Hydraulic design of A-type Piano Key Weirs

TLDR

Piano Key Weirs increase unit discharge compared to linear overflows, enabling higher reservoir supply levels and extra storage, but design criteria are scarce. The study conducts systematic physical model tests on A‑type Piano Key Weirs to derive a general head–discharge design equation and extend its applicability to reservoir approach flows. Model tests varied approach flow head, crest length, key height, and width to formulate a design equation based on these parameters, with additional case studies for reservoir approach flow scenarios.

Abstract

Piano Key Weirs (PKWs) are an alternative to linear overflow structures, increasing the unit discharge for similar heads and spillway widths. Thus, they allow to operate reservoirs with elevated supply levels, thereby providing additional storage volume. As they are relatively novel structures, few design criteria are available. Hence, physical model tests of prototypes are required. This study describes comprehensive model tests on a sectional set-up of several A-type PKWs, in which the relevant parameters were systematically varied. Considering data of former studies, a general design equation relating to the head–discharge ratio is derived and discussed. The latter is mainly a function of the approach flow head, the developed crest length, the inlet key height, and the transverse width. To extend its application range, case study model tests were analysed to provide a design approach if reservoir approach flow instead of channel flow is considered.