Herein, we summarized the current and future study topics of sediment management using bypass tunnels based on the discussions at the Second International Workshop on Sediment Bypass Tunnels (SBTs) at Kyoto in May 2017. Although reservoir sediment management using bypass tunnels has appeared since the beginning of the 20th century in Kobe, the number of SBTs worldwide is still limited. To promote the installation of SBTs as an effective sediment management measure, it is essential to appropriately evaluate their long-term advantages economically and for the restoration of the aquatic ecosystem. An abrasion model has been developed to predict the abrasion rate of tunnels from the volume of sediment transport. Further, methods to monitor sediment transport in tunnels have advanced. With a significant amount of sediment supply by SBTs, the ecosystems in the downstream reaches of dams can be restored within a few years. A precise rainfall and runoff model for predicting the inflow hydrograph and sediment is essential for the efficient operation of dam gates and SBT (e.g., diverting minimum amount of water for sediment transport). Further studies are needed to clarify the suitable grain size for transportation through SBTs in terms of both the mitigation of tunnel abrasion and promotion of the restoration of downstream ecosystems.

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