Weir Length Research Articles

Prediction of the drainage coefficient of steeply crested inclined weirs using different neural network techniques

The main objective of this work is to accurately predict in irrigation and hydraulic systems the discharge coefficient of the used sharp-crested inclined dams. Training algorithms on radial basis function RBF and multilayer perceptron MLP, and input variables such as weir height, length, inclination, and flow rates. From a tilted weir, researchers have used these training techniques as a model for various neural networks. In addition, the performance of CFNN is better than other neural networks such as RBF and MLP. The discharge coefficient Cd was the output variable. 95 test results were analysed. CFNN achieved a significant reduction in mean square errors (MSE), with values of 9.4363×10-12 and 1.6336×10-05, respectively, in the training and testing phases.

Investigation of labyrinth weirs discharge coefficient with the same length

One of the approaches to reduce flood depth in dams and rivers is the application labyrinth weirs instead of simple linear weirs. Labyrinth weirs have a longer length than linear weirs; therefore, the flood will pass through it with a lower depth. In this study, two types of triangular and semicircular labyrinth weirs were experimentally investigated. Experiments were performed in a flume with a width of 0.8 m and a flow discharge of up to 70 L/s. Eight weir models with a thickness of 4 mm were made, of which four models are triangular weirs and four models are semicircular weirs. Weirs were used in two types, one-cycle and two-cycle. The height of the weirs is 15 cm and the ratio of the weir length to the flume width (L/W) is equal to 1.57. The results showed that the increase in the total water head ratio (HT/P) decreases the discharge coefficient in all models, which is due to the increase in the Nappe interference and the local submergence. Also, increasing the number of cycles in labyrinth weirs has reduced its efficiency. The reason for this decrease is the impact of the issuing jets at the junction of the cycles and the flow disturbance over the weir. The comparison between triangular and circular weirs showed the better efficiency of triangular weirs. In addition, the results showed that the placement of the top of the cycle towards the upstream will cause a better performance in the weir. It seems that the low angle of the weir wall in the downstream with the channel wall causes the Nappe flow to collide with the channel wall and consequent local submergence will ultimately reduce the discharge coefficient.

Discharge Coefficient of Symmetrical Stepped and Triangular Labyrinth Side Weirs in a Subcritical Flow Regime

The labyrinth side weir structure is an optimal solution to regulate and divert excess flows across rivers, and irrigation and drainage channels when the opening length of the side weir is limited. Changing the geometry of the side weir is considered one way to improve its efficiency. The present study investigates the hydraulic effects of stepped labyrinth side weirs to increase their discharge capacity. To estimate the outflow over symmetrical stepped labyrinth side weir, the discharge coefficient needs to be determined. Normal triangular labyrinth side weir in one cycle mode has been modified by increasing the crest path using different steps. A total of 417 experiments were conducted on normal and stepped side weirs for various weir opening lengths, weir heights, internal head angles, and hydraulic conditions. The results were analyzed and compared. It was found that efficiency improved, and the discharge coefficient increased as the number of the steps decreased. Furthermore, the water surface profile becomes more uniform with decreasing number of steps. A lower number of steps, smaller head angle, and high weir length produce a higher discharge coefficient by approximately 15%–35% compared to a normal triangular labyrinth side weir; in addition, the Knope length decreases by approximately 40%–70% for the same effective length. Additionally, a reliable equation to estimate the discharge coefficient of the stepped labyrinth side weir was presented. The results of this study can be used to design side weirs with high hydraulic performance when the weir-included angle selected is small or there is a lack of space.

Combined Surface-Subsurface Stream Restoration Structures Can Optimize Hyporheic Attenuation of Stream Water Contaminants.

There is a design-to-function knowledge gap regarding how engineered stream restoration structures can maximize hyporheic contaminant attenuation. Surface and subsurface structures have each been studied in isolation as techniques to restore hyporheic exchange, but surface-subsurface structures have not been investigated or optimized in an integrated manner. Here, we used a numerical model to systematically evaluate key design variables for combined surface (i.e., weir height and length) and subsurface (i.e., upstream and downstream baffle plate spacing) structures. We also compared performance metrics that place differing emphasis on hyporheic flux versus transit times. We found that surface structures tended to create higher flux, shorter transit time flowpaths, whereas subsurface structures promoted moderate-flux, longer transit time flowpaths. Optimal combined surface-subsurface structures could increase fluxes and transit times simultaneously, thus providing conditions for contaminant attenuation that were many times more effective than surface or subsurface structures alone. All performance metrics were improved by the presence of an upstream plate and the absence of a downstream plate. Increasing the weir length tended to improve all metrics, whereas the optimal weir height varied based on metrics. These findings may improve stream restoration by better aligning specific restoration goals with appropriate performance metrics and hyporheic structure designs.

Experimental analysis of combined side weir-gate located on a straight channel

Flow measurement and control in open channel system for lateral flow is important to support the system management. The flow characteristics of combined side weir-gate are complicated due to changes in flow conditions along the side weir-gate section. Experimental investigation of the flow characteristics of both weir and sluice gates is crucial for predicting the flow through a combined side weir-gate structure. Although weir-gate structures are widely used for frontal flow in hydraulic structures, the same is not true for lateral flows. In this study, 650 laboratory tests were conducted to determine the flow characteristics of combined side weir-gate for subcritical flow, and the experimental results were analyzed to determine the effect of these characteristics and weir-gate geometry on discharge capacity. Interaction factor of combined side weir-gate is a function of the upstream Froude number, the ratio of gate opening to upstream flow depth, the ratio of distance between the top of the sluice gate and the weir crest to gate opening, the ratio of weir and gate length to upstream flow depth, and the ratio of weir and gate length to main channel width. Consequently, more discharge is passed through combined side weir-gate compared to side weir and sluice gates. The empirically derived equations for the discharge of combined side weir-gate show good compatibility with the experimental data.

Discharge Estimation over Piano Key Weirs: A Review of Recent Developments

The piano key (PK) weir has advanced over the labyrinth weir to increase the discharge capacity. Piano key weirs exhibit nonlinear flow behavior and are easy to place on the existing spillway or newly constructed dam with less base area. Various investigators are given equations to calculate the discharge coefficient for free and submerged flow conditions. The study focuses on reviewing the impacts of the PK weir geometry on the weir flow discharge coefficient, including weir length and height, upstream and downstream key widths, and apex overhangs. In this study, all possible aspects of PK weirs were briefly reviewed. From sensitivity analysis, it is observed that the discharge coefficient of the PK weir is more sensitive for the L/W dimensionless ratio followed by the B/P ratio. L is total length of the weir crest, W is width of the weir, B is total width of PK weir and P is height of the weir. This review paper is intended to serve as an accessible resource for hydraulic structures researchers and hydraulic engineering professionals alike interested in the hydraulics of PK weirs.

Experimental investigation of the discharge coefficient of labyrinth weirs with asymmetric cycles

This study investigated the discharge coefficient in asymmetric rectangular labyrinth weirs. A dimensional analysis was carried out which showed that the discharge coefficient is a function of dimensionless parameters, such as the ratio of asymmetric widths of left and right cycles (wL/wR), the ratio of the total hydraulic head to the weir height (Ht/P), and the weir length ratio (B/wavg). The experimental results for the discharge coefficient were found to decline as wL/wR increased or B/wavg decreased. For wL/wR = 1.19, the ratio B/wavg = 2.76 improves the discharge coefficient by nearly 12.7% compared to B/wavg = 3.1. For wL/wR = 1.42, the ratio B/wavg = 2.76 improves the discharge coefficient by nearly 34.2% compared to B/wavg = 3.1. For wL/wR = 1.70, the ratio B/wavg = 2.76 improves the discharge coefficient by nearly 30% compared to B/wavg = 3.1.

Estimating discharge coefficient of side weirs in trapezoidal and rectangular flumes using outlier robust extreme learning machine

Using the outlier robust extreme learning machine (ORELM) method, the discharge coefficient of side weirs placed on rectangular and trapezoidal canals was simulated for the first time in this study. The parameters governing the discharge coefficient of side weirs including Froude number (Fr), the ratio of the weir length to the main channel length (L/b), the ratio of the flow depth at the upstream of the side weir to the main channel width (y1/b) and the ratio of the crest height of the side weir to the flow depth at the upstream of the side weir (W/y1), the ratio of the weir length to the main channel width (L/y1), and the side wall slope parameter (m) were initially detected. Using the parameters governing, eight different input combinations were defined. By randomly selection approach, 65% of the data were considered to train the ORELM models and the rest of samples were applied to test them. The correlation coefficient, Nash–Sutcliffe efficiency coefficient, and Scatter Index for this model were calculated to be 0.937, 0.869 and 0.092, respectively. The results of sensitivity analysis indicated the ORELM model was more sensitive to the W/y1 and L/b than Fr and y1/b. The results of the ORELM model were also compared with the support vector machine optimized with genetic algorithm (SVM-GA) and extreme learning machine (ELM)) and four multiple linear regression models, with a better performance of the ORELM model. The ORELM models demonstrated a higher precision and correlation with experimental values.

Application of soft computing approaches to predict gabion weir oxygen aeration efficiency

ABSTRACT Aeration is a physical process through which air is brought into contact with water, and thereby both times of contact and contact area between water and air are enhanced. Gabion weirs are eco-friendly alternative structures having the least negative environmental impact. The paper examines the performance of the neuro-fuzzy, neural network, and Gaussian process regression (GPR) models in estimating the gabion weir oxygen aeration efficiency using the test data sets with regards to the evaluation indicators. The model utilizes non-dimensional inputs: Froude number, Reynolds number, the ratio of mean size to weir length, and porosity of gabion weir particles. The GPR with normalized poly kernel model having the highest value of correlation coefficient (CC), 0.9132, and value of root mean square error (RMSE), 0.392, outperforms all applied models and is followed by the neural network model with CC 0.8952 and RMSE 0.398. The neuro-fuzzy triangular shape with CC 0.8865 and RMSE 0.07576 is an equally performing model; nevertheless, all applied AI-based models are mostly performing well, but all mathematical models are exceptionally performing poorly except the nonlinear model with CC 0.8612 and RMSE 0.0029. To assess the relative relevance of input parameters on the output results, sensitivity and parametric analysis are also performed.

An iterative hydraulic design methodology based on numerical modeling for piano key weirs

Piano Key Weir (PKW) is a special type of overflow weir which provides an improved discharge capacity with its increased crest length. Increased discharge capacity makes this weir an attractive alternative in the rehabilitation of existing spillways. After the introduction of this new weir type, many experimental and numerical studies are conducted to understand the effect of the numerous geometrical parameters on the discharge capacity. However, empirical discharge formulas suggested by different researchers are not conforming to a unique expression mostly due to dependence on the experimental conditions from which they are derived. A numerical approach is used in the present study to investigate the dependence of discharge capacity of a PKW unit on several geometric parameters. Numerical models are developed and three-dimensional velocity fields are computed using FLOW-3D® software. Discharge efficiency of a PKW over an equivalent linear sharp-crested weir is evaluated within the practical range of parameters from 145 numerical solutions for 29 different PKW models. Numerically obtained data is used to form dimensionless expressions for the weir height and length as function of discharge efficiency which are proposed to facilitate an iterative numerical solution to meet the design requirements of a given project. This approach allows cost optimization while dimensioning the PKW for the required hydraulic capacity. The design procedure based on iterative numerical solutions is described and exemplified.

Microplastics in Combined Sewer Overflows: An Experimental Study

One of the main sources of microplastics inside surface waters is represented by combined sewer overflows (CSOs), involving severe risks for the environment. The entry of microplastics into water bodies also depends on the characteristics of sewer diversion structures used as flow control devices. In this work, an experimental investigation was carried out to evaluate the outflow of microplastic particles, consisting of different types of nylon fibers, from a side weir located on a channel with a rectangular section. A specific methodology was developed for the fiber sampling and outflow assessment after the tests were performed. For the tested configurations, an increase in fibers discharged up to 196.15% was measured as the water flow rate increased by 62.75%, combined with an increase in the side weir length up to 40% and a decrease in the crest height up to 20%. The size and weight of the different fibers showed a low impact due to their low inertia, and their motion was governed by the water flow. An empirical equation to evaluate the fiber outflow as a function of water flow rate and side weir geometric characteristics was also proposed and calibrated for the experimentally tested ranges of the dimensionless lateral water outflow Q* = 0.51–0.83 and of the dimensionless geometric parameter S* = 0.114–0.200. These first experimental results make it possible to carry out a preliminary assessment of the impact of CSOs in terms of microplastics spilled into water bodies.

Estimation of rectangular and triangular side weir discharge

ABSTRACT In this paper, a straightforward approach was applied for estimating the discharge of sharp-crested rectangular and triangular side weirs. The extensive experimental data (356 for rectangular side weir and 362 for triangular side weir) and the available data from other sources (171 for rectangular side weir and 145 for triangular side weir) were used for the analysis. The effects of approach Froude number Fr 1, ratio of weir height to upstream flow depth p/y 1, ratio of effective weir length to main channel width L/B, and ratio of effective weir length to upstream flow depth L/y 1 were studied. It was found that the parameters p/y 1, Fr 1, and L/B have a reciprocal effect on each other. Sensitivity analysis performed by using ANFIS model, showed that the relative discharge of the rectangular side weir is influenced by Fr 1, p/y 1, L/B, and L/y 1. Moreover, Fr 1 for triangular side weir and p/y 1 for rectangular side weir are the most effective parameters influencing the relative discharge. Meanwhile, L/y 1 has a secondary effect on the relative discharge of side weir. Based on dimensional analysis, new explicit equations for estimating the relative discharge for rectangular and triangular side weirs were presented. The results were also compared with previous studies. The capability of ANN, ANFIS, SVR, and GBRT methods was also evaluated in estimating the side weir relative discharge. The ANFIS model for rectangular side weir with MSE = 0.0011 and CP10% = 85.09, and SVR model for triangular side weir with MSE = 0.0011 and CP10% = 87.25 were found to be the superior models in estimating the relative discharge.

Prediction of discharge coefficients for broad-crested weirs using expert systems

ABSTRACT Broad crested weirs can be used to make discharge measurements in irrigation canals; the entrance of stepped weirs or chutes are sometimes designed as a broad crested weir structure. These structures are also sometimes used for the dam body. In this study, the Artificial Neural Network (ANN) and M5 model tree methods are used to predict discharge coefficients (Cd ) for broad crested weirs. The results from these two models are compared with nonlinear regression equations. Four series of data obtained from different rectangular broad crested weirs have been used and important dimensionless parameters have been defined. Results show that the ANN procedure is superior to the M5 model and regression approaches. The accuracy for ANN is quantified by R = 0.966 and RMSE = 0.038. All the three methods are able to provide a reasonable prediction for Cd ; the M5 model tree provides four linear equations that can be used to estimate Cd . The shape of the Cd contours shows that the effect of weir height (P) exceeds that of the weir length (L).

Energy Dissipation in Stilling Basins with Side Jets from Highly Convergent Chutes

Spillways with Highly Converging Chutes (HCCs) are a non-conventional alternative that can be applied to achieve a higher outflow capacity when the weir length exceeds the width of the valley at the toe of gravity or arch dams. This kind of spillway has been used in the past, but no general studies have yet been published. This article summarizes experimental research work aiming to increase the knowledge of the effect of some design parameters of HCCs on the energy dissipation in the stilling basin at the toe of the dam. As a comparison reference, we use the Type I stilling basins, widely known by the technical dam engineering community. The obtained results show that spillways with HCCs are a promising alternative to traditional designs, combining the ability to increase the weir length with a high capacity to dissipate energy through the impingement effect of the frontal and the side jets inside the stilling basin.

Experimental investigation of flow characteristics over asymmetric Joukowsky hydrofoil weirs for free and submerged flow

Weirs are one of the most common hydraulic structures used to regulate the upstream approach flow depth and measure the flow discharge. The hydrofoil weirs are a type of short-crested weirs that are designed based on the airfoil theory. These weirs have some merits compared to other types, such as a higher discharge coefficient, more stability, better submergence limiting condition, and lower fluctuations of the pressure and the free-surface profile. In the present study, experimental models of hydrofoil weirs with different relative eccentricities, cambers, angles of attack, and upstream slope angles are applied to investigate their hydraulic characteristics under free and submerged flow conditions. The longitudinal profiles of static pressure over different hydrofoil weirs are compared to circular-crested and ogee weirs. The results indicate that the maximum bed negative pressure belongs to the circular-crested weir, and the lowest bed pressure over the hydrofoil and ogee weirs are approximately the same. Applying a hydrofoil weir with an appropriate curvature and angle of attack instead of a circular-crested weir not only increases the structural weir height as well as the upstream water depth but also results in the lowest values of bed negative pressure, thereby reduces the potential of cavitation over the weir body, being safer hydraulic structures. The results also show that the discharge coefficient of hydrofoil weirs is greater than that of the broad- and short-crested weirs for the upstream approach flow depth relative to the weir crest to weir length h1/L > 0.12 and is greater than that of the ogee weirs for 0.35 < h1/L < 0.45. Furthermore, the derived relationships for the discharge coefficient, threshold submergence, and the discharge reduction factor due to submergence accurately predict the hydraulic characteristics of hydrofoil weirs compared to the available developed empirical relationships for these weirs and can be used efficiently for design purposes.

Experimental study of discharge coefficient of trapezoidal arced labyrinth weirs of widened middle cycle

Arced labyrinth weir is a certain type of nonlinear weirs with a very high discharge capacity. Thanks to the increased effective length and the ensuing increased discharge capacity of these weirs, they can be used in dam spillways and water regulating structures. This study focused on trapezoidal Arced labyrinth weirs (TALW) of widened middle cycle. Various experiments were performed to evaluate the effect on discharge coefficient of various geometric parameters, including the ratio of inside apex width of the end cycles to that of the middle cycle (w2/w1) and the ratio of the length of labyrinth weir (Apron) in flow direction to the width of the middle cycle (B/w1). Results of this study showed that with a decrease in w2/w1 from 0.42 to 0.30, discharge coefficient (Cd) would increase by 13–33%.

Experimental study of flow converging section side weir hydraulics

side weirs are used to control water levels as well as water diversion for various uses in canals and rivers. Due to the complexity of flow conditions in side weirs, in this study, in order to simplify the calculations and increase its efficiency, this structure was investigated in convergent channel conditions. To investigate this issue, different geometric parameters of weir and hydraulic currents were investigated. Based on the geometric parameters of the side weir, experimental scenarios were considered. Based on the scenarios, 5 side weir lengths, 4 side weir heights, and 3 downstream channel widths were considered as side weirs that were tested at different discharges. Due to the fact that different geometric and hydraulic parameters were assumed to be variable in these experiments, the effect of each on the structure was analyzed and solutions for selecting the optimal dimensions in the channel were introduced. Based on the experimental results, it was found that for a fixed upstream water height with a 19% reduction in the width of the downstream channel, the ratio of the flow deflection to the lateral channel increases by 30%. It should be noted that the change in the flow section by converging the passage channel causes the longitudinal profile of the water surface to have a minimum height fluctuation along the entire length of the structure.

Development of ANN model for discharge prediction and optimal design of sharp-crested triangular plan form weir for maximum discharge using linked ANN–optimization model

Abstract Triangular plan form weirs are advantageous over a normal weir in two ways. Within the limited channel width, use of such a weir increases the crest length and hence for a given head, increases the discharge and for a given discharge, reduces the head in comparison with a normal weir. In a previous study, researchers proposed an empirical equation to compute the discharge coefficient of a triangular plan form weir. The prediction error on the discharge coefficient was ±7% from the line of agreement. In the present study, an ANN model has been utilized to train randomly selected 70% data, with 15% tested and validation made for the remaining 15% data. The model predicts the discharge coefficient with a prediction error in the range of ±2.5% from the line of agreement, thereby decreasing the prediction error in Cd by 64%. Also, the sensitivity analysis of the developed ANN model has been performed for all the parameters (weir height, skew weir length and flow depth) involved in the study and the weir height was found to be the most sensitive parameter. Furthermore, the linked ANN–optimization model has been developed to find the optimal values of design parameters of a triangular plan form weir for maximum discharge.

Discharge Coefficients for Rectangular Broad-Crested Gabion Weirs: Experimental Study

Weirs are commonly used for making discharge measurements in irrigation canals. There are several types of weirs that are categorized based on their geometric shape or hydraulic properties. A gabion weir is a porous weir that can pass flow through its body in addition to the flow that passes over the weir. This study focuses on determining the discharge coefficients (Cd) for rectangular broad-crested gabion weirs using fabricated physical models. Dimensional analysis was carried out for finding the most effective parameters that govern the flow. Results show that the Cd of gabion weirs is 10.5% greater than that of similar solid weirs. In addition, the Cd for porous weirs in free flow conditions is 17.2% greater than that for submerged flow. For H/L>0.45 (where H is the water depth over the weir crest and L is the weir length) a porous weir acts similar to a solid weir and the effect of porosity (n) nearly vanishes. For a specified value of H/L, the ratio of submergence (Sr) for a solid weir is higher than that for porous weirs. Porous weirs with 50% porosity have lower values of Sr compared with solid weirs and weirs with lower porosities, of 45%, 41%, and 30%. Regression equations for the flow through gabion weirs were generated for free and submerged flow conditions. The derivations of equations were carried out using multivariable nonlinear regression and genetic programming (GP). Finally, a comparison of Cd in the present study with the other studies was carried out.

Prediction of the discharge of side weir in the converge channels using artificial neural networks

Considering the common use of side weirs in irrigation and drainage networks, estimation of the discharge of the side weirs has always given a consideration by water engineering researchers. Another issue about side weirs is the change in flow conditions in the weir and downstream channel. To optimize the flow conditions in the side weir, this structure is established in a converging channel to reduce the channel width and compensate the reduced discharge. The geometrical parameters assumed as variables in this study are: weir length, weir height, convergence angle and downstream channel width. About 248 experiments were performed. Three neural network models were used to estimate the discharge from the side weir. The model was constructed using MATLAB, and the dimensionless variables that were the geometrical and hydraulic ratios of the model were selected as input parameters. Four ratios were selected as inputs to the model to estimate the discharge coefficient and the discharge from the weir. Considering the outputs of the model, the neural-fuzzy networks have the least error compared to the other models, and this model estimates the discharge of side weir overflowing with 99.8% accuracy.