Labyrinth Weirs with Angled Approach Flow

Current design methods and research have primarily investigated the hydraulic characteristics of labyrinth weirs when the approach flow is perpendicular to the weir axis, a condition consistent with most in-channel and in-reservoir applications where the approach velocity is negligible. In some cases, a perpendicular approach flow and weir axis alignment may not be possible. The head–discharge characteristics of a four-cycle, 15° labyrinth weir with a channelized approach flow were evaluated with three different approach flow angles (0°, 15°, and 45°) using laboratory-scale physical models. Although the data presented are specific to the geometry of the weir and channels tested, they provide a general indication of variations in discharge efficiency as a function of approach flow angle. The experimental data were also compared with the head–discharge characteristics of a prototype labyrinth weir model study that featured significant approach flow angles. For approach flow angles under 15°, no measurable loss in discharge efficiency occurred, relative to an approach flow angle of 0°. The discharge efficiency reduced by as much as 11% for the 45° approach flow angle case. Flow instability was observed downstream of the weir, producing unique flow patterns in the labyrinth cycles and on the spillway apron.