Experimental study on scour downstream of a piano key weir with nose

Piano key weirs (PK weirs) are generally installed on low head dams to enhance the discharging capacity. Such weirs are preferred over the other spillways if the length available for the construction of the spillway is limited and high discharge is to be passed at low head to avoid flood inundation in upstream. This newfangled weir having zig-zag shape changes the flow configurations which lead to scour downstream of the weir. A study on scour formation downstream of a PK weir is presented in this paper. Experimental investigations were conducted on three cycles PK weir to investigate scour pattern downstream of inlet and outlet keys with and without solid apron. Variation in observed maximum scour depth (ds) with tail water depth (yt) was studied to examine the effect of tail water depth on the scour for different discharges. It was observed that the falling jet and impinging jet originating from the inlet keys and outlet keys were liable for the development of dip and ridge downstream of the weir. For higher discharge and lower tail water, it was observed that scour depth and length of scour are high. Scour formation was negligible in the case of high submergence downstream of the weir. However, significant reduction in the scour was observed due to introduction of solid apron downstream of weir. Finally, the present experimental PK weir scour data were checked with the predictions provided in the literature. Two equations show correct trend for the observed scour values.