Size-Scale Effects of Labyrinth Weir Hydraulics

Experimental physical model studies of open channel and reservoir hydraulic structures are often conducted by maintaining geometric similitude between the model and prototype to account for the dominant gravity and inertia forces while other fluid forces are assumed negligible. However, as the model size and/or the upstream total head decreases, other fluid forces can exceed the negligible level and influence model flow behavior. This phenomenon is referred to as size-scale effects and can be a source of error in predicting prototype flow behavior. To investigate size-scale effects related to labyrinth weirs, several weir models ranging in weir heights from P = 76 mm (0.25 ft) to 914 mm (3.0 ft) were fabricated and hydraulically tested to assess differences among head-discharge relationships and nappe behavior. Criteria to avoid size-scale effects were determined to be dependent on the model size and tolerable error