Results are presented for a model study of wave formation in the lower pool of a hydroproject.The design of hydroprojects requires knowledge of the consequences of the effect of the flows passing through the structures on the discharge channel. In that case, undercutting of the structures may, as we know, occur, the channel and banks will be deformed, the position of the water levels will be changed as compared with their natural position, and high-velocity, occasionally unstable currents, which contribute to the formation of high waves that attenuate over an extended distance from the structures, will be observed in the lower pool.Model laboratory investigations make it possible to develop a design for the structures, which will ensure their assigned in-service condition for an acceptable level of flow in the channel, and will not require expensive measures to protect the structures from scouring, a large volume of dredging to lower the backwater, stringent requirements for the maneuvering of spillways, etc.Occasionally, however, design solutions are not substantiated by investigations. It should be pointed out that currently available recommendations do not always permit objective evaluation of consequences of the effect of the flow on the channel; experimental hydraulic model studies are therefore extremely critical to the situation [1]. This will help to avoid significant in-service difficulties with the structures, and the additional expenditures required to eliminate unpredictable negative consequences of their use.Despite the existence of a large number of published research results, significant uncertainty remains for analytical assessment of the parameters of local scouring, and the dimensions of the layer of deposited scouring products -bar, and the unit pressures and static head associated with its formation. There are essentially no published data on wave formation in the lower pool, which may also significantly complicate the conditions of the current and performance of the structures, and, in addition, is associated with the status of the channel (prior to its local deformations; during their development; and, after stabilization), the operating regime of the spillways, their layout and structural features, channel parameters, etc.For example, therefore, the character of swells may be one of the basic causes of the removal from service of a scheme by which flow is discharged from the structure. At the Sayano-Shushenskoe hydroproject, model studies of the spillway with a jet discharge indicated possible development of unstable currents in the lower pool with a jump-induced wave up to 17 m high, acting alternately on one, and then the other bank where the open-distributing devices, multipurpose buildings, moorings, roads, etc. are located. Results of the investigations were the basis for one of the arguments in the decision to use a toe basin as a component part of the structures in this hydroproject. Even with the dissipation of a basic portion of the energy of the discharge flow in the toe basin, ho...
The construction of correlation curves between flows and water levels Q = f(H), varying in the downstream pool sections as a result of river-bed transformation over the operating period of hydroelectric complexes, is limited to the observed flow rate values. The calculation of the Q = f(H) correlation curves, covering the entire range of possible water flow variations, is based on solving a problem of constructing a free water surface curve using a one-dimensional mathematical model of the river flow, which accounts for the morphometry of a transformed bed of the downstream pool.
The performance of the lower pool during operation of a spillway is discussed.The spillway dam of the Bureya hydroproject ( Fig. 1) consists of eight spans each 12 m wide, which are situated at the head of the spillway with bulkheads each 3 m thick, is designed for the passage of flows in conjunction with the HPP: Q 0.1% = 10,400 + 2100 = 12,500 m 3 /sec, and Q 0.01% = = 11,200 + 2100 = 13,300 m 3 /sec with a pool differential of 117 m. The pools are merged by a discharge of flow from the dam over a distance of 200 m in a diversion channel beyond a 140-m-wide spillway where the overall width of the river is 250 m, and the average depth 15 m in the case of maximumflow passage.During passage of construction flows through eight bottom openings, local washouts of the diversion channel reached 20 m at a distance of 80 m from the dam, washouts directly at its attachment amounted to 7 m, and up to 10 m near the attachment to the abutment, whereupon undermining of stabilizing slabs was also noted. Deposition of scouring products in the form of a ridge (bar) up to 6 m high with a crest elevation of approximately 136.5 m, partitioned the channel; this led to an increase in the level at the HPP as compared with the natural conditions of up to 3 m at a passing flow rate of 500 m 3 /sec.The decision to slope the area of impingement of the discharge flow of beyond the service spillway from the left bank, along which a dirt road passes, and from the split abutment between the diversion channels of the spillway and HPP, was made in connection with the negative experience acquired with scouring of the stabilization. For this purpose, diverting springboards common to two spans are being built beyond extreme spans 1 and 2, and 7 and 8 of the spillway dam. This will solve the indicated problem, but will result in a concentration of flows in the median section of the channel, and here, to an increase in the depth of scouring, especially during the passage of spring floods in the case of fully opened basic gates.The following should be obtained from laboratory investigations for cases where different flow rates are passed:-a prediction of development of local washouts of the channel, the formation of a bar, and the hydrostatic head on the HPP;-the velocity distribution of the flow, and the height of the waves in the section with a length of up to 900 m from the axis of the dam; -information on the effect of the jet dropping directly onto the abutment and left bank, an estimate of the amount of water impinging on the abutment and terminal section of the powerhouse, and a determination of the effectiveness of the wall protecting the left-bank abutment and platform from splash; and, -information on the influence exerted by the flow on the combined stabilization of the right bank, which consists of a concrete lining and rocks of no specified size.
The results of hydraulic tests of the operational spillway of the Bureya Hydraulic Project in 2008, 2009, and 2016 are presented. The tests were intended to assess the geometric parameters of the downstream flow, the aeration and spray conditions, the hydrodynamic impact on the main gates, and the flow and wave pattern downstream between HWL = 248.30 m and TCS = 256.00 m.
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