should bear in mind that the schemes of flow division shown in Figs. 3–6 are possible only for the case when part of the discharge is throughgoing along the main channel. It is necessary to calculate the main channel with consideration that there is enough water for all diversion channels.Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 4, pp. 17–22, April, 1984.     

输水系统糙率率定方法研究

为系统研究输水渠道糙率率定方法,给出了有压输水系统、无压输水系统糙率不确定度计算公式,分析了影响糙率率定精度的关键因子。提出了基于神经网络模型和粒子群优化方法的糙率整定方法,并将该方法应用于南水北调中线工程漠道沟节制闸至唐河节制闸渠段的渠道糙率率定中。利用2016年9月—2017年8月的实时监测数据整定得到的渠段综合糙率为0.016 7。研究表明,粒子群优化方法具有很强的全局寻优能力,很适合于时变非线性系统的参数整定。     

气垫式调压室稳定断面积研究

基于刚性水锤理论,考虑了压力管道的水流惯性及实际水轮机特性和调速器作用,运用稳定性理论,推导了气垫式调压室临界稳定断面积的详细公式。在此基础上分析最不利稳定断面积的取值,根据近年来国内十个不同水头段引水式水电站的资料,进行该公式各项参数的统计分析。结果表明:气垫式临界稳定断面详细公式主要由考虑水轮机特性的引水隧洞水流惯性项F_(th1)、压力管道项F_(th2)及调速器特性项F_(th3)三部分组成,在形式上与常规调压室一致,区别仅在于(1+m×p_0/l_0)倍的系数关系。气垫式调压室最不利稳定断面积取决于最大水头与设计水头之间的某个既能满足(1+m×p_0/l_0)较大,也能满足e1的水头。随着电站设计水头的增大,系数(1+m×p_0/l_0)的值也呈线性增大趋势,不能笼统地判断气垫式调压室适用于高水头水电站,应根据电站的工程规模作进一步详细论证。