Showing papers on "Spillway published in 2019"

Experimental repetitions and blockage of large stems at ogee crested spillways with piers

Abstract: Large wood is often transported by rivers into reservoirs during heavy rainfall events. When a critical section like a spillway is blocked and discharge capacity reduced, an uncontrolled increase o...

The Past and Present of Discharge Capacity Modeling for Spillways—A Swedish Perspective

Abstract: Most of the hydropower dams in Sweden were built before 1980. The present dam-safety guidelines have resulted in higher design floods than their spillway discharge capacity and the need for structu ...

Numerical Simulation of Air–Water Two-Phase Flow on Stepped Spillways behind X-Shaped Flaring Gate Piers under Very High Unit Discharge

Abstract: Stepped spillways are commonly used under relatively low unit discharge, where cavitation pitting can be avoided by self-aerated flow. However, there are several dams in China with stepped spillways in combination with X-shaped flaring gate piers with unit design discharge considerably larger than specified in the available guidelines. Consequently, air–water two-phase flow on stepped spillway behind X-shaped flaring gate piers under very high unit discharge was investigated using Computational Fluid Dynamics (CFD) simulations. The 3-D Reynolds-averaged Navier–Stokes equations were solved, including sub-grid models for air entrainment, density evaluation, and drift-flux, to capture self-aerated free-surface flow over the spillway. The pressure on the vertical step faces was compared with laboratory data. In addition, the air–water two-phase flow characteristics and prototype step failure of the simulated prototype spillway were analyzed based on the numerical results of velocity, pressure, and air concentration. Moreover, an optimized bottom-aeration was further studied. The results reveal that the involved models can predict the air concentration near the steps. The cavitation index at the stepped surface is below the threshold value, and the air concentration is insufficient under high unit discharges. Moreover, with the proposed optimization of the aerator air entrainment can be improved and thereby cavitation erosion risk can be reduced.

Insights into the Oroville Dam 2017 Spillway Incident

Abstract: In February 2017, a failure occurring in Oroville Dam’s main spillway risked causing severe damages downstream. A unique aspect of this incident was the fact that it happened during a flood scenario well within its design and operational procedures, prompting research into its causes and determining methods to prevent similar events from reoccurring. In this study, a hydroclimatic analysis of Oroville Dam’s catchment is conducted, along with a review of related design and operational manuals. The data available allows for the comparison of older flood-frequency analyses to new alternative methods proposed in this paper and relevant literature. Based on summary characteristics of the 2017 floods, possible causes of the incident are outlined, in order to understand which factors contributed more significantly. It turns out that the event was most likely the result of a structural problem in the dam’s main spillway and detrimental geological conditions, but analysis of surface level data also reveals operational issues that were not present during previous larger floods, promoting a discussion about flood control design methods, specifications, and dam inspection procedures, and how these can be improved to prevent a similar event from occurring in the future.

Experiments and CFD modeling of high-velocity two-phase flows in a large chute aerator facility

Abstract: Mathematical formulations of two-phase flows at an aerator remain a challenging issue for spillway design. Due to their complexities in terms of water-air interactions subjected to high flow veloci ...

Spillway jet regime and total dissolved gas prediction with a multiphase flow model

Abstract: A numerical model, based on the open source code OpenFOAM, was developed to predict jet regimes and total dissolved gas downstream of spillways. The model utilizes the volume of fluid method to tra...

Numerical simulation of flow over ogee crested spillways under high hydraulic head ratio

Abstract: Ogee spillway is one of the most common types of the spillway. Researchers have attempted to investigate the hydraulics of ogee structure under hydraulic heads near the design head. Herein, an ogee...

Upstream Erosion and Sediment Passage at Piano Key Weirs

Abstract: Piano key weirs (PKWs) are a weir type characterized by an effective rating curve. Accordingly, this control structure is primarily applied at dams to increase the spillway capacity. In rec...

Effect of Height and Geometry of Stepped Spillway on Inception Point Location

Abstract: Air entrainment in a stepped spillway is very important to protect the spillway from cavitation damage. The inception point is the location where air starts entering the non-aerated flow zone. The inception point location depends on different parameters, such as the discharge, step height, and step shape. In this paper, various stepped spillways, including flat steps, pooled steps, and round steps with different step heights were numerically simulated using the volume of fluid and realizable k-e models. The results indicate that the inception point location moves downwards with the increase of the discharge of the stepped spillways. The length of the non-aerated flow zone increases with the discharge. The inception point location moves downwards as the step height decreases and the step number increases at the same discharge. The inception point location of the round stepped spillway model is much closer to the spillway crest than that of the flat stepped spillway with the same number of steps. The inception point location of the pooled stepped spillway is closer to the spillway crest than that of the flat stepped spillway, but more downstream than that of the round stepped spillway.

A multicriteria fuzzy approximate reasoning approach for risk assessment of dam safety

Abstract: The benefits of dams are unquestionable, with the water impoundment upstream and flood-control downstream usually being sufficient to increase investments and promote growth. However, their presence brings risks to the downstream population and the environment. This paper employs a fuzzy approximate reasoning for dam safety risk assessment, initially using a FAHP to weight the importance of the indicators suggested by a dam expert and then adopts linguistic variables in a two-stage risk assessment. In the first stage, we compute the risk of dam collapse, hereinafter called dam break, through indicators such as design premises and safety procedures. In the second stage, we evaluate the combined effect between the risk of a dam collapse and the socioeconomic and environmental impact on the surrounding area, hereinafter called potential risk. The danger scale of dam break and the hazard scale of potential risk were constructed. The risk assessment of the Simplicio Hydroelectric plant, located in Brazil’s Southern region, showed that the risk classification of the proposed method attached great importance to the downstream consequences. The accuracy of the evaluation results was proved through a study of the Oroville Dam, whose spillway faced a failure event. These findings indicate the importance of extracting the knowledge of experts and incorporating it in the model specification through fuzzification of variables and the rule-based construction.

Experimental research on the maximum backwater height in front of a permeable spur dike in the bend of a spillway chute

Abstract: Hydraulic experiments on installing a permeable spur dike at three positions (1/4, 1/2, and 3/4) on the concave bank of the bend of a spillway chute with three angles (45°, 60° and 75°) were carried out for studying the backwater condition in front of the permeable spur dike. Results show that the maximum backwater height occurs at the cross-section where the permeable spur dike meets the concave bank of the bend. A formula for the maximum backwater height was derived by the employment of the principle of momentum conservation, and the formula indicates that the height is influenced by the geometric parameters of the permeable spur dike and the bend, the layout of the spur dike in the bend, and the inflow discharge. Based on experimental data, a regression analysis was implemented on the water depth coefficient in the formula. Furthermore, the maximum backwater height can be obtained through the water depth at the concave bank of the end of bend when the parameters and installing pattern of the permeable spur dike are determined.

Life prediction for spillway facility side wall

Abstract: This article includes the analytical assessment of the durability and remaining life of the I-st category reinforced concrete structures by the fracture mechanics approaches, the prediction is based on the consideration of temporal changes in the structural features of a particular type of concrete. The main purpose of this work is to determine the durability of reinforced concrete structures and the remaining life of the spillway and components in the implemented modes and operating conditions that ensure their safe operation and environmental protection. When predicting the durability of the spillway reinforced concrete structures, each structure is considered as a component of the structure behavior scheme. The result of the durability predictions is presented in years, which can eventually determine the remaining life of the structural component of spillway.

3D Hydrodynamic Modelling Enhances the Design of Tendaho Dam Spillway, Ethiopia

Abstract: Hydraulic structures are often complex and in many cases their designs require attention so that the flow behavior around hydraulic structures and their influence on the environment can be predicted accurately. Currently, more efficient computational fluid dynamics (CFD) codes can solve the Navier–Stokes equations in three-dimensions and free surface computation in a significantly improved manner. CFD has evolved into a powerful tool in simulating fluid flows. In addition, CFD with its advantages of lower cost and greater flexibility can reasonably predict the mean characteristics of flows such as velocity distributions, pressure distributions, and water surface profiles of complex problems in hydraulic engineering. In Ethiopia, Tendaho Dam Spillway was constructed recently, and one flood passed over the spillway. Although the flood was below the designed capacity, there was an overflow due to superelevation at the bend. Therefore, design of complex hydraulic structures using the state-of- art of 3D hydrodynamic modelling enhances the safety of the structures. 3D hydrodynamic modelling was used to verify the safety of the spillway using designed data and the result showed that the constructed hydraulic section is not safe unless it is modified.

Development of GWO–DSO and PSO–DSO hybrid models to redesign the optimal dimensions of labyrinth spillway

Abstract: In this study, considering the importance of dams spillways redesign to provide optimal dimensions, the hybrid of particle swarm optimization, gray wolf optimization (GWO) and direct search optimization meta-heuristic approach were proposed. In this methodology, the total volume of spillway body, which indicates the amount of concrete and cost, is considered as the objective function and height of spillway, the number of cycles, apex length and angle of wall are defined as decision variables. By implementing the proposed model based on the data of the Ute dam labyrinth spillway, the optimal dimensions of spillway were determined and compared with the other studies. The results indicated that the hybrid of meta-heuristic algorithms has a very good performance in generating global optimal values, except that the GWO algorithm has a higher convergence rate. In the proposed method, the optimal dimensions provided by the hybrid algorithm led to saving in concrete and reduction of costs to 64% as compared to the existing design of dam. Investigating the optimal dimension of trapezoidal labyrinth spillway also indicates that these dimensions increase the flow capacity of the spillway to $$15{,}760\,\hbox {m}^{3}{/}\hbox {s}$$ . Finally, comparison of the optimum dimensions obtained with two trapezoidal and triangular sections showed that the optimal form for labyrinth spillway is triangular and leads to improved spillway hydraulic performance.

Stepped Spillways and Energy Dissipation: A Non-Uniform Step Length Approach

Abstract: A stepped spillway, which is defined as a spillway with steps on the chute, can be used to improve the energy dissipation of descending water. Although uniform stepped spillways have been studied comprehensively, non-uniform stepped spillways need more attention. In the interest of maximum energy dissipation, in this study, non-uniform stepped spillways were investigated numerically. To this end, within the range of skimming flow, four different types of non-uniform step lengths, including convex, concave, random, and semi-uniform configurations, were tested in InterFOAM. To evaluate the influence of non-uniform step lengths on energy dissipation, the height and number of steps in all models were fixed and equal to a constant number. The results indicated that in semi-uniform stepped spillways, when the ratio between the lengths of the successive steps is 1:3, a vortex interference region occurs within the two adjacent cavities of the entire stepped chute, and as a result, the energy dissipation increases by up to 20%.

Experimental Study of the Rooster Tail Jump and End Sill in Horseshoe Spillways

Abstract: In a horseshoe spillways, due to the collision of the falling nappes from their surround walls, in the center of spillway’s trough, a spatial hydraulic jump is formed that named “rooster tail”. This study by using the physical model of horseshoe spillway, investigates the form, height and length of rooster tail jump. Based on the analytical methods, the effective parameters on rooster tail jump’s height and height were determined and their interaction was investigated and linear relationships were proposed to predict jump’s length and height. By increasing the amount of water on the spillway’s crest and thereby increasing the velocity of flow nappe at the point of contact with the spillway’s bed, length and high of rooster tail jump, linearly increased. The result also shows that by increasing number of Froude, the length and height of jump increases and by increasing the spillway’s length, the height and length of the rooster tail jump decreases. To control of rooster tail jump in spillway’s model, two different size of end sills Inserted at downstream of spillway and result shows that by employing a sill with height of 3.8 cm and 7.6 cm, the flow depth, in average, respectively 122% and 272% increase compared to no sill conditions, also flow state change from super-critical to sub-critical. At the sill of 3.8 cm it was observed that the rooster tail jump did not submerged, but at the height of 7.6 cm the jump submerged and static pressure increased more. The results revealed that by placing the sill of 3.8 and 7.6 cm, respectively 45% and 35% of the maximum pressure entering the bed of the spillway at the collision site is reduced.

Hydraulic Model Investigation on Stepped Spillway's Plain and Slotted Roller Bucket

Abstract: In ogee spillway, the released flood water from crest to toe possesses a high amount of kinetic energy causing scour and erosion on the spillway structure. The dam projects normally have a stilling basin as an energy dissipater which has specific energy dissipation limitations. The stepped spillway is a better option to minimize kinetic energy along the chute and safely discharge water in the river domain. The Khadakwasla dam is situated in Pune, Maharashtra (India), and has scouring and erosion issues on the chute of ogee spillway and on the stilling basin. The present study develops a physical hydraulic model for the dam spillway with steps, plain and slotted roller bucket as per IS Code 6934 (1998) and IS Code 7365 (2010). Experiments were performed at heads of 4m (low head) and 6m (high head) on the developed physical models, namely on the plain and slotted roller bucket model for the ogee spillway and the plain and slotted roller bucket model for the stepped spillway. It was found that the plain roller bucket of ogee spillway dissipates 81.26% of energy at the low head, whereas the stepped spillway with slotted roller bucket dissipates the 83.86% of the energy at the high head.

Influence of reservoir shape upon the choice of Hydraulic vs. Hydrologic reservoir routing method

Abstract: The objective of the paper is to compare the hydrologic and hydraulic reservoir routing methods in term of assumptions, equations, numerical computation procedures, necessary data and advantages-disadvantages of their use. To test the results provided by the two methods, a set of two reservoirs from Romania was chosen: one long and narrow and the other one roundly shaped. Corresponding inflow hydrographs were chosen, and similar conditions were imposed for the outflow dam control structures, namely the initial water level in the reservoir to be at the Spillway Crest Level (SCL) and no outflow control. For the hydrologic method the Puls procedure was used and a program was written in Scilab to solve the continuity equation in finite differences. For the hydraulic method HEC-RAS software was used to solve the 1D Saint-Venant equations. Outflow and stage hydrographs at the dam were compared together with the stage hydrograph at the reservoir tail for the hydraulic method. Results show that the hydraulic method should be used for the long and narrow reservoirs, as it considers the backwater effect, whereas the hydrologic method can be efficiently used for all other reservoirs where this effect is negligible.

Effects of Opened and Closed Spillway Operations of a Large Tropical Hydroelectric Dam on the Water Quality of the Downstream River

Abstract: Water quality downstream of a hydroelectric dam is potentially affected by dam operations and other land uses in the river basin. Previous short-distance studies below the large Bakun Dam indicated poorer water quality during closed spillway. However, the extent of the impact is still unknown. Such knowledge is essential for mitigating the impact of the dam. Thus, the objectives of this study were to determine the water quality up to a distance of 210 km under two spillway operations, namely, closed and opened spillways, and also to determine the changes in water quality from the predam condition. Physicochemical parameters were measured at 15 stations along the Rajang River. Results of this preliminary study indicated that there were significant differences in eight out of nine water quality parameters between opened and closed spillway operations with opened spillway showing better water quality. During closed spillway, as we approached the dam, there was an increasing acidity and a decreasing oxygen content. Furthermore, as the water flows downstream, the unhealthy DO level (<5 mg/L) extended up to 165 km and the linear model showed an increasing DO rate of 0.09 mg/L per km. With opened spillway, DO decreased exponentially from 9.74 mg/L towards the downstream direction to 7.67 mg/L. The increasing turbidity and TSS in the downstream direction indicate contributions from erosion due to other land uses. The river is polluted with organics as indicated by COD of Class IV or V with sources from the dam and the activities in the river basin. Compared to the predam condition, the regulated river is less turbid but warmer and higher in ammonia. Closed spillway led to lower DO and acidic water. However, opened spillway water pH and DO were similar to those in the predam condition. Thus, it is recommended that DO be consistently high enough for the health of sensitive aquatic organisms downstream.

Discharge coefficient of a spillway with a riser perforated by rectangular orifices.

Abstract: Perforated riser principal spillways are widely used in check dams, and rectangular orifices are the preferred orifice geometry for risers constructed of brick. However, there is little res...

Analysis for the Vibration Mechanism of the Spillway Guide Wall Considering the Associated-Forced Coupled Vibration

Abstract: During the flood discharge in large-scale hydraulic engineering projects, intense flow-induced vibrations may occur in hydraulic gates, gate piers, spillway guide walls, etc. Furthermore, the vibration mechanism is complicated. For the spillway guide wall, existing studies on the vibration mechanism usually focus on the vibrations caused by flow excitations, without considering the influence of dam vibration. According to prototype tests, the vibrations of the spillway guide wall and the dam show synchronization. Thus, this paper presents a new vibration mechanism of associated-forced coupled vibration (AFCV) for the spillway guide wall to investigate the dynamic responses and reveal coupled vibrational properties and vibrational correlations. Different from conventional flow-induced vibration theory, this paper considers the spillway guide wall as a lightweight accessory structure connected to a large-scale primary structure. A corresponding simplified theoretical model for the AFCV system is established, with theoretical derivations given. Then, several vibrational signals measured in different structures in prototype tests are handled by the cross-wavelet transform (XWS) to reveal the vibrational correlation between the spillway guide wall and the dam. Afterwards, mutual analyses of numeral simulation, theoretical derivation, and prototype data are employed to clarify the vibration mechanism of a spillway guide wall. The proposed mechanism can give more reasonable and accurate results regarding the dynamic response and amplitude coefficient of the guide wall. Moreover, by changing the parameters in the theoretical model through practical measures, the proposed vibration mechanism can provide benefits to vibration control and structural design.

Modification of Classical Horseshoe Spillways: Experimental Study and Design Optimization

Abstract: Investigation of the hydraulic aspects of spillways is one of the important issues regarding hydraulic structures. This study presents a modified horseshoe spillway (MHS) constructed by adding a flow passage and an internal weir in the bed of a classical horseshoe spillway (CHS). This modification increased the discharge efficiency and eliminated the rooster-tail hydraulic jump in CHSs. Eighteen laboratory-scale MHSs in various geometric sizes, six various CHSs, and a rectangular weir of the same width were constructed and tested under the same flow conditions. Results showed that in terms of discharge efficiency and water head reduction, CHSs and MHSs were superior to the rectangular weir. Compared to CHSs, the increased discharge flowrate in MHSs due to the internal weirs could further reduce the water head and thus increased their overall efficiencies. Design parameters effecting spillways’ discharge efficiencies were investigated based on dimensional analysis. The internal to external weir length ratio in MHSs was found to be a key design factor. To determine the optimal geometric design of CHS and MHS models, cubic polynomial models considering dimensionless parameters and their interactions were fitted to the experimental results. The cubic models revealed that higher discharge efficiencies in MHSs tended to occur at relatively low water heads and high internal to external weir lengths ratios.

Effect of the Spillway Elevation on Flood Attenuation in the Bendo Dam

Abstract: Bendo dam is a multi-purpose dam which used as a flood control, irrigation, raw water, also tour place. Moreover, in this study intends to know the safety of initial dam planning and determine the effect of the spillway elevation on flood attenuation in the Bendo Dam with discharge planned. In this research is fully calculated the maximum flood discharge also the safe freeboard and compare the amount of inflow and outflow in different elevation. This analysis used unit hydrograph synthetic nakayasu as a design discharge calculation and newton raphson method as a flood routing calculation. The location in this analysis is taken at Bendo Dam Ponorogo. The data needed in this calculation was rainfall data from 1996 until 2016 in Ponorogo area also earth map in Ponorogo area from internet. In this analysis, will be calculated effect of flood attenuation with the increasing of spillway 2 m, starting from 214.6 m until peak dam are 224 m. The result of this analysis, spillway elevation are used in Bendo Dam 218.6 m was safe to build. Then, the effect of spillway elevation is increase while the elevation increase also. In return period 1000 years the lowest value was 27.863% at elevation 214.6 m and keep increasing into 29.543% at elevation 216.6 m, 30.982% at elevation 218.6 m and maximum was 32.490% at elevation 220.6 m. Then, at PMF discharge, the lowest value was 24.949% at elevation 214.6 m and keep increasing into 26.390% at elevation 216.6 m, 27.908% at elevation 218.6 m and maximum was 29.492% at elevation 220.6 m.

Uplift Pressures below Spillway Chute Slabs at Unvented Open Offset Joints

Abstract: The catastrophic failure of the spillway chute at Oroville Dam in February 2017 raised concerns throughout the water resources industry regarding design, construction, and maintenance pract...

Determination of sediment deposition of Hasanlar Dam using bathymetric and remote sensing studies

Abstract: Hasanlar Dam and Hydroelectric Power Plant are located on Kucuk Melen Creek in the Western Black Sea Basin of Turkey. The dam was constructed in 1974 to provide domestic water needs of the Duzce Province, to supply irrigation water need, to control and mitigate floods and to produce hydroelectric power. This dam has been subjected to severe sedimentation since its construction in 1974. Therefore, bathymetric field survey studies were conducted to determine storage loss in the Hasanlar Dam reservoir by sedimentation. Bathymetric survey data from the reservoir site of the Hasanlar Dam were obtained in 1979, 1999 and 2014. Analysis of the bathymetric data, GIS and remotes sensing techniques showed that storage loss in reservoir active volume between 1974 and 1999 was 24% and between 1974 and 2014 storage loss was 26%. Analysis of the bathymetric maps also showed that sediment accumulation is severe near and around the dam body and the spillway whose discharge capacity was decreased by sediment accumulation. This is extremely critical because the flood of May 1998 caused the high risk of collapse of dam due to reduced capacity of the spillway. Remote sensing technique was used to determine the future deposition of sediment in the reservoir. For this purpose, 35 points in the reservoir area were determined by comparing the relative water depths and actual water depths using satellite image of the bathymetry in July 2017 and Lake Observation Station. High correlation (R2 = 0.833) was calculated by using logarithmic nonlinear regression analysis between actual and relative water depths for those 35 control points. The average of absolute values of differences between the estimated and actual water depths was found as 1.06 m, and RMSE was calculated as 1.25 m. This analysis shows that in the future, remote sensing data can be used in the studies of determining the depth of water and the total sediment thickness. In addition, the volume of the entire reservoir can be predicted by measuring the actual water depth only at those 35 control points without making a bathymetric map of the whole dam reservoir.

Characterizations of flow over stepped spillways with steps having transverse slopes

Abstract: The top and downstream face of the embankment dams must be protected from overtopping damages happen due to extreme floods. This can be achieved by providing one of the overtopping protection systems. The most common overtopping protection systems are those which have stepped fashion. This type of protection systems consists of a series of continues steps mostly made of concrete. In this study, the effects of the transverse slope of steps on flow properties over the overtopping protection systems were explored experimentally. Steps with transverse slopes are those which have inclinations from one spillway wall towards the other spillway wall in a zigzag way. To achieve the goals of the study, three physical models, stepped spillways, were made of wood and tested in a prismatic flume. The width, depth, and length of the wooden models were 0.6 m, 0.96 m and 1.92 m respectively. Sixteen steps (with three different transverse slopes ranging from zero to 5.7°) were cut into the surface of the models from the crest to the toe. The models were then tested under various flow rates ranging from 0.003 to 0.05 m3/s. The results showed that the models with steps having transverse slope had higher energy dissipation capability compared to the model with steps having zero transverse slopes (flat steps); up to 14% higher. In addition, for the models with steps having the transverse slope, the onset of the skimming flow occurred at higher ratios of critical depth (yc) to step height (h); greater than 1.37. However, the distances of the inception points from the first step brink (inception point locations) were reduced by half, on average, for the model with steps having a transverse slope of 5.7°.

Experimental and computational study on flow over stepped spillway

Abstract: The flow over a stepped spillway has complex nature, and its characteristics are remarkably different from other kinds of spillways. This study conducts experimental investigations and numerical simulations on the flow behavior (velocity, concentration profile) and macroscopic features (interface position and self-aeration) of water and neutrally buoyant suspension of non-colloidal particles in a stepped spillway with uniform steps. The development of nappe, transition, and skimming flow regimes is experimentally investigated by using a flow visualization technique. The inception point related to air entrainments is identified in the experimental study. The inception point usually moves downstream and increases the length of the non-aerated region with the increase of flow rate. Results of numerical and experimental studies indicate that a vortex is formed in the triangular cavity below the pseudo-bottom line (imaginary line joining two adjacent step edges) in the stepped channel. This vortex rotates in a clockwise direction for a short time period and returns to the main flow to move downward in the channel. The velocity vector map from numerical simulation predicts the maximum velocity in the middle portion of the spillway, that is, near the pseudo-bottom line. A volume of fluid model coupled with a standard k-e turbulence model is used in the CFD simulations to predict the location of the air-water air-suspension interface. The results are compared with experimental measurements. The calculated interface position agrees well with the experimental measurements. The migration and transport of particles are evaluated based on a diffusive flux model of shear induced particle migration. The contour map for velocity and particle concentration shows a remarkable increase in particle concentration near the air-suspension interface.