Piano Key Weir Hydraulics and Labyrinth Weir Comparison

Abstract

A piano key (PK) weir is a type of nonlinear (labyrinth-type) control structure with a relatively small spillway footprint. No standard PK weir design procedure is available, and the amount of published information on PK weirs is limited. PK weirs have a large number of geometric parameters that can affect head-discharge performance. A PK weir geometric design has, however, been recommended in the literature, along with a head-discharge relationship specific to that PK weir geometry. To develop a better understanding of the effects of PK weir geometry on discharge efficiency, nine laboratory-scale four-cycle PK weir configurations were tested (including the recommended design). The effects of the following PK weir geometry or modifications on weir performance were partially isolated: varying the inlet-to-outlet key ratio, raising the crest via a parapet wall, rounding the upstream apex walls, and varying the crest type. The appropriateness of the recommended head-discharge equation specific to the recommended design was evaluated, and the relative head-discharge efficiency of trapezoidal labyrinth and PK weirs with respect to footprint restrictions and crest length were compared.