Author(s): Vladimir Michels
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Abstract: Rosslynne damsite geology governed spillway design. The author combined a mitre-prowed weir with probably an innovative hydraulic concept: The dual, symmetrically convergent overflows from the crest were directed tangentially onto triangular aprons which terminated on a trough formed by a longi tudinally steep and divergent chute floor; the resultant skew impact zone generating a twin-spiral central "plume" which exits through a narrow "waist. " This simple configuration has an extremely 1ow ' waist-to-channel ' contraction ratio of 1:4, effected over a minimum length, thus minimising area -dependent labour and material costs. It was tested hydraulically in a series of models, the last one to 1:36 scale, effecting stage-by-stage modifications. Comparing observed and computed data in the trough region, the main con- clusions were: 1) Hydraulic theory confirned "plume" thicknesses, its natural divergence being 10°-14° in plan. 2) From the hydraulic viewpoint alone, the "waist" could have been narrowed further. 3) Erodible rock below the "waist" precluded eliminating all lining and its substitution by a ski-jump etc. 4) At the design head, the mitre-prowed weir had a discharge coefficient of 91% of the figure for a standard-crested weir, but- the. overall spiliwayefficiency-withthe: samechannel- widthisnominally -15%: better. The proto- type spillway has satisfactorily passed 30% of the design- flood overfllow of 337 m~ (3) s~ (-1).
Year: 1985