TY - CHAP A1 - Auel, C. A1 - Sanjou, M. A1 - Okamoto, T. A1 - Kobayashi, S. A1 - Sumi, T. T1 - Mean flow and turbulence variation due to invert abrasion T2 - Proc. 2nd Int. Workshop on Sediment Bypass Tunnels, FP15, Kyoto, Japan N2 - Due to high bedload sediment transport, many sediment bypass tunnels (SBT) are prone to severe invert abrasion. However, there is little information about the flow characteristics in SBTs after invert abrasion initiated and progresses with time. In the present study, laboratory flume experiments were performed to investigate how the hydraulic conditions change after abrasion patterns developed on the invert. A typical invert abrasion pattern was produced using 3D-printing technique and implemented in the laboratory flume. Flow depths were measured to compare the initial with the abraded state. Furthermore, turbulence measurements using 2D-laser Doppler anemometry technique were performed to obtain the mean and turbulence flow characteristics. This paper describes results of these measurements focusing on the streamwise and vertical flow velocities, turbulence intensities and Reynolds shear stress. Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-151721 PB - Kyoto University ER - TY - JOUR A1 - Auel, C. A1 - Kobayashi, S. A1 - Takemon, Y. A1 - Sumi, T. T1 - Effects of sediment bypass tunnels on grain size distribu-tion and benthic habitats in regulated rivers JF - International Journal of River Basin Management N2 - Four dams in Japan and Switzerland with Sediment Bypass Tunnels (SBT) as a measure against reservoir sedimentation were monitored to analyse the effects of sediment supply on the downstream environment based on up- to downstream differences in geomorphological and biological characteristics. SBT operation times ranged from 93 years at Pfaffensprung and 17 at Asahi to only three years at Solis and no operation at Koshibu. Sediment grain size distribution was monitored, and microhabitats and invertebrates were analysed in terms of richness and composition. Results showed that grain sizes were coarser down- than upstream at dams with newly established SBTs, while they were similar or finer for dams with long SBT operation. Analysis of biotic data revealed that microhabitat and invertebrate richness was low directly below the dam but increased further downstream the longer the SBT operation. Sedentary species dominated at locations where bed conditions were stable, e.g. directly downstream of the dam at Koshibu. Recovery of downstream environment with increasing SBT operation time was disclosed by the Bray–Curtis similarity index, which evaluated an overlap between up- and downstream reaches for both microhabitat composition and invertebrate communities. With increasing operation time, both indices increased, revealing the positive effects of long-term SBT operation. Y1 - 2017 U6 - http://dx.doi.org/10.1080/15715124.2017.1360320 SP - 433 EP - 444 ER - TY - CHAP A1 - Kobayashi, S. A1 - Auel, C. A1 - Sumi, T. A1 - Takemon, Y. T1 - Effects of sediment supply by bypass tunnels on bed to-pography, grain size, and invertebrate habitat T2 - Proc. 20th IAHR APD Congress, Colombo, Sri Lanka, 5B008 N2 - To understand the effects of sediment bypass on environmental recovery of the degraded channels below dams, bed topography and bed materials above and below dam reaches were surveyed by ground-based measurements and aerial photos using quadrocopter. Coarse bed materials such as boulders were more represented below than above the Koshibu dam, where the bypass tunnel had not been in operation yet. The coarse materials formed steps and protruded in the water column within riffles and runs, both of which can increase slow-flow areas, below the dam. On the other hand, sand, gravel, and cobbles were abundant below as much as above the Asahi dam, where the bypass tunnel had been operated for >17 years. The downstream environment in terms of bed topography and grain size seems to have almost been recovered for the Asahi dam. However, less representation of large cobbles and boulders below the dam suggested a possibility of a selective deposition of coarse materials at the upstream of the bypass tunnel inlet. Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-151473 PB - IAHR ER - TY - CHAP A1 - Kobayashi, S. A1 - Auel, C. A1 - Sumi, T. A1 - Takemon, Y. T1 - Recovery of riverbed features and invertebrate community in degraded channels by sediment supply through bypass tunnel T2 - Proc. 12th Int. Conference on Hydroscience and Engineering, Tainan, Taiwan N2 - Sediment, which deposits and damages the function of reservoirs, is an essential element of aquatic habitats in downstream ecosystems. We reviewed ecosystem features of degraded channels associated with sediment deficiency below dams and ecosystem responses to changes in sediment conditions after management practices in Japan. Sediment bypass tunnel (SBT) is an effective way to transport sufficient amount of sediment to downstream ecosystems. Based on a concept of suitable mass and size of sediment for ecosystem, some effects and limitations of SBT on downstream ecosystems were discussed. Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-151447 PB - ICHE ER - TY - CHAP A1 - Auel, C. A1 - Kobayashi, S. A1 - Sumi, T. A1 - Takemon, Y. T1 - Effects of sediment bypass tunnels on sediment grain size distribution and benthic habitats T2 - River Sedimentation: Proc. 13th Int. Symposium on River Sedimentation Y1 - 2016 SP - 825 EP - 832 PB - CRC Press CY - Stuttgart, Germany ER -