Browsing by Author "Calitz, Gerard"

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    Aeration of Roberts Splitters through an Internal Gallery of a Dam
    (Stellenbosch : Stellenbosch University, 2016-12) Calitz, Gerard; Basson, G. R.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: Roberts splitters have effectively been used for more than 75 years to dissipate the flood discharge energy of more than 30 dam spillways in South Africa and abroad. Robertsโ€™ (1943) standard, unaerated splitter design procedure is, however, limited to a spillway head (๐ป) of 3.0 m, equivalent to a unit discharge (๐‘ž) of 12 m2/s. In order to avoid cavitation at higher design spillway heads, the flow is aerated by local air vents positioned on the splitters. On current dams, these air vents are individually fed by intake pipes placed in the step directly below the splitters. However, problems emerge when these pipes need to drain water entering the air vents. To avoid drowning the intake pipes, aeration through an internal gallery that is open to the atmosphere is proposed, with the end goal of increasing the unit discharge limit of Roberts splitters. A 1:20 scale hydraulic model of an ogee spillway equipped with Roberts splitters was constructed. Two aerated models, with different sized air vents, were compared to an unaerated control model in order to determine the effect that the proposed aeration system has on the cavitation risk of the splitters at prototype unit discharges (๐‘ž) of up to 50 m2/s. At the maximum tested spillway head of 7.6 m (๐‘ž = 50 m2/s), the minimum pressures and air concentration around the splitters of both aerated models increased considerably. This indicated that the proposed aeration system completely alleviates the high cavitation risk of unaerated splitters. It was further observed that the unaerated splitters were prone to drowning at high spillway heads, leading to unfavourable hydraulic conditions that should be avoided at all cost. To summarise, the addition of aeration through an internal aeration gallery can increase the unit discharge capacity of Roberts splitters to at least 50 m2/s (up by 43%, from the unaerated limit of 35 m2/s, as tested during this study) while the proposed aeration gallery provides a solution to the problem of draining the inflow water of the air vents, without jeopardising the effective aeration of the splitters.