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Advances in Spillway Hydraulics: From Theory to Practice

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A special issue of Water (ISSN 2073-4441). This special issue belongs to the section "Hydraulics and Hydrodynamics".

Deadline for manuscript submissions: closed (31 July 2022) | Viewed by 41568

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Prof. Dr. Jorge Matos

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Guest Editor

CERIS, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal
Interests: hydraulic engineering; hydraulic structures; dam hydraulics; hydropower; environmental hydraulics; experimental methods; physical modeling
Special Issues, Collections and Topics in MDPI journals

Dr. Sebastien Erpicum

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Guest Editor

UEE-HECE, Liege University (ULiege), Belgium
Interests: hydraulic engineering; hydraulic structures; environmental hydraulics; ecohydraulics; experimental methods; physical modeling; composite modeling; hydropower; flood evaluation and flood protection

Prof. Dr. Anton J. Schleiss

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Guest Editor

Ecole polytéchnique fédérale de Lausanne (EPFL), Switzerland
Interests: hydraulic engineering; hydraulic structures; dam hydraulics and safety; hydropower; reservoir sedimentation; rock scour; flood protection and forecast; high-head-pressure conduits; coupled mechanical-hydraulic problems; physical modeling; river morphology and biodiversity

Special Issue Information

Dear Colleagues,

In the past decades, significant advances have been achieved in the field of hydraulic structures for dams, in particular water release structures including spillways with chutes and their terminal energy dissipators. In addition to recent innovative projects, a large number of older spillways have been reexamined with regard to their suitability to pass the revised design flood estimates. Of these, many contain features which create complex flow patterns and make prediction of spillway capacity and performance uncertain. On the other hand, safe and reliable spillways are of paramount importance, considering that many dam failures were caused by improperly designed spillways with insufficient discharge capacity. In addition to providing sufficient discharge capacity, the arrangement of the spillway must be such that releases do not erode or undermine the downstream toe of the dam and its abutments.

In particular, the past few decades have witnessed a significant development in spillway design and in the understanding of spillway hydraulics, for a variety of reasons, such as recent advances in construction technology (e.g., roller-compacted concrete and cemented soil dams for new projects or for rehabilitation), large-scale model studies making use of sophisticated instrumentation (e.g., conductivity or fiber-optical probes for measuring macroscopic and microscopic air-water flow features, optical and LiDAR techniques), computational fluid dynamics (CFD) modeling applied to complex designs, prototype experience, as well as composite or hybrid modeling.

This Special Issue focuses on recent advances in spillway hydraulics, covering theory and applications. Topics that have not been sufficiently covered in standard design guidance are also welcome, including practical design considerations, as well as new developments from the operation, maintenance, and inspection of spillways and respective intake or terminal structures.

Prof. Dr. Jorge Matos
Dr. Sébastien Erpicum
Prof. Dr. Anton J. Schleiss
Guest Editors

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Keywords

hydraulic structures
dams
spillways
weirs—gated or ungated
chutes
energy dissipators
experimental modeling
CFD modeling
prototype tests
case studies

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Published Papers (12 papers)

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Editorial

Jump to: Research

10 pages, 254 KiB

Open AccessEditorial

Advances in Spillway Hydraulics: From Theory to Practice

by Anton J. Schleiss, Sebastien Erpicum and Jorge Matos

Water 2023, 15(12), 2161; https://doi.org/10.3390/w15122161 - 7 Jun 2023

Cited by 6 | Viewed by 3774

Abstract

Over the past decades, significant advances have been achieved in hydraulic structures for dams, namely in water release structures such as spillway weirs, chutes, and energy dissipators. This editorial presents a brief overview of the eleven papers in this Special Issue, Advances in Spillway Hydraulics: From Theory to Practice, and frames them in current research trends. This Special Issue explores the following topics: spillway inlet structures, spillway transport structures, and spillway outlet structures. For the first topic of spillway inlet structures, this collection includes one paper on the hydrodynamics and free-flow characteristics of piano key weirs with different plan shapes and another that presents a theoretical model for the flow at an ogee crest axis for a wide range of head ratios. Most of the contributions address the second topic of spillway transport structures as follows: a physical modeling of a beveled-face stepped chute; the description and recent developments of the generalized, energy-based, water surface profile calculation tool SpillwayPro; an application of the SPH method on non-aerated flow over smooth and stepped converging spillways; a physical model study of the effect of stepped chute slope reduction on the bottom-pressure development; an assessment of a spillway offset aerator with a comparison of the two-phase volume of fluid and complete two-phase Euler models included in the OpenFOAM^® toolbox; an evaluation of the performance and design of a stepped spillway aerator based on a physical model study. For the third topic of spillway outlet structures, physical model studies are presented on air–water flow in rectangular free-falling jets, the performance of a plain stilling basin downstream of 30° and 50° inclined smooth and stepped chutes, and scour protection for piano key weirs with apron and cutoff wall. Finally, we include a brief discussion about some research challenges and practice-oriented questions. Full article

(This article belongs to the Special Issue Advances in Spillway Hydraulics: From Theory to Practice)

Research

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23 pages, 5819 KiB

Open AccessArticle

Plain Stilling Basin Performance below 30° and 50° Inclined Smooth and Stepped Chutes

by Ivan Stojnic, Michael Pfister, Jorge Matos and Anton J. Schleiss

Water 2022, 14(23), 3976; https://doi.org/10.3390/w14233976 - 6 Dec 2022

Cited by 4 | Viewed by 3473

Abstract

Energy dissipators, such as stilling basins, are usually required at the toe of stepped chutes to achieve adequate and safe operation of the spillway. Stepped chute hydraulics has been extensively studied in last several decades, however, only limited knowledge is available on the stilling basin performance below stepped chutes. In particular, the effect of the chute slope remains unknown, despite being a central design issue. Therefore, an experimental campaign was performed using a 30° or 50° inclined smooth or stepped chute with an adjacent conventional plain stilling basin. The experimental results indicated that, within the stilling basin, the surface characteristics and the roller as well as hydraulic jump lengths are practically independent of the chute slope. This further strengthens the previous findings that stepped chutes require 17% longer dimensionless jump lengths and consequently stilling basin lengths. The experimental results also confirmed that stepped chutes generated increased extreme and fluctuating bottom pressure characteristics at the stilling basin entrance area. With increasing chute slope, the latter were found to significantly magnify. However, such increased magnitudes were not expected to provoke cavitation damage as stepped chute inflows induced bottom aeration at the basin entrance, irrespective of the chute slope. Full article

(This article belongs to the Special Issue Advances in Spillway Hydraulics: From Theory to Practice)

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27 pages, 9279 KiB

Open AccessFeature PaperArticle

Smooth and Stepped Converging Spillway Modeling Using the SPH Method

by Juliana D. Nóbrega, Jorge Matos, Harry E. Schulz and Ricardo B. Canelas

Water 2022, 14(19), 3103; https://doi.org/10.3390/w14193103 - 2 Oct 2022

Cited by 4 | Viewed by 2465

Abstract

Three-dimensional (3D) simulations using the smoothed particle hydrodynamics (SPH) method were performed for smooth and stepped spillways with converging walls, in order to evaluate the influence of the wall deflection and the step macro-roughness on the main non-aerated flow properties. The simulations encompassed a 1V:2H sloping spillway, wall convergence angles of 9.9° and 19.3°, and discharges corresponding to skimming flow regime, in the stepped chute. The overall development of the experimental data on flow depths, velocity profiles, and standing wave widths was generally well predicted by the numerical simulations. However, larger deviations in flow depths and velocities were observed close to the upstream end of the chute and close to the pseudo-bottom of the stepped invert, respectively. The results showed that the height and width of the standing waves were significantly influenced by the wall convergence angle and by the macro-roughness of the invert, increasing with a larger wall deflection, and attenuated on the stepped chute. The numerical velocity and vorticity fields, along with the 3D recirculating vortices on the stepped invert, were in line with recent findings on constant width chutes. Full article

(This article belongs to the Special Issue Advances in Spillway Hydraulics: From Theory to Practice)

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30 pages, 4297 KiB

Open AccessArticle

Flow at an Ogee Crest Axis for a Wide Range of Head Ratios: Theoretical Model

by Frédéric Stilmant, Sebastien Erpicum, Yann Peltier, Pierre Archambeau, Benjamin Dewals and Michel Pirotton

Water 2022, 14(15), 2337; https://doi.org/10.3390/w14152337 - 28 Jul 2022

Cited by 4 | Viewed by 2346

Abstract

The discharge coefficient of an ogee crest is a function of the ratio of the effective head to the design head. The purpose of the present study is to derive a theoretical model of this relation, which does not depend on empirical coefficients and whose predictions over a wide range of head ratios are accurate enough for practical use. The developments consider unsubmerged ogee crests without approach flow or lateral contraction effects, heads large enough to enable surface tensions to be neglected, and heads small enough to avoid flow separation. The method is based on potential flow theory, depth integration in a curvilinear reference frame, and critical flow theory. The characteristics of the crest shape are defined by the trajectory of a free jet passing over the crest at the design head. The dimensionless equations show that the position of the critical section is not at the apex of the crest. Nevertheless, they also suggest an approximate equation at the apex of the crest from which the discharge coefficient is derived, together with the local water depth, velocity, and pressure distribution. The results compare well with experimental data for head ratios between 0 and 5, which validates the underlying assumptions of the theoretical model. Full article

(This article belongs to the Special Issue Advances in Spillway Hydraulics: From Theory to Practice)

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20 pages, 2556 KiB

Open AccessArticle

SpillwayPro: Integrated Water Surface Profile, Cavitation, and Aerated Flow Analysis for Smooth and Stepped Chutes

by Tony L. Wahl and Henry T. Falvey

Water 2022, 14(8), 1256; https://doi.org/10.3390/w14081256 - 13 Apr 2022

Cited by 5 | Viewed by 3037

Abstract

Spillways of large and small dams experience flow conditions that exceed the capabilities of common water surface profile computer programs. Unique channel geometries, steep slopes, and streamline curvature demand rigorous mathematics, while phenomena associated with aerated flow and potential cavitation require special analyses, especially for stepped chutes. SpillwayPro is a generalized, energy-based, water surface profile calculation tool for both smooth and stepped chutes that integrates cavitation analysis and aerated flow effects, with separate modules supporting aerator design and the development of optimized structure profiles that meet cavitation parameter objectives. Simultaneous calculation of smooth and stepped-chute flow profiles enables the rapid assessment of the energy dissipation benefits of steps, as well as their unique aerated flow and cavitation issues. SpillwayPro’s technical basis is presented, and its results are compared to the data from prototype case studies and empirical methods developed from large-scale laboratory studies. SpillwayPro’s fundamental energy-based methods are useful for cases that differ from idealized empirical approaches and would benefit from a more rapid analysis than can be accomplished with physical or computational fluid dynamics (CFD) modeling. Full article

(This article belongs to the Special Issue Advances in Spillway Hydraulics: From Theory to Practice)

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13 pages, 16500 KiB

Open AccessArticle

Physical Modeling of Beveled-Face Stepped Chute

by Sherry L. Hunt, Kem C. Kadavy, Tony L. Wahl and Dana W. Moses

Water 2022, 14(3), 365; https://doi.org/10.3390/w14030365 - 26 Jan 2022

Cited by 4 | Viewed by 2475

Abstract

New construction practices for roller compacted concrete (RCC) overlays and stepped chutes are changing the step geometry from a traditional square-edge, vertical face to a 45° beveled face. A large-scale 3(H):1(V) (i.e., θ = 18.4°) stepped chute model was tested with a 45° beveled face step with a height (h) of 152 mm. Results were compared to data on square-edge, vertical face steps previously obtained. The distance to the inception point of free-surface aeration normalized by the surface roughness was reduced approximately 25% for the same Froude number defined in terms of roughness height. An existing inception point relationship for vertical face steps was adjusted with a best fit correction factor to predict the free-surface inception point for this chute slope and beveled face angle. Relative flow depths, mean air concentration, and energy loss data showed similar general trends for vertical face and beveled face steps, but the depths and air concentrations for beveled face steps were slightly higher for equal values of relative free-surface inception point, L_i/L, and relative step height (e.g., h/d_c). Energy loss at the free-surface inception point ranged from approximately 20 to 40% of total head for both step types. Additional research is needed to determine the generalized effects of the bevel angle and the chute slope on flow properties. This research is expected to be used by field engineers for the design of stepped chutes with beveled face steps. Full article

(This article belongs to the Special Issue Advances in Spillway Hydraulics: From Theory to Practice)

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22 pages, 5487 KiB

Open AccessFeature PaperArticle

Performance and Design of a Stepped Spillway Aerator

by Stéphane Terrier, Michael Pfister and Anton J. Schleiss

Water 2022, 14(2), 153; https://doi.org/10.3390/w14020153 - 7 Jan 2022

Cited by 5 | Viewed by 2796

Abstract

Stepped spillways are frequently limited to specific discharges under around 30 m²/s due to concerns about potential cavitation damages. A small air concentration can prevent such damages and the design of bottom aerators is well established for smooth chutes. The purpose of this study is to systematically investigate the performance of a deflector aerator at the beginning of stepped chutes. Six parameters (chute angle, step height, approach flow depth, approach flow Froude number, deflector angle and deflector height) are varied in a physical model. The spatial air concentration distribution downstream of the aerator, the cavity sub-pressure, water discharge and air discharges are measured. The results describe the commonly used air entrainment coefficient, the jet length, as well as the average and bottom air concentration development to design an aerator. The lowest bottom air concentration measured in all tests is higher than the air concentration recommended in literature to protect against cavitation damages. And, unlike smooth chutes, there appears to be no significant air detrainment downstream of the jet impact. One deflector aerator seems therefore sufficient to provide protection of a stepped spillway. Full article

(This article belongs to the Special Issue Advances in Spillway Hydraulics: From Theory to Practice)

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14 pages, 3181 KiB

Open AccessFeature PaperArticle

Bottom-Pressure Development Due to an Abrupt Slope Reduction at Stepped Spillways

by Mohammad J. Ostad Mirza Tehrani, Jorge Matos, Michael Pfister and Anton J. Schleiss

Water 2022, 14(1), 41; https://doi.org/10.3390/w14010041 - 24 Dec 2021

Cited by 3 | Viewed by 3317

Abstract

Fluctuating bottom-pressures on stepped chutes are relevant for the spillway design. An abrupt slope reduction causes a local alteration of the bottom-pressure development. Little information is available regarding the air–water flow properties near an abrupt slope reduction on stepped chutes, particularly on the local pressure evolution. Nevertheless, the option of providing a chute slope reduction may be of interest in spillway layout. The experiments presented herein include pressure distributions on both vertical and horizontal step faces, subsequent to an abrupt slope reduction on stepped chutes. A relatively large-scale physical model including abrupt slope reductions from 50° to 18.6° and from 50° to 30° was used, operated with skimming flow. The data indicate a substantial influence of the tested slope reductions on the bottom-pressure development. In the vicinity of the slope reduction, the mean pressure head near the edge of the horizontal step face reached 0.4 to 0.6 times the velocity head upstream of the slope reduction, for critical flow depths normalized by the step height ranging between 2.6 and 4.6. Full article

(This article belongs to the Special Issue Advances in Spillway Hydraulics: From Theory to Practice)

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23 pages, 5518 KiB

Open AccessArticle

Do the Volume-of-Fluid and the Two-Phase Euler Compete for Modeling a Spillway Aerator?

by Lourenço Sassetti Mendes, Javier L. Lara and Maria Teresa Viseu

Water 2021, 13(21), 3092; https://doi.org/10.3390/w13213092 - 3 Nov 2021

Cited by 4 | Viewed by 2446

Abstract

Spillway design is key to the effective and safe operation of dams. Typically, the flow is characterized by high velocity, high levels of turbulence, and aeration. In the last two decades, advances in computational fluid dynamics (CFD) made available several numerical tools to aid hydraulic structures engineers. The most frequent approach is to solve the Reynolds-averaged Navier–Stokes equations using an Euler type model combined with the volume-of-fluid (VoF) method. Regardless of a few applications, the complete two-phase Euler is still considered to demand exorbitant computational resources. An assessment is performed in a spillway offset aerator, comparing the two-phase volume-of-fluid (TPVoF) with the complete two-phase Euler (CTPE). Both models are included in the OpenFOAM^® toolbox. As expected, the TPVoF results depend highly on the mesh, not showing convergence in the maximum chute bottom pressure and the lower-nappe aeration, tending to null aeration as resolution increases. The CTPE combined with the k–

ω

SST Sato turbulence model exhibits the most accurate results and mesh convergence in the lower-nappe aeration. Surprisingly, intermediate mesh resolutions are sufficient to surpass the TPVoF performance with reasonable calculation efforts. Moreover, compressibility, flow bulking, and several entrained air effects in the flow are comprehended. Despite not reproducing all aspects of the flow with acceptable accuracy, the complete two-phase Euler demonstrated an efficient cost-benefit performance and high value in spillway aerated flows. Nonetheless, further developments are expected to enhance the efficiency and stability of this model. Full article

(This article belongs to the Special Issue Advances in Spillway Hydraulics: From Theory to Practice)

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17 pages, 2947 KiB

Open AccessArticle

Apron and Cutoff Wall Scour Protection for Piano Key Weirs

by Wyatt Lantz, Brian Mark Crookston and Michele Palermo

Water 2021, 13(17), 2332; https://doi.org/10.3390/w13172332 - 26 Aug 2021

Cited by 11 | Viewed by 4690

Abstract

Piano key (PK) weirs are used in a variety of flow control structure applications, including spillway crests and open channel diversion structures. However, to the best of authors’ knowledge, structure-specific design guidance for scour mitigation is still needed. To fill this gap of knowledge, a systematic experimental campaign was conducted by testing different configurations of horizontal aprons with a cutoff wall. Protection structures were located at the toe of the PK weir. Namely, experiments were performed at large-scale to assess the effect of three apron lengths on downstream scour hole geometry under different hydraulic conditions. It was observed that a horizontal apron deflects the plunging jets originating from the PK weir, thus significantly reducing scour. Experimental evidence allowed corroboration that significant scour depth reduction occurs for an apron length 1.5 times the weir height, with longer aprons found to provide marginal benefits. Finally, also provided herein are tools to estimate the main scour characteristics and help practitioners in optimizing apron design. Full article

(This article belongs to the Special Issue Advances in Spillway Hydraulics: From Theory to Practice)

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21 pages, 15102 KiB

Open AccessArticle

Hydrodynamics and Free-Flow Characteristics of Piano Key Weirs with Different Plan Shapes

by Yousef Sangsefidi, Hassan Tavakol-Davani, Masoud Ghodsian, Mojtaba Mehraein and Reza Zarei

Water 2021, 13(15), 2108; https://doi.org/10.3390/w13152108 - 31 Jul 2021

Cited by 15 | Viewed by 3256

Abstract

This paper focuses on Piano Key Weirs (PKWs) as an effective solution for improving the discharge capacity of spillway systems. The flow behavior in inlet and outlet keys is experimentally studied to analyze the discharge capacity of PKWs with different plan shapes (i.e., rectangular, trapezoidal, and triangular). The results show that in outlet keys, the flow aeration regimes extend to higher values of headwater ratios (H_o/P) by increasing the length magnification ratio (B/w) and apex width ratio (A/w). In addition, the local submergence length is a decreasing function of A/w, especially in high flow heads. While the total interference length enlarges by reducing A/w in lower H_o/P values (H_o/P < 0.5), a reverse trend is observed in higher headwater ratios. PKW performance may also be impacted by the flow contraction and recirculation zone in inlet keys, which intensify in higher values of H_o/P, B/w, and A/w. According to the obtained results, while the discharge coefficient is a decreasing function of A/w in H_o/P > 0.4, it may have a reverse trend in lower head conditions. In addition, a trapezoidal PKW has the highest discharge efficiency in a wide range of the studied domain (H_o/P > 0.25 and B/w ≥ 2). It can improve the discharge efficiency by around 5%, while its body volume is almost 7% smaller than the traditional rectangular PKW. However, for low-length and high-head conditions (B/w = 1 and H_o/P > 0.5), the efficiency a rectangular PKW exceeds that of the other shapes. Full article

(This article belongs to the Special Issue Advances in Spillway Hydraulics: From Theory to Practice)

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20 pages, 10140 KiB

Open AccessArticle

Air–Water Properties in Rectangular Free-Falling Jets

by José M. Carrillo, Patricio R. Ortega, Luis G. Castillo and Juan T. García

Water 2021, 13(11), 1593; https://doi.org/10.3390/w13111593 - 5 Jun 2021

Cited by 8 | Viewed by 3335

Abstract

This study analyzes the air–water flow properties in overflow nappe jets. Data were measured in several cross-sections of rectangular free-falling jets downstream of a sharp-crested weir, with a maximum fall distance of 2.0 m. The flow properties were obtained using a conductivity phase-detection probe. Furthermore, a back-flushing Pitot-Prandtl probe was used in order to obtain the velocity profiles. Five specific flows rates were analyzed, from 0.024 to 0.096 m³/s/m. The measurements of the air–water flow allowed us to characterize the increment of the air entrainment during the fall, affecting the flow characteristic distributions, reducing the non-aerated water inner core, and increasing the lateral spread, thereby leading to changes in the jet thickness. The results showed slight differences between the upper and lower nappe trajectories. The experimental data of the jet thickness related to a local void fraction of 50% seemed to be similar to the jet thickness due only to gravitational effects until the break-up length was reached. The amount of energy tended to remain constant until the falling distance was over 15 times greater than the total energy head over the weir crest, a distance at which the entrained air affected the entire cross-section, and the non-aerated core tended to disappear. The new experiments related with air–water properties in free-falling jets allow us to improve the current knowledge of turbulent rectangular jets. Full article

(This article belongs to the Special Issue Advances in Spillway Hydraulics: From Theory to Practice)

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