Weir Design Research Articles

A numerical investigation of flow over a side weir based on the experimental data

Side weirs are one of the most important and sensitive parts of flood water spreading systems. Their inappropriate or incorrect function can potentially have an adverse effect on the entire system, making it difficult for flood water spreading systems to perform correctly. Hence, it is necessary to study the hydraulic behaviour of the side weirs. One of the applications of side weirs is predicting the accurate flow measurement in irrigation and floodwater spreading systems. In this study, flow over a broad-crested side weir is numerically investigated based on experimental data under sub-critical condition. The numerical model considers flow over a side weir using Reynolds's Average Navier-Stokes (RANS) equations. The standard k-epsilon turbulence is used to account for turbulence modelling and the volume of fluid scheme was also used in the model to find the free surface of flow. The simulation results are validated by experimental data. They provide detailed analysis of flow patterns, longitudinal pressure distributions over the side weir and also outflow discharge. This study shows that existing numerical models using RANS are applicable in the design of side weirs.

A Numerical Investigation of Flow Over a Side Weir Based on the Experimental Data

Side weirs are one of the most important and sensitive parts of flood water spreading systems. Their inappropriate or incorrect function can potentially have an adverse effect on the entire system, making it difficult for flood water spreading systems to perform correctly. Hence, it is necessary to study the hydraulic behaviour of the side weirs. One of the applications of side weirs is predicting the accurate flow measurement in irrigation and floodwater spreading systems. In this study, flow over a broad-crested side weir is numerically investigated based on experimental data under sub-critical condition. The numerical model considers flow over a side weir using Reynolds’s Average Navier-Stokes (RANS) equations. The standard k-ॉ turbulence is used to account for turbulence modelling and the volume of fluid scheme was also used in the model to find the free surface of flow. The simulation results are validated by experimental data. They provide detailed analysis of flow patterns, longitudinal pressure distributions over the side weir and also outflow discharge. This study shows that existing numerical models using RANS are applicable in the design of side weirs.

Effect of Urban Debris on Hydraulic Efficiency of an Elliptical Sharp-Crested Weir

An elliptical sharp-crested weir design was developed for detention pond outlets to address discharge, pollution, and maintenance concerns. The weir was designed in an effort to efficiently pass debris through an outlet as well as having the ability to easily remove any debris attached to the weir plate. Interactions between various types of debris materials were investigated using a 1:2 Froude-scale physical model. Stage discharge data were collected to quantify reduced hydraulic efficiencies with the presence of debris in the weir plate. Nine debris tests were conducted using plastic bags, newspapers, and turf reinforcement mat material. Reductions in hydraulic efficiencies were quantified from the resulting data. Plastic bags and newspapers produced the greatest reduction in hydraulic capacity, whereas turf reinforcement mat material generated the smallest reduction. Observations regarding the ability of debris material to pass through the weir at increased flows were also made using the physical model.

Performance evaluation of two different neural network and particle swarm optimization methods for prediction of discharge capacity of modified triangular side weirs

Technical design of side weirs needs high accuracy in predicting discharge coefficient. In this study, discharge coefficient prediction performance of multi-layer perceptron neural network (MLPNN) and radial basis neural network (RBNN) were compared with linear and nonlinear particle swarm optimization (PSO) based equations. Performance evaluation of the model was done by using root mean squared error (RMSE), coefficient of determination (R2), mean absolute error (MAE), average absolute deviation (δ) and mean absolute relative error (MARE). Comparison of the results showed that both neural networks and PSO based equations could determine discharge coefficient of modified triangular side weirs with high accuracy. The RBNN with RMSE of 0.037 in test data was found to be better than MLPNN with RMSE of 0.044 and multiple linear and nonlinear PSO based equations (ML-PSO and MNL-PSO) with RMSE of 0.043 and 0.041, respectively. However, due to their simplicity, PSO based equations can be sufficient for use in practical cases.

Hydraulic Characteristics of Flow over Sinusoidal Sharp-Crested Weirs

AbstractSharp-crested weirs are widely applied in agricultural and hydraulic engineering for measuring and regulating flow. The various shapes of weirs give rise to their special characteristics. This study introduces a novel sharp-crested weir design with a sinusoidal notch, and investigates physical models of sinusoidal sharp-crested weirs of different widths and heights. The analysis aims to establish the head-discharge relationship and to inspect the three-dimensional velocity distribution and the hydrodynamic characteristics of flow in the vicinity of the weir plate. The hydraulic behavior of sinusoidal weirs is also compared with that of rectangular sharp-crested weirs. The results show that the secondary currents and the turbulence intensity in the vicinity of the sinusoidal weirs are stronger than those of rectangular weirs. Therefore, this type of weir can provide an efficient passage for floating debris and sediment.

Discussion of “Hydraulic Design and Analysis of Labyrinth Weirs. I: Discharge Relationships” by B. M. Crookston and B. P. Tullis

Discussion of “Hydraulic Design and Analysis of Labyrinth Weirs. I: Discharge Relationships” by B. M. Crookston and B. P. Tullis

Closure to “Hydraulic Design and Analysis of Labyrinth Weirs. I: Discharge Relationships” by B. M. Crookston and B. P. Tullis

The discusser would like to thank the authors for presenting discharge coefficient data for nonvented trapezoidal labyrinth weirs with quarter-round and half-round crest shapes for sidewall angles of 6, 8, 10, 12, 15, 20, and 35°. Different sets of weir models having weir height P 1⁄4 15.24 cm and P 1⁄4 30.48 cm are studied by the authors. The work by the authors in accomplishing the regression equations applicable to discharge coefficients is really appreciated. These accurate equations are applicable to the trapezoidal labyrinth weirs that have sidewall angles of 6, 8, 10, 12, 15, 20, and 35° with head to weir height ratio of 0.05 ≤ Ht=P ≤ ∼0.8 − 0.9. The regression equations presented by the authors are selected over polynomial relationships because of their improved data representation (R ≥ 0.99) and extrapolation performance (they remain well behaved up to Ht=P ≤ 2.0). It worth noting that for other wall angles between 6 and 35°, the interpolation procedure should be employed to obtain the discharge coefficients. The application of the linear interpolation technique for determining the values of the discharge coefficients for intermediate values of the sidewall angle seems to be inappropriate because of the nonlinearity of the discharge coefficient curves. However, in practice it is very suitable to have a single equation applicable to any sidewall angle between 6 and 35°. Thus, the discusser would like to introduce unified regressionbased equations for discharge coefficients (based on experimental data presented in original paper), which are valid for any sidewall angles between 6 and 35°. For this, the head to weir height ratio (Ht=P) and sidewall angle (α) are considered as independent variables in the proposed equations for discharge coefficients. It should be noted that the thickness and the crest curvature of the weirs may influence the flow pattern and cause different values of the discharge coefficient (Azimi 2013). This investigation attempts to find a generalized and unified equation for the discharge coefficient of the labyrinth weir. The proposed equation renders the authors’ study more valuable and will be accurate and easy to use in practical situations.

Study of Using Gabion to Protect Downstream Slope of Stone Weirs

In the present research, the stability of stone weirs protected by gabions and subjected to overtopping flow rates under the effect of high flow rates has been studied experimentally. Four weir models with different downstream slopes [1V:2.5H, 1V:3H, 1V:4H, 1V:5H, 1V:7.5H ] were constructed and tested. sixty experiments were carried out for four cases of gabions laying on the downstream slope, laying gabions with one layer and no connections (M-1), laying gabions with lateral connections (M-H), laying gabions with longitudinal connections (M-V), laying gabions with two layers (M-2] using three gravel diameters (11.11,15.9 and 22.25)mm. From the data analysis, many equations were obtained for the estimation of failure unit discharge in terms of equivalent gravel diameter, relative submerged intensity of gabions, gabions layer solidity, and tangent of internal friction angle of gabions, for each case of gabions laying. A simple method was presented for the design of stone weirs protected by gabions in terms of maximum failure discharge with the help of design charts obtained from the present study. Comparing results of the present study with those of other investigations show that stone weirs protected by gabions stand higher failure unit discharge than rockfill and earth weirs protected by gabions.

Discharge coefficient of rectangular sharp-crested side weirs Part II: Domínguez's method

The hydraulic design of a side weir is complicated because the flow conditions vary with distance along the weir, resulting in the 3-D nature of flow over side weirs. Accordingly, by considering the criticism on De Marchi's discharge coefficient formula (Part I), the present study examines a method proposed by Domínguez for estimating the discharge over the side weirs under a subcritical flow condition. Further, on the basis of a comprehensive analysis of the available experimental data, the merits of the practical application of the Domínguez's method were evaluated. The results reveal that the fundamental assumptions of Domínguez, e.g., constant specific energy and linear free surface profile along the side weir in the main channel centerline, are appropriately satisfied. Finally, on the basis of the dimensional analysis, novel correlations were derived for calculating the Domínguez's discharge coefficient with respect to the most significant dimensionless parameters. The estimated results compare well with the results of the model experimentation.

Effects of hydrology and river management on the distribution, abundance and persistence of cyanobacterial blooms in the Murray River, Australia

Major cyanobacterial blooms (biovolume>4mm3L−1) occurred in the main water reservoirs on the upper Murray River, Australia during February and March 2010. Cyanobacterial-infested water was released and contaminated rivers downstream. River flow velocities were sufficiently high that in-stream bloom development was unlikely. The location has a temperate climate but experienced drought in 2010, causing river flows that were well below the long-term median values. This coupled with very low bed gradients meant turbulence was insufficient to destroy the cyanobacteria in-stream. Blooms in the upper 500km of the Murray and Edward Rivers persisted for 5 weeks, but in the mid and lower Murray blooms were confined to a small package of water that moved progressively downstream for another 650km. Anabaena circinalis was the dominant species present, confirmed by 16S rRNA gene sequencing, but other potentially toxic species were also present in smaller amounts. Saxitoxin (sxtA), microcystin (mcyE) and cylindrospermopsin (aoaA) biosynthesis genes were also detected, although water sample analysis rarely detected these toxins. River water temperature and nutrient concentrations were optimal for bloom survival. The operational design of weirs and retention times within weir pools, as well as tributary inflows to and diversions from the Murray River all influenced the distribution and persistence of the blooms. Similar flow, water quality and river regulation factors were underlying causes of another bloom in these rivers in 2009. Global climate change is likely to promote future blooms in this and other lowland rivers.

Fish passage using broad-crested labyrinth weirs for low-head dams

The majority of dams can be classified as low-head dams with a headwater/tailwater difference less than 2–3 m and often span the river width. The importance of alternate fish passage designs especially for weaker fish has been established by their unsuccessful passage rates through traditional fishways. A model study was conducted on an alternate design allowing a comparison between a straight weir and a modified labyrinth weir, in a pool and weir fishway. The model was conducted at a 1:8 scale Froude model of a low-head dam. The dam was notched with a pool and weir fishway constructed in the notch and extending downstream on a ramp. Velocities and water surface profiles were recorded for both weir designs at 1:10 and 1:7 slopes using three different flow rates. Results show that the labyrinth weirs produce lateral cyclical velocities compared to the relative uniform velocities over the straight weirs with slower velocities over the downstream apexes and faster velocities over upstream points. A comparison with straight weirs shows that the broad-crested labyrinth weirs create regions potentially more conducive to fish passage. This provides an effective alternative design for fish passage at low-head dams.

Reduced flow impacts salmonid smolt emigration in a river with low-head weirs

The impacts of large dams on the hydrology and ecology of river systems are well understood, yet the impacts of low-head structures are poorly known. While impacts of small weirs on upstream-migrating fish have long been mitigated by fish ladders, it is assumed that downstream migration of surface-oriented fishes is unaffected under natural flow regimes. To test this, the effects of low-head weirs and the influence of river flow on the migration of brown trout (Salmo trutta) smolts in the River Tweed, UK, were examined. Movements of acoustic tagged smolts were quantified in 2010 and 2011 using automatic listening stations and manual tracking throughout the migration route. In both years, smolts exhibited major losses, most likely due to predators, with escapement rates of 19% in 2010 and 45% in 2011. Loss rates were greater in 2010 when flows were frequently below Q95 (20% of study period) compared to 2011 when more typical flows predominated (0% of study period below Q95). Smolts experienced significantly longer delays at weirs during 2010 than 2011, associated with the different hydrographs during emigration as well as weir design. Flow comparisons within the study periods and historical records show that low flows experienced in 2010 were not unusual. The swimming behaviour of smolts in relation to flow conditions differed between years, with smolts in 2010 increasing their rate of movement in relation to increasing flow at a faster rate than smolts in 2011. This is the first study to demonstrate river flow impacts on the migration success of wild salmonid smolts at small weirs. Because small weirs are common in rivers and because spring-summer low-flow periods may become more frequent with climate change (based on UKCIP09 models) and altered river hydrology, further research and improved management is needed to reduce the impacts of low river flows in combination with low-head weirs on salmonid smolt migration.

Water surface profile along a side weir in a parabolic channel

A side weir is an overflow structure set into the side of a channel. This structure is used for water level control in channels, diverting excess water from a main channel into a side channel and as storm overflows from urban sewage systems. Computation of water surface profile over the side weirs is essential to determine the flow rate of the side weir. Discharge estimation of the side weir is still an important research subject. Most previous research works for the side weir were carried out in main channels with rectangular, triangular, trapezoidal and circular cross sections. Analytical solutions for water surface profile along a rectangular side weir are available only for the special cases of rectangular and trapezoidal main channels on the basis of a constant specific energy. No analytical solution is available for a rectangular side weir located in a parabolic channel. This research presents an elegant analytical solution for establishing the water surface profile along a side weir located in a parabolic channel which involves the use of incomplete elliptic integrals. The solution, which yields a direct computation, should be a useful computational tool for evaluation and design of rectangular side weirs in parabolic channels.

Hydraulic Design and Analysis of Labyrinth Weirs. I: Discharge Relationships

A method is presented for the hydraulic design and analysis of labyrinth weirs based upon the experimental results of physical modeling. Discharge coefficient data for labyrinth weirs with quarter-round and half-round crest shapes are presented for sidewall angles ranging from 6 to 35°. Cycle efficiency is also introduced as a design aid, which compares the hydraulic performance of different cycle geometries. Geometric parameters that affect flow performance are discussed. The predictive accuracy of the design method is evaluated through comparisons to previously published labyrinth weir head-discharge data. The companion paper examines nappe behaviors that affect flow performance and presents hydraulic design considerations specific to nappe characteristics.

Hydraulic Design and Analysis of Labyrinth Weirs. II: Nappe Aeration, Instability, and Vibration

AbstractNappe behavior should be considered in the design of labyrinth weirs to ensure hydraulic optimization and to account for potential vibrations, pressure fluctuations, noise, and flow surging. Information regarding nappe aeration conditions (clinging, aerated, partially aerated, and drowned), nappe instability, and nappe vibrations for trapezoidal labyrinth weirs on a horizontal apron with quarter- and half-round crests (6°≤ sidewall angle ≤35°) is presented. Corresponding headwater ratio ranges and hydraulic behaviors associated with nappe aeration conditions are documented and discussed to aid in labyrinth weirs design, including design options directly related to nappe behavior (e.g., crest shape, crest roughness, vents, nappe breakers, notches, and staged cycles). The effects of artificial nappe aeration (a vented nappe) on nappe behavior and discharge capacity are also discussed, including recommended placements of nappe breakers.

Piano Key Weir Hydraulics and Labyrinth Weir Comparison

AbstractA piano key (PK) weir is a type of nonlinear (labyrinth-type) control structure with a relatively small spillway footprint. No standard PK weir design procedure is available, and the amount...

Hydraulic design of A-type Piano Key Weirs

Piano Key Weirs (PKWs) are an alternative to linear overflow structures, increasing the unit discharge for similar heads and spillway widths. Thus, they allow to operate reservoirs with elevated supply levels, thereby providing additional storage volume. As they are relatively novel structures, few design criteria are available. Hence, physical model tests of prototypes are required. This study describes comprehensive model tests on a sectional set-up of several A-type PKWs, in which the relevant parameters were systematically varied. Considering data of former studies, a general design equation relating to the head–discharge ratio is derived and discussed. The latter is mainly a function of the approach flow head, the developed crest length, the inlet key height, and the transverse width. To extend its application range, case study model tests were analysed to provide a design approach if reservoir approach flow instead of channel flow is considered.

Water Surface Profiles along a Rectangular Side Weir in a U-Shaped Channel (Analytical Findings)

AbstractSide weirs are flow-diversion devices that are widely used in irrigation and drainage systems and combined sewer systems. Side weirs are also used as an emergency structure. They are important parts of distribution channels of irrigation systems. Computation of a water surface profile over side weirs is essential to determine the flow rate of the side weir. No closed-form solution is available for a rectangular side weir located in a U-shaped main channel. The U-shaped channel possesses an important application in sewer systems. This structure is used as a transitional cross section in manholes and in changes from circular to rectangular cross sections. This research presents an elegant closed-form solution for establishing the water surface profile along a side weir located in a U-shaped channel. The solution should be a useful computational tool for evaluation and in the design of rectangular side weirs in sewer systems and U-shaped channels.

Briefing: Water surface profile over side weir in a trapezoidal channel

Side weirs or lateral weirs are widely used for water level control in water treatment plants and irrigation and drainage systems. The side weir is a fixed structure installed at one side of a channel to divert flow laterally. Computation of the water surface profile along the side weir is essential in determination of the discharge over the side weir. An analytical solution of the dynamic equation for spatially varied flow with decreasing discharge, in prismatic channels with a side weir, is available in the technical literature only for the special case of a rectangular channel based on the constant specific energy assumption. However, in irrigation networks, the most common irrigation channels are of trapezoidal cross-section. This paper presents an elegant analytical solution for establishing the water surface profile along a side weir in a trapezoidal channel. Since triangular and rectangular cross-sections are special cases of the trapezoidal cross-section, the proposed analytical solution is also applicable to these cross-sections. The solution, which yields a direct computation of the flow profile in subcritical and supercritical flow regimes, should be a useful engineering tool for the evaluation and design of side weirs in open channels.

Head-Discharge Equation for Sharp-Crested Weir with Piecewise-Linear Sides

This research presents a new weir section with n-segment linear sides and a horizontal bottom. For large n, the section sides of the weir become smooth curves. However, piecewise-linear sides provide a weir shape simple enough for ease of construction. General head-discharge equations are analytically derived for the flow discharge. The proposed weir with n-segment linear sides can be applied in an optimization procedure to produce a wide range of head-discharge behaviors. An elegant optimization model that implements the general equations is presented and applied in the design of linear and quadratic weirs. This simple model is solved using the Solver toolbox of Microsoft Excel. The versatility of the proposed weir is demonstrated by optimizing the weir parameters to obtain the maximum ranges of measurement under linear and quadratic characteristics. These weirs have least relative errors because of their linear and quadratic head-discharge relationships and are very useful as a flow recorder in irrigation canals. Optimum design parameters for these weirs are presented in a simple dimensionless form suitable for water structure designers to adjust the weir dimensions to suit field conditions. Application of the proposed weir section is not limited to these two weirs; it can also be used to design other specific weirs.