The 6th Japan-Taiwan Joint Seminar on Natural Hazard Mitigation, 2006

RESERVOIR SEDIMENT MANAGEMENT MEASURES AND NECESSARY
INSTRUMENTATION TECHNOLOGIES TO SUPPORT THEM

Tetsuya SUMI
*Department of Civil and Earth Resources Eng., Graduate School of Engineering, Kyoto University
Abstract
Reservoir sediment management approaches are largely classified into the following techniques: 1) to reduce
sediment transported into reservoirs, 2) to bypass inflowing sediment and 3) to remove sediment accumulated inreservoirs. When the sediment management measures are selected, it is necessary to consider those environmental
influences in the river from both positive and negative point of views. In order to evaluate these influences, it is also
important to develop appropriate sediment transport monitoring techniques. In this paper, state of the art of reservoir
sediment management measures in Japan and some advanced support monitoring techniques such as suspended
sediment concentration measurement and morphological change surveys in rivers and reservoirs are discussed.
Keywords: Reservoir sediment management, sediment routing system, sediment flushing, environmental impact
assessment, SMDP, 3D-laser scanner

1.

Introduction

The sediment yields of the Japanese rivers are highin comparison with other countries due to the
topographical, geological and hydrological conditions.
This has consequently caused sedimentation problems
to many reservoirs constructed for water resource
development or flood control purposes. Under suchcircumstances, studies on estimation of sedimentvolume and countermeasures for sedimentation havebeen conducted for a long time.
Currently, the reservoir sedimentation managementin Japan is embarking on new stages from two points ofview. One is, in contrast to the emergent and local
conventional countermeasures such as dredging andexcavation, the active promotion of introduction of
sediment flushing using sediment flushing outlets andsediment bypass systems, which aim at radicallyreducing the sediment inflowing and deposition.
Unazuki dam and Dashidaira dam on the Kurobe River,and Miwa dam on the Tenryu River and Asahi dam on
the Shingu River are advanced examples of using
sediment flushing and sediment bypass techniques,

which are placed as permanent measures for
sedimentation at dams. The other is, considering asediment movement zone from mountains throughcoastal areas, the initiation of a comprehensive
approach to recover a sound sediment transport in thesediment routing system.
However, these advanced techniques for sedimentmanagement aiming at long life of dams have only
been applied to a limited number, and therefore
continuous study is required. It is also important tosolve the social issues, such as consensus building on
the need for sediment management throughout thebasin people, establishment both of legal system andcost allocation system. Especially, when the sedimentmanagement measures are selected, it is necessary toconsider those environmental influences in the riverfrom both positive and negative point of views. In thatcase, development of the technique that minimizes thenegative influences such as the water quality change
caused by the sediment discharge and maximizes the
positive influences such as the recovery of the sedimentrouting system is demanded. In order to evaluate these
influences, it is important to develop appropriatesediment transport monitoring techniques.
In this paper, state of the art of reservoir sedimentmanagement measures in Japan and some advanced
support monitoring techniques such as suspended
sediment concentration measurement and morphologicalchange surveys in rivers and reservoirs are discussed.
2. Reservoir Sediment Management in Japan

単位は?
/?2 /年
3/km
m/yr

Fig. 1 Sediment yield potential map of Japan
Multi-purpose(M.O.L.I.T)
Multi-purpose(P.G.)
Multi-purpose(W.R.D.P.C.)
Water power
Irrigation
Municipal water100
Sedimentation loss(%)

2.1 Present State of Sedimentation Problems
In Japan, all dams having a storage capacity over 1
million m3 have been obliged to report sedimentcondition to the authority every year since 1980s. As of2003, from 922 dams accounting for approximately 1/3
of 2,730 dams over 15 meters in height in Japan,
annual changes in sedimentation volume and the shapeof accumulated sediment were reported. It is probably
only Japan that established such a nationwide survey
system, and such accumulated data is regarded asconsiderably valuable records on a global basis.
Fig. 1 shows the “Sediment yield potential map ofJapan” that is made by GIS using the reservoir
sedimentation records and existing geographicalfeatures and geological data (Okano et al., 2004). Fig. 2
shows the relationship between reservoir sedimentation
rate and years after dam completion (Sumi, 2003). Here,the sedimentation rate is calculated using sedimentation
volume to gross storage capacity.
Concerning the dams constructed before WorldWar II and used for more than 50 years, sedimentation
proceeded in the range from 60 to beyond 80 % insome hydroelectric reservoirs. Likewise, for the dams
constructed approximately between 1950 and 1960, orfrom the postwar years of recovery through the higheconomic growth period, and used for more than 30
years, sedimentation rates beyond 40 % are found inmany cases. The influence of sedimentation in thosehydroelectric reservoirs depends on the type of power
generation.
Following this period, meanwhile, a large numberof multi-purpose dams gradually came to beconstructed. This type of dams does not have highsedimentation rates compared to the hydroelectric type,though, the rates of 20 to beyond 40 % are found insome dams. Since maintaining storage capacity is
directly linked to maintaining the function of dams
such as flood control, the influence of sedimentation in
the multi-purpose reservoir becomes large.

80
60
40
20
0
0

10

20

30

40
50
60
70
Years after dam completion

80

90

100

Fig. 2 Relationship between reservoir sedimentation rate
and years after dam completion(Note: M.O.L.I.T.: Ministry of land, infrastructure andtransport, P.G.: Prefecture government, W.R.D.P.C.:
Water resources development public corporation)

Here, an average annual capacity loss rate for alldams is 0.24 %/year and it is very high up to
0.42 %/year in Chubu region along the Tectonic Lines
where a large amount of sediment is produced in thecatchment.
Nowadays, new concept of sediment management
is also discussed. The amount of sediment supplied
from rivers to coasts was radically reduced withconstruction of erosion control dams or storage dams inmountain areas and acceleration of the aggregate
excavation from riverbed after World War II. As aresult, various problems rose up including riverbed
degradation at downstream channel, oversimplificationof river channel, and retreat of shoreline due to thedecrease in sediment supply to the coast.
Following a recommendation by River Council ofJapan in 1997, comprehensive sediment management
in order to recover a sound sediment transport

Table 1 Sediment replenishment dams in Japan
Name ofdam

Name of river

Drainage area
(km2)

Akiha

Tenryu River,
Tenryu River
System4,490

Otakine River,
Miharu Abukuma River
System226

Ara River, Ara
River System

260

Naga- Oi River, Oi
shima*1 River System

958*2

FutaseUrayama River,Urayama Ara River
SystemHachisu River,
Hachisu Kushida River
SystemLocationYear

Shizuoka Pref '99～'05

Sediment used for
replenishment（Particle size）

PurposePrevention of riverbed
degradation and coastal erosion

Sediment accumulated
Akiha 3in reservoir
Funagira 23（Gravel 67％、Sand 29％）

(1) Prevention of downstream
Sediment accumulated
riverbed degradationin front reservoir(2) Prevention of increase in coarse（Sand 60％、Silt 28％）
grain content
Sediment accumulated'99,(1) Improvement of habitat of fishat check dam
Saitama Pref.
'01～'05 (sculpin)（Gravel ,boulder）(1) Acquisition of basic data for
Sediment accumulated justannual sediment replenishment
upstream of an embankment
dam downstream of the dam
Shizuoka Pref '00～'01 planning for Nagashima Dam(2) Determination of influence on（Average particle
downstream river environment
diameter 31mm）
Fukushima
Pref.

'99～'05(1) Improvement of habitat of fish Sediment accumulated(2)Prevention of increase in coarse in reservoir
grain content（ － ）(1) Improvement of habitat of ayu Sediment accumulated
80
Mie Pref. '02～05 (sweet fish)in reservoir(2) Prevention of riverbed degradation （ － ）(1) Disposal of sedimentSaru River,Sediment accumulated
accumulated at check dam
1,215
Hokkaido '02～04
Nibutani Saru Riverat check dam(2) Improvement of downstream（ － ）Systemriver environment
Kanna River,(1) Conservation of landscapes of Sediment accumulated
ShimoTone Riverin reservoir
322
Gunma Pref. '03～05 Sanbaseki Ravine downstream of
kubo
Systemthe dam (prevention of armoring) （Gravel)(1) Disposal of sediment
Sediment accumulated
Nunome Riveraccumulated at check dam
75
Nara Pref. '05
at check dam
Nunome Yodo River(2) Improvement of downstream（Gravel 20％、Sand 60％）
Systemriver environment(1) Prevention of increase in coarse
Ina Rivergrain content
Sediment from downstream
115
Hyogo Pref. '02～05
Hitokura Yodo River(2) Improvement of habitat of ayu river (Gravel)
System(sweet fish)*1: Sediment accumulated at Shiogo Weir downstream of Nagashima Dam is used.
*2:The size of a catchment area at Shiogo Weir *3:Distance from Shiogo Weir to a temporary place
51

Saitama Pref.

'00,'02,'03

regarding not only quantity but also quality point ofview in the sediment routing system is now being
advanced earnestly. To be more precise, the erosion
control dams in the upstream region are planned to beconverted to slit dams with notches, which are so
designed as to pass, not to trap, as much fine sedimentcarrying less risk of sediment disaster as possible. For
storage dams, sediment bypass or sediment flushingoutlets are also progressively added in order to reduce
sedimentation and accelerate sediment discharge to thedownstream and, at the same time, an attempt to returnthe excavated and dredged sediment to the downstream
river has been undertaken. Since the influence ofstorage dams on the sediment routing system is
extremely huge, it is highly meaningful to reduce
sediment trap by means of appropriate sedimentmanagement.
Based on these circumstances, needs for reservoir
sediment management in Japan can be summarized
into the following three points:
1) To prevent the siltation of intake facilities andVolume used for Average annual
Transportation
replenishment rate of reservoir
distance(×103m3/cycle) sedimentation(km)（×103m3/Year）
18～20

430

4

1～2

149

15

3～8.8

101

1*3

20～25

400

4

1～14

144

5

0.3

29

11
20

1～5.8

764

5

1

240

1

0.3

12

-

0.19-0.6

30

aggradations of upstream river bed, accompaniedby the sedimentation process in reservoirs, inorder to secure the safety of dam and river
channel.
2) To maintain storage function of reservoirs, andrealize sustainable water resources management
for the next generation.
3) From a perspective on comprehensive sedimentmanagement in a sediment routing system, torelease sediment from dams.
2.2 Reservoir Sedimentation Management in Japan
Sediment management in reservoirs is largely
classified into the three approaches: 1) to reduce
sediment inflow to reservoirs, 2) to route sedimentinflow so as not to accumulate in reservoirs and 3) toremove sediment accumulated in reservoirs.
(1) Reduction of Sediment Inflow into Reservoirs
There are two techniques to reduce the amount oftransported sediment: 1) countermeasure to control

Table 2 Sediment Bypass Tunnels in Japan and Switzerland
DesignDischarge(m3/s）

DesignVelocity(m/s)

Operation
Frequency

140

11.4

13 times/yr

1

300

10.8

-

1,417

4

200

15

-

9.0×8.2

4,000

1.8

500

Circularr = 2.8

360

2.6

74

9

10days/yr

Horseshoe

2r = 6.2

1,800

2

110

9

2～5days/yr

Name of
Dam

Country

TunnelCompletion

TunnelShape

Nunobiki

Japan

1908

Hood

2.9×2.9

258

1.3

39

Asahi

Japan

1998

Hood

3.8×3.8

2,350

2.9

Miwa

Japan

2005

Horseshoe

2r = 7.8

4,300

Matsukawa

Japan

U.C.

Hood

5.2×5.2

KoshibuJapan

Planning

Hood

Egshi

Switzerland

1976

Palagnedra Switzerland

1974

Pfaffensprung Switzerland

Tunnel Cross Section Tunnel
General(B×H(m)）Length (m) Slope （％）

2

-

1922

Horseshoe

A = 21.0m

280

3

220

10～15

～200days/yr

Switzerland

1983

Horseshoe

3.5×3.3

450

4

80

～14

1～5days/yr

Runcahez Switzerland

1961

Horseshoe

3.8×4.5

572

1.4

110

9

4days/yr

Rempensediment discharge which covers entire basin
including the construction of erosion control dams;
and 2) countermeasure to forcibly trap sediment byconstructing check dams at the end of reservoirs.
Although the catchment areas of dams have highforest cover rates, a remarkable amount of sediment is
produced in the watershed where landslides frequently
occur due to the topographical and geologicalconditions.
Since an attempt to trap sediment using checkdams is found effective for the reservoirs where bed
load of relatively coarse grain size accounts for a large
percentage of sediment inflow, many dams haveproceeded in constructing them recently. In thistechnique, a low dam is so constructed at the end ofreservoir as to deposit transported sediment, and thenthe deposited sediment is regularly removed. The
accumulated sediment can be excavated on land
except for flood time, and the removed sediment isutilized effectively as concrete aggregate. As of 2000,
the check dams have been constructed at 57 out of thedams under jurisdiction of Ministry of Land,
Infrastructure and Transport.
Recently, sediment replenishment tests have been
carried out in some dams. Trapped sediments in thesediment check dam upstream of the reservoir are
excavated and transported to the downstream of thedam. These sediments are put on the downstream
river channel temporarily and washed out by thenatural flood flows. Typical cases are descried inTable 1 (Okano et al., 2000a and 2004b). Moreover,there is an example of combining with theenvironmental flushing flow such as in the Managawa

dam and the integrated improvement of the riverenvironment is expected by the flood disturbance andthe sediment supply.
(2) Routing of Sediment Inflow into Reservoirs
Another possible approach to sedimentmanagement, next to the reduction of sediment inflow
itself, is to route sediment inflow so as not to allow it toaccumulate in reservoirs. In Japan, the following
techniques are adopted: 1) sediment bypass by directly
diverting sediment transport flow, and 2) density
current venting by using a nature of high-concentration
sediment transport flow.
In Japan, it is sediment bypass tunnels that havebeen studied most exhaustively. Although thistechnique involves high cost caused by tunnel
construction, there are several advantages such that it isalso applicable to existing dams; it does not involve
drawdown of reservoir level and therefore no storage
capacity loss; and it has relatively small impact onenvironment because sediment is discharged not so
rapidly as sediment flushing, which is described later.
Nunobiki dam is the first example of the bypass tunnel
in Japan. The reservoir to which longevity is estimatedto be only 25 years without bypass is prolonged to over
1,000 years (Sumi, Takata and Okano, 2004a).
Recently, the bypassing effect is clarified after
completion of the Asahi dam, and the planning andconstruction of the bypass have been advanced also in
the Miwa, Matsukawa and Koshibu dams.
The subjects of designing sediment bypass tunnels
are to secure the safety of sediment transport flow
inside tunnels and to take countermeasures for abrasiondamages on the channel bed surface. Among factorsthat significantly relate to these problems are grain size,
tunnel cross-sectional area, channel slope, and design
velocity. Table 2 shows some examples of existing
sediment bypass tunnels and ones under construction
and planning (Vischer et al., 1997, Sumi, Okano and
Takata, 2004). It should be understood that design
condition becomes increasingly hard if higher velocity
and larger grain size will be expected.
Density current venting, on the other hand, is atechnique to use a nature of high-concentration
sediment transport flow, which runs through relatively
deep reservoir with original channel bed of steep slope
as a density current with less diffusion, and to discharge
it effectively through outlets in timing of reaching dam.
In both techniques, the main target is fine-grained
sediment such as suspended sediment and wash load.
In multiple-purpose dams in Japan that usually havehigh-pressure bottom outlets for flood control, theeffective operation of these facilities during flood
season can increase a chance to actively discharge
fine-grained sediment.
If sediment concentration in the main river is very
high, both a flood control dam which is kept empty
except flood times in the main river and a water storage
dam in the tributary should be constructed separately inorder to reduce total sediment management costs (Sumi,
Takata and Okano, 2004b).
(3) Removal of Sediment Accumulated inReservoirs
This approach is regarded as a last resort in casesediment is accumulated in reservoirs in spite ofvarious efforts being done: 1) mechanically excavating
sediment accumulated in the upstream region ofreservoirs, 2) dredging sediment accumulated at the
middle and downstream regions, and 3) flushing out
sediment with tractive force. As for excavation anddredging techniques, it is important that the removed
sediment should be treated properly and reused.
On the other hand, sediment flushing is a techniqueto restore tractive force in a reservoir beyond its criticalforce by means of drawdown of reservoir level, andflush the deposits through bottom outlets in the dam
body with inflow water, mainly in an open channel
flow condition, to the downstream of dam. When theamount of sediment inflow is significantly large,
man-powered techniques such as excavation anddredging are hard to be adopted because of problems
involving transportation and dump site. In such a case,however, sediment flushing can be a permanentmeasure if conditions are met. Traditionally in Japan,
sediment flushing facilities such as flushing sluices andoutlets were installed at small-scale hydroelectric dams
or weirs for the purpose of discharging sedimentdeposited in the vicinity of intake. In contrast, at
Dashidaira-Unazuki dams in the Kurobe river, where alarge amount of sediment is discharged, sedimentflushing is implemented in coordination of upstream
and downstream dams (coordinated sediment flushing)(Sumi and Kanazawa, 2006).
Sediment flushing is performed at many dams allover the world (Morris and Fan, 1998, White et al.,2000). Sediment flushing is considered as an extremely
effective technique for discharging sediment in termsof harnessing tractive force in natural river channel.
However, when this technique is introduced, an
extensive study is required in the planning stages,
considering such conditions as inflow, sediment inflow,
storage capacity, grain size distribution and reservoir
operation. At the same time, it is also required toconsider measures concerning environmental problems
under sediment flushing process (Sumi, 2000a, Sumi
and Kanazawa, 2006).
Moreover, HSRS (Hydro-suction Sediment
Removal System) which can intake and discharge
sediment using only the water level differences without
the mechanical force is developed in some types inrecent years. There are stationary and movable types inthe system.
In case of the stationary type,establishment of the measures to move sediment to thesystem neighborhood in the reservoir and, in case of the
movable type, securing enough operation timecorresponding to the target sediment volume to bedischarged during a year and a safe work environment
are problems to be solved.
2.3 Promotion strategy of reservoir sedimentation
management
The problems to promote such reservoir
sedimentation management in future are priority
evaluation of reservoirs where sediment management
should be introduced and appropriate selection ofreservoir sediment management strategies.
The World Bank is advancing RESCON project(Reservoir Conservation Project) (Palmieri, 2003). It

Capacity-inflow ratio and Reservoir Life
(× No measure)100000No measures (from inner factors)

Check damReservoir Life=CAP/MAS

Flushing

10000

Scoring gate
Scoring pipe
Bypassing

1000
⑱
⑥

④

100
⑫ ⑤ ③

②
⑧

⑮
⑪

⑭
⑨

①
⑬
⑲

10
0.001

Excavating⑦⑰⑳

Dredging⑩⑯ Sediment check dam,
Sediment replenishment

Sediment bypass, Sluicing
Sediment flushing, Sediment scoring gate

0.01
0.1
1
Capacity-inflow ratio=CAP/MAR

10

1 大井
Oi
D, SP
2 千頭
Senzu
SG
3 泰阜
Yasuoka SG, D, PF
4 笠置
KasagiSG, PF
5 大間
Ooma
SG, PF
6 常盤
Tokiwa
SG
7 三浦
Miura
SP
8 平岡
HiraokaD, PF
9 佐久間 Sakuma
D
10 八久和 Hakuwa
E, D
11 井川
Ikawa
SP, E, D, PF
12 山口
Yamaguchi SG, PF
13 秋葉
Akiba
E, D, PF
14 美和
Miwa
B, E, D, CD
15 牧尾
Makio
E, D, CD
16 小渋
Koshibu
E, CD
17 松川
Matsukawa B, E, CD
18 旭
Asahi
B
19 出し平 Dashidaira F
20 宇奈月 Unazuki
F
CD ：
F ：
PF ：
SG ：
SP ：
B ：
E ：
D ：

Check damFlushing (Draw down)
Flushing (Partial draw down)
Scoring gate
Scoring pipe
Bypassing
Excavating
Dredging

Fig. 3 Representative sediment management dams in Japan
will be thought that reservoir sedimentation problem
becomes a key issue while putting the target on theredevelopment project in the future though the WorldBank has financed the developing country only to the
new construction projects. For instance, when there areseveral dams in the same water system, estimated eachreservoir life when measures are not taken is concretely
presented. And, if it is understood that remainder ofthe life is very short, the feasible sediment management
measures considering economy etc. is concretely
proposed. It will be thought that such an approach isimportant also in Japan. Especially, when several dams
exist in a water system, it is realistically difficult to
introduce the sediment management all together due tothe limit of the budget under the present situation. Then,
it is necessary to evaluate priority according to someindices.
If the dam whose priority is high is selected, it isnecessary to select a concrete sediment management
strategy. In Figure 3, dams in the Japanese wholecountry are plotted by the parameter of the turnoverrate of water (CAP/MAR=Total capacity/Mean annual
runoff) and sediment (CAP/MAS=Total capacity/Meanannual inflow sediment) (Sumi, 2003). It is thought thatthe selected sediment management measures arechanged by these two parameters. It is understood thatmeasures actually selected have changed in the order ofthe sediment flushing, the sediment bypass, sediment
check dam and excavating, and dredging as CAP/MAR
increases (decrease in the turnover rate). This isbecause of greatly depending on the volume of water tobe able to use the sediment management measure thatcan be selected for the sediment transport (Sumi,
2000b).
We are intensively studying to improve the
RESCON model based on actual records in the Kurobe
river (Sumi and Iguchi, 2005, Sumi, Takata, Iguchi andNakanishi, 2005).
3.

Monitoring techniques to support sedimentmanagement

In order to evaluate environmental influences andeffectiveness of sediment management measures suchas sediment flushing and sediment bypassing and so on,
various types of sediment monitoring techniquesshould be developed. Here, new measurement
techniques for suspended sediment concentration andmorphological changes such as sediment erosion anddeposition in rivers and reservoirs are introduced.
3.1 Suspended sediment concentration measuringsystem with differential pressure transmitter
It is important to know quantity of wash load forthe integrated sediment management from upstream
through downstream river basins. For the purpose ofenvironmental assessment to the aquatic species
during sediment discharging by sediment flushing or
bypassing, it is also important to observe high turbidity
in real time in the river. Generally, both continuousturbidity measuring and bottle sampling are used forsuspended-sediment concentration measurement inrivers or reservoirs. Here, we have developed a newsuspended sediment concentration measuring systemwith differential pressure transmitter (hereafter, wecall SMDP) (Sumi, Morita, Ochi and Komiya, 2001
& 2002).
The SMDP has advantages in long-term andhigh turbidity measurement because differential
pressure transmitter is measuring density of water
directly. Based on measuring conditions, asubmersible type and a water circulating type SMDP
are available, and both of them have shown good
performances through laboratory tests and field
experiments at the Miwa and Koshibu dams in the
Tenryu river, and Dashidaira and Unazuki dams in
the Kurobe river.
The schematic diagram of SMDP is shown in
Fig. 4. Two pressure detectors are placed verticallywith the interval H=1,000mm and connected bysmall pipes filled up with water to the differential
pressure transmitter mounted at the center of thesystem. We have developed two different unites tomeasure water with suspended sediments based on
different measuring situations. One is thesubmersible type and the other is the water
circulation type. The submersible type is shown in
Fig. 5(a). The main measuring equipment issuspended from a float and submerged in themeasuring water directly. Advantages of this type aresimple structure and easy maintenance. On the other
hand, it is necessary to secure enough water depth

h
H +h

PL

E lec tric al
S ign alHPH
ρFig. 4 Schematic diagram of SMDP

W. L.

1m×1m×0. 8 m
Float
ca.2m
Centerelevation
1. 6 mMeasuringequipment

φ0. 5 5 m

Fig. 5(a) Schematic diagram of the submergible SMDP

Measuringequipment
W. L.
P

Submergible pump

Fig. 5(b) Schematic diagram of the water circulation SMDP(b)Aimoto( Submergible SMDP)

Unazuki dam
Dashidaira dam(c)Shimokurobe (Water circulation
SMDP: Sensor and Recorder)(d)Shimokurobe(Water circulation SMDP: Intake pump)(a)Downstream of Unazuki dam( Water circulation SMDP)

Fig. 6 Sediment flushing gates of Unazuki and Dashidaira dams and SMDP installations in the Kurobe riverUnazuki dam

Rainfall（mm）
3

Discharge（m /ｓ）

0
10

Average rainfall in Unazuki
dam catchment [mm]

20

EL .m

30

1,600
1,400
1,200
1,000
800
600
400
200
0

255
250
245
240
235
230
225
220
215

Free flow

Sediment flushing

60,000SS（mg /l）

Inflow discharge (Unazuki dam) [m3/ｓ]
Outflow discharge (Unazuki dam) [m3/ｓ]
Reservoir water level(Unazuki dam) [EL .m]

Free flow

70,000Downstream of
Unazuki dam

50,000

Sediment sluicing

18:00

SS（SMDP）［ｍｇ/ｌ］
SS(Bottle sampling）［ｍｇ/ｌ］

40,000

22:00

30,00020,00010,000060,000Aimoto50,000SS（mg /l）over about 2.5～3.0 m for measuring, tokeep almost equal velocities between thehigh and low pressure detectors and toprotect the measuring equipment by
floating debris such as gravels or
driftwoods. We have solved this subject
by shielding the equipment with the shell
type cylinder. This submergible type isapplicable for measuring such as inreservoirs.
On the other hand, adopting thesubmergible type becomes difficult in thecase that the water depth changes largely
depend on time like a natural river. Then,
we have also developed the water
circulation type shown in Fig. 5(b). Here,the main measuring equipment is installed
in a water tank that is placed in land andtwo pipes are connected. One is to intake
measuring water from a river and anotheris to drain from the tank. An intake pipe isconnected to a submergible pump in riverwater.

SS（SMDP）［ｍｇ/ｌ］
SS(Bottle sampling）［ｍｇ/ｌ］

40,00030,00020,00010,00001202005/6/27

12
6/28

0

12
6/29

0

12
6/30

0

12
7/ 1

0

12
7/ 2

0

12
7/ 3

0

12
7/ 4

Fig. 7 Suspended sediment concentration measured by SMDP
during sediment flushing in the Kurobe River

Sand bar

Side bankLine 7(Riegle LMS-Z210)
2-300m, 2.5cm
accuracy

Section 5

Ononumain Unazuki reservoir

3D laser scannerPhoto 1 Unazuki reservoir and 3D laser scanner(m)

断面5_側岸変化図
Side bankslope; Section 5

Sand bar

45

40

35

30

-22.4
-22.6
-22.8
Water -23
surface -23.2
-23.4
-23.6
-23.8
-24
-24.2
-24.4
25
20 (m)

Sidebank

縦断面7_水面勾配

Water surface: Line 7
15:02
15:15
15:30
15:44
16:01
16:16
16:31
16:45
17:00

Waterwaves generated by
the antidune

-23.2
-23.4
-23.6
-23.8
-24
-24.2
-24.4
0

5

10

15

20

25

Fig. 8 Process of the side bank erosion and water surface changes in the channel

30

15:02
15:15
15:30
15:44
16:01
16:16
16:31
16:45
17:00

This type can be applicable to anywhere, if theminimum water depth for intake is secured, and is safer
than the submersible type at the time of the flood. On
the other hand, pump operation is needed forcontinuous measurement. The system has theelectromagnetic flow meter to measure quantity ofwater, and the accumulated sediment can be discharged
periodically from the valve installed at the bottom of
the tank. This water circulation type is applicable foreven at the natural rivers and we are doing field
experiment in the Kurobe River. Fig. 6 shows SMDP
installations in the Kurobe river (Sumi, Baiyinbaoligao
and Morita, 2005) and Fig. 7 shows data monitoring
results during sediment flushing operations in June-July
2005 (Sumi, Baiyinbaoligao and Morita, 2006). Highsuspended concentrations were measured up to
40,000mg/l by these systems during free flow flushing.
By analyzing these data and bottle sampling results,characteristics of fine sediment discharge during
sediment flushing of Unazuki dam have become clear.
These results are also useful to assess environmental
impacts to aquatic species by the sediment flushing.
3.2 3D laser scanner
In order to evaluate efficiency of the sedimentflushing operation from reservoirs or observemorphological changes in river channels during andafter sediment management, it is necessary to measureerosion-deposition process of sediment in reservoirs
and rivers. Recently, we have conducted fieldmeasurements with the 3D laser scanning technology(Sumi, Murasaki, Fujinaga, Nagura and Tamaki, 2004,
Sumi Murasaki, Nagura, Tamaki and Imaki, 2005) .
The 3D laser scanner used for the measurement isshown in Photo 1. Side bank erosion process of the sandbar formed in the Unazuki reservoir and water surface
profiles near by banks are shown in Fig. 8. By these data,
we can estimate that side bank of the height of 1.0-1.2m
was eroded with the speed of 7.5m/hr. Slope of water
surface is also estimated as 1/75 and water waves
generated by the antidune are also observed.
Since the bed morphological change where water andsandbars exist together complexly can be also measured
even in a night time, this technique can be used tounderstand sediment transport in a reservoir and to
estimate the sediment volume flushed out by theoperation.

4.

Conclusions

Reservoir sedimentation management in Japan isentering a new era. Although there are still technicalproblems to be solved, we believe that the importanceof sediment management will increasingly grow.
Assessing issues, depending on each case, of dam
security, sustainable management of water resources
and sediment management in a sediment routing
system, an effective sediment management plan should
be studied and materialized.
Needless to say, of course, our best endeavors should
be exerted to minimize negative environmental
influences involved in sediment management. From theabove point of view, necessary monitoring techniques
to support the sediment management in rivers andreservoirs should be intensively studied and developed.
One of new monitoring techniques, suspended
sediment concentration measuring system withdifferential pressure transmitter (SMDP) for highturbidity measurements and 3D laser scanner formorphological change surveys are useful to evaluate
sediment transport during sediment management.

References
Atkinson, E. (1996): The feasibility of flushingsediment from reservoirs, Report OD137, HR
Wallingford.
Morris, G.L. and Fan, J. (1998): Reservoir
sedimentation handbook, McGraw Hill Publishes,
New York.
Okano, M., Takayanagi, J., Fujii, T. and Ando, A.
(2004): Study of reservoir sedimentation management
based on actual sediment inflow -The case ofdevelopment of the sediment yield potential map -,Journal of Japan Society of Dam Engineers, 14(3),167-176 (Japanese).
Okano, M., Kikui, M., Ishida, H. and Sumi T. (2004a):
Study on reservoir sedimentation and the sediment
replenishment to the river below dams, Advances inRiver Engineering, Vol.10, 191-196 (Japanese).
Okano, M., Kikui, M., Ishida, H. and Sumi T. (2004b):
Reservoir sedimentation management by coarse
sediment replenishment below dams, Proceedings of
the Ninth International Symposium on River
Sedimentation, Yichang, China, Volume Ⅱ ,1070-1078.
Palmieri, A. (2003): Social and economic aspects ofreservoir conservation, The 3rd World Water Forum,
Kyoto-Chiga-Osaka., Japan.
Sumi, T. (2000a): Future perspective of reservoir
sediment management, Proc. of International
workshop on reservoir sedimentation management,
145-156.
Sumi, T. (2000b): Flushing efficiency on sedimentflushing operation in Reservoir, Journal of Japan
Society of Dam Engineers, 10(3), 211-221 (Japanese).
Sumi, T., Morita, S., Ochi, T., and Komiya H. (2001):
Developmentofthe suspended
sediment
concentration measuring system with differential
pressure transmitter, Dam Engineering, 11(3), 4-12
(Japanese).
Sumi, T., Morita, S., Ochi, T. and Komiya, H.（2002）:
Developmentofthesuspended-sedimentconcentration measuring system with differential
pressure transmitter in rivers and reservoirs, HydraulicMeasurement and Experimental Methods Conference，
EWRI-ASCE and IAHR.
Sumi, T. (2003): Reservoir sedimentation managementin Japan, The 3rd World Water Forum, The 3rd World
Water Forum, Kyoto-Chiga-Osaka., Japan.
Sumi, T., Murasaki, M., Fujinaga, K., Nagura, Y. andTamaki, H. (2004): Study on Measurement of
Erosion-Deposition Process of Reservoir Sediment
during Flushing Operation, Annual Journal of
Hydraulic Eng., Vol.48, 1147-1152(Japanese).
Sumi, T., Takata, Y. and Okano, M. (2004a):
Quantitative evaluation of a bypass tunnel to prevent
reservoir sedimentation, Advances in River
Engineering, Vol.10, 197-202 (Japanese).
Sumi, T., Takata, Y. and Okano, M. (2004b): Study on
the life cycle cost of dam projects that have flood
control and storage for water use functions separately
to reduce sedimentation management, Advances inRiver Engineering, Vol.10, 209-214 (Japanese).
Sumi, T., Okano, M. and Takata, Y. (2004): Reservoir
sedimentation management with bypass tunnels inJapan, Proceedings of the Ninth International
Symposium on River Sedimentation, Yichang, China,
VolumeⅡ, 1036-1043.
Sumi, T., Murasaki, M., Nagura, Y., Tamaki, H. andImaki, T. (2005): Study on Measurement of
Erosion-Deposition Process of Reservoir Sediment
during Flushing Operation(Part 2), Annual Journal of

Hydraulic Eng., Vol.49, 1033-1038(Japanese).
Sumi, T. and Iguchi M. (2005): Technical Feasibility
Study of Sediment Flushing in Reservoirs using the
RESCON Model, Journal of Japan Society of Dam
Engineers, 15(2), 92-105 (Japanese).
Sumi, T., Takata, Y., Iguchi M. and Nakanishi, Y.
(2005): Feasibility Study of Sediment Flushing
Operation in Reservoirs using the RESCON Model,
Advances in River Engineering, Vol.11, 285-290(Japanese).
Sumi, T., Baiyinbaoligao and Morita, S. (2005):
Monitoring of Suspended Sediment Concentration
with SMDP during Reservoir Sediment Flushing,
Advances in River Engineering, Vol.11, 315-320(Japanese).
Sumi, T.(2005): Sediment Flushing Efficiency and
Selection of Environmentally Compatible Reservoir
Sediment Management Measures, Int. Symposium on
Sediment Management and Dams, the 2nd EADC
Symposium, Yokohama, 9-22.
Sumi, T., Baiyinbaoligao and Morita, S. (2006):
Characteristics of Fine Sediment Discharge during
Sediment Flushing of Unazuki dam, Annual Journalof Hydraulic Eng., Vol.50, 913-918(Japanese).
Sumi, T. and Baiyinbaoligao (2006a): Study on
Environmental Impact Assessment of Fine Sediment
Discharge during Sediment Flushing Operationconsidering Grain Size Distribution, Advances inRiver Engineering, Vol.12, 253-258 (Japanese).
Sumi, T. and Baiyinbaoligao (2006b): Study on
Improvement of Sediment Flushing Operation in
Kurobe river by using Density Current Venting,
Advances in River Engineering, Vol.12, 265-270(Japanese).
Sumi, T. and Kanazawa, H. (2006): Environmental
Study on Sediment Flushing in the Kurobe River,22nd International Congress on Large Dams,
Barcelona, Q.85-R.16, 219-242.
Vischer, D. et. al. (1997): Bypass tunnels to prevent
reservoir sedimentation, 19th ICOLD Congress,
Florence, Q.74., 605- 624.
White, W. R., Attewill, L., Ackers, J. and Wingfield, R.
(2000): Guidelines for the flushing of sediment fromreservoirs, Report SR 566, HR Wallingford.