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Dam outlet works
Published in P. Novak, A.I.B. Moffat, C. Nalluri, R. Narayanan, Hydraulic Structures, 2017
P. Novak, A.I.B. Moffat, C. Nalluri, R. Narayanan
Dam outlet works consist generally of spillways and bottom (high-head) outlets. Spillways are basically dam appurtenances ensuring a safe passage of floods from the reservoir into the downstream river reach. The spillway design depends primarily on the design flood, dam type and location, and reservoir size and operation. The design of bottom outlet works depends primarily on the purpose of the reservoir and the sediment inflow and deposition in the reservoir.
Main aspects in dam safety assessment and principles and concepts applied
Published in Ljiljana Spasic-Gril, Dams Safety and Society, 2023
Wherever possible the design of outlet works should provide flexibility to allow the pass forward flow to be easily altered in future, for example by incorporating a replaceable orifice plate or flow control valve. The design of the outlet works should consider the safe maintenance, inspection, and operation access to culverts, pipes, and flow controls.
Modelling interactions between reservoir system operating objectives
Published in International Journal of River Basin Management, 2022
Flood control operating rules are based on emptying flood control pools as expeditiously as feasible without making releases that contribute to the exceedance of allowable flow rates at downstream gauge sites established based on within-bank channel flow capacities, road crossings, and stages at which flood damages occur. During flooding, the gates of spillway and outlet works are closed until a determination is made that the flood has peaked and flows at downstream points are below allowable flow limits. However, if the flood control pool storage capacity is forecasted to be exceeded, releases are made as necessary to prevent dam overtopping and otherwise assure dam safety. During normal conditions with storage levels below the top of the conservation pool, flood control operating rules are generally not relevant. However, if flood conditions are forecasted, water from conservation pools may be released to increase the storage capacity available for predicted flood inflows.
Hydraulic fracturing: a main cause of initiating internal erosion in a high earth-rock fill dam
Published in International Journal of Geotechnical Engineering, 2021
Morteza Salari, Ali Akhtarpour, Amin Ekramifard
Information and statistical analyses published by the International Commission on Large Dams (International Commission on Large Dams (ICOLD) 1984, International Commission on Large Dams (ICOLD) 1995) and Foster, Fell, and Spannagle (2000) show that about 30%–50% of earth dam failures are because of progressive piping and internal erosion. Failures and incidents by internal erosion of embankment dams and their foundations are categorised into three general failure modes (International Commission on Large Dams (ICOLD) 2013): (1) internal erosion through the embankment which includes internal erosion associated with through-penetrating structures such as conduits associated with outlet works, spillway walls or adjoining a concrete gravity structure supporting the embankment, (2) internal erosion through the foundation and (3) internal erosion of the embankment into or at the foundation. The third mode includes (a) seepage through the embankment eroding material into the foundation, or (b) seepage in the foundation at the embankment contact eroding the embankment material. The process of internal erosion may be broadly broken into four phases: (1) initiation of erosion, (2) continuation of erosion, (3) progression to form a pipe or occasionally cause surface instability (sloughing), and (4) initiation of a breach. The initiation phase of internal erosion occurs in four mechanisms (International Commission on Large Dams (ICOLD) 2013): (1) backward erosion (2) concentrated leaks, (3) suffusion and (4) contact erosion.
Application of adaptive neuro-fuzzy inference system for prediction of internal stability of soils
Published in European Journal of Environmental and Civil Engineering, 2019
Seepage-induced internal erosion of soils is widely observed in dams, levees and other earthen embankments. Internal erosion occurs when soil particles within an earthen embankment or its foundation are carried downstream by seepage. It starts when the erosive forces imposed by the hydraulic loads exceed the resistance of the materials in the embankment to erosion. Internal erosion customarily includes “suffusion” and “piping” phenomena. Suffusion is the entrainment of fine soil grains and their possible subsequent deposition in the pores that are formed by coarse grains; suffusion may be caused by discontinuity or segregation of soil particles and it can form large local cavities. In piping, soil particles inside the soil matrix are entrained and washed out of the matrix by concentrated seepage, forming a tubular pipe that progresses from downstream to upstream; the pipe can develop into a large tunnel that may collapse. Suffusion and piping may result in the increase of porosity and compressibility, settlement, variation of permeability and the potential for a reduction in soil strength (Xiao & Shwiyhat, 2012). Internal erosion can occur within an earthen embankment or its foundation, along conduits and their outlet works, spillway walls or concrete gravity structure supporting the embankment. In a survey of 11,192 dams, Foster, Fell, and Spannagle (2000) concluded that approximately 46% of the dam failures among the entire survey sample could be attributed to internal erosion. Internal erosion in embankment dams is one of the main causes of failures and accidents of dams, and the development of internal erosion can pose a serious threat to the stability of these water retaining structures (Bonelli, 2013).