Arced Labyrinth Weir Flow Characteristics

Abstract

The increase in predicted extreme flood event magnitudes has required the modification of many existing reservoir spillway flow control structures with more hydraulically efficient designs. The arced labyrinth is a relatively new, highly efficient, nonlinear weir design specifically applicable to reservoir applications. Flow characteristics of eleven laboratory-scale arced labyrinth weir geometries were studied at the Utah Water Research Laboratory with sidewall angles α = 12° and 20°. Rating curves, flow conditions, and discharge efficiencies were documented for each configuration to increase the hydraulic database of arced labyrinth weirs. Arced labyrinth weirs with α = 20° were found to have discharge efficiencies 5 to 10% higher than α = 12° weirs. They also generated more flow anomalies (i.e. unstable nappe aeration) due to approach flow interaction with cycle orientation and weir position. The hydraulic efficiency of projecting, traditional labyrinth weirs, as a function of abutment wall geometry, was also evaluated. No standardized design method currently exists for arced labyrinth weirs, and relatively little is known about their hydraulic characteristics; this discussion increases the hydraulic information available for the arced labyrinth weir design.