Hydraulic Characteristics of Labyrinth Weirs

Primarily, half-round crest labyrinth weirs were tested in this study with the side leg angle (a) ranging between 7 to 35 degrees. Historical data was primarily limited to quarter-round data. This study presents data and equations for estimating the discharge coefficient for labyrinth weirs with both half-round, quarter-round, and two Ogee-type crest weir shapes . A method is presented for comparing the flow capacity between weirs in order to determine the most efficient weir at a given Ht/P. For a labyrinth weir with the crest shape,# of cycles (N), and the cycle width (w) held constant, the discharge coefficient (Cct) decreases with decreasing side angle (a). Based on those same geometric constraints the weir length increases with decreasing side angle (a). The dimensionless parameter Cct*LJIW (which when multiplied by 73fig H,312 gives the flow per unit width) was used to evaluate the relative discharge capacity between labyrinth weirs. The results from this study show that at low (Hr!P) values and a side leg angle of 7 and 8 degrees, an Ogee-type crest will pass more flow than a half-round crest which will pass more flow than a quarter-round crest. The effects of nappe conditions for half-round crest weirs were determined and documented for the configurations tested. The use of centerline length (L3) is used in this study over the use of the effective length (L) presented in the research. Modifications are applied to the Tullis et al. (1995) design procedure. The effect of uniform sediment deposition upstream of a labyrinth weir was tested to determine the effect it had on the discharge coefficient Cct. Both level and ramped approach conditions to a labyrinth weir apron were tested and compared . A review of literature covering previous design procedures, and laboratory tests is presented