Weir Head Research Articles

Estimation of Discharge Coefficient of the Trapezoidal Broad Crested Weir Flow Using Support Vector Machines

Weirs are the oldest and most practical structures used to control, regulate, and measure flow in rivers or open channels. The ratio of the actual discharge, smaller than the theoretical discharge due to the separation zone and boundary layer development, to the theoretically discharge is defined as the discharge coefficient (Cd). Cd values are depended on the hydraulic properties of the open channel flow and the type and geometric properties of the weir. In this study, a total of 88 weir head (H0) of the trapezoidal broad crested weir with different upstream and downstream slopes are experimentally measured and Cd values are calculated according to the weir characteristics. Calculated Cd values are estimated by using eight different input combinations with the dimensionless parameters. Three different kernel functions (Linear, Polynomial and Gaussian) of Support Vector Machines method are used. To determine the performance of the models, Root Mean Square Error (RMSE), Mean Absolute Percentage Error (MAPE), and the coefficient of determination (R2) values are employed. As a result of the study, the Gaussian kernel function is the most successful model and the input combination is H0/L (L as crest height), ɛ (H0/(H0+L)), upstream slope (α) and downstream slope (ꞵ) parameters are found to be most successful model to estimate Cd values.

Comparación de la disipación de energía en aguas abajo de aliviaderos escalonados y desconcertados de vertederos de tecla de piano

Heavy seasonal rains over a dam reservoir can lead to huge floods and consequent failure of the dam structure. One way of controlling the adverse effects of heavy rains is to use weirs with larger dimensions such as piano key weirs (PKWs). In spite of raising the overall costs of the project, these weirs are preferred due to their high culvert capacity. PKWs can cause damage to the dam by creating water jets downstream. An effort was made in the present study to examine the energy dissipation due to installation of steps and baffles with different sizes on piano key weirs. The results showed that small baffles and large steps caused maximum energy losses of 85 and 80% in the studied weirs respectively. It was also found that the weir energy dissipation over the spillway was inversely related to its slope angle (the angle between the weir outlet and the vertical wall of the steps/baffles). The other findings were: (1) increasing the flow rate reduced the effect of the steps on the energy loss; (2) the Weber number was directly proportional to the energy loss; and (3) the ratio yc/H (critical depth to the weir head ratio) was directly proportional to the energy loss.

Effects of Outlet Shrinkage on Hydraulics in Hyper-Concentrated Sediment-Laden Flow

Finding an appropriate shape for the releasing building is thoroughly relevant given the energy dissipation and safety requirements of a high dam in a sediment-laden river. Thirty-six physical experiments on trajectory energy dissipation were conducted, researching the influence of three overflow shapes (contraction ratios of 0.5, 0.4, and 0.3) with four sediment concentrations (0, 50, 150, and 250 kg/m3) on the discharge, flow regime, and hydrodynamic pressure of a plunge pool slab. The experimental results demonstrated that the flow coefficient gradually decreased as the contraction ratio decreased in a relatively high weir head, regardless of the sediment concentration. The water nappe narrowed and the length of the longitudinal trajectory increased as the outlet shrinkage and sediment concentration decreased. With the increase in sediment concentration, the nappe regime approached stability, and the flow in the plunge pool tended toward small rolling, causing the impact pressure and fluctuating pressure to increase. Changes in overflow shape had little effect on the position of pressure peak, but the value became lower as the ratio diminished. The influence on the hydrodynamic pressure by outlet shrinkage became attenuated while the sediment concentration increased. The fluctuating energy and vortex scale were enhanced due to the increased viscosity with increasing sediment concentrations.

A Topology-alterative Algorithm for Transient Dynamic Hydraulic Response Investigation

In this paper, a hexahedra-based topology-alterative algorithm is proposed to simulate dynamic boundary issues of the gate opening motions in water conservancy projects. The algorithm, which cooperates with the two-phase, incompressible solver of OpenFOAM platform, enables researchers to investigate transient hydraulic characteristic variations comprehensively. Two benchmark experiments were performed to validate the numerical results under the working conditions of moving sluice gates and unsteady weir head. The time history response of water level and pressure on specified monitoring points, flow pattern scenario near moving gate, furthermore, the development of antisymmetric-revolving vertical vortices around gate piers were recorded to assess the accuracy of the proposed model. The cross-contrasting results show that the relative error of weir flow time is less than 5.00 %. Moreover, good agreement has been obtained about time history curves of free surface elevation and pressure between numerical and experiment solutions. The vivid flow pattern shows the simulating capability of the current model and indicates an inspiring way to numerically investigate generation mechanism of vertical vortex inside gate grooves. The proposed algorithm is believed to be a useful utility on the further investigation on flow variation in real hydraulic engineering applications, such as improvement of semi-empirical discharge formulas, reduction of cavitation damage, elimination of pipe hammer pressure even spectral analysis of sluice gates with a fluid structure interaction interface.

Experimental study on pressure and aeration characteristics in stepped chute flows

The free flow on the step surfaces has received much attention for its representative body type, flow structure, water-air two phase flow, cavitation, and many complex issues. The experiments about the time-averaged pressure and aeration concentration distribution on the step surface show that the vertical plane of steps will inevitably experience negative pressure, which must rely on adequate aeration concentration to avoid cavitation damage. However, the self-aerated flow at the head section has a relatively low aeration concentration, and the concentration of the entire steps decreases with the increasing of weir head, the minimum appears in the vicinity of the corner, and the location is close to the minimum pressure. Thus, it is necessary to set aerator in the upstream end of the step surfaces to avoid cavitation damage.

Weir velocity formulation for sharp-crested rectangular weirs

Discharge in open channels can be measured by sharp-crested rectangular weirs. Generally, measured head over the weir crest is substituted into an empirical formula derived from energy considerations to calculate the discharge. Assumptions made on the derivation are taken into account by defining a discharge coefficient that fits into the experimental data. In this study, a physical quantity, the average velocity over the weir section defined as ‘weir velocity’ is directly formulated as function of weir geometry and head over the weir. Weir velocity plotted against the weir head has a universal behavior for constant weir width to channel width ratio independent of the weir size. This unique behavior is described in terms of weir parameters to calculate the discharge without involving a discharge coefficient. Combining weir velocity data for variable weir widths provides a basis for direct formulation of discharge. The weir velocity exhibits simpler functional dependency on weir parameters in contrast to the discharge coefficient.

Acoustics of weirs: Potential implications for micro-hydropower noise

There is great potential for the expansion of the small or micro scale hydropower network. Of the 43 thousand weirs in the UK there are only 500 consented hydro schemes. Planning applications for such schemes require a noise assessment. Noise evaluation of a proposed renewable scheme is often complicated by the turbine sites having distinct noise characteristics in the first instance, which are often caused by the weirs themselves. Three types of weir were studied: Broad Crest weirs were studied in detail; this is complimented by further studies in Flat V and Crump weirs. Flow data was collected for ten sites from the Environment Agency and the National Rivers Flow Archive to assess the collected Sound Pressure Level (SPL) and calculated Sound poWer Level (SWL) in relation to various river flows. Weir head height, width and meteorological data were also collected. It has been shown that the SPL data collection method used was the right choice, as the greatest amplitudes at the water impact interface at all weir types was recorded. SPL and SWL were found to be within a 36–82 dBz and 45–86 dBz range respectively for all weir types. These values can be used in computer simulations of sound propagation. The mean SPL and SWL difference between the weir types are 6.1 dBz and 6.3 dBz. Head height has the greatest effect on SPLs. Attenuation with distance was found to be similar to that of a free field line source in general.

Discharge characteristics of skew weirs

Skew weirs are used for reducing afflux while passing a certain discharge. Herein, the discharge characteristics of a sharp-crested skew weir are explored. The concept of elementary discharge coefficient is utilized for predicting the discharge. Based on experimentation, an equation for the discharge coefficient of skew weirs is determined as a function of weir head to weir height and the weir angle relative to the channel axis. The discharge over skew weirs is well predicted.

Discharge formula for rectangular sharp-crested weirs

Sharp-crested rectangular weirs used for discharge measurement in channels and laboratories are experimentally investigated. Height and width of weir plate are the two parameters characterizing the head-discharge relationship. Laboratory experiments are conducted by measuring the discharge and the head over the weir for variable weir heights and widths. Applicability of various formulations for the discharge coefficient are investigated. Experiments indicate that discharge is independent of weir height, when the weir is operated within an appropriate discharge range. Average velocity over the weir plotted against the weir head displays universal characteristics such that it can be used in the expression of discharge over the weir, eliminating the need for a discharge coefficient. The head-discharge relationship for a rectangular weir has distinct features for the partially contracted weirs and for the fully contracted slit weirs.

Scour around a side‐weir at a 30° section of a 180° alluvial curved channel

AbstractLocal depths of clear‐water scour around side‐weirs located at a 30° section of a 180° alluvial bend have been investigated experimentally in this paper. Relations between the depth of clear‐water scour as a function of time and approach flow intensity have been established. Regression analysis has been applied between the equilibrium depth of scour and the dimensionless parameters of approach flow intensity (V1/Vc, approach flow velocity/critical velocity at the threshold conditions of bed material), water head ratio ((h1− p)/h1, weir head over the side‐weir/water depth in the main channel), and weir crest height (b/p, width of main channel/side‐weir crest height) at θ = 30°. Although there is no scour when approach flow intensity is less than 0.55, the scour equilibrium depth increases almost linearly with the ratio of approach flow intensity, and the maximum value of scour depth occurs at a depth when the approach flow intensity is equal to 1.0 at the 30° section of a 180° alluvial curved channel. The location of the maximum scour hole occurs at the downstream of side‐weir sections close to the outer bank of the main channel and it moves toward the downstream direction with an increase of the dimensionless parameters of approach flow intensity as well as the water head ratio, the weir crest height and the side‐weir length (L/r, length of side‐weir/radius of main channel from the bend centre). Copyright © 2007 John Wiley & Sons, Ltd.

Relationship of first step height, step slope and cavity in X-shaped flaring gate piers

The energy dissipation of X-shaped flaring gate piers ahead of a stepped spillway was adopted in the Suofengying Hydroplant. Under the circumstance that the first step is higher than others, at the step surface an aerated cavity occured behind piers. The interaction of the weir head, the elevation difference between crest and chamber outlet, the first step height, the slopes of weir end and step, and the size of cavity, was investigated, the expression was derived to characterize their relationship, and the corresponding curves were plotted. The comparison of the calculated and simulated results with the measured data was performed. When the slopes of step and weir end are equivalent, the relative height difference between the first and second steps becomes the main factor influencing the aerated cavity. These findings may be useful in practical applications.

Effect of specific energy variation on lateral overflows

A numerical model was used to study the effect of change in specific energy height along a side weir on flow. Discharge coefficient was considered as a local variable that includes flow depth and the angle of the deflected water jet along side weir. Hydraulic profile on the weir plane and the hydraulic head on the weir were obtained using two dimensionless parameters ψ and m as a function of Froude number. Flow depths and flow rates were then computed and minimum standard errors were determined based upon these parameters. The agreement between computed values and observations was demonstrated. It was concluded that rates of flow are considerably affected by the variation of specific energy along the side weir when weir head is based on flow depth at the weir plane. Considerable deviations from the constant specific energy assumption may be observed in this case specially when a great change in flow rates exists along side weirs with zero end discharges.

V‐Notch Weir Calibration Using New Parameters

Monitoring of wastewater discharge requires measurements of both quality and quantity to satisfy federal regulations. The use of 90-degree V-notch weirs to measure discharge at outfalls is common. In many instances the weirs are placed in culverts or other space-limited locations such that the traditional calibration parameter, head over the weir notch, is difficult to measure. Two other parameters can be specified, which involve measurements at the weir plate. These have the advantage of not requiring that an elevation datum be established. The first is measurement of depth of flow over the weir notch using a common meter stick. The second is the measurement of width of flow at the weir crest using a modified machinist's caliper. Both techniques yielded reliable measurements using a sample data set obtained from 12 students asked to perform the measurements. Measured discharge varied no more than ± 5% from actual at one standard deviation, and no more than ± 10% at two standard deviations. It was concluded that the two new parameters were adequate substitutes for traditional weir head measurements.

A Report on the Fauna of the Estuaries of the River Tamar and the River Lynher

The following is an account of a faunistic investigation covering those parts of the Rivers Tamar and Lynher which are affected by the tide, and was carried out during a period of six months from June to November, 1928.Description of the Area.The Tamar forms a portion of the boundary between Devon and Cornwall and flows in a southerly direction along a more or less winding course. (Chart.) The extent of the stream dealt with is from Plymouth Sound to Weir Head, some 19 miles inland measured along the water course. For about 6 miles downstream from Weir Head, the valley is rather narrow with rock exposures at different places on the convex side of bends, the water being confined to a well-defined channel with steep sides, which are uncovered by the vertical contraction of the stream at low water. The remainder of the river, down to the sea has, generally, a mud bank on each side, except at occasional bends where rock is present, which is exposed at low water by the lateral contraction due to reduction in level. The upper 4 miles of this region has narrower mud-banks than has the lower portion. These mud-banks or -flats are for the greater part more or less plane surfaces, which may slope gradually into the bed of the main channel, as happens in the lower portion of the area, or they may slope suddenly downwards at the edge, thus forming a well-marked bank to the main channel. In many cases their landward edges lie below high-water neap tide, but in others they slope imperceptibly into the adjoining land surface.