Piano Key Weir: Reservoir versus Channel Application

The piano key (PK) weir is a relatively new nonlinear weir geometry that can be used to increase spillway discharge capacity over linear weir geometries, particularly when the weir footprint area is restricted (e.g., spillways on the crest of a concrete dam). The majority of the published PK weir research (e.g., head-discharge curves) has been based on channelized applications (sectional PK weir models in laboratory flumes). The head-discharge characteristics of crest-of-dam PK weir applications are influenced by the approach flow conditions. Using a laboratory-scale physical model, the hydraulic efficiency of a PK weir design was tested with varying approach flow depths, upstream apron slopes, and abutment details. In general, discharge efficiency increased with increasing approach flow depth, steeper approach aprons, and improved abutment geometries that reduced the effects of flow separation.