Discussion of “Performance and Design of Labyrinth Weirs”

The Metropolitan Water Sewerage and Drainage 1 Board, Sydney, Australia (MWS&DB) has constructed so far two large labyrinth weirs, serving as reservoir overflow control structures.The first was completed in 1941 atWoronoraDam , the second in 1970 at Avon Dam.In both cases the weir discharges into an after-bay which forms the transition between the weir and a deep, narrow spillway channel, cut in rock.The longitudinal axis of the weir is straight in plan in the case of Woronora Weir, and curved (with radii downstream) in the case of Avon Weir.The weirs are reinforced concrete structures (Figs. 15 and 16).Three dimensional hydraulic model studies were carried out for both spillways, modeling the force-bay, the weir, the after-bay, the spillway-cut and a specific length of the natural water course downstream.Separate performance studies were also carried out in testing channels with single and multiple bays of varied configurations (Fig , 17).Parameters of Woronora and Avon Weirs are listed in Table 3.The test results of the model studies, carried out in the MWS&DB Hydraulics Laboratory, appear to be in close agreement with the authors' findings regarding the performance of the labyrinth weir.In Table 4 model measured rating-curve data are given for a free discharge condition.New symbols used were: CL = ~L/(Lh 1 • 5 ), Cw = QLI( Wh 1 • 5 ), coefficient of discharge, L = total developed weir length, and W = total width of weir.The description of the flow pattern over a labyrinth weir is a major hydrodynamic assignment on its own.The falling nappe has a corrugated, curtainlike appearance.The corrugations (which are along the profile of the nappe