Dam Asset ManagementDam Asset Management ProjectProjectSustainable Reservoir Sediment ManagementSustainable Reservoir Sediment Management

Kyoto UniversityKyoto UniversityGraduate School of Management Graduate School of Management

Tetsuya SUMITetsuya SUMI

Reservoir SedimentationReservoir Sedimentation

ダム堤体

L.W.L

H.W.L

上流部

堆砂性状

粘土・シルト主体 砂主体 礫・砂主体

堆砂の肩

土質区分

平均的な粒度分布（単位：%）

礫=0、砂=10、粘土＝50、シルト＝40

礫=10、砂＝45、粘土＝30、シルト＝15

礫=30、砂＝40、粘土＝20、シルト＝10

細粒分Fc Fc=90%以上

中流部

下流部

Fc=45～50%程度 Fc=30%以下

自然含水比ｗ w=100%以上 w=50～60%程度 w=40%以下

Ig=10%程度強熱減量Ig Ig=8%程度 Ig=4%程度

有機物・栄養塩

密度・間隙比 小　　　　　　　　　←→　　　　　　　　　　　　　大

大　　　　　　　　　←→　　　　　　　　　　　　小

（頂部堆積層）（底部堆積層）（前部堆積層）

（ウォッシュロード）

掃流砂浮遊砂（ウォッシュロード）

ウォッシュロード＋浮遊砂 浮遊砂＋掃流砂

デルタ

Clay, silt Mainly sand Sand and gravelSize

Water content

Ignition loss

Bed loadSuspended loadWash load

Bed load+Suspended loadWashload+Suspended load

Upstream areaMiddle area

Downstream area Delta

Bottom set bed Fore set bed Top set bed

Washload

Delta

Sedi

men

t pr

oper

ty

Grain size content(%)

Gravel=0, Sand=10, Clay=50, Silt=40

Gravel=10, Sand=45, Clay=30, Silt=15

Gravel=30, Sand=40, Clay=20, Silt=10

Fine sediment

Small Large

Ig=over10% Ig=ca.8% Ig=ca.4%

Nutrients Small Large

Density, Porosity

w=over100% Fc=45-50% Fc=lower30% Fc=over90%

w=50-60% w=lower40%

Dam body

単位は㎥/㎢/年m3/km2/yr

Reservoir Reservoir sedimentation sedimentation in Japanin Japan

Itoigawa-Shizuoka Tectonic Line

Median Tectonic Line

In 922 dams of 18 billion mIn 922 dams of 18 billion m3 3 volume,volume,

→→ total sedimentation 7.4%total sedimentation 7.4%

annual loss 0.24%/yrannual loss 0.24%/yr

•• National Inventory of reservoir sedimentationNational Inventory of reservoir sedimentation2730 dams (>15m high) with 23 billion m2730 dams (>15m high) with 23 billion m33 capacity.capacity.

Sedimentation progress of all reservoirs over 1 million mSedimentation progress of all reservoirs over 1 million m3 3

have been reported annually to the government from 1980s.have been reported annually to the government from 1980s.

Sediment yield Sediment yield potential map potential map of Japanof Japan

Total sedimentation lossesTotal sedimentation losses

0

20

40

60

80

100

0 10 20 30 40 50 60 70 80 90 100Years after dam completion

Sedi

menta

tion loss

(%)

Multi-purpose(M.O.L.I.T)Multi-purpose(P.G.)Multi-purpose(W.R.D.P.C.)Water powerIrrigationMunicipal water

–– Some Some hydroelectric damshydroelectric dams constructed before World War II more than constructed before World War II more than 50 years50 years oldold →→ 60 to 80 %60 to 80 %, but problems are depend on the cases. , but problems are depend on the cases.

–– Many cases from 1950 and 1960 through the high economic growth Many cases from 1950 and 1960 through the high economic growth period more than period more than 30 years old30 years old →→ beyond 40 %. beyond 40 %.

–– From 1960s, large numbers of From 1960s, large numbers of multimulti--purpose damspurpose dams →→ 10 to 30 % 10 to 30 % Maintaining effective storage capacity is critical for flood conMaintaining effective storage capacity is critical for flood controltrol

and water supply.and water supply.

Total average sedimentation rate 7.4% (1.35 /18.3 billion m3)Total average sedimentation rate 7.4% (1.35 /18.3 billion m3)

Reservoir sediment management measures in JapanReservoir sediment management measures in Japan

Sediment bypass tunnel

Dredging

Sediment scoring gate

Sediment check dam

Diversion weir

Afforestation

Sediment supply

Excavating

Trucking

Density current venting密度流排出

河川土砂還元

Sediment Routing

Reducing Sediment Inflow

Sediment Removal

NunobikiNunobiki DamDam

布引ダム貯水池

分水堰 トンネル呑口

トンネル 吐口

平常時は 貯水池へ流入

洪水時には バイパストンネルへ

平常時は 余水吐きから下流へ

バイパストンネルが 設置されるまでの旧河道

分水堰地点

生田川

布引ダム貯水池

集水面積　・全体　9.83k㎡　・分水堰より下流0.47k㎡

Tunnel outlet

NunobikiReservoir

Diversion weir H=3m, B=12m

Tunnel inlet

Usually flow into reservoir

Usually spilled water flow to downstream

Diverted water flow into a bypass tunnel

V=759,521m3

H=33.3m

Rokko Mountainsdeep weathered

granite, steep slopesA=9.8km2

A=0.47km2

Dam: 1900Bypass Tunnel: 1908

Ｌ＝258m

Osaka

KyotoKobe

Ikuta river

DamDamPurpose:

Drinking water supply

Comparison of sedimentation progress with Comparison of sedimentation progress with and without a bypass tunneland without a bypass tunnel

0

500,000

1,000,000

1,500,000

2,000,000

2,500,000

3,000,000

3,500,000

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

Measurement

Without bypass tunnel

With bypass tunnel

Reservoir Capacity

貯水池内堆砂量 (m3)

Reservoir Capacity (V=759×103 m3)

バイパスがない場合1926年付近で満砂バイパス

トンネル設置1908年

Sed

imen

tatio

n vo

lum

e (m

3)

Bypass tunnel completion in 1908

Fully sedimentation without a bypass tunnel in 1926

Need for reservoir sedimentation managementNeed for reservoir sedimentation management3 points3 pointsSafety Management for Dams and RiversSafety Management for Dams and Rivers

To prevent the To prevent the siltationsiltation of intake and other hydraulic of intake and other hydraulic facilities and aggradations of upstream riversfacilities and aggradations of upstream rivers

Sustainability of Water Storage VolumeSustainability of Water Storage Volume

Comprehensive Management of Sediment Routing Comprehensive Management of Sediment Routing System in a River Basin and Connected Shoreline System in a River Basin and Connected Shoreline ScaleScale

To prevent riverbed degradation, river morphology change To prevent riverbed degradation, river morphology change and coastal erosion caused by shortage of necessary and coastal erosion caused by shortage of necessary sediment supply from upstream including damssediment supply from upstream including dams

Comprehensive Management of Sediment Routing System Comprehensive Management of Sediment Routing System in a River Basin and Connected Shoreline Scalein a River Basin and Connected Shoreline Scale

Check dam

Storage reservoir

Riverbed degradation

Coastal erosion

Balancing of sediment transport from the source of the river to the coast

River environment change

Sedimentation

Lack of sediment supply

Sediment flow monitoring

Bed load Suspended load Wash load

Akibadam(1958,35MCM)

Sakuma dam(1956,327MCM)

Yasuoka dam(1936,11MCM)

Hiraoka dam(1951,43MCM)

Miwa dam(1959,30MCM)

Koshibu dam(1969,58MCM)

TenryuTenryu River, River, A=5,090kmA=5,090km22

TenryuTenryu River River Mouth

1946

1961

2001

Mouth Sediment Sediment suppysuppy

Yasuoka dam (1936)

Hiraoka dam (1951)

Sakuma dam (1956)

Akiba dam (1958)

Miwa dam (1959)

Koshibu dam (1969)DicreaseDicrease

TenryuTenryu River Dam River Dam Redevelopment ProjectRedevelopment Project Sakuma dam

Akiba dam

HSRS: Hydro-suction Sediment Removal System

Sediment Transport: Transport sediment in reservoir by dredging or other methods

秋葉ダム

佐久間ダム

① 排砂バイパストンネル

④ スルーシング ・フラッシング

② 吸引方式＋排砂トンネル＋湖内輸送

⑦ 吸引方式＋排砂トンネル＋湖内輸送（2 ダム連続）

③ 密度流排出

⑥ 排砂バイパストンネル （2 ダム連続）

⑤ 吸引方式 ＋排砂トンネル

＋湖内輸送

Sakuma dam

Akiba dam

③Density Current Venting

①Sediment Bypass Tunnel

②HSRS+Sediment Bypass+Sediment Transport

⑥Sediment Bypass Tunnel(Two dams)

④Sluicing ・Flushing

⑦HSRS+Sediment bypass+SedimentTransport (Two dams)

⑤HSRS+Sedimentbypass+SedimentTransport

ConclusionConclusionAnalysis of each facilities and proper maintenance Analysis of each facilities and proper maintenance planning is necessary for the sustainable reservoir planning is necessary for the sustainable reservoir management under the limited budget.management under the limited budget.

Asset ManagementAsset ManagementReservoir health is indispensable and, especially, Reservoir health is indispensable and, especially, sedimentation is the key factor for long term use.sedimentation is the key factor for long term use.

Sediment Management for Intergenerational Sediment Management for Intergenerational EquityEquityIn order to solve sedimentation problems,In order to solve sedimentation problems,１）１）Technically, economically feasibleTechnically, economically feasible and and environmentally environmentally

compatiblecompatible countermeasurescountermeasures are requested.are requested.２）２）Integrated river basin management considering Integrated river basin management considering sediment sediment

routing systemrouting system is important.is important.Coordinating sediment management of multiple Coordinating sediment management of multiple reservoirsreservoirs in a river basin is the next step. in a river basin is the next step.