Seite - 138 - in Book of Full Papers - Symposium Hydro Engineering

Fig. 5 Variation of cavitation index along the FCO Spillway chute For a release of 4248 m3/s (150,000 ft3/s), the cavitation index falls below 0.2 near Station 975 m (3200 ft), with a minimum value of 0.11 near the dentate structures. However, the air concentration is about 8%, which is about the minimum air concentration recommended to prevent cavitation damage. This is consistent with the historical performance of the FCO Spillway chute. Past maintenance records show that damage to the chute due to cavitation for flows up to 4248 m3/s (150,000 ft3/s) was negligible [5]. If the initial aeration entrained by the gate piers is considered, the chute should be able to convey flows up to 8382 m3/s (296,000 ft3/s) without cavitation damage. The need for aerators in the new FCO Spillway chute is still an on-going issue. While model results suggest aerators may reduce potential for chute cavitation, models available are based on certain assumptions not necessarily valid for Oroville Dam. Further, current designs, while efficient for certain flows are less efficient for flows which are larger and/or smaller than the flows. Finally, maintenance of feasible designs is a significant concern. As of December 2017, analysis continues, and no final design decision has been taken regarding aeration. 6.1.4. Model Validation Measured velocity, flow depth, and air content data along the modified FCO Spillway chute are not yet available to calibrate or verify the models. The model results (velocity and flow depth) from the 1-D model were confirmed by comparing 138