DamDam AssetAsset ManagementManagement ProjectProject SustainableSustainable ReservoirReservoir SedimentSediment ManagementManagement

KyotoKyoto UniversityUniversity GraduateGraduate SchoolSchool ofof ManagementManagement

SUMISUMI

TetsuyaTetsuya ReservoirReservoir SedimentationSedimentation

Washload+Suspended load Bed load+Suspended load 掃流砂 ウ ォッ シ ュロ ー ド＋ 浮遊砂 浮遊砂 ＋ 掃流砂 Bed load Damダム堤体 body Suspended浮遊砂 load Fore set bed Wash load Bottom set bed （前部堆積層） Top set bed （ウォッシュ） （底部堆積層） （頂部堆積層） ロード H.W.L 堆砂の肩Delta （ウ ォWashloadッ シ ュロ ー ド） L.W.L Downstream area下流部 Deltaデルタ Middle area Upstream area 中流部 上 流部

土質区分Size 粘土・Clay,シル ト 主体silt Mainly砂主体 sand Sand礫・ 砂主体and gravel Grain平均的な size Gravel=0,礫=0、砂=10、 Gravel=10,礫=10、砂＝45、 Gravel=30,礫=30、砂＝40、 Sand=10, Sand=45, Sand=40, content(%)粒度分布 Clay=50,粘土＝50、 Silt=40 Clay=30,粘土＝30、 Silt=15 Clay=20,粘土＝20、 Silt=10 堆 （単位：%） シル ト＝40 シル ト＝15 シル ト＝10 Fc=over90% 砂 Fine細粒分Fc sediment Fc=90%以上 Fc=45～50%Fc=45-50%程度 Fc=lower30%Fc=30%以下 性 自然含水比ｗWater content w=100%w=over100%以上 w=50～60%w=50-60%程度 w=lower40%w=40%以下 状 Density,密度・間隙比 Porosity 小 Small ←→ 大 Large Ignition強熱減量Ig loss Ig=over10%Ig=10%程度 Ig=ca.8%Ig=8%程度 IIg=ca.4%g=4%程度 Sediment property 有機物・Nutrients栄養塩 Large大 ←→ 小 Small ••ReservoirReservoirNationalNational InventoryInventory ofof reservoirreservoir sedimentationsedimentation sedimentationsedimentation2730 dams (>15m high) with 23 billion m3 capacity. ininSedimentation JapanJapan progress of all reservoirs over 1 million m3 have been reported annually to the government from 1980s.

In 922 dams of 18 billion m3 volume, → total sedimentation 7.4% annual loss 0.24%/yr

Itoigawa-Shizuoka Tectonic Line Sediment yield potential map Median Tectonic Line of

m単位3/kmは㎥/ ㎢2/yr/ 年 TotalTotal sedimentationsedimentation losseslosses

100 Multi- purpose(M.O.L.I.T) Multi- purpose(P.G.) % Multi- purpose(W.R.D.P.C.) 80 Wat e r po we r Irrigation 60 Munic ipal wat er

40

20 Sedimentation loss(

0 0 102030405060708090100 Years aft er dam completion

– Some hydroelectric dams constructed before World War II more than 50 years old → 60 to 80 %, but problems are depend on the cases. – Many cases from 1950 and 1960 through the high economic growth period more than 30 years old → beyond 40 %. – From 1960s, large numbers of multi-purpose dams → 10 to 30 % Maintaining effective storage capacity is critical for flood control and water supply. Total average sedimentation rate 7.4% (1.35 /18.3 billion m3) ReservoirReservoir sedimentsediment managementmanagement measuresmeasures inin JapanJapan

Excavating Sediment check dam

Diversion weir

Afforestation Sediment bypass tunnel

Dredging Trucking

Reducing Density current venting Sediment Inflow Sediment scoring gate 密度流排出 Sediment Routing

Sediment Removal 河川土砂還元 Sediment supply Ikuta river Kyoto NunobikiNunobiki DamDam Dam Kobe Purpose: Dam: 1900 Osaka Drinking Bypass Tunnel: 1908 water supply Diversion weir Usually flow H=3m, B=12m Rokko Mountains 平常時は 分水堰 into reservoir deep weathered 貯水池へ流入 トンネル呑口Tunnel inlet granite, steep slopes 洪水時にはＬ＝258m A=9.8km2生田川 バイパストンネルへ バイパストンネルがDiverted water flow into 設置されるまでの旧河道 a bypass tunnel

A=0.47km2 Tunnelトンネル outlet 分水堰地点 吐口 布引ダム貯水池

集水面積 Nunobiki ・全体 9. 83k㎡ 布引ダム貯水池 ・分水堰より下流0. 47k㎡ Reservoir

3 V=759,521m Usually spilled water H=33.3m 平常時は flow to余水吐きから下流へ downstream ComparisonComparison ofof sedimentationsedimentation progressprogress withwith andand withoutwithout aa bypassbypass tunneltunnel

3, 500, 000 Measur ement 3, 000, 000 Wi t hout bypass t unnel ) 3 Wi t h bypass t unnel 2, 500, 000 Re s e r v o i r Ca p a c i t y 2, 000, 000 Fully sedimentation Bypass バイパスがない場合 バイパス 1926年付近で満砂without a bypass 1, 500, 000 tunnelトンネル設置 tunnel in 1926 completion1908年 in 1908

貯水池内堆砂量 貯水池内堆砂量 ( m 1, 000, 000 Reser voi r Capaci t y ( V=759× 103 m3) 500, 000

0

Sedimentation volume (m3) Sedimentation 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 NeedNeed forfor reservoirreservoir sedimentationsedimentation managementmanagement 33 pointspoints „„ SafetySafety ManagementManagement forfor DamsDams andand RiversRivers To prevent the siltation of intake and other hydraulic facilities and aggradations of upstream rivers

„„ SustainabilitySustainability ofof WaterWater StorageStorage VolumeVolume

„„ ComprehensiveComprehensive ManagementManagement ofof SedimentSediment RoutingRouting SystemSystem inin aa RiverRiver BasinBasin andand ConnectedConnected ShorelineShoreline ScaleScale To prevent riverbed degradation, river morphology change and coastal erosion caused by shortage of necessary sediment supply from upstream including dams Comprehensive Management of Sediment Routing System in a River Basin and Connected Shoreline Scale

Balancing of sediment Sedimentation Check dam transport from the source of the river to the Storage coast reservoir

Riverbed Lack of degradation sediment supply

Sediment flow River monitoring environment Coastal erosion Bed load change Suspended load Wash load (1936,11MCM) Miwa dam(1959,30MCM)

Hiraoka dam(1951,43MCM) Koshibu dam(1969,58MCM)

Sakuma dam(1956,327MCM)

Akiba dam(1958,35MCM)

TenryuTenryu 22 River,River, A=5,090kmA=5,090km TenryuTenryu RiverRiver MouthMouth SedimentSediment suppysuppy Yasuoka dam (1936)

1946 Hiraoka dam (1951) (1956) Akiba dam (1958) Miwa dam (1959) 1961 DicreaseDicrease Koshibu dam (1969)

2001 TenryuTenryu RiverRiver DamDam RedevelopmentRedevelopment ProjectProject Sakuma dam

HSRS: Hydro-suction Sediment Removal System Akiba dam Sediment Transport: Transport sediment in reservoir by dredging or other methods ③③Density 密度流排出 Current Venting ④ ④ スルーシングSluicing ・ Sakuma佐久間ダム dam Flushing ・フラッシング 秋葉ダムAkiba dam

⑤ HSRS+Sediment 吸引方式 ①①Sediment 排砂バイパストンネル Bypass Tunnel bypass+Sediment＋排砂トンネル Transport＋湖内輸送 ②HSRS+Sediment② 吸引方式＋排砂トンネル＋湖内輸送 Bypass+Sediment Transport ⑦HSRS+Sediment 吸引方式＋排砂トンネル＋湖内輸送 bypass+Sediment ⑥Sediment Bypass Tunnel Transport (Two（2 ダム連続）dams) ⑥ 排砂バイパストンネル (Two （2dams) ダム連続） ConclusionConclusion „„ AnalysisAnalysis ofof eacheach facilitiesfacilities andand properproper maintenancemaintenance planningplanning isis necessarynecessary forfor thethe sustainablesustainable reservoirreservoir managementmanagement underunder thethe limitedlimited budget.budget. AssetAsset ManagementManagement „„ ReservoirReservoir healthhealth isis indispensableindispensable and,and, especially,especially, sedimentationsedimentation isis thethe keykey factorfactor forfor longlong termterm use.use. SedimentSediment ManagementManagement forfor IntergenerationalIntergenerational EquityEquity „„ InIn orderorder toto solvesolve sedimentationsedimentation problems,problems, １）Technically, economically feasible and environmentally compatible countermeasures are requested. ２）Integrated river basin management considering sediment routing system is important. „„ CoordinatingCoordinating sedimentsediment managementmanagement ofof multiplemultiple reservoirsreservoirs inin aa riverriver basinbasin isis thethe nextnext step.step.