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Main aspects in dam safety assessment and principles and concepts applied
Published in Ljiljana Spasic-Gril, Dams Safety and Society, 2023
Spillway options include gated or uncontrolled spillways. Gated spillways require expensive mechanical and electrical components and require additional specialist maintenance and operation. Determining a safe operating plan also requires careful consideration, balancing operator response times, rate of flood rise, and balancing reservoir safety with downstream flood risk. Passive spillways, without gates or other operating systems, are therefore preferred. Where a gated system is considered necessary the whole life cost-benefit and technical necessity of the system should be demonstrated.
Water Resources Engineering
Published in P.K. Jayasree, K Balan, V Rani, Practical Civil Engineering, 2021
P.K. Jayasree, K Balan, V Rani
A spillway is a structure designed to “spill” flood waters under controlled conditions. It is a provision for storage and detention dams to release surplus water or floodwater that cannot be contained in the allotted storage space. This action prevents overtopping, which can be particularly destructive in the case of earth fill and rock fill dams, both of which can fail completely when overtopped. The Spillways can be uncontrolled (normally) or controlled. Concrete dams normally incorporate an over-fall or crest spillway, but embankment dams generally require a separate side-channel or shaft spillway structure located adjacent to the dam.
Water Harvesting
Published in Sandeep Samantaray, Abinash Sahoo, Dillip K. Ghose, Watershed Management and Applications of AI, 2021
Sandeep Samantaray, Abinash Sahoo, Dillip K. Ghose
Spillways are structures provided in reservoirs to discharge outflow from them, at controlled velocities, for domestic use or for the outflow of excess water during an emergency. Such situation arises in those types of reservoirs which are constructed by putting up a dam or an embankment. In dug-out ponds, invariably water is directly pumped out for use. Such ponds are located in those places where there is no provision for any drainage. The dug-out ponds are constructed below the ground surface on all sides and there is no danger of breach or over-toppling of retaining wall (dam) and its failure. Therefore, no emergency spillways are required to be provided. However, the inflow to the pond is regulated.
Investigation of Hydraulic Characteristics and Air Concentration of a 3D Simulated Air-Water Flow on a Spillway with an Aerator Device (A case study)
Published in ISH Journal of Hydraulic Engineering, 2022
Saeed Shayanseresht, Mohammad Manafpour
Supplying water for different agricultural and industrial sectors and in the potable form is of great importance in arid and semi-arid regions such as Iran. The spillway is one of the hydraulic structures that plays an important role in providing sufficient dam safety during flood periods. This structure controls the dam reservoir water level based on the normal design elevation and discharges the additional flood water to the downstream of the dam when the storage capacity of the reservoir is full. Flow velocity in the discharge channel (chute) of high-head dam spillways is very high. Therefore, the optimal design of the chute for high-speed flow and the proper transferring of the flow to the downstream is of great importance. Based on Falvey’s (1990) research, Pfister and Hager (2010a) reported that several noticeable spillway damages occurred during the 1960s and 1980s. Experience from physical studies shows that performing experiments on hydraulic models is a costly and time-consuming process. The rapid growth in the field of computer technology in terms of computer memory and processing speed has enabled numerical modelling of spillway flows using Computational Fluid Dynamics software.
Hydraulic model studies for optimising the design of two tier spillway – a case study
Published in ISH Journal of Hydraulic Engineering, 2019
R. R. Bhate, K. T. More, M. R. Bhajantri, V. V. Bhosekar
In search of new potential sites on the tributaries of mighty Bramhaputra, one may face challenges like narrower valleys and high discharges with very high head available for power generation. Accommodation of low level Breastwall spillways having adequate capacity is a big challenge due to narrow topography and fragile geology. Such situation may lead to consideration of some innovative type of spillway design like multitier spillways. In this type of spillway arrangement, the lower level sluices are provided to handle both sediments and flood. The size of low level opening has a structural tab due to forces on gates due to very high head and large pier thickness. Therefore, it is necessary to provide another set of spillway at an adequate higher location to tackle for the remaining flood. This makes the hydraulic system complex. Thus, the design of spillway and energy dissipator becomes very involved requiring extensive model studies. The present case study for Siang Lower H.E. Project, Arunachal Pradesh describes the hydraulic model studies carried out on a 1:55 scale 2-D sectional model for evolving the design of two tier spillway and energy dissipator (CWPRS 2012).
Mitigating cavitation on high head orifice spillways
Published in ISH Journal of Hydraulic Engineering, 2021
R.R. Bhate, M.R. Bhajantri, V.V. Bhosekar
Spillways are the significant and integral part of dam design and construction and constitute a relatively large component of the total cost. Spillways are designed as flood outlets to safely convey floods to the river downstream from the dam and to prevent overtopping of the dam. The ongoing and future dam building activity in Himalayan region involves more complex flows with unprecedented flash floods due to melting of snow or cloud bursting causing high velocity flows carrying heavy sediment load with it. Orifice spillways are the best type of spillways evolved in such hydrologic and geologic scenario. Orifice spillways are provided with its crest very near to the river bed to facilitate the flushing of sediments through the spillway openings. While tapping the potential of the rivers like tributaries of Brahmaputra, designers face the challenge of deep and narrow valleys, high design flood with head over spillway crest exceeding 50 m. These high head spillways can experience the flow velocities as high as 30 to 50 m/s. As the flow velocity at the boundary of a spillway increases, the potential for damage to the structure by cavitation erosion also increases with the velocity (Falvey 1990). Due to inherent surface roughness and geometrical irregularities usually associated with concrete structures, such spillways are susceptible to cavitation damage. These spillways experience negative pressures over crest profile and cavitation index drops down 0.2. Considering the paramount importance of spillway to operate with utmost integrity, and the large capital investment, the destructive effects of cavitation damage to spillway chute must be prevented, or at least, the chances of its occurrences must be minimised.