Showing papers on "Spillway published in 2011"

Laboratory measurements and multi-block numerical simulations of the mean flow and turbulence in the non-aerated skimming flow region of steep stepped spillways

Abstract: We present and discuss the results of a comprehensive study addressing the non-aerated region of the skimming flow in steep stepped spillways. Although flows in stepped spillways are usually characterized by high air concentrations concomitant with high rates of energy dissipation, the non-aerated region becomes important in small dams and/or spillways with high specific discharges. A relatively large physical model of such spillway was used to acquire data on flow velocities and water levels and, then, well-resolved numerical simulations were performed with a commercial code to reproduce those experimental conditions. The numerical runs benefited from the ability of using multi-block grids in a Cartesian coordinate system, from capturing the free surface with the TruVOF method embedded in the code, and from the use of two turbulence models: the \({k{-}\varepsilon}\) and the RNG\({k{-}\varepsilon}\) models. Numerical results are in good agreement with the experimental data corresponding to three volumetric flow rates in terms of the time-averaged velocities measured at diverse steps in the spillway, and they are in very satisfactory agreement for water levels along the spillway. In addition, the numerical results provide information on the turbulence statistics of the flow. This work also discusses important aspects of the flow, such as the values of the exponents of the power-law velocity profiles, and the characteristics of the development of the boundary layer in the spillway.

Developing flow in skimming flow regime on embankment stepped spillways

Abstract: In hydraulic engineering, stepped spillways are effective structures in regard to both energy dissipation and re-aeration processes. It is well known that flow depths and flow velocities generally depend on the spillway geometry in terms of slope and step-induced macro-roughness height on the one hand and the discharge on the other hand. Moreover, these parameters affect the air entrainment process and hence, the amount and the size of entrained air bubbles which are directly linked to the specific air–water interface being of particular significance for oxygen transfer. In this study, physical model investigations on a stepped spillway scaled 1:10 of varying step height, chute angle and discharge are conducted with the objective to analyse the development of these air–water flow properties in the non-uniform flow region. Measurements of air–water mixture velocity and air concentration are carried out by the use of an intrusive double-tip conductivity probe. It is found that the step-induced macro-roughne...

Effects of freshwater input on nutrient loading, phytoplankton biomass, and cyanotoxin production in an oligohaline estuarine lake

Abstract: Pulsed river water events can increase nutrient levels potentially translating into enhanced primary production, phytoplankton community shifts, and bloom formation. The Bonnet Carre Spillway is a managed river diversion which can be used to redirect a significant amount of Mississippi River water into Lake Pontchartrain, reducing the risks of flood in the downstream communities during runoff seasons. We investigated nutrient enrichment and consequent changes in phytoplankton biomass, including toxic species in Lake Pontchartrain during and after a 1-month Bonne Carre Spillway opening in 2008. Water samples were collected along a 30 km transect. A freshwater plume was found to have formed by the strong river input that had limited mixing with the lake during the opening. The plume and lake water gradually mixed together after the Spillway was closed, indicated by the reduction of the horizontal salinity gradient. The river pulse increased the lake nitrate and dissolved reactive phosphorus concentrations to more than five times the lake background in the plume stations. Nutrient concentrations decreased rapidly after the Spillway closure as the plume dissipated. Diatoms and chlorophytes dominated the system during the opening. After the Spillway closure, there was a shift over time from diatom dominance to toxic cyanobacteria dominance that corresponded to more stable, warmer, and nutrient-limited water conditions. Associated toxins were present and varied over time and space. Further research on the phytoplankton assemblages on the lake is needed in subsequent, non-Spillway opening years to evaluate the impact of river water pulses on the development of these toxic cyanobacterial blooms.

The Formation and Behaviour of Natural and Artificial Rockslide Dams; Implications for Engineering Performance and Hazard Management

Abstract: The formation and behaviour of natural and artificial rockslide dams are reviewed to update the well-known work of Costa and Schuster [1]. Rockslide dams block surface drainage to form upstream lakes. They may occur naturally due to landslides or as a result of engineered rock slope failure. As evidenced by the 2010 Hunza event (Pakistan), the stability of rockslide dams is a major consideration in landslide risk assessment in mountain terrain, particularly with respect to the possibility of a destructive downstream flood resulting from a breach of the dam. The damming of a river by a rockslide may require immediate engineering response to mitigate the hazard. However, failure by breaching is less frequent than long-term stability. These issues are examined with reference to nine case histories of rockslide dams and rockslide-dammed lakes; Gohna (1894), Rio Barrancas (1914), Condor-Sencca (1945), Mayunmarca (1974), La Josefina (1993), Tsao-Ling (1999), Yigong (2000), Tangjiashan (2008), and the Hunza (2010). The case histories also illustrate the utility of digital terrain data (especially the SRTM-3 data set obtained in February 2000) and remote sensing imagery to obtain accurate estimates of the impoundment volumes and other geomorphic data on rockslide-dammed lakes. Methods of estimating peak breach discharge and downstream flood effects exist but are still largely empirical in nature. Measures to mitigate hazard associated with rockslide-dammed lakes include the construction of a spillway over the rockslide debris, a by-pass tunnels through the abutments of the debris dam, the implementation of dam and lake-level monitoring and failure warning systems to mitigate downstream damage. A review of some well-documented examples show that these measures have had been applied with mixed success in the past. Natural rockslide dams are commonly used for foundations for conventional constructed dams. Artificial rockslide dams are created by rock slope failure induced by large-scale explosion (blast-fill dams). The largest blast-fill dam yet constructed is the Medeo Dam, a debris flow retention structure near Alma-Ata, Kazakhstan. Rockslide dams and their geomorphic effects may create an important legacy in the landscape through massive accumulations of lake sediments, impact on river channels, and effects on river long-profiles.

Emergency response to the Tangjiashan landslide-dammed lake resulting from the 2008 Wenchuan Earthquake, China

Abstract: Natural landslide dams triggered by earthquakes are a common feature and a significant hazard in high-relief, tectonically active areas. The great Wenchuan Earthquake of May 12, 2008 created 256 natural dams, of which 34 presented significant risks to downstream areas in the event of their uncontrolled failure. Out of the 34 large landslide dams that warranted mitigation, we discuss Tangjiashan landslide dam in detail. Emergency response to the Tangjiashan landslide-dammed lake in the following weeks and months successfully reduced the risk, and the advantages and disadvantages of various countermeasures that were applied are summarized here. Successful strategies relied on accurate scientific assessments, on timely execution of the countermeasures, and on the correct design of sluiceway (spillway) channels across the landslide dams. Retrospective assessment indicates that the following improvements would be more beneficial: (1) Sluiceway channels utilizing a combination of cross-section types, rather than simply trapezoidal in shape; (2) increased channel slope, which is more than the original gradient of the river; (3) better protection of inlets and outlets to control the planned incision rates; and (4) channels lined to better control the incision rate. We discuss applications of the concept of artificially controlled failure, and we submit these observations for the benefit of those responding to future seismic catastrophes.

Numerical Modeling of Probable Maximum Flood Flowing through a System of Spillways

Abstract: The results of a numerical model study of probable maximum flood (PMF) flow through a system of spillways consisting of an existing service spillway and a new auxiliary spillway are presented. A commercial computational fluid dynamics (CFD) code, Fluent, was used to solve the time-dependent Reynolds-averaged Navier-Stokes equations, a standard turbulence k-e model with wall functions, and a water volume of fluid fraction equation. A two-dimensional approach velocity profile was used at the upstream inlet cross section. Water levels, flow splits between the existing and auxiliary spillways, and flow patterns were predicted and compared. A tentative design was chosen, constructed, and tested in a 1:54 scale physical model. Testing results were used to validate the CFD model. Results demonstrate that the CFD model is validated as accurate in the prediction of water levels in the reservoir, the integrated approach used is cost-effective and efficient in optimizing the designs of the auxiliary spillway, the tentative design cannot pass the PMF at the maximum pool level which suggests further modifications being necessary in the physical model.

Neural Network Application in Reservoir Water Level Forecasting and Release Decision

Abstract: Reservoir dam is one of the defense mechanism for both flood and drought disasters.During flood, the opening of the dam's spillway gate must be adequate to ensure that the reservoir capacity will not over its limits and the discharges will not cause overflow downstream. While, during drought the reservoir needs to impound water and release adequately to fulfil its purposes.Modelling of the reservoir water release is vital to support the reservoir operator to make fast and accurate decision when dealing with both disasters.In this paper, intelligent decision support niodel based on neural network (NN) is proposed. The proposed model consists of situation assessment, forecasting and decision models.Situation assessment utilized temporal data mining technique to extract relevant data and attribute froni the reservoir operation record.The forecasting model utilize NN to perform forecasting of the reservoir water level, while in the decision model, NN is applied to perform classification of the current and changes of reservoir water level. The simulations have shown that the performances of NN for both forecasting and decision models are acceptably good.

Experimental parametric study for hydraulic design of PKWs

Abstract: The implementation of a new type of labyrinth spillway, called PKW (Piano Key Weir) reveals as a performing alternative for increasing the overflow capacity of existing dams. The optimal hydraulic design of such structure is however not obvious due to the large number of involved parameters. The present work explores experimentally the most relevant geometrical parameters, such as width, length, height and slope of keys and also the upstream and downstream flow conditions. The rating curve of a unit structure is then analysed considering the following dimensionless parameters: (i) the total developed crest length over PKW width (L/W), (ii) the inlet over outlet key widths (Wi/W0), (iii) the vertical over the horizontal shapes (P/Wi), and (iv) the vertical height of the dam over the PKW height (Pd/P). A non-linear global stepwise regression approach is then applied to fit the most influent parameters in order to provide a mathematical formulation for the hydraulic design of a PKW. The discussion reveals that there is not only one optimal solution from the hydraulic point of view. The ideal solution can then only be selected when considering local and economical constraints related to excavation, materials, construction techniques and particularly to the downstream energy dissipation system.

Design of Gravity Dam by Genetic Algorithms

Abstract: The design of a gravity dam is performed through an interactive process involving a preliminary layout of the structure followed by a stability and stress analysis. This study presents a method to define the optimal top width of gravity dam with genetic algorithm. To solve the optimization task (minimize the cost of the dam), an optimization routine based on genetic algorithms (GAs) was implemented into an Excel spreadsheet. It was found to perform well and GA parameters were optimized in a parametric study. Using the parameters found in the parametric study, the top width of gravity dam optimization was performed and compared to a gradient-based optimization method (classic method). The accuracy of the results was within close proximity. In optimum dam cross section, the ratio of is dam base to dam height is almost equal to 0.85, and ratio of dam top width to dam height is almost equal to 0.13. The computerized methodology may provide the help for computation of the optimal top width for a wide range of height of a gravity dam. Keywords—Chromosomes, dam, genetic algorithm, global optimum, preliminary layout, stress analysis, theoretical profile. I. INTRODUCTION ASICALLY, gravity dams are solid concrete structures that maintain their stability against design loads from the geometric shape and the mass and strength of the concrete. Generally, they are constructed on a straight axis, but may be slightly curved or angled to accommodate the specific site conditions. Gravity dams typically consist of a nonoverflow section(s) and an overflow section or spillway. The two general concrete construction methods for concrete gravity dams are conventional placed mass concrete and RCC. Dam profiles consist of nonoverflow and overflow section. The configuration of the nonoverflow section is usually determined by finding the optimum cross section that meets the stability and stress criteria for each of the loading conditions. The design cross section is generally established at the maximum height section and then used along the rest of the nonoverflow dam to provide a smooth profile. The upstream face is generally vertical, but may include a batter/fillet to increase sliding stability or in existing projects provided to meet prior stability criteria for construction requiring the resultant to fall within the middle third of the base. The downstream face will usually be a uniform slope transitioning to a vertical face near the crest. Based on U.S. Army Corps of Engineers (1), the slope will usually be in the range of 0.7H-1V and 0.8H-1V, depending on uplift and the seismic zone, to meet the stability requirements. Two basic loading conditions are used in gravity dam design. Loadings that are not indicated should be included where applicable (2):

Prediction of Scour Depth in Downstream of Ski-Jump Spillways Using Soft Computing Techniques

Abstract: Scour of bed in downstream of a ski-jump spillway is a critical phenomenon that can endanger the spillway stability. The present paper deals with application of soft computing techniques like classification and regression tree (CART), support vector machine (SVM) and M5 for the prediction of downstream scour of the spillways. The results of testing data set present CART model as the best among the other computing methods. The results of models showed that CART produces better prediction of the scour in the downstream of the spillway compared to other techniques. However, the other techniques are better than the available empirical relationships for the prediction of scour.

A Brief Assessment of a Dam and Its Failure Prevention

Abstract: Dams are artificial lakes created to reserve water for a particular purpose. Reports on failure of dams are common things nowadays. Effects of dam’s failure on man and environment are well known, which require preventive measures. This article presents a brief assessment of a dam in Nigeria and suggested necessary failure preventive measures. The dam site was visited (up and down streams), selected soil and geological properties of the dam were conducted with a particular attention to the release of water from the reservoir as seepage, or filling of the reservoir by silt from erosion. Hydrology and hydraulic data of the study area and spillway were obtained and analyzed. The study revealed that the soil is mainly sandy-loamy soil of averagely sand (73.99 ± 3.12), clay (8.53 ± 0.18), and silt (17.48 ± 1.88). Geological structure of the soil revealed that the study area is in basement complex. The reservoir capacity is 177,000,000 m3 with about 18.5-m hydraulic high, silting rate of 0.301% per year. Hydraulic conductivity, transmissivity, and specific discharge were found to be of high side of 9.31 × 10−4 m/s, 5.08 × 10−4 m2/s, and 98.25 m/year, respectively. It was concluded that the current problems of the dam are high silting rate and seepage, big trees on the embankment and beside the spillway. All these may lead to failure of the dam in the following ways: lack of water in the reservoir due to seepage and silting, eutrophication and non-potable of the water due to silting and collapse of the embankment due to the presence of big trees. It was suggested that necessary and urgent solutions such as removal of trees from embankment, desilting and seepage control must be provided for safety of lives and properties.

Determination of Crest Coefficient for Flow over Trapezoidal Labyrinth Weir

Abstract: 4 Abstract: Use of Labyrinth spillway is particularly suitable where the spillway width and upstream water surface are limited and larger discharging capacities are required. It is an effective method to increase the spillway crest length without an associated increase in structure width. It consists of a series of relatively slender walls having a respective plan form, shaped generally triangular or trapezoidal with a vertical upstream face. Continued efforts are being focused towards development of design curves with different shapes and configurations. The research presented here mainly aims at determining the crest coefficient for flow-over trapezoidal labyrinth weir by conducting experimentations at wide range of values of side wall angles ( ) from 6° to 30°.

Velocity Distribution and Energy Dissipation along Stepped Chutes Lined with Wedge-Shaped Concrete Blocks

Abstract: Stepped channels lined with wedge-shaped concrete blocks may constitute a low-cost alternative to provide overtopping protection of embankment dams if the discharge capacity of existing spillways is not adequate or even to be used as the main spillway of newly built embankment dams This paper addresses the velocity distribution and the energy dissipation, downstream of the inception point, on stepped chutes lined with wedge-shaped concrete blocks An experimental setup was developed with two flumes designed with a relative scale of 1:25 Air concentration was measured with an optical probe in several cross sections of both flumes The velocity profiles along chutes lined with wedge-shaped blocks with the upper face sloping downstream were analyzed The measurements' accuracy was checked by comparing discharges indicated by a facility flowmeter and obtained by the integration of velocity and air concentration profiles The effect of the steps-slope in the energy dissipation is studied Values of the Darcy-Weissbach friction factor are proposed for this type of chute lining, for transition flows, and for skimming flows

Evaluation of Behavioral Guidance Structure on Juvenile Salmonid Passage and Survival at Bonneville Dam in 2009

Abstract: Pacific Northwest National Laboratory (PNNL) conducted an acoustic-telemetry study at Bonneville Dam in 2009 to evaluate the effects of a behavioral guidance structure (BGS) in the Bonneville Dam second powerhouse forebay on fish passage and survival through the second powerhouse (B2), the dam as a whole, and through the first powerhouse and spillway combined The BGS was deployed to increase the survival of fish passing through B2 by increasing the percentage of outmigrating smolts entering the B2 Corner Collector (B2CC)—a surface flow outlet known to be a relatively benign route for downstream passage at this dam The study relied on releases of live Juvenile Salmon Acoustic Telemetry System tagged smolts in the Columbia River and used acoustic telemetry to evaluate the approach, passage, and survival of passing juvenile salmon Study results indicated that having turbine 11 in service is important for providing flow conditions that are comparable to those observed in pre-BGS years (2004 and 2005) and in 2008 This study supports the US Army Corps of Engineers continual effort to improve conditions for juvenile anadromous fish passing through Columbia River dams

Innovative Design and Construction of a High RCC Gravity Dam in High Seismic Intensity Region

Abstract: A few innovative designs and construction measures are introduced to build a roller-compacted concrete (RCC) gravity dam with a height of 160 m (524.96 ft), whereas the design peak ground acceleration of the dam site is 0.3995 g. The grouting construction joints are designed between the plant and dam parts to enhance the earthquake-resistant ability of the dam. To improve the lateral stability of the dam, the depth of the construction joint is only 2/3 of the dam thickness in each roller-compacted layer, and the joints are filled with nonwoven fabrics. This treatment causes the construction joints to be weakly connected induced joints, which are not only good for temperature stress release but also enhance the integrity of the dam. Steel bars are embedded in high-tensile stress zones to ensure dam safety. Some other aspects, such as layout of the stilling basin, spillway chute design, high-pressure consolidation grouting of dam foundation, the reinforcement of slumping mass on the left bank, and other en...

Mapping seepage in the tailrace channel, Bhama-Askhed dam: a case study

Abstract: The Bhama-Askhed irrigation dam, with a side spillway, is located on the Bhama river, Maharashtra, India where the bedrock is chlorophacitic porphyritic basalt. During the monsoon of 2005, thirteen reinforced concrete panels in the tailrace channel area were raised and displaced, exposing the underlying rock. Continuous oozing of water was observed in the tailrace channel at RD 83 m. Nuclear logging and tracer studies were conducted in boreholes drilled 6 m below the foundation level, to identify weak and porous zones and ascertain the seepage path. The nuclear logging identified weak zones at about 34 m depth corresponding to a red breccia zone. The tracer studies established the interconnection between the red breccia in the dam foundation and the oozing water at RD 83 m in the tailrace channel. The studies assisted in the determination of suitable remedial measures for the treatment of the red breccia zone and the recommendation of proper drainage holes in the tailrace channel area to release uplift pressures.

Hydraulic characteristics of converse curvature section and aerator in high-head and large discharge spillway tunnel

Abstract: The hydraulic characteristics and cavitation erosion near the converse curvature section in the high-head and large discharge spillway tunnel have been important issues of concern to the hydropower project. In this paper, the evolutions of hydraulic elements such as pressure, flow velocity, wall shear stress, etc. in the converse curvature section are analyzed and the impacts of bottom aerator on hydraulic characteristics are discussed, with the commercial software FLUENT6.3 as a platform and combining the k-ɛ model and VOF method. The flow pattern in the converse curvature section of spillway tunnel is given by the three-dimensional numerical simulation. It indicates that the pressure changes rapidly with great pressure gradient from the beginning to the end of the curve. It also shows that the shear stress on side wall just downstream the end of the converse curvature curve is still increasing; the aeration cavity formed downstream the bottom aerator may cause the side wall pressure decreased to worsen the cavitation characteristics near the side wall. By means of the physical model experiment, the three-dimensional aerator composed of side wall baffling aerator and bottom aerator is studied, the baffling aerator suitable for the water flow conditions with water depth of 6.0 to 8.0 m and flow velocity of 35 to 50 m/s is proposed.

Characterization of Fish Passage Conditions through a Francis Turbine, Spillway, and Regulating Outlet at Detroit Dam, Oregon, Using Sensor Fish, 2009

Abstract: Fish passage conditions through two spillways, a Francis turbine, and a regulating outlet (RO) at Detroit Dam on the North Santiam River in Oregon were evaluated by Pacific Northwest National Laboratory for the U.S. Army Corps of Engineers (USACE), Portland District, using Sensor Fish devices. The objective of the study was to describe and compare passage exposure conditions, identifying potential fish injury regions within the routes. The study was performed in July, October, and December 2009 concurrent with HI-Z balloon-tag studies by Normandeau Associates, Inc. Sensor Fish data were analyzed to estimate 1) exposure conditions, particularly exposure to severe strike, collision, and shear events by passage route sub-regions; 2) differences in passage conditions between passage routes; and 3) relationships to live-fish injury and mortality data estimates. Comparison of the three passage routes evaluated at Detroit Dam indicates that the RO passage route through the 5-ft gate opening was relatively the safest route for fish passage under the operating conditions tested; turbine passage was the most deleterious. These observations were supported also by the survival and malady estimates obtained from live-fish testing. Injury rates were highest for turbine and spillway passage. However, none of the passage routes tested is safe for juvenile salmonid passage.

Hydraulic of siphon spillway by physical and computational fluid dynamics.

Abstract: 3 Abstract: Siphon spillway is a hydraulic structure which has been used in many dams and irrigation networks. Estimation of pressure distribution within this structure and head-discharge, relationship are the most important design's parameters of siphon. At present the hydraulic of siphon spillway usually is done by physical modeling. Physical modeling requires many times. On the other hand, numerical modeling has the advantage of doing very fast. Therefore it is the main purpose of this study to show that, the numerical model also can be performed to have accurate results. To reach the purpose of this study first a physical model of siphon spillway was constructed and placed in a test flume in hydraulic laboratory of Azad university- Garmsar branch. At the same time an available CFD program, which solves the Navier-Stokes equations, was run by using data obtained from physical model. The result of investigations shows that: Comparison of discharge coefficient in pressurized spillway with both free and submerged outlet shows that submerging in outlet is effective in promotion of spillway efficiency. It is shown that there is reasonably good agreement between the physical and numerical models for both pressures and discharges and CFD modeling can be used for this purpose.

Overview of Dam Development in Nigeria

Abstract: This paper attempts to put together details of dams’ development in Nigeria. Case studies of dam-related incidents were highlighted. A typical case study of Kainji dam safety monitoring assessment was analysed and discussed. From the results obtained it is observed that majority of the piezometer plot of the spillway points to improving stability especially from year 2000 to 2001. The data collected and analysed indicated some displacement of about 25 mm. in some blocks, which shows an abnormal behaviour and require need for closer observations. The tape extensometers reading and the rod extensometer were briefly discussed.

Gated Spillways Operation Rules Considering Water Surface Elevation and Flood Peak: Application to Karkheh Dam

Abstract: In this research, a multi-stage operating policy for routing flood hydrographs through reservoir with two different operation policies for gated spillways is presented. The first approach presents releases the flood only based on observed reservoir water surface level. In the second approach, both observed reservoir water surface level and flood peak in upstream gagging station forms the release policy. As a distinct privilege, none of the policies needs flood forecasting making them adaptable to any flood with any return period. In order to demonstrate the performances of the proposed models, we operated the gated spillway of Karkheh reservoir by using flood hydrographs with different return periods. The results of simulation show that the second method out performs the first method and results in smaller flood peak in downstream.

Spillway chute structure

Abstract: The utility model relates to a spillway chute structure, with features of simple structure, easy air entrainment to alleviate cavitations, convenient construction, so as to ensure safe operation of the chute bottom plate. The spillway chute structure is vertically arranged on a bank slope bedrock gradually steeping and comprises chute side walls and a chute bottom plate between the side walls and composed of an upstream bottom plate and a downstream bottom plate, characterized in that: a ridge-top small flip bucket, a vertical ridge and a horizontal bottom plate connected in turn are poured into the space between the upstream bottom plate and the downstream bottom plate and aeration vertical holes are arranged on the side walls of the chute at the two sides of the upstream end of the horizontal bottom plate. The spillway chute structure is suitable for the bank slope type spillway, especially when the chute bottom plate of the spillway chute needs the gradually steeping slope.

Experimental Study on Gabion Stepped Spillway

Abstract: Use of rocks and gabions in hydraulic works, especially in the area of river engineering, has been increased during recent decades. Gabion stepped spillway is a type of hydraulic structure which is designed for river bed protection. Most of the flow kinetic energy is dissipated when flow cascades from one step to another. Therefore, in most cases, the stilling basin is not considered at the downstream end of spillway, and because of this a scour hole may develop. The main objective of this study is to conduct a series of experimental tests to investigate the mechanism of scour hole downstream of the stepped spillway. A total of 19 tests were conducted. The results of this study reveal that the scour hole dimensions in simple stepped spillway are larger than the pooled stepped spillway. Three equations have been presented for prediction of maximum scour hole depth. Design procedure is presented for gabion stepped spillway.

CFD Analysis on the Performance of an Overturnable Water Gate for Reservoir Spillway

Abstract: The automatic overturnable water gate for the spillway of a reservoir is one method of increasing the water storing capability of small agricultural reservoirs. Overturning and restoring of the water gate are the key points of its design, but it has been very difficult to analyze their effects through field measurements because of the difficulties in designing artificial experimental conditions. Accordingly, a 2-D CFD (computational fluid dynamics) numerical simulation was designed to overcome the weaknesses of field experiments as well as compare their efficiencies under various conditions. The water-air interface was determined by the VOF method, and the motion of the gate was modeled using the dynamic mesh method and the user defined functions (UDF). The accuracy of the CFD model was examined using the hydrostatic estimation data and the results were found reasonable. The restoration of the gate, as the critical problem, was significantly affected by the water's dynamic force, and the CFD analysis suggested some remedies to improve the gate operation. The study also indicated that CFD simulation could be effectively used to design and evaluate various hydraulic structures.

PKWeir and flap gate spillway for the Gage II Dam

Abstract: The Gage II concrete arch dam shows some limiting constraints in its structural behavior when submitted to particular hydrostatic and thermal load conditions. Its sensitivity to low temperature has led to determine two different maximum water levels during winter and summer, respectively. Therefore, a new complementary spillway, composed by a PKWeir and a flap gate weir has been designed by EDF and optimized using a physical scaled model at LCH. The experimental tests have been carried out for different configurations of the spillway. The output flow capacities of the PKWeir and the flap gate weir including their interaction through the restitution channel have been also investigated. The geometric optimization process has been conducted on several spillway parameters: number of the PKWeir units, its position relative to the flap gate weir, and the height, width and bottom slope of the restitution channel. The tested configurations have been compared based on their flow output capacity.