Seite - 691 - in Book of Full Papers - Symposium Hydro Engineering

3. EXPERIMENTAL OBSERVATION 3.1. WATER PROFILE ALONG THE SPILLWAY Test of water surface profiles are conducted along the spillway, started from the crest through the stepped spillway and the energy dissipator using the design discharges. The water flow on stepped chute is known as the nappe, transition, and the skimming regimes (Yasuda 1997; Chanson & Toombes 2002). Based on the results, the flow from the crest spill smoothly and relatively well distributed, for low discharges the flow at the beginning of the steps are splash out of step, while for higher discharges the flow more smoothly over the stepped spillway. Since there are no changes in the upstream condition, the water profile is still the same in all scenario. Figure 3 shows that at the downstream of the center pier the flow is not smooth and splash over due to the rectangular shape of the downstream end of the pier. Fig. 3. Upper Cisokan spillway model with discharge Q1000yrs The inception point occurred and started to shift more downstream in regards of increased discharge from nappe to skimming regime. In particular for high discharge, the hydraulic jump occurred and seemed has not dissipated properly which may cause local scouring at downstream of the dam especially when the downstream area is not protected (see Figure 4). 691