Design, operation and morphological effects of bypass tunnels as a sediment routing technique

Abstract

Sediment Bypass Tunnels (SBTs) are a sediment routing technique. During floods, sediment-laden water is conveyed through the tunnel to the dam tailwater. SBTs feature several advantages over other measures against reservoir sedimentation. First of all, SBTs have demonstrated to be quite effective with sediment bypass efficiencies of up to more than 90%, thus considerably extending the reservoir life, i.e. the theoretical duration until the reservoir is completely filled with sediment. Secondly, they have positive effects on downstream eco-morphology, because sediment conveyance may significantly decelerate or even stop riverbed incision and increase the habitat quality and morphological variability below a dam reservoir. Mainly sediments provided from upstream river reaches are conveyed through SBTs since remobilization of accumulated sediments in the reservoir hardly occurs. An SBT can thus greatly improve the sediment continuity despite river impoundment by dams. In this paper the main design features, operational aspects and eco-morphological effects of SBTs are presented.