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Introduction to Civil Engineering
Published in P.K. Jayasree, K Balan, V Rani, Practical Civil Engineering, 2021
P.K. Jayasree, K Balan, V Rani
There are different types of dams classified based on function and construction material. Based on the material of construction, dams are categorized as earthen dam, masonry dam, and concrete dam. Based on the function of dams, they are categorized as storage dam, flood control dam, diversion dam, and coffer dam. A storage dam is constructed for water storage. The stored water may be used for drinking, irrigation, or hydroelectric power generation. A flood control dam is constructed for the temporary storage of flood water and then to discharge it gently so that the downstream side is shielded against the destructive effects of floods. A diversion dam is constructed to divert water from a river to a channel for irrigation. A cofferdam is a temporary structure constructed to divert water so that a safe construction area can be prepared during the construction of bridges and other underwater constructions.
Planning, Project Cost Estimation, and the Future of Small Hydropower (SHP): Large Hydro and Its Various Schemes and Components
Published in Suchintya Kumar Sur, A Practical Guide to Construction of Hydropower Facilities, 2019
A small hydro project is mainly based on ROR where the size of a dam is very small, and even in some cases a weir serves the purpose of diverting water. It does not need any water storage and depends on the flow of water, resulting in no adverse environmental effects on locals. A small hydro plant consists of the following components: Diversion dam/weir: It is constructed in the river to divert water from the main flow through an intake structure. A diversion dam is constructed either with concrete or stone masonry or rock fill as per design requirements.Intake structure: Flowing water, required for generation of power, is tapped by a structure from river or canal or reservoir is known as an intake structure. It may be low head or high head and it is constructed either parallel or perpendicular to the river flow where spiral flow is strong. Raised crest or trench intake is suitable for low head diversion. It is suitable for a narrow river with flow 5 m3/sec and above and trench intakes shall be suitable for a steep river in 1 in 20 with flow 10−15 m3/sec. Its function is to ensure requisite quantity of water intake and to draw quality water from the river by segregating any floating materials, debris, vegetation, or logs and to provide smooth entry so as to ensure minimum disturbance. The intake structure consists of appurtenances like a trash rack, curtain wall, settling trap, and gate.Tunnel or open channel: It is used to carry water from the intake structure to the sedimentation tank and an onward journey to the fore bay or surge shaft. It follows the contour of terrain as per requirements to have a sufficient slope so that requisite flow of water is maintained.Sedimentation tank: The sedimentation tank is used to trap sand, silt or any suspended material from the water so as to avoid any damage being caused to the turbine. It should conform to the specifications of the turbine.Fore bay: A pond which regulates the water head before the start of the penstock. It also stores a daily or weekly load to ensure the demand of electricity. It also facilitates the gentle flow condition of water. The layout of the fore bay is governed by the topographical and geological condition of the site. The location of the fore bay and power house should be selected so that the penstock has minimum length. It provides small storage for a few minutes to supply water to the turbine. It also serves as the final sedimentation tank where floating debris is either passed through an intake or swept into the channel to be removed before entering the turbine area. In many occasions, as per necessity, a balancing reservoir is provided in addition to the forebay or in place of the fore bay with larger storage for a few hours for diurnal basis.
Closed-form analytical solution for infinite-depth seepage below diversion dams considering the width of cutoff wall
Published in ISH Journal of Hydraulic Engineering, 2023
Seyyed Hossein Mojtahedi, Mahmoud F. Maghrebi
So far, no solution has been available in the readily accessible literature to determine the effect of cutoff wall width on seepage flow characteristics. This study investigates the closed-form analytical solution for infinite-depth seepage below a diversion dam where the cutoff wall at the downstream end has a certain width. The analytical solution to the main problem is obtained by using conformal mapping and Schwarz-Christoffel transformation (hereafter abbreviated as SCT). Moreover, this research aims to calculate the variations in hydraulic gradient and seepage discharge for the distance from the downstream end using a simple method based on the Darcy equation combined with conformal mapping. The method for obtaining the equation of hydraulic gradient variations is applied to extend the existing solutions in two cases: i) a diversion dam with double cutoffs and ii) a diversion dam with a depressed floor. The main problem of the study is further compared with these two cases through the graphs and a design example.
Mitigating cavitation on high head orifice spillways
Published in ISH Journal of Hydraulic Engineering, 2021
R.R. Bhate, M.R. Bhajantri, V.V. Bhosekar
The studies were conducted for orifice spillway on 101.5 m high and 213.7 m long concrete gravity diversion dam. Seven orifice openings of size 6.1 m wide x 12.6 m high with crest level at El. 990 m. have been provided to pass a design flood (PMF) of 11,811 m3/s along with Glacial Lake Outburst Flood (GLOF) of 1,170 m3/s. The discharge intensity for design discharge is 300 m3/s/m. The velocity is about 30 m/s on the spillway surface. The FRL has been fixed at El. 1045 m. Radial gates have been provided at the downstream face of breastwall for controlling the outflow discharge. The equation of the downstream profile is X2 = 195 y. Figure 1 shows cross-section of the spillway. Experiments were conducted on a 1:40 scale 2D sectional model in a flume for assessing the pressure profiles. The accepted equations for similitude, based on Froudian criteria were used to express mathematical relationship between the dimensions and hydraulic parameters of the model and the prototype. Photo 1 shows the view of the model.
Case study on debris-flow hazard mitigation at a world natural heritage site, Jiuzhaigou Valley, Western China
Published in Geomatics, Natural Hazards and Risk, 2020
Wanyu Zhao, Yong You, Xiaoqing Chen, Jingfeng Liu, Jiangang Chen
There is a 41° angle between the No. 2 diversion dam and the gully. The discharge, that passes through the No. 2 diversion dam (i.e. the discharge diverted by the no. 1 diversion dam in the forward direction, ) is 39.05 m3/s. One-third of the discharge diverted in the forward direction is 13.02 m3/s. Based on the hydraulic practical weir equation, a trapezoid-shaped overflow gate with a bottom width (b1) of 8.00 m results in debris-flow material passing through the trapezoid-shaped overflow gate with a height (H1) of 1.00 m. Two-thirds of the discharge is diverted laterally to the debris-flow depositional fan on the left side of the gully, i.e. = 26.03 m3/s. Based on the lateral diversion calculation, when the width (b2) of the lateral diversion inlet is 8.00 m, the height (H2) of the debris-flow material passing through the lateral diversion inlet is 1.70 m.