Sediment Movement over Type A Piano Key Weirs

Abstract

This investigation deals with the mechanics of movement of singular quartz gravel and coarse sand riverbed particles upstream and over the inlet key of three Type A piano key weir (PKW) models, which were recorded with a high-speed camera. Acoustic Doppler velocimeter was used to obtain the upstream bed shear stress. The sediment threshold and regime over the upstream bed were compared with the previous investigations and found to be within the ranges. Generally, a sediment particle decelerates as it approaches the inlet key, but accelerates over it due to flow contraction and an increase in shear stress. Rolling and saltation regimes were observed over the key. The maximum particle velocity at the key end was highest in the 1-cycle model, then the 2-cycle model, then the 3-cycle model. Computational fluid dynamics (CFD) simulation shows a rapid increase in shear stress at the key end. For the used models, PKW required 17%–43% of additional shear stress on the upstream bed to pass sediment over the key. This study is useful for the in-channel application of PKW and sediment flushing over it.