Experimental Evaluation of Hydraulic Performance of Modified Piano Key Weirs

Nowadays, Labyrinth and piano key weirs are suggested as appropriate options for modification of those weirs which are faced with the problems as passing the probable maximum flood. Piano key weirs (PKWs) have been developed for the substitution of Labyrinth weirs which their footprint areas are restricted. In this study, to evaluate the hydraulic efficiency and discharge coefficient of the PKWs, totally 377 experiments are conducted on the 18 physical models in both contracted and not contracted PK weirs. From the experimental results, in all PKWs, the discharge coefficient and the efficiency of the cycle by increase of the head water ratio (HT/P), first increase and then decrease. Nonetheless, discharge coefficient of the modified PKWs (modified by increasing and reshaping the weir crest as well as installing the fillet) was increased by 10% when compared to the non-modified weirs. In the contracted PK weirs, the PK₁ weir at HT/P≤0.18, has the highest discharge coefficient, but with the increasing of the discharge, the discharge coefficient decreases and at HT/P≥0.3 reaches to the lowest magnitude. Nonetheless, in contrary to the non-contracted weirs, increasing Wi/W₀ leads to discharge coefficient reduction in the contracted weirs.