Overflow Weir Research Articles

Large-Scale Performance Evaluation of Various Woven Silt Fence Installations under Nebraska Highway Conditions

Sediment barriers are used on construction sites to protect downstream waterbodies from the impacts of sediment-laden stormwater runoff. Although ubiquitous on construction sites, many sediment barrier practices lack performance-based testing to determine effectiveness and treatment mechanisms, with previous evaluations being limited to conditions local to the Southeastern U.S., with conditions in other regions remaining untested. Testing was conducted to determine the effectiveness of woven silt fence barriers and provide structural improvements to common installation methods. Testing was conducted using a large-scale sediment barrier testing apparatus at the Auburn University—Stormwater Research Facility. The results from testing indicate that Nebraska DOT standard silt fence installations can be improved to reduce the risk of structural failures such as undermining, complete installation failure, slow dewatering, and overtopping. To improve structural performance, four modifications (a 15.2 cm [6 in.] offset trench, wooden posts, a dewatering board with an overflow weir, and a dewatering board with an overflow weir with adjusted post spacing) were tested. On average, 83% of introduced sediment was retained behind the tested barriers. The water quality results across the testing of standard and modified installations indicated that stormwater treatment was due to sedimentation within the impoundment formed by silt fence installations and not filtration through geotextile fabric.

Downstream migration and hydropower dam passage of a Danubian cyprinid, Rutilus meidingeri, at the Seeache River, Austria

Downstream passage at a hydroelectric power plant of pearlfish (Rutilus meidingeri), a cyprinid species endemic to the Danube catchment, was examined. Forty pearlfish were trapped in the fish pass during their upstream migration, tagged with telemetry transmitters and subsequently released to the upstream section of the weir. The tagged fish were monitored to determine their descending behaviour and ability to overcome the obstacle through three possible corridors: a bypass channel, the overflown weir, and a vertical slot fish pass. Pearlfish used the entire 2.7 km of the river by successfully migrating further upstream and also by descending past the obstacle back to Lake Attersee through the bypass channel (65 %), and the weir overflow (35 %). No fish utilised the fish ladder as a descent corridor, even though 82 % of the fish were registered in the vicinity of the entrance to the facility. Apart from the unfavourable positioning of the fish pass for downstream migration, the discharge conditions proved to be decisive for the choice and availability of the descent corridor as well as the behaviour during descent. Significant delays in power plant passage occur both in the forebay and at the used corridors. Even if the ability to find corridors and the passability of adult pearlfish can be proven, further measures appear to be necessary for the safe migration and protection of the endangered species.

Aeration strength analysis of overflow weir in siphon well based on numerical simulation of water–air two‐phase flow

AbstractThe phenomenon of water aeration is serious after the overflow weir in the siphon well at the cooling water circulation system of coastal power plants. At present, designing special hydraulic structures is an effective way to reduce the intensity of aeration. In this paper, three engineering structure schemes were designed, and the three‐dimensional Realizable k–ε turbulence model was used. The volume of fluid method was introduced to capture the free water surface, and the unstructured grid was used to construct the two‐phase turbulent flow field. The aeration concentration and pressure distribution, obtained by numerical simulation, were basically consistent with the physical model test results. The results showed that the flow field at the orifice plates of cases 1 and 2 changed drastically, and the turbulent kinetic energy downstream of the orifice plate decreased with the increase of the number of holes. As for case 3, it showed that the high‐speed water flow fell into the water cushion pool, tumbling and sucking up a lot of air, and the turbulent kinetic energy and Reynolds stress were significantly greater than the other two cases. The hydraulic structure changed the cavitation characteristics of the downflow water, and the sequence of aeration concentration of the horizontal section was case 3 > case 1 > case 2. The aeration concentration was only 9.18%–17.86% in case 2. The aeration concentration at stable time is expressed as a function of the relative water depth y/y90 and the turbulent diffusion coefficient D. The distribution formula of aeration concentration was established, and its validity was verified by literatures. The results of this study will provide a certain reference for in‐depth analysis of water–air mixing motion characteristics, and simultaneously, it will have a guiding significance for the design of siphon well defoaming engineering.

Assessment of interfacial turbulence treatment models for free surface flows

The modelling of complex free surface flows is challenging due to the mobility and deformability of the interface and air entrainment characteristics, which are highly affected by turbulence. With the framework of Reynolds averaged Navier–Stokes (RANS) models and the volume of fluid (VOF) method, turbulence quantities at the air–water interface tend to be over-estimated. In this study, interfacial turbulence treatment methods including the buoyancy modification model based on the simple gradient diffusion hypothesis (SGDH) and Egorov’s turbulence damping model are investigated. Furthermore, due to the unconditionally unstable characteristics of the standard k-ε turbulence model, the stabilized k-ε turbulence model is applied as a comparison. The turbulence attenuation performance using different interfacial turbulence treatment methods in the vicinity of the interface is compared and discussed for stratified flows and free overflow weirs for aerated and non-aerated nappe scenarios. The turbulence quantities and free surface profile under different flow conditions are validated against experimental data and an analytical model. The results show that for free surface waves, both the SGDH model and the turbulence damping model give strong improvements in turbulence production compared with the standard k-ε model. The SGDH model augments the turbulence kinetic energy (TKE) in the unstable stratification, leading to unphysical behaviour for the partially dispersed and separated flow.

The Overshot Gate as a Flow-Measuring Device

The overshot gate is a commonly used adjustable overflow weir for regulating the upstream water level in open channels. The amount of gate movement is proportional to the water level change. However, to effectively manage the water flow, it is also important for operators to accurately measure the flow rate in the channel. This study examines an overshot gate installed at the end of a laboratory flume to estimate the flow rate under various free flow conditions. This study investigates different gate angles ranging from 9.6° to 90° to evaluate their impact on the flow properties and the discharge coefficient. The analysis of the results indicates that the maximum flow rate values can be achieved with gate inclinations from 15.5° to 47.2° with relatively lower head; the inclined alignment of the gate decreases the effective gate height which consequently increases the gate efficiency. The use of the overshot gate is advantageous over the normal gate when channel depth is limited and higher discharge is required at relatively lower head. In this study, at the highest gate inclinations, the water surface is significantly stable having the lowest values of the approach Froude number. In addition, the head to gate height ratio decreases with raising the gate due to the reduced vertical contraction of the channel. Finally, this paper proposes an empirical equation for estimating the discharge coefficient based on the gate inclination, which demonstrates good accuracy in the specified range.

Modelling the hydraulic characteristics of diaphragm fishways and the effects on fish habitats

Diaphragm fishways are often used in fishway engineering construction. Although there are an increasing number of new types of fishways, other types of diaphragm fishways can be derived from the combination or evolution of the following three basic types of fishways: vertical slot, overflow weir and orifice. To compare the hydraulic characteristics of different foundation types of fishways, the operations of vertical slot fishways, overflow weir fishways and orifice fishways are calculated by numerical simulation, and we comprehensively compare the flow field characteristics and application scenarios of various types of fishways from the two dimensions of hydraulic characteristics and application characteristics. This paper analyses the hydraulic characteristics of the flow field, such as velocity distribution and turbulent kinetic energy, and analyses the application characteristics of the fishway from the aspects of applicable flow, favourite swimming speed range, explosive swimming speed, fish passing position, and the matching characteristics of typical target fish. It is concluded that the vertical slot fishway can be widely applied to different target fish species due to its own advantages, such as less impact from environmental conditions. The characteristics of the overflow weir fishway and orifice fishway need to be analysed in combination with the hydraulic characteristics of the fishway, the swimming ability of the target fish species and the natural environmental conditions.

Effects of ecological restoration on water quality and benthic macroinvertebrates in rural rivers of cold regions: A case study of the Huaide River, Northeast China

Various human activities can damage the structure of rural rivers ecosystems and reduce their self-purification capacity. In Northeast China, the cold climate also poses serious challenges to river restoration. What types of restoration technology should be adopted and what impacts the restoration project will bring, in terms of river ecological function improvements, should be further discussed. To investigate the effects of ecological restoration projects and different restoration measures on water quality and benthic macroinvertebrates of rural rivers in cold regions in Northeast China, benthic macroinvertebrates and 10 indicators of water quality including ammonium (NH4+-N), nitrate (NO3–-N), total nitrogen (TN), total phosphorus (TP), chemical oxygen demand (COD), dissolved oxygen (DO), water temperature (Tem), pH (pH), electrical conductivity (EC) and chlorophyll-a (Chla) were monitored. We analyzed the temporal and spatial changes of benthic macroinvertebrates and 6 typical water quality indicators including NH4+-N, NO3–-N, TN, TP, COD and DO, which were collected in 4 seasons at 7 typical river sections. The Water Quality Index (WQI) was used to evaluate the seasonal and spatial variation of water quality during monitoring period, and a new WQImin model consisting of six crucial parameters, i.e., pH, DO, NH4+-N, TN, TP and COD, was established by principal component analysis. The results showed that the ecological restoration project enhanced the self-purification capacity of the river, and increased diversity of benthic macroinvertebrates. The maximum removal rates of the main pollution indicators NH4+-N, NO3–-N, TN, TP and COD were 96.49 %, 43.92 %, 49.69 %, 8.3 % and 25.95 %, respectively. The maximum increase rates of DO and benthic macroinvertebrates diversity were 77.96 % and 310.9 %, respectively. The operation effect of the restoration project had an obvious seasonal effect, with the best effect during the spring and summer. The project still has good repair effect in winter. In terms of water purification, the effect of the overflow weir combined with aquatic organisms was better than that of the single overflow weir in the river channel. There was the best effect of the engineering measures in summer. The ecological restoration project can improve the river water quality and the benthic macroinvertebrates conditions. Compared to before the restoration, WQImin values increased 168.81 % and 44.21 % in winter and summer, respectively, and Shannon index increased 6.57 % and 41.67 % in summer and autumn, respectively.

Local Scour at Triangular Labyrinth Side Weirs Located on an Alluvial Channel

The studies on labyrinth side weirs have received considerable attention in existing literature. A mobile bed, which causes significant morphological bed changes, can be induced by the side overflow weir. In this study, the local scour depths that occur near a triangular labyrinth side weir at a 90° angle in a straight channel with an alluvial bed were experimentally examined under steady flow conditions with free overflow of the weir. Based on a dimensional analysis applied according to the parameters of the study, it was determined that dimensionless equilibrium scour depth is dependent on the approach flow intensity, dimensionless side weir crest height, dimensionless median grain size, dimensionless side weir opening, and dimensionless volumetric amount of upstream sediment feed under live-bed scour conditions. For different combinations of weir opening length and weir height, data for a set of 81 runs were obtained. The results show that an increase in weir crest height results in a decrease in dimensionless maximum scour depth. In the clear-water scour experiments, sediment deposits were observed downstream of the weir. In the live-bed scour experiments, the dimensions of the scours and sediment deposits that occurred upstream and downstream of the weir exhibited periodic changes. Good consistency was attained in the developed empirical equations between the calculated and measured values of the equilibrium scour depth.

A New Concept of Frontal Migration System for Fish ‒ for Overflow Weirs and River Sills

Abstract In this paper we present a new frontal migration system for fish which could be used for overflow weirs and river sills. Since movement of fish is the most crucial thing in the healthy river environment fish passes are necessary to predict in any place where hydraulic structures are designed or any river engineering works are applied in the river channel. Thus in our paper we are giving a proposal of a new fish migration system when any river cross section weirs, sills or other low head hydraulic structures are planned. We hope our system would be built one day proving the advantage of using it.

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.

A hybrid gene expression programming model for discharge prediction

The head–discharge relationship of an overflow weir is a prerequisite for flow measurement. Conventionally, it is determined by regression methods. With machine learning techniques, data-driven modelling becomes an alternative. However, a standalone model may be inadequate to generate satisfactory results, particularly for a complex system. With the intention of improving the performance of standard gene expression programming (GEP), a hybrid evolutionary scheme is proposed, which is coupled with grey system theory and probabilistic technique. As a gene filter, grey relational analysis (GRA) eliminates noise and simulated annealing (SA) reduces overfitting by optimising the gene weights. The proposed GEP-based model was developed and validated using experimental data of a submerged pivot weir. Compared with standalone GEP, the GRA–GEP–SA model was found to generate more accurate results. Its coefficients of determination and correlation were improved by 3.6% and 1.7%, respectively. The root mean square error was lowered by 24.8%, which is significant. The number of datasets with an error of less than 10% and 20% was increased by 15% and 12%, respectively. The proposed approach outperforms classic genetic programming and shows a comparative error level with the empirical formula. The hybrid procedure also provides a reference for applications in other hydraulic issues.

Chance‐constrained model predictive control a reformulated approach suitable for sewer networks

AbstractIn this work, a revised formulation of chance‐constrained (CC) model predictive control (MPC) is presented. The focus of this work is on the mathematical formulation of the revised CC‐MPC, and the reason behind the need for its revision. The revised formulation is given in the context of sewer systems, and their weir overflow structures. A linear sewer model of the Astlingen benchmark sewer model is utilized to illustrate the application of the formulation, both mathematically and performance‐wise through simulations. Based on the simulations, a comparison of performance is done between the revised CC‐MPC and a comparable deterministic MPC, with a focus on overflow avoidance, computation time, and operational behavior. The simulations show similar performance for overflow avoidance for both types of MPC, while the computation time increases slightly for the CC‐MPC, together with operational behaviors getting limited.

Modeling CO2, H2S, COS, and CH3SH Simultaneous Removal Using Aqueous Sulfolane–MDEA Solution

In this study, a rate-based absorption model coupled with an improved thermodynamic model was developed to characterize the removal of acid components (CO2 and H2S) and organic sulfur (COS and CH3SH) from natural gas with an aqueous sulfolane–MDEA solution. First, the accuracy of the thermodynamic model was validated by comparing the calculated partial pressure of CO2, H2S, and CH3SH with those of the experimental data reported in the literature. Then, the industrial test data were employed to validate the absorption model and the simulation results agreed well with the experimental data. The average relative errors of the removal rates of CO2, COS, and CH3SH are 3.3%, 3.0%, 4.1%, respectively. Based on the validated coupled model, the total mass transfer coefficient and mass transfer resistance of each solute component at different column positions were analyzed. The effects of the gas–liquid ratio, overflow weir height, and absorption pressure on the absorption performance of each component were studied, and the influence of the acid component concentration in the feed gas on the removal efficiency of methyl mercaptan (CH3SH) was also discussed. It is found that the improved absorption model can better characterize the absorption performance and be conducive to the optimal design of the absorber column.

Performance assessment of a constructed wetland using a numerical modelling approach

Water samples were collected from a constructed wetland in Armstrong Creek, Geelong, for eight storm events. For each sampling, a single surface sample was collected at the deepest point of five equidistant transects across the wetland in the 12, 36 and 60 h following the storm events. The samples were tested for total suspended solids (TSS), total nitrogen (TN) and total phosphorous (TP). The results from the five transects were averaged and used to develop an empirical exponential decay model for the wetland. The wetland model was integrated within a catchment model based on the 1-D Stormwater Management Model (PCSWMM), which estimates the runoff from the contributing catchment into the wetland. The catchment model was calibrated/validated using water quality data collected from 8 storm events and flow data measured over a period of 22 months at sites located in Geelong. The catchment model was validated against water level measurements in the wetland showing good agreement with a correlation coefficient of 0.78 (p < 0.05). The wetland water quality model was validated against water quality data obtained from field sampling with correlation coefficient of 0.749 (p < 0.05), 0.491 (p < 0.10) and 0.856 (p < 0.05) for TSS, TN and TP respectively. A full year simulation was run using rainfall obtained for 2018 (assumed to be a typical year) to assess wetland performance. The model results show that annual loads (kg/yr) retained were 66%, 55% and 50% for TSS, TN and TP, respectively. These results exceed the design retentions of 45% for TP and TN, but not the 80% required for TSS as stipulated by the Victorian Stormwater Quality Objectives (2017). Further modelling, increasing the detention volume by raising the overflow weir crest elevation by 0.5 m resulted in an additional 6% retention in TSS. This is still insufficient to meet the 80% target. The main conclusion of this study is that through the proposed combined sampling and modelling approach, the annual wetland pollutant treatment levels within the constructed can be accurately identified. As water quality assets are designed based on annual treatment levels, this approach provides a cost-effective method of appraising wetland performance.

Large-scale hybrid accidental urban wetland for polluted river purification in northern China: Evidence and implications for urban river management

Hybrid accidental urban wetlands (HAUWs) are expected to be a potential low-cost and highly efficient alternative means of minimizing pollutant loads from municipal areas as compared to the single-stage system being used. These unexpected HAUWs are created not through deliberate restoration, but as a result of water infrastructure decisions by local government. However, information on the long-term purification efficiency of large-scale HAUW improving eutrophic urban rivers is largely unexplored. An in-situ HAUW system consisting of a rubber dam, detention pond, accidental urban wetland, and overflow weir was evaluated at the field-scale for the purification of a eutrophic urban river in Zhangjiakou City, Hebei Province. The results for seven months of operation demonstrated that the effluent TP and NH4-N in the HAUW system could comply with the Grade III of Chinese National Surface Water Quality Standards. Average removal efficiencies for TN, NH4-N, NO3-N, TP, and PO4-P in the summer–autumn period of 52.6, 65,8, 56.6, 51.4, 58.2 and 88.3%, respectively, were recorded. These removal efficiencies were 59.4, 61.5, 65.6, 57.1, 59.4 and 65.7% higher than the respective values in the spring period. Furthermore, removal rates of nutrients were highly sensitive to temperature and showed seasonal trends. Further analysis showed that, with the application of the HAUW system, a total of 92.1, 69.5, 57.3, 37.8, 33.2, 12.4, 14.5, 7.3, 3.4% removal of Al, Mn, Cd, Pb, Zn, Ni, Fe, Ni, and As was achieved. Mean removal rates of TN, NH4-N, NO3-N, TP, TDP, PO4-P in the summer–autumn period were 2- 5 times higher than in those recorded in the early spring period. These results suggest that a variety of contaminant elimination mechanisms were offered by the HAUW, including enhanced hydraulic resistance, sedimentation, plant assimilation, microbial biofilm growth on roots’ surface and the HAUW design. Overall, this study demonstrated that the monitored HAUW could be another feature of the urban landscape that could help minimize pollutant loading to surface urban water bodies. This function is especially true in warm periods, in a similar way as natural wetlands or purposely built constructed wetlands. Nonetheless, managing these accidental treatment systems to maximize pollutant dissipation in the long-term would necessitate appropriate management strategies.

Sustainable Improvement of Water Quality in Urban River Network by Rotating Overflow Weir—Case Study of Changzhou City in China

Water diversion is a practical and commonly used approach to improve the water quality of rivers in urban plains in China. This paper researches using rotating overflow weirs as the primary engineering solution to facilitate water diversion and improve the water quality of the river network in urban plain area of Changzhou, including hydrodynamic modeling, field tests, and application. The water diversion scheme, including clean water source, water transfer paths, quantity, and rate, was designed based on its current terrain and river systems. The Yangtze River was selected as a high-quality water source, and its two tributaries were utilized as clean water paths. Four rotating overflow weirs were proposed to create three stages of hydraulic gradient. Clean water can flow naturally and orderly in the researched urban river network without pumps. The required clean headwater level and clean water distributions were modeled hydrodynamically. Four temporary weirs were constructed at design locations to conduct field tests. And the water diversion scheme and its water quality improvement had been verified by field tests. Afterward, four permanent rotating overflow weirs were built. Currently, the monitoring results show the design water transfer scheme reaches expectations. The flow velocity in most rivers has been increased to 7cm/s from standstill in Changzhou's main urban plain area. The composite water quality of 93% river cross-sections monitored has been improved from Class V to Class Ⅲ and all have been improved to Class IV and above.

Modeling and analysis of heat transfer in submerged combustion vaporizer under supercritical pressure

Submerged combustion vaporizer (SCV) is widely used as a device to vaporize liquefied natural gas (LNG) stored in cryogenic state, which is effective in peak shaving and emergency response in LNG vaporization stations and receiving terminals. In this paper, a heat transfer calculation model of SCV based on numerical calculation is established and its accuracy is verified by a practical case. Based on this model, the applicability of different heat transfer models inside tube to SCV heat transfer is studied, among which the deviation of Petukhov model is the smallest, which is 0.38%. The increase of gas holdup and fouling thermal resistance inhibits the heat transfer to some extent, so it is necessary to increase the water bath temperature to make up for the lack of heat transfer coefficient under high relative load. In terms of agitating the water bath more fully and reducing the gas holdup inside overflow weir, the effect of 0.090 flue gas tube opening ratio is better than 0.022. The application of this calculation model can provide theoretical reference for heat transfer analysis and optimal design of SCV.

System for controlled distribution of non-demand-covering water availability: concept, design and modelling

Abstract This paper presents a novel water supply system to distribute limited water resources with varying quantity. The system enables a controlled, planned and, thus, fair distribution of the water availability independently from the consumption patterns. The system input is transported by gravitation through a branched pipe system to decentralised storage tanks. Each storage tank is allocated to a supply unit which comprises several consumers and, possibly, distribution structures connecting the consumers and the tank. At every junction the water is divided by a distribution tank with several chambers that are separated by weir overflows. Water that is not consumed is redistributed in the system automatically. The concept, the components, planning criteria and system design as well as the system modelling are described within the paper. The application of the solution in a supply area located in northern Vietnam is outlined.

Hydraulic modeling of combined sewers overflow integrating the results of the SWMM and CFX models.

This study proposes a methodology for the calibration of combined sewer overflow (CSO), incorporating the results of the three-dimensional ANSYS CFX model in the SWMM one-dimensional model. The procedure consists of constructing calibration curves in ANSYS CFX that relate the input flow to the CSO with the overflow, to then incorporate them into the SWMM model. The results obtained show that the behavior of the flow over the crest of the overflow weir varies in space and time. Therefore, the flow of entry to the CSO and the flow of excesses maintain a non-linear relationship, contrary to the results obtained in the one-dimensional model. However, the uncertainty associated with the idealization of flow methodologies in one dimension is reduced under the SWMM model with kinematic wave conditions and simulating CSO from curves obtained in ANSYS CFX. The result obtained facilitates the calibration of combined sewer networks for permanent or non-permanent flow conditions, by means of the construction of curves in a three-dimensional model, especially when the information collected in situ is limited.

Design of hydraulic’ tools for students’ practicum

Fluid mechanics and hydraulics subject is a subject that explains the concepts of the nature of fluids (liquids and gases) when stationary or moving, or when interacting with other fluids or solid objects. One of the courses in this subject related to hydraulics is about open channels. Many students have difficulties understanding this material and not able to describe abstract concepts because they were not doing experiments with the open channel. The purpose of this research is to develop hydraulic devices for open channels that can be used by students for practicum. The methods used to develop these tools are the study of literature, determination of design concepts, exploration of design scenarios, toolmaking, testing, evaluation, and improvement the tools. These tools are also equipped with a microcontroller to regulate water flow, the slope of the water-retaining plate to display hydraulic jumps and adjust the pump power. The test results show that the tool can provide consistent results, both from flowrate, weir overflow coefficient, and Froude numbers.