Abrasion Prediction at Kayraktepe Sediment Bypass Tunnel in Turkey

Sediment accumulation in reservoirs is a challenging issue that concerns most of the reservoirs worldwide. Use of sediment bypass tunnels is one of the potential solutions to reduce sediments deposited in reservoirs. However, the sediment bypass tunnels could face major invert abrasion problems due to intense bedload sediment transportation. Three existing abrasion prediction models are introduced developed respectively by Ishibashi (1983), Sklar and Dietrich (2004), and Auel et al. (2015). Those models are applied to estimate the abrasion of the Kayraktepe sediment bypass tunnels in Turkey. The Ishibashi (1983) model results reveal some discrepancies when compared to laboratory data, which reflects that its grinding stress term gives much higher values than its particle impact term does. However, when examining the effect of particle impact term by neglecting the grinding stress, the model predicts consistent results. The model by Auel at al. (2015) demonstrates reasonable predictions in case of regulated abrasion coefficient values are used. The model of Sklar and Dietrich (2004) predicts the lowest abrasion value due to its development according to the subcritical flow conditions. In Kayraktepe dam, the flow condition in sediment bypass tunnels are supercritical flow, thus the Sklar and Dietrich (2004) model does not fit for abrasion estimation. Modifications are made to the Sklar and Dietrich (2004) model are the revised model shows great improvement on the abrasion prediction. It is concluded that the estimation of sediment transport rate using commonly adapted theoretical or empirical formulations tends to be predicted more than the real transport rate and results in the over-estimation of the abrasion rate. It is recommended to modify the formulations and equation coefficients with the inputs of the field data on laboratory measurements for bettering the abrasion prediction.