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Screens have proven to be an effective choice for decreasing scour downstream of small hydraulic structures. This paper studies experimentally the performance of an inclined perforated sill with a fixed porosity of 41.1% and varied height. Six different relative heights (from 0.34 to 2.25) and inclination angles of screens (30 ˚, 60 ˚, 90 ˚, 120 ˚, and 150) were tested under different flow conditions. The presence of a screen in the stilling basin reduced the maximum scour depth until the relative screen height was less than two compared to the no-screen case. A relative screen height greater than two increases the maximum scour depth. The best relative height of the screen is found to be approximately unity from the scour point of view. while the relative energy loss increases positively with the relative screen heights. Moreover, the vertical angles provide the best conditions for scour and energy dissipation. Finally, an empirical equation was developed to predict the maximum scour depth. A good agreement was found between the results of the predicted equation and the experimental results, with a mean relative error of about 6%. [ABSTRACT FROM AUTHOR]

A numerical simulation using Flow-3D software was conducted to study the characteristics of forced hydraulic jump. The purpose of this study is mainly to improve the efficiency of the stilling basin for increasing energy dissipation. The generated model is a spillway followed by a stilling basin that contains scattered baffle blocks as energy dissipators in different shapes and arrangements, placed in regular or staggered rows, and followed by a positive step at the same height. Sixty runs were considered, and each configuration of baffle blocks was tested under five values of discharge (80, 100, 120, 140, and 160 liters per second). The numerical results showed that the obstacles have a significant effect on improving the flow characteristics and increasing energy dissipation. The best case is installing seven rows of circular baffle blocks in a staggered way at equal distances in the stilling basin, and the relative energy loss ranges from 50% to 60% according to flow conditions. [ABSTRACT FROM AUTHOR]

The hydraulic jump is a natural phenomenon that occurs when the flow transitions from a supercritical flow to a subcritical flow within a short distance. The hydraulic jump is considered one of the most effective methods of dissipating energy through the stilling basin downstream of the control structures. The energy dissipation in the stilling basin contributes to protecting the area downstream of the control structures from erosion which may cause the collapse of the structure. The aim of this study is to calibrate the Flow 3D program using practical experiments. A three-dimensional numerical simulation was performed using the Flow 3D program to investigate the dissipation of energy due to a hydraulic jump through stilling basins with a negative step and compare the results of the study with the results of the practical experiments. (The simulated experiments in this paper using the Flow 3D program were performed at the National Centre for Water Research, Egypt.) It was clear from the comparison that the program has a high ability to simulate the phenomenon and to show results that are close to reality with an error of not more than 10%. [ABSTRACT FROM AUTHOR]

Stilling basins are designed to reduce the high kinetic energy of supercritical flow in a downstream spillway. The USBR II stilling basin is distinguished by chute blocks fixed at the upstream end and a dented sill at the downstream end, allowing for the effective dissipation of excess energy. This research investigates the effect of chute-block geometry on the hydraulic performance of the USBR II stilling basin. Six modified chute-blocks with identical dimensions and spacings as standard blocks were constructed and evaluated for six incoming Froude-number values. The results indicate that chute blocks containing stepped side walls are more effective than standard blocks, increasing energy dissipation by 1.47% and decreasing the sequent depth ratio by 3.91%. Blocks with gradually increased spacings lose 0.7% more energy than standard blocks and reduce the sequential depth ratio by 1.91%. However, blocks with prismatic spacings and top surface angles of 152 degrees, relative to the downstream slope of the spillway, are less effective than standard blocks with energy dissipation reduced by 2.73% and the depth ratio increased by 7.24%. [ABSTRACT FROM AUTHOR]

Abstract Energy dissipater in the stilling basin is a structure designed to protect downstream of the spillway from erosion and scour by reducing flow energy in the energy dissipation pool. Energy dissipation pool is an important element of hydraulic structures as a transition between the high-velocity flow and the sensitive tail water. The aim of this study is to investigate the energy dissipation ratios of baffle blocks which constructed in Type III stilling basin with different geometric shapes by using physical and numerical modeling methods. In all types of baffle blocks, the block heights and widths are chosen equally, and the total baffle block lengths are designed to be 50% of the stilling basin width. Energy dissipation ratio of the baffle blocks in 4 different geometric shapes was determined in 3 different layouts as single row, two rows and two rows without threshold structure, in a total of 12 different designs and 7 different flow rates are tested. In addition, these experimental studies were tested in the FLOW-3D software program, and the results of experimental and numerical studies were compared. As a result of the study, it was determined that the T-shaped energy-dissipating block had the highest energy dissipation ratio, and it was observed that the results obtained from the experimental studies and the FLOW-3D software were similar to each other with in the range of 5%.

ABSTRACT Turbulent flow is responsible for a significant portion of damages and failures in dams. This paper sought to introduce novel approaches to the estimation of typical parameters used in the design of stilling basins. The standard deviations of pressure samples of 24 hydraulic jumps were analysed throughout the stilling basin longitudinal centreline, and the positions of maximum pressure fluctuation were identified. Next, mean and extreme pressures occurring at this position were calculated. Finally, these parameters were plotted against the inflow Froude number and curves were adjusted to the data. The position where maximum turbulence of undular, weak and oscillating jumps occurs varies according to the Froude number. Steady and strong jumps are more likely to induce negative pressures on the stilling basin. The findings of this paper broaden the knowledge on which regions of the stilling basin must receive special attention, and on how to minimize the chances of damages.

Energy dissipater in the stilling basin is a structure designed to protect downstream of the spillway from erosion and scour by reducing flow energy in the energy dissipation pool. Energy dissipation pool is an important element of hydraulic structures as a transition between the high-velocity flow and the sensitive tail water. The aim of this study is to investigate the energy dissipation ratios of baffle blocks which constructed in Type III stilling basin with different geometric shapes by using physical and numerical modeling methods. In all types of baffle blocks, the block heights and widths are chosen equally, and the total baffle block lengths are designed to be 50% of the stilling basin width. Energy dissipation ratio of the baffle blocks in 4 different geometric shapes was determined in 3 different layouts as single row, two rows and two rows without threshold structure, in a total of 12 different designs and 7 different flow rates are tested. In addition, these experimental studies were tested in the FLOW-3D software program, and the results of experimental and numerical studies were compared. As a result of the study, it was determined that the T-shaped energy-dissipating block had the highest energy dissipation ratio, and it was observed that the results obtained from the experimental studies and the FLOW-3D software were similar to each other with in the range of 5%. [ABSTRACT FROM AUTHOR]

Stepped spillways have become increasingly popular due to the low-cost of construction and high efficiency. A stepped spillway is a hydraulic structure that is an integral part of the dam that allows the safe passage of overtopping flows. In this paper, an experimental study was employed to investigate the stepped spillway with four steps of 32 cm height and 54 cm width contracted by wing wall width (C) = 0.2 from the width of the flume. Eighteen runs were carried out considering different positions, heights, and widths of the baffle to increase the energy dissipation resulting from this contraction stepped spillway. The results indicated that the best position of baffles was (a/y2) = 1.4, the relative baffles height was (hb/y1) = 0.95, and the best relative baffles widths (wb/W) = 0.68, compared with cases of contraction stepped spillway without baffles. The results showed that the baffles on the stilling basin downstream stepped spillway increase the energy dissipation. Simple formulae were also deduced to evaluate the energy parameters. [ABSTRACT FROM AUTHOR]

This paper presents a new scour model (SM) that is able to evaluate the rock scour development, shape, ultimate depth and probability of occurrence. The model takes into account two main scour mechanisms: (1) the maximum rock crack extension that mainly depends on the geology, rock characteristics/mechanics and hydraulic fracturing analysis; and (2) the isolated rock block stability that depends on the flow hydraulics and rock block dimensions. The former defines the ultimate extent of the fractured area in a rock matrix where the isolated rock blocks can be detected; only in this area, the rock block stability analysis can be performed afterwards. The isolated rock block stability has been studied in the literature; on the contrary, the information related to the rock crack propagation in dissipaters is limited, which is investigated in this paper. Here, the expected maximum rock crack extension is defined by a threshold on the stress intensity factor. The rock stress intensity factor is investigated via stochastic approaches, compatible with the stochastic nature of the turbulent bottom pressure field, with the support of physical hydraulic modelling results. The proposed SM is a physically based model that couples the hydraulics and geological aspects of scour phenomena, allowing a realistic evaluation of the rock scour. This is drawn out by the comparison between the maximum scour depth computed via the rock block stability analysis and the maximum depth of rock matrix fractured area where the isolated rock blocks can be formed by the incident flow; the smallest depth gives the expected scour. The ultimate scour could be significantly smaller than the one computed via the approaches in the literature, especially for compact rocks suitable for unlined dissipaters. This highlights the relevance of this study that takes into account the high-velocity flow characteristics such as aeration and turbulence effects as well as the main geomechanical characteristics of the whole rock mass obtained by geological surveys. Furthermore, the SM stochastic approach makes it suitable in the risk-based design of dams, hydropower outlet works and other hydraulic structures as well as dam stability assessment. The model is validated using well-known real-life scour cases in the literature such as Wivenhoe and Cabora Bassa dams. A design example is included in the paper demonstrating the evaluation of the rock scour downstream of a large dam. Highlights: The paper presents a novel probabilistic rock scour model applicable to hydraulic structures. The model is able to evaluate the rock scour development, ultimate depth and probability of occurrence in unlined dissipaters. This physically-based model couples the hydraulics and geological aspects of scour phenomena allowing a realistic evaluation of the rock scour. The model is suitable for the risk-based design of dams, hydropower outlet works and other hydraulic structures as well as dam stability assessment. The model is validated using knowing real-life scour cases in the literature such as Wivenhoe and Cabora Bassa dams. [ABSTRACT FROM AUTHOR]

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When designing dam spillway structures, the most significant consideration is the energy dissipation arrangements. Different varieties of baffle blocks and stilling basins have been used in this context. However, the hydraulic jump form of stilling basin is considered to be the most suitable. The main objective of this research was to introduce four different baffle block shapes (models arranged from A to D, installed at slopes 0.00, 0.04, 0.06 and 0.08 in the stilling basins). To illustrate the consequences for the qualities of pressure-driven bounce, each model was attempted in the bowl. The trials applied Froude numbers between 6.5 and 9.2. The puzzle square model D provided the best outcomes compared to the models A, B, C and smooth. Model D with different models at inclines 0.00, 0.04, 0.06 and 0.08 was used to consider the impacts of perplex hinders on water driven-bounce when bed slants were changed. When the model D baffle used instead of a smooth bed at 0.08 slope, the reduction in y2 / y1 reached 12.8%, and Lj / y1 was 18.9%. Among the different bed slopes, a normal decrease in y2 / y1 ranged from approximately 10.3%, whereas the normal decrease in Lj / y1 was about 13.8% when the model D baffle was used instead of the model A baffle with a horizontal slope bed of 0.00. The results show that the new shapes led to a decrease in sequent profundity proportion and length of jump proportion; however, the energy dissipation proportion increased.

The high flow velocity downstream of weirs and gates can cause the destruction of erosive beds in rivers or even non-erosive channels. To reduce the flow's kinetic energy, structures are needed to consume this energy. Expansion basins are often used downstream of structures such as weirs, gates, and chutes to increase energy dissipation in hydraulic jumps. Various methods are used to stabilize asymmetric hydraulic jumps in abrupt expanding channels. In this study, the interaction of multiple submerged water jet injection systems with S-type hydraulic jump for stabilizing and stabilizing the hydraulic jump was investigated. The different configurations of the jet system were tested with Froude numbers 7.4, 8.7, and 9.5, and finally, three optimal configurations were selected as configurations 1, 2, and 3. In order to investigate the performance of the jet injection system under other hydraulic boundary conditions, flow velocities downstream of the jet system were measured for three optimal configurations with different depths of the tailwater. Comparison of the results of using a water jet injection system with S-type hydraulic jump showed that the energy and momentum correction coefficients in all different configurations were significantly reduced. The highest relative energy loss was observed in configuration 3, equal to 68.42%. The results showed a good performance of the jet injection system in stabilizing the asymmetric hydraulic jump S and reducing the length of the stilling basin. [ABSTRACT FROM AUTHOR]

Cross-section expansion can be a convenient solution to enhance the performance of stilling basins. However, under certain working conditions, the undesired phenomenon of flow instability can result in asymmetric flow with less efficient dissipation and high local velocity concentrations in the tailwater channel. This paper presents an experimental investigation on a recently proposed dissipator consisting of a series of cross beams, tested in various geometric configurations and under different hydraulic conditions. The effectiveness of the device is first analyzed in terms of flow uniformity and velocity in the channel bed while also providing a theoretical explanation of the observed dissipative mechanisms. Furthermore, in a second phase, the performance of the system is tested under variable tailwater conditions, with the description of the three-dimensional flow patterns observed in the downstream channel. The results suggest that the installation of this type of dissipator allows for the benefits of cross-section expansion while avoiding its damaging effects. [ABSTRACT FROM AUTHOR]

Recently, neural network appears as powerful tool for scientist and engineers' applications, a wide range of phenomenon are simulated using this approach successfully. The basic concept of this approach depended on the human brain and how a huge number of neurons transmit the information to result the output activities. This approach has the ability to work with the lack in information by storing the phenomenon behavior in the entire network. In this study, the capacity of NN model to foresee the most extreme scour profundity information downstream of (DS) abrupt extending stilling bowls (SESB) is examined. The information utilized for preparing the system are gathered utilizing a lab flume 30 cm wide, 30 cm deep and 17.5 m working segment long. Distinctive stream conditions and diverse extension are utilized through the test program. 80% of the information are utilized for preparing the system while the remainder of the information are utilized for approving and testing the created ANN model. (80, 15, 5) % of data are taken for training, testing and holdout respectively to build the model, from the result, ANN technique is the best method to predict the maximum scour depth due to high correlation where R2 is found to be 0.98 in that proposed model in this study. [ABSTRACT FROM AUTHOR]

When designing dam spillway structures, the most significant consideration is the energy dissipation arrangements. Different varieties of baffle blocks and stilling basins have been used in this context. However, the hydraulic jump form of stilling basin is considered to be the most suitable. The main objective of this research was to introduce four different baffle block shapes (models arranged from A to D, installed at slopes 0.00, 0.04, 0.06 and 0.08 in the stilling basins). To illustrate the consequences for the qualities of pressure-driven bounce, each model was attempted in the bowl. The trials applied Froude numbers between 6.5 and 9.2. The puzzle square model D provided the best outcomes compared to the models A, B, C and smooth. Model D with different models at inclines 0.00, 0.04, 0.06 and 0.08 was used to consider the impacts of perplex hinders on water driven-bounce when bed slants were changed. When the model D baffle used instead of a smooth bed at 0.08 slope, the reduction in y2 / y1 reached 12.8%, and Lj / y1 was 18.9%. Among the different bed slopes, a normal decrease in y2 / y1 ranged from approximately 10.3%, whereas the normal decrease in Lj / y1 was about 13.8% when the model D baffle was used instead of the model A baffle with a horizontal slope bed of 0.00. The results show that the new shapes led to a decrease in sequent profundity proportion and length of jump proportion; however, the energy dissipation proportion increased. [ABSTRACT FROM AUTHOR]

Pressure fluctuations are a key issue in hydraulic engineering. However, despite the large number of studies on the topic, their role in spatial hydraulic jumps is not yet fully understood. The results herein shed light on the formation of eddies and the derived pressure fluctuations in stilling basins with different expansion ratios. Laboratory tests are conducted in a horizontal rectangular flume with 0.5 m width and 10 m length. The range of approaching Froude numbers spans from 6.4 to 12.5 and the channel expansion ratios are 0.4, 0.6, 0.8, and 1. The effects of approaching flow conditions and expansion ratios are thoroughly analyzed, focusing on the dimensionless standard deviation of pressure fluctuations and extreme pressure fluctuations. The results reveal that these variables show a clear dependence on the Froude number and the distance to the hydraulic jump toe. The maximum values of extreme pressure fluctuations occur in the range 0.609

As part of the search for safe and economic design criterion to line slabs of stilling basins, the present study is one of the first to calculate the center of pressure, uplift forces, and momenta from a spatiotemporal analysis of the pressures measured above and below instrumented slabs in a physical model. Controlled release of the waterstops, and variation in the dimensions of expansion joints and in the gap between foundation and the lining slab were carried out in order to consider their effects on the magnitudes of uplift forces and momenta. An offset of the center of pressure from the slab’s center of gravity was identified. The objective of this work was to consider the failure mechanism induced by momentum in the slab’s design. Design criterion to make the lining slab’s thickness to length between 6 and 12 times the incident flow depth, is proposed, and this is compared to other design criteria.

This research studies the hydraulic behavior and the problem solving alternatives of original until final design, and the most effective stilling basin and downstream regulator channel for decreasing back water from the upstream water level in the dam foot. The methodology consists of physical modeling in the Laboratory of River and Swamp, Department of Water Resources, Faculty of Engineering, University of Brawijaya. The methods include the USBR for the hydraulic analysis, the Hind's formulation for the side channel analysis, the energy equation by analyzing the standard step for the transition and the chute way analysis, and the USBR type III for designing the stilling basin. A square cross-section with the Manning coefficient of 0.40 is used for determining the control of the Tail Water Level (TWL) and a trapezoidal crosssection with the Manning coefficient of 0.39 is used for the final design. However, the equation of Schotlisch and Veronise is used for the local scouring analysis. The result of Model Test and analysis indicates that there are some differences among the analysis in every point of the building. Therefore, the relative error is needed to know how big the error in the comparison result. [ABSTRACT FROM AUTHOR]

The present article is the second of a series of seven, all relative to energy dissipators that can be used in hydraulic works. The whole group of these articles conform a monograph about the subject that is being prepared by the author, concluding it by the middle of the 2017 year and later on incorporating it into a new edition - in preparation - of the textbook "Spillways and Intake Structures." This second article is a detailed presentation about two structures of energy dissipation that have a wide universal use. [ABSTRACT FROM AUTHOR]

In the present study, the effect of inlet flow condition of a stilling basin on the hydrodynamic parameters of flow as well as velocity and pressure distributions, vorticities, pressure fluctuations, turbulence intensities, and hydrodynamic loads were investigated. To do so, two practical and usual cases of flow at the downstream of a bottom outlet and downstream of a chute spillway were simulated and analyzed. To verify the numerical simulations, a scaled physical model was employed. Large eddy simulation and volume of fluid models were used to simulate the turbulence and free surface, respectively. Results showed that when moving the place of the formed hydraulic jump at the first 25% length of the stilling basin, pressure fluctuations were on average 42.6% more at downstream of the chute spillway in comparison with bottom outlet. However, in the middle of the stilling basin length due to the impact of the jet at the downstream of the bottom outlet model, the pressure fluctuations were on average 47.3% more than the pressure fluctuations at the downstream of the spillway model. The maximum values of vorticity and turbulence intensity occurred in the section of hydraulic jump formation in the stilling basin. [ABSTRACT FROM AUTHOR]

Serious damage may occur to concrete hydraulic structures, such as water galleries, spillways, and stilling basins, due to the abrasive erosion caused by the presence of solid particles in the flow. This underlines the importance of being capable in providing characterization of the concrete from the point of view of its vulnerability to abrasive erosion, in order to improve the design of the structure and the material selection. Nevertheless, the existing apparatus for concrete abrasive erosion testing are either far from allowing realistic simulation of the actual environment in which this phenomenon occurs, or show a large degree of complexity and cost. An alternative method has been developed with the aid of Computational Fluid Dynamics (CFD). CFD was first employed to verify the effectiveness of a new laboratory equipment. Afterwards, a parameter has been introduced which, by successful comparison against preliminary experiments, proved suitable to quantify the effect of the fluid dynamic conditions on the concrete abrasive erosion, thereby opening the way to CFD-based customization of the apparatus. In the future, the synergy of numerical and physical modelling will allow developing predictive models for concrete erosion, making it possible to reliably simulate real structures. [ABSTRACT FROM AUTHOR]

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

The paper presents the results of an experimental study carried out to investigate the effect of geometric and hydraulic parameters on energy dissipation and location of the hydraulic jump, with a change in the height of roughness elements and the divergence of walls in different discharges. Experiments were conducted in a horizontal rectangular basin with gradual expansion 0.5mwide and 10mlong. Four physical models were fixed in the flume. The measured characteristics of the hydraulic jump with different divergences ratio (B = b1/b2 = 0.4, 0.6, 0.8, 1) and the inflow Froude numbers (6 < Fr1 < 12) were compared with each other and with the corresponding values measured for the classical hydraulic jump. The results showed that the tailwater depth required to form a hydraulic jump and also the roller length of the hydraulic jump and the length of the hydraulic jump on a gradual expansion basin with the rough bed were appreciably smaller than that of the corresponding hydraulic jumps in a rectangular basin with smooth and rough bed. With the experimental data, empirical formulae were developed to express the hydraulic jump characteristics relating to roughness elements height and divergence ratio of wall. Also, the applicability of some empirical relationships for estimating the roller length was tested. [ABSTRACT FROM AUTHOR]

The present paper deals with a United States Bureau of Reclamation (USBR) Type II stilling basin, which is characterized by blocks at the end of the chute and a dentated sill at the end of the basin. For this basin, USBR only gives overall design criteria concerning basin length and block dimensions on the basis of the assumption that the hydraulic jump remains confined within the sill. No considerations are provided concerning possible different jump types, pressure regimes, and forces acting on the sill. To comply with such a lack, an experimental campaign was undertaken that focuses on the differences among hydraulic jump types that can occur in a USBR Type II stilling basin. Jump types can range between submerged and spray jump types; accordingly, dimensionless relations are provided to predict jump type and position for assigned boundary conditions, with particular concern about the submerged/nonsubmerged distinction. Considerations about the drag force and drag coefficients are provided, along with estimates of pressure extreme fluctuations. Finally, an evaluation of the dissipation efficiency is presented for both submerged and nonsubmerged jumps, enabling comparisons among different jump types and with classical hydraulic jump. [ABSTRACT FROM AUTHOR]

The spillway gates of the Petitcodiac Causeway, a hydraulic structure ~35 km upstream of the mouth of the Petitcodiac River in New Brunswick, Canada, were permanently opened in April 2010. The short-term effect opening the spillway gates had on downstream intertidal mudflats of the upper Bay of Fundy was investigated. Specifically, a multivariate before-after-control-impact design was used to determine if opening the spillway gates affected the invertebrate community (crustaceans, polychaetes, and molluscs), abiotic sediment conditions (sediment water content, mean particle size, penetrability, and depth of the apparent redox potential discontinuity), or resource availability (sediment chlorophyll a concentration and organic matter content) of five intertidal mudflats (two impacted sites, three reference sites) spanning Chignecto Bay, the northern arm of the upper Bay of Fundy, up to 5 months post-opening. No biologically or statistically meaningful differences were detected between impacted and reference sites for any of the measured variables. This suggests that opening the causeway did not have a quantifiable impact on these intertidal mudflats, at least within half a year of the opening. This is likely a result of the macrotidal nature of the Bay of Fundy that overwhelmed any immediate changes to hydrodynamics that occurred after the opening of the causeway gates. [ABSTRACT FROM AUTHOR]

The article deals with problems connected with harbor and offshore strips wave protection. An effectiveness analysis of existing protection methods has been conducted; essential measures for coast protective structures improvement have been defined. A unique quickly protecting structure has been designed. Experimental research results of constructed coast protection works model done in hydrowave tray have been enclosed. Structural evaluation of proposed construction has been made; conclusions about feasibility as well as expediency of using such type of construction have been drawn. Upgrade options of the construction have been considered. [ABSTRACT FROM AUTHOR]

Hydraulic structure undermining attributable to scour can cause structural damage or collapse. Experiments were performed in a laboratory channel on scour downstream of a stilling basin of a low-head spillway to ascertain the feasibility of air injection for scour reduction, an idea that has not been previously attempted. Various hydraulic flow conditions without air injection indicate that the condition of stilling basin water elevation lower than the spillway crest, under high headwater-to-tailwater depth ratio, results in the deepest scour. Over 120 experiments were performed to determine the optimal parameters for scour reduction by air injection. It was found that optimal scourreducing conditions consist of (1) air injection at an air-to-water velocity ratio of 251, (2) vertical air injection at the same elevation as the stilling basin exit point, (3) using diffuser hole diameters corresponding to a ratio of air-to-water velocity equal to 251 spanning the entire width of the stilling basin, and (4) a diffuser hole spacing 0.04 times the diffuser width. Scour can thus be reduced by approximately 59% near the structure. Air compressors and diffuser pipe diameter and hole sizes corresponding to these conditions would be required in prototype installations. [ABSTRACT FROM AUTHOR]

One of the main causes of lining damage in stilling basins and at the toe of chute spillways is the global instantaneous uplift forces due to the difference in pressure acting on the upper and the lower surface of protection slabs or rock elements. Spillway stilling basin linings can be built according to two different techniques: using sealed joints or unsealed joints. In the case of sealed joints, the pressure underneath the slab is constant and the uplift force results from the pressure fluctuations acting on the slab. In the case of unsealed joints, the pressure propagation at the lower surface of the slab, being transferred through the joints, should also be considered. The aim of the paper is to study, define, and compare the design criteria in these two cases. In the present study, the pressure field on the slab is evaluated according to a recent method based on the Taylor hypothesis, whereas the pressure propagation under the slab is computed by a new 3D model based on unsteady flow analysis of seepage through porous media. By this approach, it is possible to consider the effect of finite thickness foundation layers, typical in the case of weirs for run-of-river power plants, earth dams, and rock-fill dams. Furthermore, to complete the presented design criteria, the dynamic behavior of anchored slabs is experimentally investigated with reference to the sealed joint case due to a lack of studies in the literature. [ABSTRACT FROM AUTHOR]

As part of the search for safe and economic design criterion to line slabs of stilling basins, the present study is one of the first to calculate the center of pressure, uplift forces, and momenta from a spatiotemporal analysis of the pressures measured above and below instrumented slabs in a physical model. Controlled release of the waterstops, and variation in the dimensions of expansion joints and in the gap between foundation and the lining slab were carried out in order to consider their effects on the magnitudes of uplift forces and momenta. An offset of the center of pressure from the slab's center of gravity was identified. The objective of this work was to consider the failure mechanism induced by momentum in the slab's design. Design criterion to make the lining slab's thickness to length between 6 and 12 times the incident flow depth, is proposed, and this is compared to other design criteria. [ABSTRACT FROM AUTHOR]

Laboratory experiments were conducted in order to investigate the effectiveness of a new scour countermeasure consisting of a horizontal extension plate (EP) downstream of a gated spillway-stilling basin structure. These experiments were performed on a 1:30 scale model of one of the South Florida Water Management District (SFWMD) gated spillway structures, the S65E gated spillway, because it has experienced worrisome downstream scour. Currently, riprap is the only scour countermeasure documented for these structures. EPs of various lengths were installed downstream of the stilling basin, and the equilibrium scour was measured. It was found that a plate length of approximately 1.88 times the exiting flow depth was the shortest length that resulted in significant scour reduction and downstream scour translation. Measured flow patterns reveal that the EP altered the flow patterns by transferring the plunging flow downstream and eliminating the near-bed reattachment and surface recirculation, possibly due to a decreased interaction between the plunging flow and the stilling basin face. [ABSTRACT FROM AUTHOR]

In this paper, a raft-typed wave energy dissipator is proposed, and a mathematical model for the hydrodynamics of such a dissipator is presented, based on Reynolds-averaged Navier–Stokes equations. The model is validated by a comparison of the numerical results with the results of other investigators. The validated model is then utilized to examine the effect of wave height, wave frequency, damping coefficient, flow velocity on wave energy dissipation ratio and wave transmission coefficient for a hinged twin-raft wave energy dissipator. Our results reveal that the differences in behaviour exhibited by an inviscid fluid and a viscous fluid can be large and vary considerably, depending on the flow velocity. [ABSTRACT FROM AUTHOR]

The paper presents the results from detailed experiments of the statistical structure of turbulence pressure fluctuations at the bottom of hydraulic jumps, with special reference to the spillway stilling basins lining design. Here, the whole spatial correlation structure of the fluctuating pressure field is required in order to evaluate slab stability. This is computed via simultaneous acquisition of the point pressure fluctuations on a dense grid in the hydraulic jump region, requiring a severe experimental work. As an alternative, one can evaluate the pressure spatial correlation structure via autocorrelation using one point pressure acquisition and applying the Taylor hypothesis. To adopt the Taylor hypothesis, one must know the pressure propagation celerity in space that can be obtained by comparing the whole spatial pressure correlation with the pivot point pressure autocorrelation. The experiments were performed by simultaneous pressure acquisitions at the bottom of a hydraulic jump for Froude numbers of the incident flow ranging from 4.9 to 10.3. From experiments, a criterion to define the pressure celerity as a function of the incident flow velocity is presented. The results highlight a good agreement between the relevant pressure statistical parameters as measured and the ones computed using the Taylor hypothesis. The comparison between the slab thicknesses, as computed via Taylor hypothesis, with the ones retrievable in literature, as obtained by direct force measurement on instrumented slabs in laboratory conditions, highlights the accuracy of the proposed approach that presents undeniable practical advantages. [ABSTRACT FROM AUTHOR]

Analyses of measured pressures using multiple sensors above and below a slab subject to supercritical flow and hydraulic jump are presented. Pressures were measured in a physical model constructed in the Hydraulic Laboratory of the Universidad del Valle in Cali, Colombia. Details such as expansion joints, waterstops, slab thickness, and soil-slab separation were simulated. Inflow was full and partially developed, with Froude numbers ranging from 2.84 to 11.6. The role of the expansion joints and waterstops in the generation of uplift pressure and hydraulic gradient below the slab were identified using pressure fields above and below the slab, in multiple tests. The results of this research are critical for the design of bottom slabs in hydraulic structures, which are required to withstand uplift forces and prevent internal erosion problems. [ABSTRACT FROM AUTHOR]

Eco-friendly hydraulic structures (such as block ramps, rock weirs and stepped gabion weir) are generally made of rocks placed in two or more layers on a sloped bed. They are usually used in mountainous rivers to control sediment transport. The downstream stilling basin plays an important role in terms of both energy dissipation and erosion control. In addition, a correct design of the downstream stilling basin can create an optimal habitat for fish species in the river. Therefore, in the present work, an attempt was made to control the scour depth downstream of a block ramp using rock structures. In particular, the analysis was focused on scour characteristics in the presence of a protected and enlarged downstream channel. Namely, an abrupt symmetrically enlarged channel was simulated downstream of block ramps. Eco-friendly protection structures, such as rock sills, were tested to limit the erosive process. Rock sills were placed transversally at different longitudinal and vertical positions in the stilling basin and scour morphology variations were investigated. Experiments were carried out for two different ratios of the width of the channel to the width of the ramp and three different ramp slopes. Several scour morphologies were distinguished and classified. In addition, empirical relationships were derived, by which it is possible to estimate the main scour geometry characteristics. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This research introduces an approach to predict maximum scour depth, scour hole length, and the length of the deepest point of the scour hole at equilibrium conditions at downstream of stilling basins by using the GEP. Five non-dimensional parameters in terms of physical properties of bed sediments, stilling basin length, tail water depth, and discharge of spillway were considered as input variables to evaluate the scour hole geometry. The GEP model was developed using experimental datasets collected from literature. Results of the GEP models were compared with those obtained using ANFIS and non-linear regression analysis. Performances indicated that the proposed GEP models to characterize scour hole geometry produced more accurate results than the other methods. In addition, results of sensitivity analysis to define the most effective independent parameters on scour hole geometry were reported. Finally, proper application of the proposed model has been confirmed as the GEP-based best formulation, which is a useful soft computing tool for prediction of scour hole geometry at downstream of a stilling basin. [ABSTRACT FROM AUTHOR]

Barrage Regulators are considered one of the most important hydraulic structures that used to control the released discharge and upstream and downstream water levels. New barrages are constructed on the River Nile instead of the oldest ones, which are not able to resist the requirements of increasing head difference upon their gates. The present study was focused on investigating experimentally the effect of sill over stilling basin of Nagaa Hammadi regulator on the length of reverse flow behind sill, velocity at the end of stilling basin, energy dissipation, length of submerged hydraulic jump and scour formation downstream regulator apron. Experimental work was carried out on a re-circulating flume with 1.0 m wide, 26.0 m long and 1.2 m deep, with discharges range from 40 to 190 l/s. It is found that the sill over stilling basin has great effect on flow characteristic and local scour depth formed downstream regulator especially for sill with right and slopped faces at the upstream and downstream, respectively. The present study shows that, the reverse flow length downstream sill decreases as the submergence ratio and Froude number increase. In addition, using sill with right upstream and slopped face at downstream with Ls/L=0.6, reduces the length of submerged hydraulic jump by 59% in average and thus leads to decrease stilling basin length. Local scour depth downstream hydraulic structures were reduced by 43%. Moreover, the energy dissipation was increased by 30% compared to the no sill case. Finally, Empirical equations are developed using multiple linear regressions analysis. [ABSTRACT FROM AUTHOR]