Weir Structures Research Articles

Experimental and numerical investigations of the mixing processes of pollutants at notched weirs in rivers

This study experimentally and numerically investigated the mixing processes at a notched weir to examine the relationship between the mass exchange coefficient and geo-hydraulic factors of notched weirs. Laboratory experiments on idealized notched weirs with variable notch spaces, notch heights, and hydraulic factors were performed to measure the flow field dynamics and depth-averaged concentration fields of the solute tracer. The experiment results demonstrated that flow separations occurred upstream of the notched weir. These flow structures controlled the horizontal storage zone and tracer mixing between the main flow and storage zone. The tracer cloud exhibited a longer retention time as the storage zone area increased. The normalized value of measured mass exchange coefficients by mean flow velocity, ke /Umean ranged from of 0.11 to 0.25, approximately one order larger than the values obtained in previous studies on lateral transient storage zones, such as lateral groin fields, and cavities, which implied that the notched weir in this study generated a storage zone with a fast exchange process and relatively weak storage effect. Numerical simulations with expanded geometric and hydraulic conditions revealed that the mass exchange coefficient was strongly correlated with the geometric factors, such as the notch space and height, and hydraulic factors, such as the Froude and Reynolds numbers. An empirical relationship applicable to rivers with notched weir structures under low-flow conditions (Fr < 0.1) was proposed based on the experiment and numerical results. The performance of the proposed empirical relationship showed a satisfactory level of R2 of 0.87. This relationship can be applied as a tool for estimating the mass exchange coefficient of notched weirs using easily measurable field data in rivers.

The Factors Affecting Stability and Durability of Flow Diversion Simple Weirs in Muchinga Province of Zambia

The effectiveness of simple weirs and the ability of rural farmers to construct durable weirs are still areas of concern in rural areas in Zambia. The objective of this study is to investigate the factors contributing to the varying levels of durability of the simple weir structures used for the diversion of river flows. This study was conducted in five districts where 33 simple weirs located in similar geographical zones were analyzed for their longevity. The research delved into catchment and climatic variables, as well as the social and psychological perception of simple weirs. This study conducted interviews with key informants who were familiar with the use of simple weirs in Muchinga Provinces between 26 December 2023 and 15 January 2024 using semi-structured questions. The findings of this study indicated that simple weirs constructed on relatively square-shaped catchments and narrow-shaped catchment areas were less vulnerable to damage and easy to operate and maintain. The study also found that climatic factors such as storm rainfall events had little impact on the operation and maintenance of these weirs in Muchinga province, as most sites are in the rainfall shadow while farmers’ views about the structures varied from site to site. Overall, planning is necessary for implementing small or large irrigation structures.

Spatiotemporal Variation Analyses of Water Quality, Fish Ecological Guilds, and the Longitudinal Connectivity in Musim Stream

The main objectives of this study were to analyze the spatiotemporal variations of water quality, fish ecological guilds and longitudinal connectivity in the weirs of Musim Stream. Fish were collected at 44 sites during spring and fall seasons for the analysis of trophic guilds, tolerance guilds, and the ecological stream health, based on FAI model. Total 33 species were observed in the stream and the dominant species were &lt;i&gt;Zacco platypus&lt;/i&gt; and &lt;i&gt;Squalidus qracilis majimae&lt;/i&gt;. Mean values of BOD and COD, as an indicator of organic matter pollution, showed high in the drought spring and low in fall (post-monsoon season). Also, TP showed same pattern with the BOD and COD pattern. The hierarchical clustering, based on the fish compositions, classified as three groups (up-stream, mid-stream and the down-stream). Based on the NMDS (Non-metric Multidimensional Scaling) analysis of fish abundance, high similarity was observed between S1-S5 sites, which were consistent with the results of hierarchical cluster analysis. Fish ecological guilds in the upper stream showed a high similarity between the insectivore and sensitive species, while in the middle and lower reaches, high similarity was found between the omnivore and intermediate species. Evaluations of longitudinal connectivity, based on the structural and hydrological characteristics of the weir, indicated all disconnections by the weirs, except for S15, in the spring. Stream ecological health, based on the FAI model, was significantly (&lt;i&gt;p&lt;/i&gt; &lt; 0.05, n=37) influenced by the height of overflow (&lt;i&gt;Hu1&lt;/i&gt;). Overall, our study suggests that the longitudinal connectivity, based on the weir structures, flow regime and fish swimming capacity, were blocked off by the weirs in the stream. The results provide valuable insights for securing river management strategies and served as the fundamental data for stream restoration in the future.

Ecological connectivity analysis based on the fish community in Jeongan Stream

This study focused on the longitudinal connectivity analysis, based on fish communities in the aspect of spatial variations of 34 sites from upstream to downstream. The Fish Assessment Index (FAI), based on ecological guilds and species composition, was applied to compare the ecological health among the sampling sites. The total number of 35 fish species, were sampled during the study period with dominant species of &lt;i&gt;Zacco platypus&lt;/i&gt; (35.4%) and &lt;i&gt;Zacco koreanus&lt;/i&gt; (11.8%). Cluster analysis showed that all sites were categorized as 4 distinct group communities (A, B, C, D). Non-metric multidimensional scaling analysis showed distinct difference between upstream (A, B) and downstream groups (C, D). Indicator Value Analysis (IndVal method), conducted to identify indicator species within each group, indicated that the species favoring upstream environments Rhynchocypris oxycephalus for the Group A and Iksookimia koreensis for the Group B. In contrast, the analysis indicated that the species with a preference for downstream habitats Pseudogobio esocinus for the Group C and Carassius auratus for the Group D. Ecological health, based on the FAI scores, showed a declining pattern toward the downstream, along with an increasing proportion of tolerant species and omnivores within the fish community. Overall these findings suggest the compositions of fish communities, as four groups, were modified by the weir structures and organic matter, nutrient pollutions.

Sedimentation issues of the Four Major Rivers Restoration Project in South Korea

In 2009, South Korea started a large multi-purpose water project on its four major rivers. The main purposes of the Four Major Rivers Restoration Project (FMRRP), which are directly related to water itself, were: (1) securing water resources to combat water scarcity; (2) reducing flood risks by riverbed dredging and reinforcing levees; and (3) restoring the river's environmental functions. Despite socio-environmental opposition, the project was completed in 2011. This article reviews the sedimentation issues raised during and after the FMRRP regarding technological developments and the lessons learned from the project. A total of five sedimentation issues raised directly from the project are reviewed in this article: (1) riverbed dredging and sediment redeposition; (2) tributary headcut; (3) riverbed scour downstream of the movable weir structures; (4) sedimentation management schemes; and (5) a near-prototype river experiment facility. Each issue is addressed by identifying and analyzing field data, developing new numerical models, and testing at a large-scale experiment facility. From this project, we have found that a comprehensive numerical technique is required to predict the sediment issues as mentioned above in a watershed-scale riverwork.

Optimised multi-objective design of weir structures

Diversion head works, also called weirs or barrages, are structures constructed across rivers or canals to store water or raise the water level. The design of diversion weir structures involves calculating the depth, length and thickness of the horizontal and sloping aprons and sheet pile cut-offs. The design parameters of a diversion weir structure, which have complex non-linear relationships, are traditionally determined using empirically derived recommendations and iterations to achieve structural stability against failures due to scour, uplift, sliding, piping and overturning. However, current design approaches do not explicitly explore the trade-offs between the many relevant design objectives and thus fail to reveal possibly superior designs. A multi-objective optimisation design approach for a diversion weir structure is proposed in this article. A free and open-source code that can be used as a design tool is also provided. The method is demonstrated on a stylised design problem. The results show that the method reveals solutions with diverse balances of stability metrics and cost, with the optimal relationships of parameter values of components also varying based on the relative cost of the construction materials for sheet piles and aprons.

Comprehensive Study for Engineering usage of Sustainable Concrete using Recycled Coarse Aggregates, Crumb Rubber and Steel Fibers

As per records of Transparency Market Research, yearly construction waste is expected to reach 2.20 billion tons by the year 2025. With such a large volume of construction and demolition trash, the 3R’s (Reduce, Reuse and Recycle) play a vital role in waste management. According to the EPA (Environmental Protection Agency), C&D garbage rose by 220 percent in metropolitan cities from 1990 to 2018. The present study focuses on usage of substitution by recycled coarse aggregate with natural coarse aggregates on the outskirts of major metropolitan centers, as well as crumb rubber, a waste created by tire waste disposal, to make the concrete more inexpensive and eco-friendlier. The study also supports the usage of crumb rubber waste that can be safely used for hydraulic structures with less load, such as weir structures or smaller check dams, while a 50 percent replacement of recycled coarse aggregate with natural coarse aggregate had the same strength as normal concrete, which is useful in sustainable concrete practices and can help reduce the generation of C & D waste. In this study, the concrete made up of using recycled aggregate is also mixed with steel fibers to enhance its workability.

Computation of energy dissipation across the type-A piano key weir by using gene expression programming technique

Abstract Energy dissipation across the weir and dam structures is a vital economic and technical solution for designing the downstream morphology of any hydraulic system. Accurately estimating the energy over any hydraulic system using traditional empirical formulas is tedious and challenging. Consequently, employing new and precise techniques still in high demand is crucial. In this study, the authors developed an empirical model for estimating the residual energy downstream of the type-A piano key weir (PKW) using gene expression programming (GEP) by considering six non-dimensional parameters: headwater ratio, magnification ratio, inlet to outlet width ratio, inlet to outlet key bottom slopes, inlet to outlet overhang portions and the number of cycles. The performance of the proposed models has been compared to empirical equations using the statistical factors coefficient of determination (R2), concordance coefficient (CC), and root mean square error (RMSE). The computed relative residual energy values using the proposed models are within ±10% of the observed ones. The proposed GEP model predicted the relative residual energy satisfactorily, with coefficients of determination of R2 = 0.978 for training, 0.980 for testing and root mean square errors (RMSE) of 0.032 and 0.029 for the training and testing datasets, respectively.

Gene expression programming for computing energy dissipation over type-B piano key weir

Computation of energy dissipation over weir (or spillway) structures is vital to solving numerous engineering problems, notably during floods. Therefore, an accurate estimation of the energy dissipation at the base of the spillway is essential. The spillways must be designed to spill large amounts of water at high efficiency with high structural performances without causing any damage to the structure or its surroundings. Energy dissipation over weir structures is difficult to predict using conventional formulas based on empirical methods. Consequently, new and accurate techniques are still highly demanded. In this study, Gene Expression Programs (GEP) were used to estimate the relative energy dissipation at the base of type-B Piano Key Weirs (PKWs) by taking three non-dimensional parameters into account: headwater ratio, magnification ratio, and the number of cycles. The performances of the GEP model were compared with empirical equations based on statistical factors coefficient of determination (R2), and root mean square error (RMSE). The computed values of the relative residual energy using the proposed models are within ±5% of the observed ones. Results indicate that the proposed GEP model predicted the relative residual energy satisfactorily with the coefficient of determination (R2 = 0.9979 for training, 0.9980 for testing) and root mean square error (RMSE) of 0.0099, 0.0092 for training and testing datasets, respectively.

Utilization of ANN technique to estimate the discharge coefficient for trapezoidal weir-gate

Abstract Developing and assessing the performance of water projects and irrigation networks is based on many factors, such as flow measurement. Weir and gate structures have been extensively utilized for flow measurement and to get rid of sediments. The process of modeling and estimating the coefficient of discharge in the weir is an essential part of hydraulic engineering. Recently the application of computer skills was adopted instead of traditional methods. In the present study, the artificial neural network (ANN) was adopted to estimate the coefficient of discharge for a combined weir that consisted of the trapezoidal weir and rectangular gate. For this purpose, the experimental data were collected and analyzed. The dimensional analysis was used to identify the effective dimensionless parameters related to the discharge coefficient. The developed ANN network structure was designed as 6-10-1 and adopted the default scaled conjugate gradient algorithm for training using SPSS V24 software. It was found that the proposed model with ten neurons was highly accurate in predicting the discharge coefficient. The sensitivity analysis was adopted to assess the performance of the ANN using different numbers of effective input parameters. Assessing five models, the ratio of upstream head to gate height (H/d), slope of trapezoidal angle (tan θ), and the ratio of distance between weir and gate and gate height (y/d) parameters are adequate for estimating the discharge coefficient compared to other parameters. ANN model with input parameters of H/d, h/d (h is the flow depth over the trapezoidal weir), b g/d (b g is the gate width), tan θ, b g/b (b is the total width of flume), and y/d shows reasonable accuracy with acceptable statistical indicators, coefficient of determination (R 2 = 0.87), relative error (RE = 0.096), and mean squared error (MSE = 1.86) for the discharge coefficient. The ANN model gave a good idea about which factors are more effective on the discharge coefficient, and the process of training the network is more accessible than the traditional method which represent the discharge coefficient by equation.

Experimental and numerical analysis of weir structures in open channel flows

Weirs are important water structures used to hold water in dams and canals and to safely transfer water from upstream to downstream. Due to these features, these structures, which have been used for years, have many different designs. In this study, a rectangular labyrinth weir and an inclined-bed rectangular weir were studied experimentally and numerically. The weir geometries used in the experiment were produced in a 3D printer and transferred to the numerical simulation with the same dimensions. The discharge and discharge coefficients corresponding to five different upstream heights obtained from the experiment and numerical simulation were obtained and the data were compared.

Seismic probabilistic risk assessment of weir structures considering the earthquake hazard in the Korean Peninsula

Seismic safety evaluation of weir structure is significant considering the catastrophic economical consequence of operational disruption. In recent years, the seismic probabilistic risk assessment (SPRA) has been issued as a key area of research for the hydraulic system to mitigate and manage the risk. The aim of this paper is to assess the seismic probabilistic risk of weir structures employing the seismic hazard and the structural fragility in Korea. At the first stage, probabilistic seismic hazard analysis (PSHA) approach is performed to extract the hazard curve at the weir site using the seismic and geological data. Thereafter, the seismic fragility that defines the probability of structural collapse is evaluated by using the incremental dynamic analysis (IDA) method in accordance with the four different design limit states as failure identification criteria. Consequently, by combining the seismic hazard and fragility results, the seismic risk curves are developed that contain helpful information for risk management of hydraulic structures. The tensile stress of the mass concrete is found to be more vulnerable than other design criteria. The hazard deaggregation illustrates that moderate size and far source earthquakes are the most likely scenario for the site. In addition, the annual loss curves for two different hazard source models corresponding to design limit states are extracted.

Water Budget Analysis Considering Surface Water–Groundwater Interactions in the Exploitation of Seasonally Varying Agricultural Groundwater

In South Korea, groundwater intended for use in greenhouse cultivation is collected from shallow riverside aquifers as part of agricultural activities during the winter season. This study quantified the effects of intensive groundwater intake on aquifers during the winter and examined the roles of nearby rivers in this process. Observation data were collected for approximately two years from six wells and two river-level observation points on the study site. Furthermore, the river water levels before and after the weir structures were examined in detail, because they are determined by artificial structures in the river. The structures have significant impacts on the inflow and outflow from the river to the groundwater reservoirs. As a result, a decline in groundwater levels owing to groundwater depletion was observed during the water curtain cultivation (WCC) period in the winter season. In addition, we found that the groundwater level increased owing to groundwater recharge due to rainfall and induced recharge by rivers during the spring–summer period after the end of the WCC period. MODFLOW, a three-dimensional difference model, was used to simulate the groundwater level decreases and increases around the WCC area in Cheongwon-gun. Time-variable recharge data provided by the soil and water assessment tool model, SWAT for watershed hydrology, was used to determine the amount of groundwater recharge that was input to the groundwater model. The groundwater level time series observations collected from observation wells during the two-year simulation period (2012 to 2014) were compared with the simulation values. In addition, to determine the groundwater depletion of the entire demonstration area and the sustainability of the WCC, the quantitative water budget was analyzed using integrated hydrologic analysis. The result indicated that a 2.5 cm groundwater decline occurred on average every year at the study site. Furthermore, an analysis method that reflects the stratification and boundary conditions of underground aquifers, hydrogeologic properties, hydrological factors, and artificial recharge scenarios was established and simulated with injection amounts of 20%, 40%, and 60%. This study suggested a proper artificial recharge method of injecting water by wells using riverside groundwater in the study area.

Experimental analysis of flow characteristics over hydrofoil weirs

The rounded crested weirs are commonly used for discharge measurements and this overflow structures have advantages such as stable overflow pattern and good accuracy. Hydrofoil weirs with streamlined properties are similar to the ogee weirs and can be used as a spillway profile. The hydraulic features of flow over hydrofoil weirs created by the NACA0018, NACA0021 and NACA0024 hydrofoil geometry placed in an open channel are investigated experimentally under free-flow conditions. The velocity field of hydrofoil weir flows are measured by one-dimensional Laser Doppler Anemometer. Experimental velocity profiles are measured along the middle section of the channel, especially around the weir structure, to determine the boundary layer separation. According to the determination of optimum weir structure the free surface profiles, pressure distributions on weir surfaces, experimental discharge coefficients and head losses over weir structures are determined for different structure and flow conditions. Pressure distributions over the hydrofoil weir are presented. In addition, the relationships between discharge coefficient (Cd) and flow rate (Q), specific total head (H/R), relative weir height (P/H), relative total head (H/P) and dimensionless total energy head upstream of the weir (H/L) are investigated.

Weirs Control Phosphorus Transfer in Agricultural Watersheds

Sediments may act as a source or sink of ions from water, especially phosphorus (P). After the erosion process, the challenge is to retain suspended sediments inside the watershed area. We hypothesize that weir structures may mitigate P transfer from agricultural soils to aquatic systems. To test this, the present work aimed to evaluate P chemical fractions present in bottom sediments retained in the water reservoir of weirs built in two intensive agricultural watersheds and we discuss the sink/source behavior of these sediments. Samples of bottom sediments were collected from 12 reservoirs of weirs in two smalls Brazilian watersheds. Chemical P fractionation including adsorption and desorption kinetics was performed. Total P varied from 398 to 958 mg kg−1. The easily and potentially desorbed phosphorus were correlated with the clay content and the concentrations of Fe, Mn, and Al, extracted by ammonium oxalate and dithionite-citrate-bicarbonate solutions, which are the carriers of highly reactive functional groups with phosphate. Bottom sediments have high maximum adsorption capacity under unrestricted phosphorus supply condition, while under natural condition (low anthropogenic pressure), the sediments were not saturated and therefore low desorption occurred. Only 1.34% and 7.75% of total P was in readily and potentially bioavailable P forms. The bottom sediments accumulated in reservoirs from anthropogenic areas acted as P source to water, while those from preserved areas (natural pasture or riparian forest) acted as sink of P from water. The storage of water and sediment contaminated with P in reservoir of weirs may be an efficient and temporary practice to mitigate the transfer of P to watercourses.

The evaluation of the effect of nappe breakers on the discharge capacity of trapezoidal labyrinth weirs by ELM and SVR approaches

The labyrinth weir is one type of overflow design used to direct and transfer water in open channels and to provide both routine flow and flood passage over dam spillways. Labyrinth weirs are primarily used at sites where the available spillway width is limited. Due to the increase in crest length, a labyrinth weir provides an increase in discharge capacity relative to conventional weir structures. It is important that the discharge coefficient be accurately represented to ensure appropriate and economical design. The discharge coefficient of trapezoidal labyrinth weirs (TLW) is estimated by using extreme learning machines (ELM) and support vector regression (SVR) techniques in this study. Additional discharge coefficient prediction models have been developed for applications that include the use of nappe breakers (NB). These are frequently included in the design as a mechanism to reduce the impact of vibrations and oscillations on these weirs. A total of 1128 test runs for discharge coefficient measurements of TLW with/without NB were performed in the present study. The statistical criteria used for the evaluation of the performance of models are Mean Absolute Error (MAE), Root Mean Square Error (RMSE), Root Relative Squared Error (RRSE), Mean Absolute Percentage Error (MAPE) and Determination Coefficient (R2). Results of this investigation suggest that the models using Extreme Learning Machines (ELM) and Support Vector Regression (SVR) methods are successful in modeling the discharge coefficient of TLW with/without NB. The best correspondence between model and observation occurred using the ELM model; this resulted in an RMSE for the TLW with/without NB of 0.0188 and 0.0158, respectively.

Blast Responses and Vibration of Flood‐Defense Structures under High‐Intensity Blast Loadings

This study presented the blast behavior of flood‐defense structures subjected to high‐intensity loadings such as blast shock waves. In order to understand the blast behavior of weir structures, PHAST program was used to predict blast loadings in consideration of material reactivity and congestion levels. Environment factors such as weather data and atmospheric parameters were also considered in this study. Then, nonlinear dynamic analyses were performed using the ABAQUS platform to evaluate structural responses and blast vibration of concrete weir structures subjected to various types of blast loadings, due to uncertainties of the magnitude and durations of blast loads as a function of distance from the explosion. It was shown that the blast damage to concrete weir structure was significantly influenced by congestion levels or material reactivity. Also, the stress concentration under blast loading was observed at the connection area between the concrete weir body and stilling basin.

Predication of discharge coefficient of cylindrical weir-gate using adaptive neuro fuzzy inference systems (ANFIS)

Settlement of sediments behind weirs and accumulation of materials floating on water behind gates decreases the performance of these structures. Weir-gate is a combination of weir and gate structures which solves them Infirmities. Proposing a circular shape for crest of weirs to improve their performance, investigators have proposed cylindrical shape to improve the performance of weir-gate structure and call it cylindrical weir-gate. In this research, discharge coefficient of weir-gate was predicated using adaptive neuro fuzzy inference systems (ANFIS). To compare the performance of ANFIS with other types of soft computing techniques, multilayer perceptron neural network (MLP) was prepared as well. Results of MLP and ANFIS showed that both models have high ability for modeling and predicting discharge coefficient; however, ANFIS is a bit more accurate. The sensitivity analysis of MLP and ANFIS showed that Froude number of flow at upstream of weir and ratio of gate opening height to the diameter of weir are the most effective parameters on discharge coefficient.

Pressure fluctuations on underflow gates of weirs due to upstream vortex generation

Weir structures with underflow gates are used in channels, rivers or reservoirs to control water levels, such as keeping constant upstream water level. Designing control structures is a sensitive task, as their reliability influences not only the safety of the weir structure but also of up and downstream structures or settlement areas vulnerable to flooding. Further, during extreme events not only the ultimate limit state but also the serviceability of the control structure has to be assured, as the flood events are regulated through these structures. The scarcity of extreme events causes limited experience of gate operation during those conditions. Various hydrodynamic effects determine the load distribution and dynamic loading of the gates. Additionally different water levels and gate positions cause a large variety of load cases. Within this paper the horizontal hydrodynamic load influenced by vortices forming upstream of low head gates with underflow is investigated. The results of a hydraulic model test for a specific combination of gate position and upstream water level are given as mean pressure, extrema of pressure amplitudes and power spectral density, as commonly used as input data for stochastic design approaches.

Simulation-based optimization of in–stream structures design: bendway weirs

Bendway weirs are one of the most practical in–stream rock structures utilized to protect the outer bend of meandering streams and rivers from erosion. We present development of a simulation-based paradigm for effective design of bendway weir structures to enhance meandering stream bank stability and control lateral migration. To do so, we employ the St. Anthony Falls Laboratory Virtual StreamLab (VSL3D) code to elucidate the flow and sediment transport phenomena induced by interaction of flow, mobile bed, and in–stream structures in large rivers under prototype conditions. We carried out numerous numerical experiments to systematically simulate various arrangements of bendway weir in two river test-beds and gaining insights into the physical mechanisms via which such bendway weirs modify turbulent flow, sediment transport and scour processes. The so-gained physical insights are then taken into account to develop a set of practical physics-based design criteria for optimal placement of bendway weirs in large rivers.