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     

生物膜泥沙床面对水体紊动影响的实验研究

泥沙床面生长生物膜后水流紊动特性将发生变化,进一步影响到泥沙的起动,悬浮和输移特性。本文采用d500.1 mm的天然沙,对相同水流条件下无生物膜生长和有生物膜生长床面以上的水流内部结构进行研究。实验中采用多普勒声学流速仪(ADV)测量了垂向流速,对比分析了生物膜生长前后,时均流速、雷诺应力、紊动强度以及紊动猝发事件在垂向上的变化,并初步分析了这些变化对泥沙运动的影响。结果表明:生物膜生长后,同流量条件下的垂向平均流速增加,床面阻力减小;对比无膜沙床面,有膜沙床面在发生冲刷的水力条件下,雷诺应力、紊动强度均有所减小,从而会影响到悬沙的浓度分布;同时猝发事件发生率在垂向上的变化也使得生物膜泥沙床面的泥沙起动更加困难。     

The influence of coarse particle mobility on scour depth in salmonid spawning habitat

This study examined the influence of flow hydraulics and coarse particle mobility on bed scour adjacent to coho salmon (Oncorhynchus kisutch) redds in a coastal California watershed for a bankfull flood. It was theorized that coarse particle mobility (i.e., mobility of particles larger than the median bed particle size, D₅₀) exerts a strong control on bed scour depth. Maximum scour depth at the study sites was found to be negatively correlated with flow shear stress, which is dissimilar to findings from previous scour studies in spawning reaches. This resulted from a relatively similar coarse particle size (D₈₄) for all study sites and a negative relationship between shear stress and coarse particle exposure to flow (or the D₈₄/D₅₀ ratio), which together caused sites with low shear stress to have a high degree of localized coarse particle mobility and an associated high maximum scour depth. This study provides new insights into the vulnerability of spawning reaches with low flow energy to redd scour and highlights the need to consider the mobility of coarse particle sizes explicitly when examining the dominant controls on redd scour.     

临界底坡变化规律及相应均匀流流态判别

临界底坡在均匀流中可以用作判别水流流态,临界底坡随流量的变化规律随着断面形式的变化而有所不同。针对3种不同的断面形式,从理论上推导出它们的最小临界底坡公式。分析结果显示:矩形、圆形和U形3种不同的过水断面均存在最小临界底坡,iKmin分别为26.13n2     

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     

混流式水轮机上冠空腔结构内部流场及单向流固耦合分析

为研究上冠空腔结构对混流式水轮机水力性能与结构特性的影响,建立了不含上冠空腔结构（No UpperCrown Cavity Structure,NUCCS）和含上冠空腔结构（Upper Crown Cavity Structure,UCCS）的两种混流式水轮机全流道几何模型,基于SST湍流模型、顺序耦合法、预应力模态分析,对NUCCS与UCCS的两种混流式水轮机展开数值模拟和单向瞬态流固耦合计算,发现泄水锥处上冠空腔结构可减少转轮内部二次流动损失。在0.8Q_d、Q_d和1.2Q_d的3种流量工况点,分别对混流式水轮机展开瞬态流固耦合计算,对比研究转轮结构的应力应变特性。研究发现含UCCS时,转轮等效应力和变形量均有减小。在小流量0.8Q_d工况点,转轮结构等效应力及应变较小,其最大变形点位于下环附近。在设计流量Q_d和大流量1.2Q_d工况点,转轮等效应力及应变较大,其最大变形点位于上冠附近。在NUCCS与UCCS的转轮进行预应力模态分析时,发现上冠空腔结构对转轮的模态影响很小。本文研究内容可为提升混流式水轮机设计水平提供一定参考依据。     

A hydrogeomorphic dynamics approach to assess in‐stream ecological functionality using the functional flows model,part 1—model characteristics

The functional flows model integrates hydrogeomorphic processes and ecological functions for stream physical habitat evaluations. Functional flows are discharge values that serve ecological uses. Assessments of functional flows are based on evaluation of shear stress dynamics. The analysis is based on the occurrence of sediment transport regimes defined by threshold values of Shields stress estimated from discharge (Q), a parameter (f) governing depth response to incremental discharge changes, water surface slope (S) and media grain size (D₅₀). As an example, the model was tuned for fall‐run Chinook salmon spawning. Ecological functions studied were bed occupation (spawning, incubation and emergence) and bed preparation (river bed reworking periods)—both reliant on shear stress dynamics. A numerical experiment and sensitivity analysis using a wide range of realistic values of input variables indicated the effect of each variable on flow functionality. Combinations of S = 0.001, 0.005 and 0.01, D₅₀ = 0.02, 0.05, 0.1 m, f = 0.2, 0.3, 0.4, 0.5 and four sediment transport stages produced 144 scenarios. Ranges of functional flows were greater for scenarios for low f (0.2) with low slope (0.001,0.05), for high f (0.5) with small grain size (0.02 m) and for intermediate low f (0.3) with coarse grain size (0.1 m). The functional flows model incorporates in‐stream habitat processes by including metrics of hydrologic, hydraulic, geomorphic and ecologic dynamics. Model uncertainties related to input data, calculation algorithms, and model structure are analysed. Functional flows analysis can be useful in studying water management alternatives to improve habitat conditions for target species and lifestages. Copyright © 2009 John Wiley & Sons, Ltd.     

An ANFIS-based approach for predicting the bed load for moderately sized rivers

A total of 346 sets of bed-load data obtained from the Kinta River, Pari River, Kerayong River and Langat River were analyzed using four common bed-load equations. These assessments, based on the median sediment size (d₅₀), show that the existing equations were unable to predict the measured bed load accurately. All existing equations over-predicted the measured values, and none of the existing bed-load equations gave satisfactory performance when tested on local river data. Therefore, the present study applies a new soft computing technique, i.e. an adaptive neuro-fuzzy inference system (ANFIS), to better predict measured bed-load data. Validation of the developed network (ANFIS) was performed using a new set of bed-load data collected at Kulim River. The results show that the recommended network can more accurately predict the measured bed-load data when compared to an equation based on a regression method.     

应用双作物系数模型估算温室番茄耗水量

准确估算作物耗水量对于合理利用有限的水资源和制定合理的灌溉制度至关重要。本文利用3个生长季的西北地区日光温室番茄水量平衡计算耗水资料,率定和验证双作物系数模型SIMDual Kc在日光温室条件下的适用性。结果表明耗水模拟值与实测值有较好的一致性。模型估算的平均标准误差为0.55 mm·d-1,平均绝对误差为0.44 mm·d-1。模型估算的番茄初期、中期和后期的基础作物系数分别为0.50、0.85和0.55。番茄生育初期蒸发占耗水的比例最大为22.8%;发育期最小,仅为3.2%。3年全生育期总蒸发量占总耗水量的比例平均为5.9%,表明温室生产中植株蒸腾为耗水最主要部分。     

Analysis of the relationship for determining the bed load in sand channels

Conclusion The results of the analysis showed that in flatland rivers with a sand channel withu _*u _*0 where movement of the bed load is realized mainly in the form of steep waves and ripples [5], for determining the bed loadq _bd GGI's relationship (1), in whichq _bd is represented as a function of the height of the bed formsh _w, should be used. This relationship gives results substantially differing from the results calculated by relationships in whichq _bd is expressed as a function of the size of the sediment particlesd (8), (9) and valid for conditions not characteristic of sand channels of flatland rivers. Whenu _*t u _*<u _*0, when there is still no mass traction of all fractions of the channel deposits, the Einstein (8) or Paintal (15) relationships are more substantiated for all channels, but for practical calculations for sand channels of flatland rivers one can assume thatq _bd=0 whenu _*<u _*0.Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 5, pp. 47–50, May, 1989.     

RBF神经网络模型在砂土液化判别中的应用研究

以时松孝次收集的砂土液化数据为研究对象,选取黏粒含量ρ_c、相对密实度D_r、临界深度d_s、竖向有效应力σ′、地下水位d_w、地震震级M、最大地面水平加速度α_max和标准贯入次数SPT-N等8个砂土液化的主要影响因素作为RBF神经网络的输入参数,利用MATLAB7.0中的神经网络工具箱,对部分样本数据进行训练和测试。并利用建立的RBF神经网络模型分析了各因素对砂土液化的影响规律。结果表明：砂土液化判别指标随α_max的增加而增大,随SPT-N和d_w的增加而减小。研究成果表明,建立的RBF网络模型完全满足砂土液化判别的精度要求,能够精确模拟输入和输出之间复杂的非线性映射关系,具有较高的预测精度,具有重要的工程应用价值。     

Characterization of natural and environmental flows in New Brunswick,Canada

A good understanding of the natural flow regime plays an important role in many hydrological studies. Also important in such studies is the quantification of environmental flows. This study focuses on flow metrics that best describe the natural flow regime and the hydrological characteristics for rivers in New Brunswick (Canada) as well as quantifying environment flows for these rivers. New Brunswick rivers have a mean annual flow (MAF) of approximately 23 L s^?1 km^?2, which is also reflective of the water availability. The frequency analysis showed that low flows (T = 2–50 years, where T is the recurrence interval) were all below the 10% MAF. Environmental flow methods based on the MAF and flow duration analysis (median flow) showed good regional regression equations. However, flow duration methods showed high variability especially at flows between Q₈₀ and Q₁₀₀. Flow targets based on the 25% MAF, Q₅₀ and 70% Q₅₀ were used to estimate environmental flows, particularly during low‐flow periods (winter and summer). Results showed that the 70% Q₅₀ method should be used with caution in summer as this method provided flows in the range of 15–16% of MAF. Other methods provided environmental flows higher than 15% MAF, thus, providing better flow protection for aquatic habitat. When comparing water availability for off‐stream use (river flow–environmental flow), different parts of New Brunswick were found to be deficient in flows (i.e., river flows less than environment flows—no extractable water) during the summer and winter low‐flow periods.     

异重流潜入现象探讨Ⅱ:浑水水槽实验与分析

在上篇回顾异重流潜入现象研究中前人水槽实验情况和理论分析成果的基础上,本篇首先对浑水水槽实验测得的潜入点上下游沿程断面上的流速分布、含沙量分布及浑水潜入形成异重流的交界面曲线等数据进行分析,求得不同进槽流量、含沙量的进口水沙条件下潜入点处的密度Froude数Fp判别值;其次考虑潜入点Fp与其下游异重流水深hd等因素的关系,进行水库和引航道异重流潜入的理论分析,应用能量方程、动量方程分析得到忽略掺混的4种Fp与hd/hp的表达式,并与实验数据作比较,两者较接近;再将以往各学者的理论研究Fp的表达式略作推演,获得同本文推导公式近似或相同的公式,以便同本文实验资料进行比较。     

异重流潜入现象探讨Ⅰ:水槽实验与理论分析成果回顾

本文对异重流潜入现象中各种潜入点水槽实验、理论分析和数值计算成果进行回顾,并探讨不同进口水沙条件下异重流潜入点的水沙特性、潜入点与其下游异重流水沙因子的关系,全文以两篇分述。本篇介绍各家用浑水、盐水和冷水进行实验,在已知进口水沙(盐水或冷水)条件下,获得潜入点断面的密度Froude数Fp,且Fp为某一定值;水库壅水区Fp值在0.5~0.8之间,引航道口门处Fp在0.25左右。在潜入点理论分析、模型数值计算方面,探讨了潜入点Fp值同掺混系数、阻力系数以及潜入点下游异重流深度hd与潜入点水深Fp之比的关系;各家建立不同概化图形并应用能量、动量方程进行分析,求得不同形式的Fp表达式;有学者利用紊流水沙模型进行数值计算与水槽实验的Fp值或hp进行对比,获得基本符合实际的结果。     

The spatial arrangement of Neritina virginea (Gastropoda: Neritidae) during upstream migration in a split‐channel reach

This paper relates differences in flow hydraulics between a main channel (MC) and a side channel (SC) of a river to patterns of upstream migration by Neritina virginea (Neritidae: Gastropoda), a dominant diadromous snail in streams of Puerto Rico (Greater Antilles). Near‐bed water velocity, snail density and shell size were measured on a weekly basis between August and December 2000 along cross‐sections in a main channel (MC) and an adjacent channel (SC) under a bridge crossing of the Río Mameyes of Northeastern Puerto Rico. Near‐bed velocity and water depth were used to compute Reynolds (Re) and Froude (Fr) numbers, and to classify flows within each channel. During base flow conditions (<2 m³ s⁻¹), flow was chaotic and supercritical (Fr > 1) in the MC, and non‐chaotic and subcritical (Fr < 1) in the SC. Higher mean densities (>100 ind m⁻²) of relatively small snails (mean ± s.d., 6.3 ± 2.8 mm) were consistently recorded in the MC. Conversely, the SC had lower mean densities (<20 ind m⁻²) and significantly larger snails (7.6 ± 2.4 mm). Within the MC, migratory groups preferred near‐bed velocities > 0.8 m s⁻¹. Within the SC, they preferred the channel thalweg and depths > 30 cm. The spatial arrangement that was observed between and within the channels may be related to food resources, predation pressure or biomechanics. Characteristics of preferred upstream migration pathways of N. virginea must be accounted when building road crossings in coastal streams with diadromous fauna. Published in 2007 by John Wiley & Sons, Ltd.     

Entrainment of riparian gravel and cobbles in an alluvial reach of a regulated canyon river

Many canyon rivers have channels and riparian zones composed of alluvial materials and these reaches, dominated by fluvial processes, are sensitive to alterations in streamflow regime. Prior to reservoir construction in the mid‐1960s, banks and bars in alluvial reaches of the Gunnison River in the Black Canyon National Monument, Colorado, USA, periodically were reworked and cleared of riparian vegetation by mainstem floods. Recent interest in maintaining near‐natural conditions in the Black Canyon using reservoir releases has created a need to estimate sediment‐entraining discharges for a variety of geomorphic surfaces composed of sediment ranging in size from gravel to small boulders. Sediment entrainment potential was studied at eight cross‐sections in an alluvial reach of the Gunnison River in the Black Canyon in 1994 and 1995. A one‐dimensional water‐surface profile model was used to estimate water‐surface elevations, flow depths, and hydraulic conditions on selected alluvial surfaces for discharges ranging from 57 to 570 m³/s. Onsite observations before and after a flood of 270 m³/s confirmed sediment entrainment on several surfaces inundated by the flood. Selective entrainment of all but the largest particle sizes on the surface occurred at some locations. Physical evidence of sediment entrainment, or absence of sediment entrainment, on inundated surfaces generally was consistent with critical shear stresses estimated with a dimensionless critical shear stress of 0.030. Sediment‐entrainment potential over a range of discharges was summarized by the ratio of the local boundary shear stress to the critical shear stress for d₅₀, given hydraulic geometry and sediment‐size characteristics. Differing entrainment potential for similar geomorphic surfaces indicates that estimation of minimum streamflow requirements based on sediment mobility is site‐specific and that there is no unique streamflow that will initiate movement of d₅₀ at every geomorphically similar location in the Black Canyon. Copyright © 2000 John Wiley & Sons, Ltd.     

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.     

Assessing channel geometry in response to land use disturbance in a low-relief,glacially conditioned setting

Bankfull stage, the highest flow elevation contained by a river channel before overbank flooding occurs, is the presumed threshold for channel morphological change. At bankfull, the channel boundary experiences the highest shear stress, producing somewhat predictable hydraulic relationships and a cross-sectional form. However, land use and glacial conditioning can profoundly impact a channel's geomorphic responses. Two common methods characterize bankfull flow: one based on flow frequency and other based on channel form. This study considers a simplified approach to identify upstream land use relative to estimates of bankfull flow versus a channel's geometric form. The approach compares archived geomorphic surveys of 140 river reaches in southern Ontario, Canada, to 2-year flood quantiles modelled from historical flood data of 207 gauge stations. Flood frequency analysis determines that annual maximum series (AMS) datasets, fitted to optimized probabilistic distributions, underestimate discharge for low-magnitude, high-frequency flood events compared to partial duration series (PDS) datasets. For smaller drainage areas (<100 km²) associated with an extensive agricultural activity and/or urbanization, the estimates of bankfull discharge (Q_bf) generated by cross-sectional channel geometry are greater than the gauge-derived Q₂ values. Channels impacted by high levels of upstream land use disturbance show statistically significant lower width-to-depth ratios (p < 0.001) and a trend towards a finer D₅₀ bed material, suggesting enhanced surface runoff delivering more mobile finer sediments and channel confinement or incision. This research quantifies the formative bankfull stage to better understand the link between land use and a channel's ‘natural’ hydrogeomorphic response in a low-relief, glacially conditioned setting.     

Bulk drag of a regular array of emergent blade-type vegetation stems under gradually varied flow

The drag induced by flow through vegetation is affected by the velocity, shape of vegetation stems and wake interference among stems. To account for the interference effects, previous works generally related the bulk drag coefficient of vegetation to the solid volume fraction ϕ of the vegetated zone, and the trends of the results were found to be inconsistent. In this work, a systematic laboratory study has been carried out to investigate the effect of the distribution pattern of vegetation stems on the hydrodynamics of gradually varied flow through emergent blade-type vegetation. The finite artificial vegetation patches of solid volume fractions ranging from 0.005 to 0.121 have been used and the stem Reynolds number ranges from 500–2600. The longitudinal water surface profiles have been measured, and the effect of increasing roughness density with respect to varying longitudinal and lateral spacing under the flow conditions is examined. The momentum equation that relates the vegetation resistant force and water surface profile has been used to obtain the mean bulk drag coefficient C_d of the canopy. The results show that C_d decreases with increasing stem Reynolds number, decreases with increasing ϕ at fixed lateral spacing due to sheltering effect, and increases with ϕ at fixed longitudinal spacing due to channeling effect. An empirical equation has been obtained relating C_d to the lateral and longitudinal spacing instead of ϕ.     

Hydrologically Based Environmental Flow Methods Applied to Rivers in the Maritime Provinces (Canada)

The demand for water withdrawal continues to increase worldwide. These water withdrawals from rivers can affect fish habitat and aquatic life. As such, environmental flow assessment methods are used in order to protect rivers against excessive water withdrawals. The concept of environmental flow relates to the quantity of water required in rivers to sustain an acceptable level of living conditions for aquatic biota at various phases of their development. For many agencies, environmental flow methods are essential in environmental impact assessments and in the protection of important fisheries resources. The present study deals with the evaluation of hydrologically based environmental flow methods within the Maritime Province of Canada. In total, six hydrologically based environmental flow methods were compared using data from 52 hydrometric stations across the region. Some methods provided adequate environmental flow protection (e.g. 25% mean annual flow and Q₅₀ flow duration method); however, other methods did not provide adequate flow protection (e.g. Q₉₀ flow duration method and 7Q10 and 7Q2 low‐flow frequency). The 70% Q₅₀ method provided adequate flow protection only under good baseflow conditions and should be applied with extreme caution. The present study shows the importance of the hydrologic flow regime, particularly as it pertains to the baseflow component, as a significant determinant in the level of instream flow protection. © 2014 Her Majesty the Queen in Right of Canada. River Research and Applications © 2014 John Wiley & Sons, Ltd.