Sulaimani Journal for Engineering Sciences (SJES)

Location of inception point of alternating steps stepped spillways

1, a Burhan S. Muhammed 2, a Kawa Z. Abdulrahman

a University of Sulaimani, College of Engineering, Department of Water Resources Engineering

Abstract

This study explored the effects of flat-stepped spillways having alternating steps on the inception point location. Two wooden stepped spillways with a longitudinal slope of 26.6° were constructed in a rectangular flume and tested at various discharges, ranging from 0.003 to 0.05 m3/s. Each model had twenty-seven steps, and the channel's width, depth, and length were 0.605 meters, 1.35 meters, and 8 meters. The outcomes showed that the Alternating Model (MA), compared to the Regular Model (MR), has shortened the inception point distance (Li) from the downstream crest of the spillway by an average of 27% (e.g., the Li of the MR model was 59 cm, and the Li of the MA model was 43 cm). The MA model's skimming flow was discovered to begin at higher discharges, at yc/h 1.24 (as opposed to yc/h=0.98 for the MR model). Two equations were also developed to compute the inception point positions for flows over the MA and MR stepped spillways.

Keywords:

stepped spillway, Inception point, skimming flow, alternating steps.

References

[1] J. G. Chatila and B. R. Jurdi, “Stepped Spillway as an Energy Dissipater,” Canadian Water Resources Journal / Revue canadienne des ressources hydriques, vol. 29, no. 3, pp. 147–158, Jan. 2004, doi: 10.4296/cwrj147.

[2] S. Felder and H. Chanson, “Energy dissipation, flow resistance and gas-liquid interfacial area in skimming flows on moderate-slope stepped spillways,” Environ Fluid Mech, vol. 9, no. 4, pp. 427–441, Aug. 2009, doi: 10.1007/s10652-009-9130-y.

[3] R. M. Boes and W. H. Hager, “Two-Phase Flow Characteristics of Stepped Spillways,” J. Hydraul. Eng., vol. 129, no. 9, pp. 661–670, Sep. 2003, doi: 10.1061/(ASCE)0733-9429(2003)129:9(661).

[4] A. Amador, M. Sánchez-Juny, and J. Dolz, “Characterization of the Nonaerated Flow Region in a Stepped Spillway by PIV,” Journal of Fluids Engineering, vol. 128, no. 6, pp. 1266–1273, Nov. 2006, doi: 10.1115/1.2354529.

[5] M. Chamani and N. Rajaratnam, “Characteristics of Skimming Flow over Stepped Spillways,” p. 8.

[6] J. Matos and K. H. Frizell, “Air Concentration and Velocity Measurements on Self-Aerated Flow Down Stepped Chutes,” in Building Partnerships, Minneapolis, Minnesota, United States, Sep. 2000, pp. 1–10. doi: 10.1061/40517(2000)321.

[7] I. Ohtsu, Y. Yasuda, and M. Takahashi, “Flow Characteristics of Skimming Flows in Stepped Channels,” J. Hydraul. Eng., vol. 130, no. 9, pp. 860–869, Sep. 2004, doi: 10.1061/(ASCE)0733-9429(2004)130:9(860).

[8] Jumaily, D.K.K.E.; Lami, M.K.A. Study of Conveniency of Using Stepped Spillway in Roller Compacted Concrete Dams (RCCD). Eng. Technol. J. 2009, 27, 2964–2977.

[9] S. L. Hunt and K. C. Kadavy, “Inception Point Relationship for Flat-Sloped Stepped Spillways,” p. 11.

[10] G. Zhang and H. Chanson, “Hydraulics of the Developing Flow Region of Stepped Spillways. I: Physical Modeling and Boundary Layer Development,” J. Hydraul. Eng., vol. 142, no. 7, p. 04016015, Jul. 2016, doi: 10.1061/(ASCE)HY.1943-7900.0001138.

[11] A. S. Ali and O. S. Q. Yousif, “Characterizations of flow over stepped spillways with steps having transverse slopes,” IOP Conf. Ser.: Earth Environ. Sci., vol. 344, no. 1, p. 012019, Oct. 2019, doi: 10.1088/1755-1315/344/1/012019.

[12] H. Chanson, “Prediction of the transition nappe/skimming flow on a stepped channel,” Journal of Hydraulic Research, vol. 34, no. 3, pp. 421–429, May 1996, doi: 10.1080/00221689609498490.

[13] J. Wu, B. Zhang, and F. Ma, “Inception point of air entrainment over stepped spillways,” J Hydrodyn, vol. 25, no. 1, pp. 91–96, Feb. 2013, doi: 10.1016/S1001-6058(13)60342-X.

[14] C. A. Gonzalez and H. Chanson, “Hydraulic Design of Stepped Spillways and Downstream Energy Dissipators for Embankment Dams,” no. 4, p. 22, 2007.

[15] M. Chamani and N. Rajaratnam, “Onset of Skimming Flow on Stepped Spillways,” p. 3.

[16] N. Rajaratnam, “Skimming Flow in Stepped Spillways,” Journal of Hydraulic Engineering, vol. 116, no. 4, pp. 587–591, Apr. 1990, doi: 10.1061/(ASCE)0733-9429(1990)116:4(587).

[17] I. R. Wood, P. Ackers, and J. Loveless, “General Method for Critical Point on Spillways,” Journal of Hydraulic Engineering, vol. 109, no. 2, pp. 308–312, Feb. 1983, doi: 10.1061/(ASCE)0733-9429(1983)109:2(308).

[18] T. Hepler, J. Young, B. Crookston, and J. Crowder, “Successful Overtopping Protection Projects in the Eastern U.S.,” p. 10, 2018.

[19] S. L. Hunt and K. C. Kadavy, “Inception Point Relationship for Flat-Sloped Stepped Spillways,” p. 11, 2009.

[20] A. S. Ali and O. S. Q. Yousif, “Effects of Step Transverse Slopes on Locations of Inception Point of Flow over Stepped Spillways,” p. 7, 2020.

[21] “Chanson - 1993 - Stepped spillway flows and air entrainment.pdf.”