Introduce of CPK Spillway and Study of Its Discharge Coefficient under Free Flow Regime

Document Type : Research Paper



      Flood is a stochastic phenomenon and successful and construction of economic dam in flood discharge system is very important. In recent years, non-linear overflows, as a solution, helped designers and engineers of water sciences. In this study, new non-linear overflow weirs as CPK spillways are introduced. Discharge coefficient tests were performed under various scenarios geometry of the overflow in order to investigate the ability of the hydraulic overflow flood discharge. To study the effect of the slope floor of inlet and outlet keys (Z) on the current discharge coefficient, the slope of 1 : 0.5, 1 : 1 and 1 : 1.5 (Horizontal : Vertical) were designed and built. Then in each of the three phase variation in the slope floor of inlet and outlet keys (Z) built and tested. The results indicated that by increasing the slope of inlet and outlet keys (Z), discharge flow rate will be increased. This also increases the number of cycles at low heads, leading to an increase in the flow discharge coefficient. In large heads, the feature of vortex breaking in overflows with the less number of cycles is noticeable. The results showed that the coefficient of discharge in CPK spillway is to 2.2 bigger than in a circular vertical sharp edged weir. Due to the small dimensions of this type of overflow compared to similar types, this nonlinear overflows can be considered as an efficient and economic flood discharge system for introduction to the scientific community of the country.


1-    نصیری، س.، کبیری سامانی، ع. و ک. اصغری. 1395. مدل سازی عددی میدان جریان در اطراف سرریزهای مدور قائم با ورودی کلید پیانویی. نشریه علمی پژوهشی هیدرولیک، 11(1)، 53-66.
2-    نیک صفت، غ. 1380. تئوری و کاربرد مدل‌های هیدرولیک در طراحی سازه‌های آبی. نشریه شماره 41، وزارت نیرو کمیته ملی سدهای بزرگ ایران.
3-    Anderson, R. and B. Tullis. 2011. Influence of Piano Key Weir geometry on discharge. Proceeding International Workshop on Labyrinth and Piano Key Weirs. Liege Belgium.
4-    Anwar, H.O. Weller, J.A. and M. B, Amphlett, 1978. Similarity of free vortex at horizontal intake. Journal of Hydraulic Research, 16(2): 95–106.
5-    Daggett, L. L. and G. Keulegan. 1974. Similitude in free surface vortex formations. Journal of Hydraulic Division, ASCE, 100(HY11): 1565–1580.
6-    Hecker, G.E. 1987. Fundamentals of vortex intake flow. In: Swirling flow problems at intakes. In:Knauss J, editor. IAHR hydraulic structures design manual 1. Balkema, Rotterdam, NL,Pp.13–38.
7-    Jain, A. K., Ranga Raju K. G.  and R. J.Garde. 1978. Vortex formation at vertical pipe intakes. Journal of Hydraulic Engineering, 104(10): 1429-1445.
8-    Odggard, A. 1984. Free-surface air core vortex. Journal of Hydraulic Engineering, 112(7): 610-620.
9-    Kabiri-Samani, A. and A. Javaheri. 2012. Discharge coefficient for free and submerged flow over Piano Key weirs. Journal of Hydraulic Research, 50(1): 114-120.
10- Keller, J., Moller, G. and R. M. Boes. 2014. PIV measurements of air-core intake vortices. Flow Measurement and Instrumentation, (4): 78-81.
11- Lemperiere, F. and A. Ouamane. 2003. The piano keys weir: A new cost-effective solution for spillways, International Journal of Hydropower and Dams, 10(5): 144-149.
12- Lemperiere, F., Vigny, J.P., and A. Ouamane. 2011. General comments on Labyrinth and Piano Key Weirs: The past and present. Proceedings International Conference. Labyrinth and Piano Key Weirs Liege B, 17-24, CRC Press, Boca Raton, FL.
13- Leite Ribeiro, M., Bieri, M., Boillat, J. L., Schleiss, A. J., Delorme, F. and F. Laugier. 2009. Hydraulic capacity improvement of existing spillways. Design of Piano Key Weirs, In Proceedings of 23rd Congress of CIGB/ICOLD, Brasilia.
14- Leite Ribeiro, M., Pfister, M., Schleiss, A.J. and J.L. Boillat. 2012. Hydraulic design of A-type Piano Key Weirs. Journal of Hydraulic Research, 50(4): 400–408.
15- Shemshi, R. and A. Kabiri-Samani. 2016. Swirling flow at vertical shaft spillways with circular piano-key inlets. Journal of Hydraulic Research, 55(1): 1-11.
16- Taylor, G. 1968. The performance of labyrinth weirs. Doctoral Dissertation, University of Nottingham.
17- Vischer, D. L., and W.H., Hager. 1998. Dam hydraulics. Wiley Series in Water Resources Engineering, Zürich, Switzerland, ISBN: 978-0-471-97289-1.
Volume 40, Issue 2
September 2017
Pages 209-221
  • Receive Date: 08 January 2016
  • Revise Date: 25 September 2017
  • Accept Date: 16 July 2016
  • First Publish Date: 23 August 2017