Jorge Matos

• Instituto Superior Técnico, University of Lisbon

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...

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...

In recent decades, stepped chutes followed by a stilling basin became a standard for spillways of dams. The comprehensive knowledge of stepped chute approach flows on internal air–water flow properties of the hydraulic jump is still too limited for an appropriate design of stilling basins. Therefore, an experimental campaign was performed on a larg...

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 co...

The lack of sidewalls in a spillway leads to lateral expansion of the flow and, consequently, a non-uniform transversal flow rate distribution along the chute. The present work shows the velocity field measured in a physical model of a 1 V:0.8 H steeply sloping stepped spillway without sidewalls. An application of a Bubble Image Velocimetry (BIV) t...

This paper studies the effects of an air bubble curtain on surface water waves. Water particle velocities and free surface elevations were measured simultaneously at two cross-shore locations downstream of the air bubble curtain. Measurements were carried out for regular waves using different air bubble curtain configurations. Free surface elevatio...

Stepped spillways have been increasingly used to handle flood releases from large dams associated with hydropower plants, and it is important to evaluate the fluctuating pressure field on the steps. Hydraulic model investigations were conducted on three 53° (1V:0.75H) sloping and relatively large-stepped chutes to characterize the mean, fluctuating...

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. Neverthel...

Large wood increases the morphological and hydraulic complexity of rivers, yet it may block and modify the flood discharge capacity of hydraulic structures. To assess the related risk, blockage probability estimation for hydraulic structures such as reservoir spillways is needed. This work presents unstudied parameters for blockage of large wood wi...

Advances of roller compacted concrete (RCC) in the construction of concrete dams has significantly influenced the development of stepped spillways. The latter are now more frequently implemented in the rocky abutments of embankment dams. The energy dissipation downstream of stepped chutes is mostly ensured by stilling basins. Such stilling basins a...

The blockage of weirs or bridges by in-stream wood can reduce the flood discharge capacity, leading to hazardous situations. To assess the related risk, blocking probabilities quantifications are needed. However, large wood has a random behaviour and it is challenging to accurately evaluate the blockage process and the influence of different large...

The smoothed particle hydrodynamics (SPH) method was used to simulate the flow over smooth and stepped spillways in the nonaerated, skimming flow regime. Two-dimensional numerical simulations were carried out using the DualSPHysics software and compared with experimental data on a 2H:1V sloping spillway for smooth and stepped inverts. Continuous in...

In recent decades, the advancement of knowledge on the hydraulics of labyrinth weirs has resulted mainly from physical modeling. In this study, numerical simulations of free-flow and submerged labyrinth weirs were conducted for a large sidewall angle, using commercially available computational fluid dynamics software, for three different turbulence...

In the last decades numerous stepped spillways were built, mostly on the downstream face of roller compacted concrete (RCC) dams. Stilling basins are often used as an energy dissipater. Although the hydraulics of stepped chutes was extensively investigated in the last decades, only fragmentary information is available on the hydraulic characteristi...

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 of the reservoir water level may occur. This study aims to statistically analyse the importance of repetitions for the accuracy of experimental campaigns...

Abrupt slope changes on stepped chutes may have a major effect on the hydraulics of skimming flows. The present study shows that the minimum discharge tested in the skimming flow regime leads to higher values of flow bulking depth (Y 99), bottom air concentration (C b), and mean (depth-averaged) air concentration (C mean). These observations are re...

Large wood (LW) elements are often transported by rivers into reservoirs during heavy rainfall events. Large wood has important environmental attributes that benefit the diversification of riverine ecosystems. There are several studies dealing with the transport and behaviour of LW inside streams. However, during flood events, LW tends to create ja...

The air entrainment effect on wave breaking is of the highest importance for the wave energy dissipation. Wave breaking is a complex phenomenon with several physical processes, making it difficult to quantify the contribution of the air in the energy dissipation process. This study presents a different approach where the wave propagation is exposed...

An accurate description of the hydrodynamics in the non-aerated region of the skimming flow on stepped spillways is of outmost importance, particularly in small structures at large discharges. In addition, the flow features upstream of the inception point of air entrainment determine the flow behavior in the downstream self-aerated region. In this...

Resumo Neste estudo o método Hidrodinâmica Suavizada de Partículas (SPH) foi utilizado para simular o escoamento de água sobre um descarregador de cheias em degraus, com dimensões semelhantes a um modelo físico reduzido. O descarregador possui declividade típica de barragens de aterro (1V:2H), e opera sob regime de escoamento deslizante sobre turbi...

The presence of dissolved oxygen (DO) in water flows is an important factor to ensure the aerobic conditions recognised as beneficial to prevent the occurrence of detrimental effects. The incorporation of DO in wastewater flowing in sewer systems is a process widely investigated in order to quantify the effect of continuous reaeration through the a...

Several stepped spillways have been built in recent decades, mostly integrated in the downstream faces of roller compacted concrete dams. Among them, only a few have changing bottom slopes. Comprehensive information on the effect of a slope change on the flow features is lacking. This paper reports a systematic study of air entrainment and flow bul...

In this study the Smoothed Particle Hydrodynamics (SPH) method is used to simulate skimming flows over stepped spillways. Skimming flow can be briefly described as a main water or air-water flow forming a coherent stream above the pseudo-bottom defined by the plane tangent to the step edges; secondary, recirculating flows occur in the cavities form...

Blocking probability at spillway inlets under driftwood impact

Energy dissipation within hydraulic structures continues to be one of the major issues facing the designer of new or rehabilitated facilities, such as for overtopping protection of embankment dams. The energy dissipation characteristics of stepped spillways have been well documented, both for low-and high-head dams. Interestingly, much of the gener...

Wave breaking is an important phenomenon in coastal protection due to the dissipated energy. Such phenomenon is also responsible for the nearshore sediment transport caused by the generated turbulence and currents. The aim of this work is to apply two different CFD numerical codes to simulate accurately spilling and plunging wave breaking. Numerica...

O presente trabalho visa estudar numericamente a influência de uma alteração da configuração em planta de um canal na propagação de ondas. Para tal, foi utilizado o modelo OpenFOAM® baseado nas equações RANS (Reynolds –Averaged Navier-Stokes). Foram realizadas simulações 2D e 3D para o caso de um canal de ondas de largura variável que configura um...

Numerous stepped spillways were built to date, namely on RCC gravity dams or on valley flanks besides embankment or rockfill dams, while some others are currently under design or construction. In some cases, slope changes may be required on stepped chutes, due to the topography, leading to reduced excavation and related economic benefits. A quite l...

We discuss, apply and validate several physics-based criteria for air entrainment into flows on steep stepped spillways, using laboratory observations and numerical results published elsewhere. To the best of our knowledge, this is the first time a validation of these criteria is undertaken for any chute flow in general, and for the skimming flow i...

Stepped weirs and dam spillways have been increasingly used for handling flood releases, due to their inherent benefits, particularly those related to energy dissipation. Among the diversity of construction techniques for which a stepped chute turns out to be an attractive solution, the popularity of roller compacted concrete placement on new and r...

This paper presents results of a first step aiming at modelling the transfer of oxygen in manhole drops. An experimental study was previously conducted at IST, Lisbon, focusing on the hydraulics and reaeration on a vertical drop followed by a hydraulic jump. In the present research, a CFD code was used to replicate the experimental tests. The scope...

Cavitation on spillways has proven to be an undesirable condition. The formation of vapor-filled bubbles and cavities and their eminent collapse has led to significant damage to major spillway components and appurtenant structures worldwide. Although stepped spillways are thought to be less prone to cavitation damage than smooth spillways, designer...

The nonaerated region may occupy a large portion of the skimming flow in steep, stepped spillways, particularly for relatively high unit flow rates. In spite of the numerous contributions on the hydraulic properties at both the inception point of air entrainment and the aerated region, much less is known regarding the flow in the nonaerated region....

Stepped spillways are known to have a higher energy dissipation potential when compared to a smooth invert chute of identical slope. Therefore, the length of downstream energy dissipators can be reduced. To date, little is known about the effect of the stepped profile on the stilling basin performance. Therefore, new measurements were carried out o...

The IAHR Hydraulic Structures Section, jointly with the Instituto Superior Técnico (IST) and the Portuguese Water Resources Association (APRH), organised the International Junior Researcher and Engineer Workshop on Hydraulic Structures (IJREWHS'06). The international workshop addressed conventional and innovative aspects of hydraulic structures des...

We present and discuss the results of a comprehensive study addressing the non-aerated region of the skimming flow in steep stepped spillways. Although flows in stepped spillways are usually characterized by high air concentrations concomitant with high rates of energy dissipation, the non-aerated region becomes important in small dams and/or spill...

A three-hole pressure probe with back-flushing, combined with an electrical conductivity probe, was developed to perform the simultaneous measurement of the magnitude and direction of the velocity vector in complex air-water flows, where the flow direction is not known prior to data acquisition. Such situation typically occurs inside and around the...

The development of a three-hole pressure probe with back-flushing combined with a conductivity probe, used for measuring simultaneously the magnitude and direction of the velocity vector in complex air–water flows, is described in this paper. The air–water flows envisaged in the current work are typically those occurring around the rotors of impuls...

RESUMO A manutenção de elevados valores da concentração de oxigénio dissolvido é importante para garantir condições de aerobiose em redes de drenagem de águas residuais, evitando a formação de gases tóxicos e odores indesejáveis e a potencial corrosão de materiais do sistema. A ocorrência de singularidades ao longo dos sistemas de drenagem de águas...

In order to study air-water flows in physical models of hydraulic structures or in field experimentation, velocity data are often needed. In this paper, the authors review the application of three different types of instrumentation on measuring velocities in air-water flows of low or high air content: the back-flushing Pitot tube, the double fiber-...

Experimental investigations have been conducted in stepped spillway model chutes assembled at the National Laboratory of Civil Engineering (LNEC), Lisbon, at Nihon University (UNIHON), Tokyo and at the University of Queensland (UQLD), Australia. In the present paper, the research is focussed on the interactions between entrained air bubbles and cav...

The U.S. Bureau of Reclamation (Reclamation) developed instrumentation to measure air concentration and water velocity in large flumes as well as in smaller indoor models, namely the large outdoor flume facility located at Colorado State University (CSU) in Fort Collins, Colorado, and the stepped spillway model chute assembled at the National Labor...

Experimental investigations have been conducted in two steep stepped spillway model chutes assembled at National Laboratory of Civil Engineering (LNEC) - Lisbon and at the Technical University of Catalunya (UPC) - Barcelona, respectively. In LNEC's facility, the research focussed essentially on air concentration and velocity data along the chute, w...

Air-water flows occur in numerous types of hydraulic structures, as well as in hydraulic machinery like the Pelton and the Cross-Flow turbines. Due to the complexity inherent to the analytical and numerical study of highly turbulent air-water flows, experimental research has played a major role in the last decades, with the notable development of i...

Air entrainment and flow bulking along a steeply sloping stepped chute are analysed as a function of the characteristic depth used for defining the free-surface. The results of this investigation show that both the mean air concentration and the bulked depth may be considerably influenced by the definition of the free surface. They also show that t...

The majority of studies on the hydraulics of stepped spillways has been centered in the air-water flow region and undertaken with the use of physical models. However, for certain geometry, higher discharges can lead to a non-aerated flow along the spillway, of special interest in small embankment dams designed for relatively large overtopping flows...