Page - 697 - in Book of Full Papers - Symposium Hydro Engineering

According to the scouring results, scouring condition without downstream protection can be dangerous for the dam structure due to scouring problem. Downstream protection such as riprap can be a good solution for this issues as a transition zone from the massive structure and the river bed. 4. CONCLUSIONS Upper Cisokan Dam was investigated using hydraulic laboratory experiments using various discharge. Based on the observation, it's known that water profile on stepped spillway at high discharge were dominant by skimming regime and already dissipated from the stepped chute to energy dissipator. Pressure distribution along the dam spillway is vary. It is also found that some negative pressure occurred. Therefore, if needed, aerator can be implemented to avoid cavitation effect. Based on its Froude number, the energy still not fully dissipated by the energy dissipator downstream of the spillway which may cause scouring. Hence, downstream protection such as riprap is needed to minimize the scouring effect. The final simulation shows that the stone riprap protection is effective to use to reduce the depth of the scouring from 3 meters into 0 meters. Ultimately, the stepped spillway can be implemented on the Upper Cisokan Dam after adding some additional treatment such as aerator and riprap protection. 5. ACKNOWLEDGEMENTS The author also would like to thank Mrs. Yiniarti Eka Kumala for her valuable assistance that helped to improve the quality of this paper. Also for colleagues at Hydraulic Laboratory, Research Center for Water Resources, Ministry of Public Works and Housing for the support and opportunity to conduct dam investigation. REFERENCES [1] Chanson H, Toombes L. Experimental Investigations Of Air Entrainment In Transition And Skimming flows Down A Stepped Chute. Canadian J Civil Eng. 29(1):145–156. 2002. [2] Chanson H. Forum Article: Hydraulics Of Stepped Spillways. J Hydraul Eng, 2000, 126(9): 636—637 [3] Ohtsu I, Yasuda Y. Characteristics Of Flow Conditions On Stepped Channels. In: Holly Fm, Alsaffar A, Editors. Proceedings Of 27th Iahr Congress, San Francisco, Usa, D, 583–588. 1997. 697