SPILLWAYS

RESUMEN: El diseño hidráulico de vertederos del tipo Morning-Glory constituye una muy buena alternativa en ciertos proyectos, debiendo atenderse especialmente todo aspecto relacionado con la necesidad de evitar que estas estructuras operen en carga, es decir con descarga sumergida con control de orificio. Si esta circunstancia estuviera presente, además de alterarse la capacidad de descarga, se produce un cambio de régimen en la transición vertedero-orificio, caracterizada por inestabilidades que se pueden describir mediante la variación local del campo de presiones. En este artículo se efectúa un análisis de las condiciones de inestabilidad, partiendo de las experiencias realizadas sobre un modelo físico, efectuándose una caracterización de los parámetros turbulentos que se presentan en dichas condiciones. ABSTRACT: The hydraulic design of Morning-Glory spillways is a very good alternative in certain projects, being necessary especially to consider all matters relating to the need to prevent submerged discharges, it means with controlled underwater discharge orifice. If this circumstance is eventually present, the discharge capacity is modified and there will be a change of hydraulic regime form spillway to orifice control, which is characterized by instabilities that can be described by local variation of the pressure field. This article presents an analysis of the conditions of instability, based on the experiences made on a physical model, carrying out a characterization of turbulent parameters presented in these conditions. PALABRAS CLAVES: vertederos Morning-Glory; cambio de régimen; inestabilidades.

High dams have been/are being constructed along the R.Nile for various uses thus creating a cascade arrangement in the same flow valley. It is because of this setup that the possibilities of hazards resulting from exceedingly excess discharge from one upstream Dam due to different reasons, puts the downstream structures at danger as well as the environment. Particularly, this study was prompted considering the prevalence of the Nalubaale Hydropower Dam wall which surpassed its design life. This dam also has the largest reservoir in the world of 270 BCM. This paper gives insights of real time management of a cascade. It covers design requirements, modelling, simulation and instruments involved and their relevance in the automation of the spillways to suit a safe existence of Cascade dams. Implementation improved the operation and management of Hydro Power Plants in the following ways: Reduce the chances of over topping in any of the dams in the cascade, Reduce chances of over flooding of any one reservoir, Reduce the risk of dam wash away and failure of the structures, Reduce the chances of unnecessary spilling of water in the reservoirs, Helps to guide decision making during capacity tests and improves Emergency Preparedness and Response actions for Cascade dams. 2.0 METHODS AND APPROACHES USED 2.1 Conceptual design To study the cascade system, one has to zero to two dams at a time. In this method, focus was given to the first two Dam walls (taking Nalubaale and Kiira as one since they are in parallel) while basing at Bujagali HPP.

Perencanaan pelimpah dipengaruhi oleh beberapa aspek teknis yaitu: kondisi topografi, geologi/geoteknik, jenis  material dasar sungai - morfologi sungai, hidrologi dan hidrolika. Kondisi topografi dan geologi/geoteknik berpengaruh terhadap pemilihan letak pelimpah dan rencana jalur saluran peluncur.  Jenis material dasar sungai - morfologi sungai  berpengaruh terhadap pemilihan jenis peredam energi. Hidrologi yang terkait dengan debit banjir rancangan berpengaruh terhadap dimensi kebutuhan lebar pelimpah sedangkan hidrolika yang terkait dengan profil muka air berpengaruh terhadap perencanaan bentuk bangunan secara hidrolis dan kebutuhan dimensi bangunan yang aman terhadap stabilitas konstruksi.
Alternatif perencanaan pelimpah yang sesuai dengan kondisi di daerah studi adalah tipe pelimpah overflow dengan sistem saluran peluncur dan peredaman energi ganda. Diperlukan peredam energi ganda karena pada sistem peluncur ini terdapat perpindahan alinyemen horisontal, sehingga saat akan menuju perpindahan ke alinyemen horisontal harus dibuat peredam energi pertama yang digabung dengan saluran terminal (terminal channel), dimana saluran terminal di desain sesuai dengan kebutuhan hidrolik untuk mendapatkan aliran kritis sebelum aliran mengalir menuju ke saluran peluncur kedua / peredam energi kedua. Dari peredam energi kedua ini selanjutnya aliran disalurkan ke saluran akhir (escape channel) menuju ke sungai asli.
Dari perhitungan hidrologi didapatkan hasil debit banjir rancangan dengan kala ulang 1000 th : Inflow Q 1000 th = 50,69 m3/det , Outflow Q 100 th = 26,35 m3/det. Sedangkan untuk debit banjir rancangan maksimum yang mungkin terjadi (Probable Maximum Flood, PMF) : Inflow Q PMF = 100,98 m3/det, Outflow Q PMF = 54,89 m3/det. Pada nilai outflow tersebut masing – masing mempunyai tinggi muka air  di atas ambang pelimpah H maks 100 th  = 1,33  m , H maks  PMF = 2,18. m
Secara teknis dari hasil perencanaan diperoleh lebar ambang pelimpah 8,00 m, tinggi ambang 2,50 m. Panjang saluran transisi 20,00 m, lebar saluran transisi mengecil dari 8,00 m ke 5,00 m. Panjang saluran peluncur pertama 35,00 m, slope 0,43 , lebar 5,00 m. Peredam energi pertama USBR Tipe III, panjang kolam olak 17,00 m , lebar 5,00 m. Saluran terminal dibentuk dengan dimensi menyesuaikan kebutuhan hidrolik dengan lebar saluran hulu dan hilir 5,00 m. Saluran peluncur kedua direncanakan dengan panjang 67,50 m , slope 0,212 dan lebar 5,00 m. Peredam energi kedua USBR Tipe III, panjang kolam olak 20,00 m , lebar 5,00 m. Saluran Akhir (escape channel) direncanakan dengan lebar lebar 5,00 m , slope 0,0037 dan panjang saluran 121,80 m.
Dari perhitungan stabilitas konstruksi sesuai dengan dimensi yang direncanakan, pada tinjauan kondisi keadaan normal, banjir 1000 th dan PMF serta gempa diperoleh hasil bahwa seluruh konstruksi yang direncanakan aman terhadap guling, geser dan daya dukung tanah pondasi, sehingga dengan demikian perencanaan ini telah memberikan nilai keamanan stabilitas yang memenuhi syarat secara teknis.

RESUMEN El proyecto de las obras de erogación de crecidas de la presa El Bolsón, sobre el río Albigasta, en la provincia de Catamarca, prevé su construcción mediante la tecnología del hormigón compactado a rodillo. Los nuevos lineamientos del proyecto establecen la posibilidad de disponer dos vertederos, uno de ellos sobre el cuerpo de la presa y el auxiliar sobre el cierre lateral de margen derecha. Tomando particularmente en cuenta el vertedero principal, cabe la posibilidad de definir distintas alternativas, así como variantes posibles en relación con la estructura de conducción (rápida convencional o rápida escalonada) y la estructura de disipación. En este artículo se presentan los aspectos más importantes relacionados con el análisis de alternativas de vertederos, la definición de sus dimensiones finales, el estudio de variantes para la conformación de una rápida lisa o una escalonada y el diseño hidráulico del cuenco disipador de energía. Se exponen los elementos que han permitido optar por una rápida escalonada, con escalones de 1.20 m de altura. Finalmente, se presentan algunos aspectos vinculados a la verificación del funcionamiento hidráulico de las obras sobre un modelo físico a escala 1:60, con especial énfasis en la rápida escalonada del vertedero principal. ABSTRACT El Bolsón dam project, on the river Albigasta, in the province of Catamarca, foresees his construction by means of the technology of the roller compacted concrete. The new lineaments of the project establish the possibility of arranging two spillways, one of them on the main dam and the auxiliary one on the side closing of right margin. Taking particularly into account the principal spillway, different alternatives can be defined for this structure, as well as different possibilities concerning the steeped spillway (conventional, it means smooth surface, or stepped) and the energy dissipation device. This article deals with the most important aspects related to the analysis of alternatives for the spillways, their final dimensions, the study of steeped spillways (smooth or stepped) and the design of the stilling basin. The reasons of having adopted the solution of a stepped spillway with 1.20 m-high steps are exposed. Finally, some aspects involving the hydraulic behavior of the structures, which were analyzed by means of a 1:60 length scale physical model, are also presented, paying particular attention on the principal spillway. PALABRAS CLAVES: Presas, hormigón compactado a rodillo, vertederos, rápidas escalonadas, disipación de energía, modelos físicos.

Morning glory spillways with drop inlets are normally employed in dams built on narrow valleys or placed on steep slopes. In Iran, morning glory spillways have been commonly used in large Dam projects such as Sefidrood dam, Alborz dam, and Haraz dam. Physical models should be built to accurately determine hydraulic parameters of the flow and flow field in spillways. Establishment of a physical model involves extravagant costs and conditions that cannot be justified in some cases. Therefore, suitable numerical models can be proposed for such circumstances. Using FLOW3D numerical models, 3-dimensional numerical modelling of the flow was calibrated and validated by experimental information associated with morning glory spillway of Alborz dam and accuracy of numerical modelling was determined by relative error of numerical model. So it was attempted to determine flow pattern and control conditions of morning glory spillways in different modes using boundary conditions, inlet conditions and grid spacing of flow field and project rating curve of morning glory spillways. According to the results of numerical model, relative error of numerical modelling equals 6.4% for calculating discharge rate of the spillways. Numerical modelling error is 7.6% for determining depth parameter of the flow in spillway crest in comparison with experimental results.

Insufficient spillway capacity has been the cause of one-third of all dam failures.
An innovative and effective way of increasing the spillway capacity is to use a Labyrinth weir in
the modified form of PKW having range of specific flow from 3 to 1000m3/s/m. As the flow
approaches towards the PKWeir, it was observed that the Z-component of the velocity of water in
lower levels increases which enhances the flushing capacity. One of the important observations is
that with decrease in discharge from higher flow to medium flow; Z component velocity is getting
lowered by about 14 percent. Increase in discharge from lower to medium flow Z component
velocity is getting increased by about 40 percent. It indicates that at lower discharge, upward
velocity component is appreciably more which may be helpful for significant amount of sediment
suspension at lower discharge also. For flood flow, it was found that there has been reduction of
around 25–30% of submergence depth with respect to ogee spillway. Induced flow characteristics
near PKW and tractive stress exertion by flowing water in the inlet cell are capable to flush out
even the coarser sand particles.

The changes in the height of the head water in duckbill spillways in different discharges due to the increase of the crest length, is more limited. Flow discharge coefficient in duckbill spillways is a function of the total head water, spillway height, wall thickness, shape and type of the crest and angle of the side walls with flow direction. Using dimensional analysis and providing dimensional variables enables that factor affecting the behavior and duckbill spillway relations with presence of guide vanes are fully investigated. In this study, using a dimensional analysis, a relation was found between the flow discharge coefficient in the duckbill spillways with the presence of guide vanes. The results of the theory with laboratory conditions were also examined. The tested model is a triangular duckbill spillway with apex angle of 45˚. The crest of spillway has smooth edge. The width of the guide vanes was considered as a coefficient of the length of one side of the duckbill spillway with a height equal to the spillway height. According to the results, the range of the flow coefficient for the duckbill spillway is greater than the straight spillway, which shows that changing the water depth the flow discharge coefficient in the duckbill spillway is greater than the flow discharge coefficient in the straight spillway. The ratio of the length of one cycle of spillway to the water depth, the ratio of the height of the spillway to the water depth, the Froude number, the ratio of the spillway width to the waterdepth, the ratio of the guide vane width to the water depth, the number of guide vanes and the location of deployment can be influenced in the flow discharge coefficient in the duckbill spillway with flow guide vanes.

Stepped spillways have a wide range of applicability as a hydraulic structure in large dams to dissipate energy of high-velocity flows at a downstream area of dams as well as release overflows into the downstream. In this study, the numerical simulation of the flow over the stepped spillway was investigated by using Flow3D software as an analytic flow field. The RNG k-ε model was applied as the turbulence model, and Volume Of Fluid (VOF) model was used to determine the free surface flow profiles. At the first stage, the model was verified by reliable experimental data. Then, in order to investigate the various features of skimming flow regime, 112 numerical spillway models was designed, which 96 models were stepped spillway models and 16 models were smooth spillway models (i.e. WES profile). In these numerical experiment, two step sizes, six configuration, four passing discharge and four profile slopes (15, 30, 45 and 60 degrees) with various relative discharges were considered to investigate the energy dissipation and discharge coefficient rates. The results indicated that discharge coefficient rate and energy dissipation rate have inverse relationship. Also it was observed that when relative discharges increased, energy dissipation rate decreased and discharge coefficient rate increased.

Arief Satria M.
Biro Penelitian dan Pengembangan, Perum Jasa Tirta I
Jl. Surabaya 2a, Malang

ABSTRAK
Maksud dari studi ini adalah untuk mengetahui nilai CWL (Control Water Level) maksimum yang diijinkan setiap bulan di Waduk Sutami dan Lahor berdasarkan analisa penelusuran banjir debit PMF (probable maximum flood) Dalam rangka mengantisipasi kemungkinan terjadinya overtopping akibat debit banjir PMF (QPMF) sebagai upaya pengeloaan risiko bendungan di Wilayah Sungai Kali Brantas. Studi ini perlu dilakukan mengingat Bendungan Sutami dan Lahor pada saat perencanaan masih didesain dengan debit banjir pada kala ulang 1000 tahun (Q1000 th) sedangkan standart keamanan bendungan yang ditetapkan oleh Komisi Keamanan Bendungan saat ini adalah debit banjir PMF. Metode yang digunakan dalam penelitian ini adalah analisa hidrologi debit banjir rancangan Q1000 dan QPMF serta penelusuran banjir di kedua waduk tersebut yang dilakukan secara simultan, karena kedua waduk ini terhubung oleh terowongan penghubung Waduk Lahor dan Sutami. Dari hasil analisa hidrologi QPMF tahunan yang berpotensi terjadi pada Bendungan Sutami nilainya adalah 11.629,14 m3/dt, dimana nilai QPMF ini setara dengan 2,31 x Q1000 th. Sedangkan QPMF tahunan yang berpotensi terjadi di Bendungan Lahor nilainya adalah 2.731,00 m3/dt, dimana nilai PMF ini setara dengan 2,70 x Q1000 th. Berdasarkan hasil analisa penelusuran banjir QPMF bulanan diperoleh hasil bahwa nilai CWL maksimum bergerak pada rentang nilai elevasi muka air waduk minimum + 257,00 m dan maksimum + 267,00 m. Dimana nilai ini memberikan hasil bahwa pada Bendungan Sutami masih berpotensi terjadi overtopping sebanyak 3 kali kejadian dalam satu tahun dengan tinggi air 3,09 m di atas elevasi puncak bendungan. Oleh karena itu untuk mengantisipasi kemungkinan terjadi overtopping, secara struktural perlu dilakukan pembuatan pelimpah darurat pada Bendungan Sutami, sedangkan pada Bendungan Lahor dengan adanya tinggi parapet setinggi 1 m sudah tidak berpotensi terjadi overtopping.

High velocities or abrupt changes in the flow direction may cause damages in hydraulic structures. Based on experiments, presence of a little amount of air near the solid boundaries reduce significantly cavitation damages. To protect several hydraulic structures such as chutes and bottom outlets from cavitation damages, normally aerators are used to introduce air to water flow. When water jet passes over aerators, large amount of air induce to flow and it would be transported downstream of aerators devices. However, most of entrained air might be detrained dramatically and immediately after strike of the jet to bed of spillway. In this study experimental data were used to analysis bottom air concentration transport. These data were collected for a wide range of different type of bottom aerators. Regression analysis were applied on these data and finally a simple equation based on water jet length was derived which could be used to predict the bottom air concentration along the chute.

The Spillway of Nagarjuna Sagar dam across Krishna River was severely eroded during the floods of 2009 due to cavitation which was resulted from the negative pressures developed over the spillway. On further investigation of the problem, it was found that there was a large deviation of the existed profile of the spillway from the design profile, which actually led to the development of negative pressures in such a magnitude that could create the problem. In the present study area, attempt has been made on Nagarjuna sagar Dam for investigation of pressures on spillway using air vents; study has been carried out by providing air vents of 0.01 m and 0.02 m at desired elevations for free and gated conditions in vents 1, 2 and 3 for various discharge conditions. The negative pressures obtained in different pressure levels of vent numbers has been determined and the results show that negative pressures are observed in vent 2 and 3 at different pressure points.

The labyrinth spillways are utilized to cater a more discharge capacity than straight overflow spillways. The capacity of a labyrinth spillway has dependents on total head, effective crest length, and discharge coefficient. The labyrinth spillway is utilizing as an overflow structure in large reservoirs. In the present study, guide vanes were utilized to increment the discharge coefficient of triangular labyrinth spillway. The different configurations of guide vanes on the upstream face of the spillway in a rectangular horizontal channel were examined. These different configurations were repeated for 3 widths of guide vanes. Experiments were operated for sub-critical, stable and free overflow conditions. Finally, the results show that the discharge coefficient of the triangular labyrinth spillway putting guide vanes had higher values than that of simple triangular labyrinth spillway. Putting 4 guide vanes in the first-quarter and fourth-quarter of two side legs can increment the discharge coefficient up to 18 %.

The labyrinth spillways are utilized to cater a more discharge capacity than straight overflow spillways. The capacity of a labyrinth spillway has dependents on total head, effective crest length, and discharge coefficient. The labyrinth spillway is utilizing as an overflow structure in large reservoirs. In the present study, guide vanes were utilized to increment the discharge coefficient of triangular labyrinth spillway. The different configurations of guide vanes on the upstream face of the spillway in a rectangular horizontal channel were examined. These different configurations were repeated for 3 widths of guide vanes. Experiments were operated for sub-critical, stable and free overflow conditions. Finally, the results show that the discharge coefficient of the triangular labyrinth spillway putting guide vanes had higher values than that of simple triangular labyrinth spillway. Putting 4 guide vanes in the first-quarter and fourth-quarter of two side legs can increment the discharge coefficient up to 18 %.

The changes in the height of the head water in duckbill spillways in different discharges due to the increase of the crest length, is more limited. Flow discharge coefficient in duckbill spillways is a function of the total head water, spillway height, wall thickness, shape and type of the crest and angle of the side walls with flow direction. Using dimensional analysis and providing dimensional variables enables that factor affecting the behavior and duckbill spillway relations with presence of guide vanes are fully investigated. In this study, using a dimensional analysis, a relation was found between the flow discharge coefficient in the duckbill spillways with the presence of guide vanes. The results of the theory with laboratory conditions were also examined. The tested model is a triangular duckbill spillway with apex angle of 45˚. The crest of spillway has smooth edge. The width of the guide vanes was considered as a coefficient of the length of one side of the duckbill spillway with a height equal to the spillway height. According to the results, the range of the flow coefficient for the duckbill spillway is greater than the straight spillway, which shows that changing the water depth the flow discharge coefficient in the duckbill spillway is greater than the flow discharge coefficient in the straight spillway. The ratio of the length of one cycle of spillway to the water depth, the ratio of the height of the spillway to the water depth, the Froude number, the ratio of the spillway width to the waterdepth, the ratio of the guide vane width to the water depth, the number of guide vanes and the location of deployment can be influenced in the flow discharge coefficient in the duckbill spillway with flow guide vanes. Keywords: Dimensional analysis, Flow Discharge Coefficient, Flow Guide Vane, Sharp Crested Spillway, Theoretical

The integral project of spillways and energy dissipators has to ensure the pass of
the design flood without endangering the stability of the dam. In low ogee spillways, a hydraulic
jump stilling basin allows normally the restitution of the flow to the river with a low residual
energy that must be compatible with the characteristics of the riverbed. Air-entrainment devices
to reduce cavitation risks are often included as an additional safety element. The location of
these hydraulic structures in shallow waters with very rich fishes population can present an
excellent performance from the hydraulic viewpoint but hazardous for the normal development
of those fishes. This situation was reached in Yacyretá dam, where the excessive amount of air
into the flow was responsible of the massive fishes mortality as a consequence of having
exceeded the standard values of total dissolved gases (TDG). In the present article, the variables
considered for the refurbishment of the spillways are presented, having taken as design
condition the reduction of air-entrainment in the spillway and the energy dissipator.

The labyrinth spillway continues to be a popular type of the control structures. The focus of the present study is that on the optimization of the shape of the labyrinth spillway through the minimization of the construction costs because the use of it is a suitable solution in the rehabilitation process of existing reservoirs. An adaptive neural fuzzy inference system (ANFIS) model was developed to determine the discharge coefficient of the labyrinth spillway as a function of the angle between alignment of the crest and direction of flow, the relative depth of flow over spillway and its crest height. Differential evolution (DE) algorithm and genetic algorithm (GA) were adopted to minimize the spillway cost as the objective function by considering certain hydraulic conditions as the constraints of the optimization procedure. The results indicated that DE and GA can respectively reduce 19.3% and 16.6% the construction cost of a real benchmark design.