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Energy dissipation basin
Published in James C.Y. Guo, Wenliang Wang, Junqi Li, Urban Drainage and Storage Practices, 2023
James C.Y. Guo, Wenliang Wang, Junqi Li
A drop is often employed to stabilize the streambed in a waterway. A drop structure is composed of a submerged dam (weir), which raises the water depth to create backwater effects in the upstream direction and also to lower the channel floor by 3 to 5 feet immediately downstream of the drop structure. Under backwater effects, the incoming flow slows down. The potential for upstream bed erosion and bank scours is alleviated. However, downstream of the drop needs to be protected from the impingement of the jet flow on the channel floor. Often, a plunging basin, as shown in Figs 17.15a and b, is placed at the downstream end of a drop structure.
Flood channel design
Published in James C. Y. Guo, Urban Flood Mitigation and Stormwater Management, 2017
The purpose of a drop structure is to reduce the flow velocity and to satisfy a set of design criteria on permissible flow Froude number. Therefore, it is convenient to relate Equation 7.11 to flow Froude number. Aided with Equation 7.5, the proposed slope is calculated as
Design Aspects of Hydraulic Structures for Hydro-Power Development at Canal Drops
Published in C.V.J. Varma, A.R.G. Rao, Renewable Energy Small Hydro, 2020
A drop structure on a canal is primarily meant to negotiate the fall in water levels in the canal from upstream to downstream of the drop site without damaging the canal section. When once a rigid structure is introduced for the safety of the flexible canal section at the drop site, the drop structure itself will be exposed to the differential head created due to fall in water levels. And to safeguard the structure against this differential head, a sufficiently long and sufficiently thick floor is required at the base of the drop wall, with sufficiently deep cutoffs underneath at the upstream and downstream ends of this floor. The purpose of the floor is for safety against uplift pressures exerted by seepage flow occurring in the sub soil below the floor and that of the cutoffs for safety against scours caused in the canal bed at upstream and downstream ends of the floor due to surface flow in the canal above bed. In. addition, the downstream end cutoff serves to keep the exit gradient of seepage flow at the downstream end of the floor within safe limits of the bed soils. The differential head considered in the -floor design is for either of the two flow conditions in the canal(viz) (i) when there is full flow in the canal from upstream to downstream side of the drop and (ii) when there is no flow in the canal but with still water standing upto crest level of drop on upstream side and no water on downstream side, whichever in more. The maximum differential head for full flow condition is the difference between the upstream and downstream full supply levels in the canal plus the average unbalanced head in the region of formation of hydraulic jump or standing wave in the cistern forming part of the downstream portion of the floor, while that for no flow condition is the difference between the upstream and downstream canal bed levels plus the height of crest of drop wall above upstream canal bed level or, in other words, the difference between the crest level of drop wall and downstream canal bed level. The crest of drop wall is raised over the upstream canal bed level to an extent of not more than 40%of full supply depth in the upstream canal in order to maintain the depth-discharge relationship of the normal canal section upstream of the drop at lower discharges in the canal.
Quantitative study of water impact on land value in Jakarta
Published in Urban Water Journal, 2023
Ahmad Gamal, Lailatul Rohmah, Cynthia Adelina Perangin Angin, Widya Laksmi Larasati, Ahmad Aki Muhaimin, Risty Khoirunisa, Dwinanti Rika Marthanty
Flood, which is mainly caused by rain runoff, is a common disaster in Jakarta thus require a control system. A flood disaster system covers structural and non-structural methods (Kodatie, 2013 in Boatwright et al. 2014; Sörensen and Emilsson 2019; Wicaksono and Herdiansyah 2019). The structural methods include (a) flood control buildings such as dam, retention pool, check dam, groundsill, drop structure, retarding basin, and polder; (b) river improvement and regulation systems such as embankment, river improvement, by pass/short cut, floodway, and special drainage system. The non-structural methods of flood control system include watershed management, land use arrangements, erosion control, development and regulation of flood areas, emergency mitigation system, flood warning system, law enforcement, assurance, and information distribution. Additionally, more nature-oriented approaches such as vegetative conveyance systems and infiltration areas for rain runoff are included in the non-structural methods (Boatwright et al. 2014; Sörensen and Emilsson 2019).
Application of soft computing approaches to predict gabion weir oxygen aeration efficiency
Published in ISH Journal of Hydraulic Engineering, 2023
KM Luxmi, N. K. Tiwari, S Ranjan
Fluidic devices enhance the DO quantity in canals, lakes, and other water bodies; even if the water is in brief contact with the fluidic device, the same amount of oxygen transfer occurs that would take place over numerous miles in a stream at a singular fluidic device. Fluidic devices can be recognized as the crucial and vigorous structures in maximizing the pace of oxygen transfer by aeration instinctively because of substantial eddy mixing followed by generation of ample amount of air bubble. Aeration mechanism itself is a very complex process, and different types exist depending upon the kinds of fluidic devices. Fluidic structures can broadly be categorized as non-drop and drop structures. In non-drop fluidic structure, devices like flumes (Parshall and Venturi) are used to compute the flow rate in level and zero slope canal (Dursun 2016). The principle of oxygen transfer (aeration) is that it steps up the velocity of flow by a reduction of the body sides in the converging portion. The reduction and drop accelerate the flow velocity from a low to a high at the throat portion and from fast to slow at a diverging portion at the downstream side of the flume, causing oxygen transfer due to aeration. The principle mechanism in the drop structures like cascades or step channels is completely different from that of drop structures like weirs. In cascades, the overflow can be broadly divided into skimming flow and jet flow. For the skimming flow, overflow discharge is high or cascade step is narrow, while when jet flow occurs, either overflow discharge is low or cascade step is wide. Further, in skimming flow, the water skims over the faces and corners of the step and is retarded due to the development of the circulating region, which further enhances the self aeration process by momentum exchange in the flow, while in the case of jet flow, aeration takes place with the steps, which act as a series of overfalls where the water is free-falling from one step to other (Ohtsu et al. 2004). However, in the case of drop structure as a weir, aeration depends upon the plunging velocity, roughness, shape, and geometry of the receiving water aeration pool. Both the shape and depth of the water aeration pool control the residence time and penetration depth of the air bubbles (Tsang 1987).