The probable maximum flood (PMF) is used for the xxi assessment of maximum flood potentials in spillway sizing of new dams and in evaluating the adequacy of existing hydrologic structures. Determination of the PMF begins with the estimation of the probable maximum precipitation (PMP) for a particular dam site. Selecting hydrologic methods and assumptions for converting PMP to PMF, which are most appropriate for Utah conditions, is important to meet current inflow design flood (IDF) safety standards. The objectives of this study were (a) to demonstrate a maximization approach to PMF determination, (b) to evaluate effects of basin characteristics and isohyetal or uniform rainfall pattern on PMP and hence PMF, (c) to evaluate uncertainties due to hydrologic procedures through sensitivity studies, (d) to analyze historical events for indications of actual loss rates, (e) to analyze historical snowpack and melt conditions for critical snowmelt conditions, (f) to assess implications of this study for a degree of conservatism index, and (g) to evaluate the implications of the study for the selection of procedures for PMF determinations. A sensitivity study was conducted to evaluate the hydrologic methods and assumptions (e.g., loss rates, unit hydrographs, basin subdivision, temporal storm distribution, flood routing, and antecedent events) which may be used in northern Utah PMF studies. The maximization of local storm PMF produced a higher peak reservoir stage than using basin average PMP only. Evaluation of effects of basin characteristics on PMF showed that local storm PMP is critical for basins up to about 2,000 square miles in northern Utah. Estimation of maximum probable rain-on-snow flood conditions for Porcupine Basin for April, May, and June revealed that there are significant increases in peak flows and flood volumes due to the contribution of snowmelt in the months of May and June. The results from the degree of conservatism assessment performed on local storm PMF estimates for Porcupine Basin showed that the overall effect of assumptions made and procedures followed in a typical PMF determination is almost certainly a conservative estimate.

As more dams experience spillway flows from flood events, identification and analysis of erosion in auxiliary rock surface spillways has become a primary focus in maintaining dam integrity. The spillway erosion risk assessment developed for this research is based on parameters identified and discussed in previous research as the leading factors influencing spillway damage from erosion. Parameters applied in this analysis were channel geometry, stream hydrology, and geologic materials. Channel geometry is described by the length of spillway channel and slope of the spillway floor; stream hydrology is classified by the peak discharge and its duration; and geologic material is identified by its behavior in resisting erosion. The Sites Spillway Erosion Analysis (SSEA) was used to produce a risk assessment based on U.S. Army Corps of Engineers case histories. The risk assessment was used to classify and refine model uncertainties, an important advancement in evaluating spillway erosion.

Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2006. / Stepped spillways constructed of roller compacted concrete (RCC) is a hydraulic and cost effective measure to dissipate energy of large water flows over the spillway of a dam. Stepped spillways, like other spillway types, have its limitations and a measure to improve the energy dissipation effectiveness is proposed. Two hydraulic models were constructed at the hydraulics laboratory of the Department of Water Affairs and Forestry (DWAF) in Pretoria, South Africa. The scales of the models were 1:20 and 1:30. The study proposes the use of triangular protrusions applied over the spillway surface. The protrusions have the same height as the steps, with the width of the protrusions varying. The triangular protrusions deflect the water sideways resulting in higher energy losses. The results indicate that the protrusions reduce scouring at the toe of the dam, thus increasing the roughness of the steps. It also indicate that aeration occur earlier than with normal stepped spillways. An optimal spacing, lateral and across the steps, are proposed. The construction of the protrusions is also discussed, as well as the cost implications. It is concluded that the protrusions are effective at a unit discharge up to 35 m3/s.m. This value is however dependent on the configuration of the apron downstream of the toe of the dam. It is proposed that protrusions be added on the downstream face of the dam on every second step, with one protrusion and then no protrusion alternating in the flow path. It is recommended that the protrusions be cast in situ.

To avoid the large amount of damage that floods can cause, spillway tunnels are used to control water levels. To ensure the safety of water transportation through spillway tunnels, the behaviour of the water throughout the tunnel is important to know. Physical experiments are time consuming and expensive, hence CFD simulations are a profitable option for investigating the performance of the spillway tunnel. In this project, simulations of water flow in a spillway tunnel were executed. A three dimensional model of the spillway tunnel in Zipingpu Water Conservancy Project was created in the software ANSYS Gambit. A coarse, middle and fine mesh with both hexahedral- and tetrahedral elements were also created for the model in ANSYS Gambit. The meshes were imported to ANSYS Fluent where the simulations, and a convergence analysis were made. The water flow was set to be described by the Reynolds-Averaged Navier-Stokes model, using the pressure solver, k-epsilon model and the VOF model. Physical experiments had previously been performed, and the simulated results were compared to these, in an attempt to find the parameters to replicate the experimental results to the greatest extent possible. The inlet velocity of the tunnel was known and the inlet boundary was set as a velocity inlet. The ceiling of the tunnel was set as a pressure inlet, the floor and walls were set as wall, and the outlet was set as pressure outlet. The simulated results showed similar behavior as the experimental results, but all differed from the experimental results. The grid convergence index, estimating the results' dependency on the mesh was 6.044 %. The flow was analyzed, and where the flow had unfavorable characteristics, such as a high cavitation number, the geometry of the spillway was altered in ANSYS Gambit to investigate if an improved geometry for the spillway tunnel could be found. The water flow in the revised geometry was simulated in ANSYS Fluent, and results showing flow with lower cavitation numbers was found.

O método Hidrodinâmica Suavizada de Partículas (em inglês: Smoothed Particle Hydrodynamics - SPH) foi utilizado para o desenvolvimento de um estudo numérico envolvendo descarregadores lisos e descarregadores em degraus (considerando escoamento deslizante sobre turbilhões), com paredes laterais paralelas e paredes convergentes, usando o software DualSPHysics. Muitas vezes é conveniente utilizar a construção de descarregadores com maior largura na crista, e menor largura do descarregador, para adaptação das limitações físicas locais. O estreitamento do descarregador de forma gradual até atingir a largura da seção de jusante é feito por meio de paredes laterais convergentes, que por sua vez induzem à formação de ondas estacionárias laterais, e consequentemente aumento da altura do escoamento junto às paredes. Existem poucos estudos na literatura sobre esse tema, justificando o estudo numérico desenvolvido neste trabalho. O modelo numérico foi desenvolvido com base em um modelo físico do Laboratório de Hidráulica e Recursos Hídricos do Instituto Superior Técnico, Portugal, sendo os resultados experimentais obtidos em estudos anteriores. A instalação experimental é composta por um descarregador com declividade de fundo de 26,6º, e ângulo das paredes de 0º; 9,9º e 19,3º em relação ao plano vertical. As simulações foram realizadas em duas ou três dimensões, conforme a condição de largura constante ou convergente. Os resultados foram comparados com dados experimentais em termos de alturas do escoamento na parede e no eixo do descarregador, perfis de velocidade na região não-aerada do escoamento, e largura da onda estacionária lateral. Para as simulações tridimensionais, também foram elaborados gráficos de isolinhas para a altura do escoamento, podendo-se observar a extensão das ondas estacionárias laterais conforme a condição de superfície lisa ou em degraus, e a elevação de água junto às paredes. Em geral, houve boa aproximação entre dados numéricos e experimentais, verificando-se a aplicabilidade do método SPH para simular o escoamento deslizante sobre turbilhões em estruturas em degraus, ou estruturas convencionais de paramento liso. / A numerical study using the Smoothed Particle Hydrodynamics method (SPH) was developed for smooth and stepped spillways (for skimming flow regime), with converging and non-converging sidewalls, using the software DualSPHysics. In numerous situations, it is convenient to built spillways with longer width at the crest and narrower width at the downstream end of the spillway, depending on the site constrains. The gradual narrowing of the spillway width is usually made through converging sidewalls, which induce the formation of shockwaves, leading to higher flow depths along the sidewalls. Few studies in the literature were carried out in this research topic to date, justifying the numerical study developed in this project. The numerical model was based on a physical model assembled at the Hydraulic and Water Resources Laboratory of the Instituto Superior Técnico, Portugal, using experimental data obtained in previous studies. The experimental setup was composed by a spillway with slope of 26.6º, and angles of converging sidewalls of 0º, 9.9º, and 19.3º in relation to the vertical plane. Two-dimensional or three-dimensional simulations were carried out according to the condition of constant width or converging walls. The results were compared with experimental data, related to the flow depths at the centerline and sidewall of the spillway, the velocity profiles on the non-aerated region, and the lateral standing wave width. Regarding the three-dimensional simulations, contours of the flow depth were also represented, to visualize the extent and height of the sidewall shockwaves, according to the smoothed or stepped face. In general, a good agreement was obtained between numerical and experimental results, which confirms the ability of the SHP method to simulate the skimming flow over stepped spillways, or the flow on more conventional, smooth spillway chutes.

O método Hidrodinâmica Suavizada de Partículas (em inglês: Smoothed Particle Hydrodynamics - SPH) foi utilizado para o desenvolvimento de um estudo numérico envolvendo descarregadores lisos e descarregadores em degraus (considerando escoamento deslizante sobre turbilhões), com paredes laterais paralelas e paredes convergentes, usando o software DualSPHysics. Muitas vezes é conveniente utilizar a construção de descarregadores com maior largura na crista, e menor largura do descarregador, para adaptação das limitações físicas locais. O estreitamento do descarregador de forma gradual até atingir a largura da seção de jusante é feito por meio de paredes laterais convergentes, que por sua vez induzem à formação de ondas estacionárias laterais, e consequentemente aumento da altura do escoamento junto às paredes. Existem poucos estudos na literatura sobre esse tema, justificando o estudo numérico desenvolvido neste trabalho. O modelo numérico foi desenvolvido com base em um modelo físico do Laboratório de Hidráulica e Recursos Hídricos do Instituto Superior Técnico, Portugal, sendo os resultados experimentais obtidos em estudos anteriores. A instalação experimental é composta por um descarregador com declividade de fundo de 26,6º, e ângulo das paredes de 0º; 9,9º e 19,3º em relação ao plano vertical. As simulações foram realizadas em duas ou três dimensões, conforme a condição de largura constante ou convergente. Os resultados foram comparados com dados experimentais em termos de alturas do escoamento na parede e no eixo do descarregador, perfis de velocidade na região não-aerada do escoamento, e largura da onda estacionária lateral. Para as simulações tridimensionais, também foram elaborados gráficos de isolinhas para a altura do escoamento, podendo-se observar a extensão das ondas estacionárias laterais conforme a condição de superfície lisa ou em degraus, e a elevação de água junto às paredes. Em geral, houve boa aproximação entre dados numéricos e experimentais, verificando-se a aplicabilidade do método SPH para simular o escoamento deslizante sobre turbilhões em estruturas em degraus, ou estruturas convencionais de paramento liso. / A numerical study using the Smoothed Particle Hydrodynamics method (SPH) was developed for smooth and stepped spillways (for skimming flow regime), with converging and non-converging sidewalls, using the software DualSPHysics. In numerous situations, it is convenient to built spillways with longer width at the crest and narrower width at the downstream end of the spillway, depending on the site constrains. The gradual narrowing of the spillway width is usually made through converging sidewalls, which induce the formation of shockwaves, leading to higher flow depths along the sidewalls. Few studies in the literature were carried out in this research topic to date, justifying the numerical study developed in this project. The numerical model was based on a physical model assembled at the Hydraulic and Water Resources Laboratory of the Instituto Superior Técnico, Portugal, using experimental data obtained in previous studies. The experimental setup was composed by a spillway with slope of 26.6º, and angles of converging sidewalls of 0º, 9.9º, and 19.3º in relation to the vertical plane. Two-dimensional or three-dimensional simulations were carried out according to the condition of constant width or converging walls. The results were compared with experimental data, related to the flow depths at the centerline and sidewall of the spillway, the velocity profiles on the non-aerated region, and the lateral standing wave width. Regarding the three-dimensional simulations, contours of the flow depth were also represented, to visualize the extent and height of the sidewall shockwaves, according to the smoothed or stepped face. In general, a good agreement was obtained between numerical and experimental results, which confirms the ability of the SHP method to simulate the skimming flow over stepped spillways, or the flow on more conventional, smooth spillway chutes.

This thesis deals with the numerical modeling of water overflow over the front spillway. The aim of the thesis is to calculate various types of turbulent models and to assess the overflow coefficient on a sharp front spillway. The model was created in free software SketchUp, but the modeling itself was carried out in FLOW-3D software. The content of the work is a description of used software, design and calculation.

This thesis deals with the design of small reservoirs at Vyškov na Moravě. Projected reservoirs’ dams are earth-fill and homogenous and each one is equipped with the bottom water outlet and the emergency spillway. The first reservoir, located on the tributary of the Drnůvka river, has the fountain type emergency spillway and the feed pipe bottom water outlet. The reservoir of the Merchanice river, situated at the Vyškov airport, is equipped with the lateral emergency spillway and the feed pipe bottom water outlet. The third design is the reconstruction of the Marchanka reservoir projecting the dam raise. For this small reservoir two variants of functional installations were elaborated.

Το θέμα της παρούσας εργασίας είναι η μελέτη της ροής ύδατος εντός ανοιχτού αγωγού ορθογωνικής διατομής κατά την περίπτωση όπου έχουμε υπερχειλιστή λεπτής στέψης και ανάντη αυτού παρουσιάζεται ανισοκατανεμημένη παροχή. / Flow study in the downstream of one spillway with thin top, inside an rectangular open channel, in cases of uneven supply upstream of spillway.

<p>Today’s climate changes will probably give rise to precipitation in Sweden, which will cause more floods in Swedish rivers. Many of the Swedish rivers are regulated and have lots of hydro-electro power plants. Higher floods in the rivers will give greater water loads on the dams, which mean that a higher discharge through the sluice gates and in the spillway channels is needed. High discharge of water in a spillway channel can create scour of the material in the channel. Usually, for spillways in Swedish hydropower plants, this material is rock and the scour is in form of rock blocks. Scour downstream of dams can in the worst case endanger the dam construction.</p><p>The purpose of this study was to identify the extent and the type of rock scour that may appear in spillway channels of Swedish hydro power plants. The scour in rock material in a spillway channel is usually caused by pressure fluctuations in the water, which can cause large differences in pressure on the top and bottom surfaces of blocks. This pressure difference can be high enough to lift whole blocks. The main factors that affect this kind of scour are the crack pattern of the rock mass, the geometry of the spillway, the discharge of water and the surface fluctuation in the water. In this study a numeric model analyse, a field study and a literature study has been made in order to examine the influence on scour of the orientation of cracks in a rock mass. A rock mass containing a group of cracks with small or no dip is more likely to scour when it is exposed to discharging water. The orientation of the cracks in a rock mass relative to the direction of the water flow has also an impact on the capacity of the rock mass to resist scour.</p><p>In the field study the scour pattern in the spillway channels of the hydro power plants in Ligga, Harsprånget, Porjus, Satisjaure and Seitevare was examined. The scour of rock mass in the spillway channels in Ligga, Harsprånget and Porjus has been extensive. The rock mass in these channels has bedding cracks of small distances. This is probably the reason why these rock masses are sensitive for loads from discharging water. The rock mass in the spillway channel in Satisjaure has lots of cracks and is also very sensitive for loads from discharging water. This channel has been rebuilt during 2004.</p><p>There are different methods to predict the ability of a rock mass to resist scour. The Erodibility Index Method is a semi-empirical method that is verified by field observations in the USA. In this work the ability to apply this method on Swedish channels has been examined with field observations from Porjus, Harsprånget and Seitevare. As the Erodibility Index Method seemed to work in the case of these three spillways, it was also applied on the spillways in Satisjaure and Ligga.</p><p>Measures to reduce the energy in the discharging water in the spillways are very effective to reduce the risk of scouring in the rock mass. Blasted stairs in the rock mass in a channel or a stilling basin downstream the sluice gate is something that can reduce the energy in discharging water. Further documentary of spillway channels, like mapping and laser scanning, would contribute to a further verification of the Erodibility Index Method and to get a general survey of the risk of scour in Swedish spillways.</p> / <p>Dagens klimatsituation ser ut att ge ökad mängd nederbörd i Sverige, vilket innebär att de svenska älvarna kommer att utsättas för allt högre vattenflöden. De flesta av Sveriges älvar är reglerade, d v s längs älvarna finns en mängd större och mindre dammar. Ett högre flöde i älvarna innebär även rikligare tillrinning till dammarna vilket medför att avbördningen från dem måste bli större. Avbördningen från dammarna sker genom utskov och höga vattenflöden i utskovskanalerna kan orsaka erosion på det berg som kanalen vanligen består av. Erosionen är av typen ”blockerosion” där hela bergblock av större eller mindre storlek lösgörs från bergmassan. I värsta fall kan blockerosionen krypa uppströms och erodera dammkroppen bakifrån, vilket skulle kunna innebära att dammen brister.</p><p>Syftet med detta arbete var att identifiera omfattning och typ av bergerosionsproblem som uppkommer i utskovskanaler. Blockerosion uppkommer i regel då forsande vatten skapar tryckskillnader mellan övre och undre ytan på block. Tryckskillnaden kan då skapa tillräckliga lyftkrafter för att block ska lossna. De huvudsakliga faktorerna som styr blockerosionen är bergmassans sprickighet och material, utskovskanalens geometri och vattnets flöde och ytfluktuation. Genom litteraturstudie, numerisk modellanalys samt fältstudie har inverkan på blockerosionen av sprickriktningar utretts. En bergmassa som innehåller sprickgrupper som har liten, nära horisontell, stupning är känslig för vattenbelastning. Stupningsriktningen i förhållande till flödesriktningen har också betydelse för blockerosionen. Stupningsriktning i flödesriktningen gör bergmassan mer känslig för belastning av forsande vatten och gynnar därmed erosionen.</p><p>Utskovskanalerna i Ligga, Harsprånget, Porjus, Satisjaure samt Seitevare har undersökts med avseende på erosionsrisk. Erosionen i Ligga, Harsprånget och Porjus har varit omfattande och detta beror troligtvis på att dessa kanaler har subhorisontella bankningssprickor med litet sprickavstånd. I Satisjaure är bergmassan mycket sprickig, varför denna kanal är mycket känslig för vattnets belastning. Där har dock åtgärder vidtagits så att kanalen ska tåla sitt dimensionerande flöde. I Seitevare är erosionsrisken i kanalens övre del liten.</p><p>Det finns olika metoder för att bedöma erosionsrisken i en bergmassa. Erosionsindexmetoden är en semiempirisk metod som är verifierad med platsobservationer i USA. Med hjälp av observationer från Porjus, Harsprånget och Seitevare har erosionsindexmetodens tillämplighet på svenska kanaler undersökts. För dessa tre observationer verkar metoden fungera bra och har därför även använts i kanalerna i Satisjaure och Ligga.</p><p>Energidämpande åtgärder i kanalerna, såsom energiomvandlargropar och utsprängda trappor i kanalerna, har visats sig vara mycket effektivt för att minska erosionsrisken. En noga dokumentering av utskovskanaler, som t ex kartering och inmätningar, skulle bidra till att erosionsindexmetoden kunde verifieras ytterligare och att en översiktlig bedömning av erosionsrisken i utskovskanaler enkelt kan erhållas.</p>