Hydraulic performance of Piano Key Weir Dr.Adil M. Raheem 1 , Tara Haydar Aurahman 2 {dr_adilraheem@yahoo.com 1 ,tarahaydar86@gmail.com 2 } Assistant professor, College of Engineering, Al-Kitab University-Altun Kopri 1 , lecturer in Dam and Water Resources Engineering, College of Engineering, University of Salahaddin, Erbil 2 Abstract: PKWs are considered an effective solution for dam designs which require either high specific discharge efficiency or low reservoir level. The influence of piano key weir geometry on discharge capacity was studied and for this purpose, twenty-seven physical models of two types(Aand D) of piano key weir and rectangular labyrinth weir(RLW) were constructed and tested, Dimensional analysis was carried out to find the influence of the geometric parameter on discharge capacity ratio .Prediction equations for discharge capacity ratio were found and compared with equatins for other investigators.The discharge capacity ratio of PKW was increased with increasing the value of (Wi/Wo). For PKW type A, the discharge capacity ratio was increased by (25%) with increasing the value of Wi/Wo from 0.5 to 2 , increasing the head over PKW, leds the discharge capacity ratio to be decreased.and variation in the height of PKW (P) doesn't affect the hydraulic performance of PKW . The discharge capacity ratio of PKW increased by(27%) with increasing the value of (L/W) from 3 t0 7. PKW type A was founded more efficient than the other types. Keywords: hydraulic, weirs, piano, flow, discharge. 1. Introduction The discharge capacity of free crest or ungated over fall spillways or weirs is directly proportional to the length of the crest for a given upstream head. Its length can be increased by using curved, undulated or corrugated weirs instead of straight linear weirs, which increase the discharge for a given head. In recent year's people have developed different types of weirs with different shapes and all of them aimed to increase the discharge capacity. The main advantages of the PK weir regarding labyrinth weirs are its reduced footprint. PKW was developed specifically for smaller control structure footprint applications. For some spillway applications, the control structure footprint length (B) and width (W) may be limited, e.g. narrow dam crest, for such cases, some of the benefits of the traditional labyrinth weir are lost, and alternative non-linear weir designs need to be considered.[1]- [9]. Many of the current dams need spillway reconstruction to increase their hydraulic efficiency, development, improvement in hydrological analysis with a modern technique for discharge estimation and for a higher requirement of dam safety, For this purpose, the new innovative shape of labyrinth weir called PKW is an interesting option. [11]. Goulours dam in France was the prototype of the Piano Key Weir which was constructed and completed in 2006 and the second prototype of PKW was constructed at Saint-Marc dam in France and completed in 2008. Until today little research has been conducted on Piano Key Weir, as they IMDC-SDSP 2020, June 28-30, Cyberspace Copyright © 2020 EAI DOI 10.4108/eai.28-6-2020.2297967