Staged Labyrinth Weir Hydraulics

Labyrinth weirs with multiple crest elevations (i.e., staged labyrinth weirs) can be used in spillway design to confine base flows to a section of the crest and/or satisfy discharge hydrograph requirements. However, inadequate hydraulic design information is available specific to staged labyrinth weirs. In this study, the flow characteristics of various staged labyrinth weir configurations (laboratory-scale) were tested. Observations of staged labyrinth weir flow characteristics are presented. The influences of the lower stage length, depth, and location on discharge were studied and head-discharge relationships were experimentally determined. The accuracy of a head-discharge predictive technique on the basis of superposition and traditional labyrinth weir empirical data was also evaluated. Relative to the experimental results, the superposition technique estimations were generally within ±5% for all configurations tested except at lower headwater depths, where maximum estimation errors occurred (maximum of 15%). When discharge was limited to the lower stage weir segment, the predictive discharge errors were up to 20% for some notch configurations. This indicates the discharge of the lower stage segment is location-specific because of the complexity of the labyrinth weir geometry.