Major impacts by Reservoir Sedimentation ダムの安全
下流の河床地形変化

Downstream
Geomorphology
Degradation and Bedarmoring 下流の生態系

Downstream
Ecosystem
Reduced ecosystem
health (Biodiversity,quality and quantity offood resources, waterquality) with the combination of changes inseasonal flow, flood
frequency and magnitude

Source: S. A Kantoush, T.
Sumi and Y. Takemon 2011

ダム堆砂の影響

Dam Safety
Clogging of intake
and outlet

貯水池の持続可能性

Reservoir
Sustainability
Reduction of storage
capacity

洪水リスク

Flood Risks
Upstream Channel
Aggradation

Classification of sediment management strategies for reservoirs 貯水池土砂管理方策
土砂流入防止

土砂排除

土砂通過

通砂排砂(Source: Sumi)(i) Reduction of sediment input by
controlling erosion and trapping
upstream sediment loads
貯砂ダム(ii) Routing sediments by bypass, off
stream reservoirs, sediment sluicing(drawdown routing) and as well as
密度流土砂
venting of turbid density currents
バイパス
排出還元
(iii) Sediment removal by dry
その他適応策excavation, dredging, drawdown/pressure flushing and Hydro-suction
Sediment Removal System.
ダム撤去 (iv) Adaptive strategies by reallocate
発電排砂
storage, dam heightening, operationalClassification of sediment management strategies for reservoirs (Morris, 2015) control and dam decommissioning2

土砂通過対策 （通砂，バイパス，密度流排出）

Chapter 3. SEDIMENT ROUTING BY BOTTOM OUTLETS,
SLUICING AND SEDIMENT BYPASS TUNNELS
Sediment Routing is to pass through sediments into the tailwater downstream of the dam.
Various effective techniques can be applied: Direct bypassing around the dam using tunnels or channels
 Diverting to an off-channel reservoir
 Passing sediments through the reservoir by either sluicing or turbidity current venting

河道外貯留
バイパス(Source: Morris）
3

Sediment Bypass Tunnels バイパス
• Worldwide, limited numbers of sediment bypass
tunnels (SBTs) have been constructed because of
topographical, hydrological or economic conditions.

スイス• Bypass tunnels have many advantages
 Can be constructed even at existing dams
 Prevents a loss of stored reservoir water

caused by the lowering of the reservoir water level.
 Relatively small impact on the environment downstream because inflow
discharge can be passed through tunnels naturally during flood time.

日本• Recently, Switzerland and Japan have started initiative
 1st Workshop in Zurich (2016, ETH-VAW), 2nd Workshop in Kyoto(2017, KU-DPRI), 3rd Workshop in Taipei (2019, NTU).

• In submitted four reports, (R.22) is summarizing
all SBT data worldwide and Swiss and Japaneseexperiences are reported in (R.40) and (R.19).
• Upgrading anti-abrasion design for flood tunnel
based on the Swiss experience is reported in (R.4).

トンネルインバートの摩耗対策

台湾
4

New challenges on Sediment Bypass Tunnel

第３回排砂バイパス国際会議（2019, April 9-12）国立台湾大学

Pressure fluctuation
Diversion, Gate operation

下流河川の環境変化の評価(R.28)
Sediment
deposition

Abrasion
Riverbed geomorphology, Water
quality, Aquatic environment etc

Upstream(R.19)

Tunnel inside(R.40)

Downstream

Tachigahata Dam (1905)

History of SBT in Japan and Switzerland

排砂バイパストンネルの歴史
Nunobiki Dam (1908)

ブラタモリ（神戸港編）
2017.2.18「赤道を越えても腐らない水」を供給＝有機物を含む土砂の流入防止、として紹介

1900 布引五本松
ダム（バイパスなし）

流入土砂による堆積が顕著（危機感）

1908 布引五本松ダムに逆導入（バイパス設置）

1905 立が畑ダム(当初からバイパスあり）

土砂流入を効果的に防止第３回排砂バイパス国際会議（2019, April 9-12）
国立台湾大学https://www.iwsbt2019.info/7

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