京都大学防災研究所年報 第 53 号 B 平成 22 年 6 月
Annuals of Disas. Prev. Res. Inst., Kyoto Univ., No. 53 B, 2010

River Morphology and Sediment Management Strategies for Sustainable Reservoir inJapan and European Alps

Sameh A. KANTOUSH and Tetsuya SUMI
Synopsis
Sustainability of Alpine reservoirs is severely threatened by sedimentation
resulting from natural geomorphologic processes. Management of sedimentation in
Alpine reservoirs cannot be apprehended by a standard generalized rule or procedure.
The paper aims at identifying, measuring technique to assess the risk of reservoir
siltation with and without countermeasures in Japanese and European Alps. Furthermore,
analyzing how human interventions and climate changes may alter sediment fluxes,
morphological patterns and in river basin system. Maintaining the “Healthy Life of theRiver Basin” is the ultimate goal of the paper by applies integrated sedimentmanagement, to realize the sustainable utilization of water resources and ecologicalenvironment protection, and achieve harmony between humans and nature. The results
show that, the successful reservoir sediment management proceeds from a permanentchange in river management. This may involve strategies to enhance water and sediment
release by a combination of several countermeasures. In big Alpine reservoirs, turbidity
currents are often the governing process in reservoir sedimentation by transporting finematerials in high concentrations.
Keywords: Alpine reservoirs, reservoir sedimentation, sediment management in reservoir,
sediment control strategies, sustainable reservoir, dam impacts

1.

Introduction

Sediment transport and deposition in alpine
rivers is responsible for numerous problems related
to reservoir sedimentation, river training and flood
protections. Dams and their reservoirs areconstructed and operated for multipurpose
including power generation, flood protection,
drinking water, agricultural water supply, recreation,
fishing, and others. Until now the common
engineering practice has been to design and operate
reservoirs to fill with sediment. With such an
approach, the consequences of sedimentation andproject abandonment are left to be taken care of by
future generations. For many dams this future has
already arrived. Therefore we need to develop
ingenious solutions for integrated sediment andwater management; unless we will lose the struggle
to enhance the available water resources andecological environment.
Necessary elements of sediment management
strategies for sustainable reservoirs are to collectenough data of deposited sediment for evaluationand select a suitable management technique for caseby case. Furthermore, it is important to establish
techniques for redeveloping existing dams, byconstruction of sediment bypass, and to develop
environmental impact assessment approaches.
These techniques minimize the minus impacts suchas water quality change, and maximize the plus
impacts such as the recovery of sediment routing.
Considering a sediment movement zone fromalpine mountainous regions through coastal areas, acomprehensive approach has already been started in― 821 ―

Japan to recover a sound sediment circulation in thesediment transport system. Reservoir sedimentation
management is placed as one of the top priorities;
therefore, the meaning of reservoir sedimentation
management should be widely shown.
Reservoir sedimentation problems are common
in all countries, whether they are developed ordeveloping countries. Therefore, it is necessary to
exchange knowledge and collaboratively work for asolution with countries having the same problems.
Schleiss et al., (2008) presented the reasons,problems of reservoir sedimentation, and possible
measures against sedimentation. Putting its
experience to use, Japan intends to make greatinternational contributions to the promotion ofreservoir sedimentation management in the field oftechnological development in future.
1.1 Alpine region conditions
Alpine environment are characterized by highenergy potential and characteristic landformelements, high elevations, steep slopes, rocks, andavailability of snow and ice (Barsch and Caine,1984). In respect of sediment transport processes
the specific hydrologic, geomorphologic, andclimatic conditions of alpine regions are regarded
as the major driving forces.
Japan has geologically young mountains, steep
and short rivers with flashy flow regimes, anddensely populated floodplains (Oguchi et al., 2001).
Generally, the Pacific side of Japan has heavy rainin June and July (rainy season) and between Augustand October (Typhoons) (Matsumoto, 1993). The
combination of steep catchments and heavy storms
results in widespread hill slope failures andlandslides and extensive flood discharges (Oguchi,
1996). On the other hand, from a topographicalpoint of view, many rivers in Japan are very steep
which run down over a short distance frommountains of 2,000 to 3,000 meters above sea levelto lowland areas (Fig.1). This figure illustrates therelative steepness of Japanese rivers. Although the
Shinano River (Fig.1) is the longest river in Japan,
its gradient is still greater than most of the rivers inother countries. The annual average precipitation isapproximately 1,700 mm, and, sometimes, intensive
rainfall such as 100 mm in an hour or 200 to 500
mm in a day can be recorded. These topographical,

geological and hydrological conditions have great
impacts on sediment yield in river basins, andconsequently reservoir sedimentation has been
accelerated especially in Chubu and Hokuriku
region which is located in the center of the mainisland.
For the European Alps the annual precipitation
can reach values of more than 3.000 mm in highranges while transpiration may drop to 100 mm
over snow covered areas. Significantly higher
values for precipitation of 6.000 mm per year oreven more are reported from gauging stations fromother parts of the world (Schaedler and Bigler,1992). While the intensity of rain-/ snowfall
together with the presence and condition ofsnowfields mainly affects the short-term run-off,seasonal changes of storage or release of waterfrom snowfields affects the annual discharge.

Fig. 1 Longitudinal profiles of Japanese andEuropean rivers (Takahashi and Sakaguchi, 1976)
1.2 Dam impacts
Regardless of their purpose, all multipurpose
dams trap sediment and inevitably lead to physicaland ecological changes downstream of the reservoir
site, as well as in the reservoir itself, and in somecases also upstream. Kondolf (1997) has described
that, by changing flow regime and sediment load,dams can produce adjustments in alluvial channels,
the nature of which depends upon thecharacteristics of the original and altered flow
regimes and sediment loads. Downstream impacts
develop through discontinuity in downstream
gradients, e.g., sediment supply, water quality,
temperature, flow and sediment regimes. Sediment
deficit is not only an environmental issue but also asocio-economic problem, for instance due to loss of― 822 ―

reservoir capacity (e.g., Fan and Springer, 1993;
Morris and Fan, 1998). In addition, dams alter thedownstream flow regime of rivers (Williams and
Wolman, 1984), which controls many physical andecological aspects of river form and processes,
including sediment transport and nutrient exchange(Poff et al., 1997).
Morphological effects on the river channel (e.g.,
Kondolf and Matthews, 1993; Kantoush et al.,2010) that includes riverbed incision, riverbank
instability, upstream erosion in tributaries,
groundwater over drafting, damage to bridges,
embankments and levees (e.g., Kondolf, 1997;
Batalla, 2003), and changes in channel width.
Hydrological effects caused by dams include
changes in flood frequency and magnitude,
reduction in overall flows, changes in seasonal
flows, and altered timing of releases.
2.

Sediment rates

Today’s worldwide annual mean loss of storage
capacity due to sedimentation is already higher than
the increase of the capacity by construction of newreservoirs (Boillat et al., 2003). Thus, sustainable
use of the reservoirs is not guaranteed on the longterm. The time evolution over the last century of thewater storage capacity and volume losses due toreservoir sedimentation in Japan, Switzerland andFrance are presented in Fig.2. To maintain theexisting dams and their facilities over the long term
becomes an essential policy issue.
35000
Storage Capacity in Japan
Reservoir Sedimentation in Japan

30000

Storage Capacity in Switzerland

Storage Capacity（MCM)

Reservoir Sedimentation in Switzerland

25000

Japan: sedimentation rate 0.24%/yr

Storage Capacity in France
Reservoir Sedimentation in France

Because of the following reasons: sedimentation
is proceeding more than expected in many dams;
the share of the dams having a design life of morethan 50 years, such as multi-purpose dams where
maintaining storage capacity is absolutely
necessary, will rapidly increase in the future; anddue to social changes in environment-conscious
trend and an era of low-growth economy. Figure 2
shows the relationship between the changes in thereservoir storage capacity and the storage capacity
loss due to sedimentation in Japan. While thestorage capacity is being increased by theconstruction of new dams, it is being lost by anaverage rate of 0.24 %/year. The figure shows thatthe average in Switzerland about 0.2% of thestorage capacity and in France is 1.08%. The
evolution in Switzerland of the water-storage
volumes lost due to reservoir sedimentation, andthat of the installed water-storage capacity over thelast century with the estimated future development
are also presented in the same Fig.2. The lower
sedimentation rate in Switzerland is due to thegeologic characteristics, mainly rocky mountains,of the catchment areas at high altitudes.
There are no accurate data on the rates ofreservoir sedimentation worldwide, but it iscommonly accepted that about 1–2% of theworldwide storage capacity is lost annually(Jacobsen, 1999). A detailed collection of
sedimentation rates in regions all over the world
can be found in Fig.3. The volumes ofwater-storage capacity lost due to reservoir
sedimentation and the volumes of installed
water-storage capacity in the world are presented in
Fig.3. The graph shows the evolution over the lastcentury, and the predicted future development.

20000

15000
France: sedimentation rate 1.08%/yr

10000

5000
Switzerland: sedimentation rate 0.20%/yr

0
1900

1950

2000

2050

2100

Time (Years)

Fig. 2 Development and estimated evolution of
installed water storage capacity and volumes lost
due to reservoir sedimentation in Japanese andEuropean countries.

Fig. 3 Global reservoir sedimentation rates (Basson,
G. 2009).

― 823 ―

3.

Sustainability of reservoirs

The concept of sustainability applied toagriculture developed, ground water development,
and road engineering. The optimization of sedimentremoval methods as a dam group is inexpensive if adam group was linked with each other for sedimentmanagement. The essential concept of sustainable
development is that the welfare of future generation
should logically figure into the projectdecision-making (Morris et al., 2008). Reservoirs
arguably represent today’s class of non-sustainableinfrastructure. The objective of management is tominimize the adverse effect that deposition in areservoir has on its operations. The sustainability ofreservoir should seek to balance sediment inflow
and outflow across the reservoir while maximize
the long-term benefits, the concept of sustainability
is shown in Fig.4.
This may involve strategies to minimize
sediment inflow, enhance sediment release, or
combination of several countermeasures for coarse
and fine sediments. Examples of each facilities andpropermaintenancesustainable
reservoir
management under the limited budget are presented.
Technically,
efficienteconomicallyandenvironmentally countermeasures, the coordinating
sediment management of multiple reservoirs in ariver basin, are discussed. The main development
patterns for reservoirs and sustainable development
are summarized in Fig.4. Several methods for
sediment management are available and have been
implemented in practice.
Sediment
impacts
assessment

Namingof priority
dam

Actions

Sedimentation
process
assessment

Economicassessment

Screening of
Sediment
management
Implementation
countermeasures
Monitoringof control
measures

Long‐term
Sustainabilityof reservoir

Criteria

Maximizing
sediment
releaseCost andbenefits
Feasibility of
sediment
strategy

SafetyEnvironmental
and social
Biodiversity
Water
quality

Food
supplyEnvironmental
compatibility
Habitatdiversity

Fig. 4 Concept of a sustainable alpine reservoir.

The latter essentially implies that the current
generation uses resources in a consumptive manner,leaving the problems of dealing with its remains tofuture generations without providing resources to
do so. The ultimate objective is to achieve a masterplan for sustainable countermeasures for
sedimentation in reservoir, integrated strategy for
management assessment, and stochastic sedimentinflow, which includes variable levels of social,environmental and climatic impacts on river basin
system management. Integrated models of sedimentflow and morphological dynamics in both regulated
and free flowing rivers are necessary. Integration ofdifferent skills and approaches through provision ofeffective reservoir sediment management system toprolong the reservoir lifetime as illustrated in Fig.5,
should allow the research to obtain some significant
advances in the understanding of dam impacts.

Fig. 5 Illustration of prolongation of the reservoir
lifetime.
Definitions of sustainable development haveproliferated, but the following basic concepts aremost relevant from the standpoint of water
resources infrastructure:[1] Guaranty security and acceptablefunctioning of the infrastructure for its purposes(drinking water, irrigation, energy production, etc);[2] Today’s patterns of infrastructuredevelopment should preserve the capacity of thereservoir and maximum possible time offunctioning. Not compromise the ability of future
generations to access these same resources;[3] Produce minimum impact to theenvironment and maintain biological diversity;[4] Minimize the potential for catastrophic
disasters resulting from infrastructure failure;[5] Avoid activities that create a legacy of― 824 ―

environmental
restorationorinfrastructure
rehabilitation obligations that disproportional on
future generation;[6] Take into account all processes:
hydrological regime (floods and drags), soil erosion,
climate change, environment and associatedecosystems, water & sediment continuity.
Requiring a reservoir life measured in terms ofthousands years instead of decades will demand
new methods of analyzing costs and benefits. For
all these reasons, developing new techniques toevacuate the fine and coarse sediment to maintainthe functionality, and at the same time ecologicallyrehabilitating the involved landscape would be
economically and environmentally beneficial for all
types of reservoirs.
4.

Sediment management of alpine
reservoirs

According to the time scale of sedimentmanagement, we can distinguish three phases: (1)short term phase requiring immediate corrective
actions to improve conditions that are getting worse(Corrective management), (2) medium term phasewith management direct at prevention of creation ofproblems (Preventive management), (re-suspend thesediment and optimal reservoir geometry), and (3)long-term phase that include accountability for
future generations sustainable management.
Among the several methods hypothesized formaintaining water reservoir volumes and forkeeping satisfactory levels of functionality, theperiodical removal of sediments is one of the mostcommon engineering techniques.
Why sediment management is needed?
The need for the reservoir sedimentmanagement in Japan can be summarized into thefollowing three points:[1] To prevent the siltation of intake facilities andaggradations of upstream river bed, accompaniedby the sedimentation process in reservoirs, in order
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 transport system, torelease sediment from dams.
The point in [1], as stated above, became major
concerns in the middle-scale hydroelectric dams
constructed in early years and the following
measures were then taken: to install sedimentscouring gates and locally discharge sedimentaccumulated in front of the intake facilities, or touse spillway to accelerate traction and discharge of
sediment deposited at the end of reservoir.
The point in [2] is an important issue in the
future. As shown in Figs.2 and 3, the reservoirs inJapan are now facing a critical question of
sedimentation. The point in [3] represents a newpolicy in Japan. The amount of sediment supplied
from rivers to coasts was radically reduced withconstruction of erosion control dams or storage
dams in mountain areas and acceleration of theaggregate excavation from riverbed after WorldWar II.
As a result, various problems rose up including
riverbeddegradation
atdownstream,
oversimplification of river channel, and retreat ofshoreline due to the decrease in sediment supply tothe coast. The sediment budget throughout Japan isoutlined in Fig.6. Sediment of approximately 200
million m3 (MCM) is produced from mountainareas every year. A volume of 100 MCM is
deposited in reservoir or others, and the remaining
100 million m3 is discharged into downstream
rivers. In the latter, 4 MCM is allocated for gravelexcavation.

4.1

Fig. 6 Sediment budget in Japan (Sumi 2003).

― 825 ―In the years from 1950 to 1960, however, aconsiderable amount of aggregate was taken, so thatthe amount of sediment supplied to coasts throughestuaries was remarkably reduced. Regarding thesediment budget for the sand fraction whichconstitutes coasts, erosion (350 thousand m3)
surpasses deposition (250 thousand m3) andtherefore coastal erosion is still proceeding. At
present, it is said that eroded coasts account for
approximately 60 % of the Japanese shoreline ofabout 34 thousand km.
Furthermore, approximately 40 % of thaterosion is involved in the decrease in the amount of
sediment supplied from rivers, including reservoir
sedimentation. A sediment transport systemrepresents a target region for management, in which
attention is focused on the movement of sediment in
the range form mountainous region to coastal
region, compared to a water system representing theconventional movement of water. The need for
management of sediment, which covers from thesediment supply mountain through the downstream
river and coastal region, has been growing.

Classification

Sediment Management Strategies

Sediment
yield
Reduction

TimingNonseasonal

4.2 Strategies of sediment control
Controlling reservoir sedimentations means infact the control of sediment deposition in reservoir.
It consists of three basic strategies:[1] Sediment yield reduction: to reduce sedimentinflow to reservoirs. Apply erosion control
techniques to reduce sediment yield from tributarycatchments. These techniques will typically focus
primarily on soil stabilization, and revegetation.
[2] Sediment routing: to pass sediment inflow
around or through the reservoir so as not toaccumulate in reservoirs, by employing techniquessuch as drawdown flushing and turbidity release.
[3] Sediment removal: to remove sedimentaccumulated in reservoirs by dredging or
excavation or hydraulically.
Fig.7 shows how sediment management isundertaken and classified. And some representativedams and examples from Europe and Japan, which
exercise sediment management, are listed. Further
studies needed for the improvement of reservoir
sediment management (De Cesare & Lafitte, 2007).

Methods and details of
sediment control measures

Place
Catchment,
River USof reservoir

Settling and off-stream storage basins

Sabo Area, Changing from sediment checkdams to sediment control dams

Slope and bank protection, River
regulation

Miwa, Koshibu,
Nagashima,
Matsukawa

Sediment check dams

Gatless outlets
Bottom outlet

Koshibu, Futase,
KigawaLuzzoneKatagiri

Glockner-Kaprun

YahagiTourtemagne

Dashidaira,Unazuki

Bodendorf,
Gebidem, Verbois

Sediment scoring gate

Senzu, Yasuoka

Feistritz, Edling

Sediment scoring pipe

Ikawa
Nunome, Akiba,
Futase, Murou

Annabrucke

Sediment
Replenishment
Recycling for
concrete aggregate

Miwa, Yasuoka,
Hiraoka

Gated outlets
Sediment
sluicing

Seasonal

Inside ofreservoir

Seasonal

Insidereservoir

Turbidity
current
venting
Drawdown
flushing
Partialflushing

Sediment
RemovalNonseasonal

End ofreservoir

MechanicallyNone-gate & curtain wall
Selective withdraw
inletsSubmerged dam,
groynesflushing outlet

HydraulicallyEgschi, Rempen,
Palagnedra
Luzzone, Livigno
Orden, Ligistbach

GrimselSediment syphoning

SakumaMargaritze,
EmossonBodendorf,
Genissiat
Margaritze,
Sylvenstein, Forni
LuzzoneSediment
redistribution

SakumaPieve di CadoreDry
excavation
Dredging

Insidereservoir

BeninarAsahi, Miwa,
Koshibu,Yokoyama,
Sabaishigawa,Dshidaira, Unazuki
Masudagawa

Sediment bypass

Sediment
Routing

Examples ofdams in Europe

Afforestation and Vegetation practices

End ofreservoir

End ofreservoir

Examples ofdams in Japan

Miwa, Yanase

Fig. 7 Classification of strategies of sediment control in Japanese and European reservoirs.

― 826 ―

(1) Sediment yield reduction into reservoirs
A reduction of sediment yield by soil
stabilization in the catchment area can be very
effective, and can solve the reservoir sedimentation
problem in a sustainable way. Where the climaticconditions allow vegetation practices, the soil canbe protected from erosion by afforestation orvegetation screens. In catchment areas without
vegetation, as for example the high Alpine
catchment areas, erosion protection can only beachieved with engineering measures such as gully
control, as well as slope and bank protection works
on rivers. If the reservoir is supplied by water
diverted from neighboring catchments, carefulattention will be needed to trap the sediment fromthe intake. This will include settling of coarse grain
sizes in the impoundment by a diversion dam orweir and providing settling basins to remove
suspended sediment (Boillat et al., 2003). One
example of settling basins from Switzerland isshown in Fig.8.

Fig. 8 Plan view of the water intake of La fouly,
part of the hydroelectric scheme of Emosson(Switzerland) (Boillat et al. 2003)
There are two techniques to reduce the amountof transported sediment: 1) countermeasure tocontrol sediment discharge which covers entire
basin including the construction of erosion control
dams; and 2) countermeasure to forcibly trap
sediment by constructing check dams at the end ofreservoirs. Although the catchment areas of dams
have high forest cover rates, a remarkable amountof sediment is produced in the watershed wherelandslides frequently occur due to the topographicaland geological conditions. When sediment yield isalso expected from side slopes surrounding dam
reservoirs, a project to buy and preserve a certain
plot of forest as a greenbelt has been implemented

by dam administrator itself. On the other hand,
check dam is effective to stop sediment and preventfrom sediment disasters downstream. Open checkdams can be divided into two categories, beam damand slit dams characterized by a different
management of sediment transport: beam dams arecharacterized by wide openings.
To be more precise, the erosion control dams in
the upstream region are planned to be converted toslit dams with notches, which are so designed as topass, not to trap, as much fine sediment carrying
less risk of sediment disaster as possible. Photo 1
shows the upstream check dam of Koshibu reservoir,
which was constructed in 1978. The sedimentdeposited at check dams should be excavated anddisposed regularly (Sumi 2000). Open check dams
assembled from steel pipes (Photo 2) or concretedams having slit are built to stop sediment only attimes when sediment outflow is great and to let
sediment rundown into lower basins when waterand sediment outflow is small. The accumulated
sediment can be excavated on land except for floodtime, and the removed sediment is utilized
effectively as concrete aggregate.

Photo 1 Upstream check dam of Koshibu dam Japan(Sumi et al., 2006)

Photo 2 Slit check dam from steel pipes
http://www.dpri.kyoto-u.ac.jp/rcfcd/sabo/index.htm
A private plant for taking aggregate is shown in
Photo 2. Securing of both a financial source and a― 827 ―

disposal method becomes absolutely necessary inorder for check dams to fulfill their primaryfunction in a sustainable way.

Photo 3 Private plant for taking aggregate (Japan)(2) Sediment routing in reservoirs
Another possible approach to sedimentmanagement, next to the reduction of sedimentinflow itself, is to route sediment inflow so as not toallow it to accumulate in reservoirs. In Japan andEurope the following techniques are adopted: 1)
sediment bypass by directly diverting sedimenttransport flow, and 2) turbidity current venting byusing a nature of high-concentration sedimenttransport flow.
In Japan, it is sediment bypass tunnels that havebeen studied most exhaustively. Although thistechnique involves high cost caused by tunnel
construction, it is also applicable to existing dams;
it does not involve drawdown of reservoir level andtherefore no storage capacity loss; and it has

relatively small impact on environment because
sediment is discharged not so rapidly as sedimentflushing, which is described later. The subjects ofdesigning sediment bypass tunnels are to secure thesafety of sediment transport flow inside tunnels andto take countermeasures for abrasion damages on
the channel bed surface. Among factors thatsignificantly relate to these problems are grain size,
tunnel’s cross-sectional area, channel slope, anddesign velocity.
Table 1 shows some examples of existing
sediment bypass tunnels and the ones underconstruction and study. It should be understood thatdesign condition becomes increasingly hard if
higher velocity and larger grain size will be
expected. Density current venting, on the other
hand, is a technique to use a nature ofhigh-concentration sediment transport flow, whichruns through relatively deep reservoir with original
channel bed of steep slope as a density current withless diffusion, and to discharge it effectively
through outlets in timing of reaching dam. In bothtechniques, the main target is fine-grained sedimentsuch as suspended sediment and wash load. In themultiple-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.

Table 1 Comparison of sediment bypass tunnels in the Japan and Europe

Name of Dam

Country

TunnelCompletion

TunnelShapeTunnelTunnel General Design Design
Cross
Operation
Length Slope Discharge Velocity
SectionFrequency
(m)
(m/s)
（％）
(m3/s）(B×H(m)）

Asahi

Japan

1998

Hood

3.8×3.8

2,350

2.9

140

11.4

13 times/yr

2r = 7.8

4,300

1

300

10.8

-

Miwa

Japan

Under
constructionHorseshoe

MatsukawaJapan

Planning

Hood

5.2×5.2

1,417

4

200

15

-

Egshi

Switzerland

1976

Circularr = 2.8

360

2.6

74

9

10days/yr

Palagnedra

Switzerland

1974

Horseshoe

2r = 6.2

1,800

2

110

9

2～5days/yr

Pfaffensprung Switzerland

1922

Horseshoe A = 21.0m2

280

3

220

～
200days/yr
10～15～14 1～5days/yr

RempenSwitzerland

1983

Horseshoe

3.5×3.3

450

4

80

Runcahez

Switzerland

1961

Horseshoe

3.8×4.5

572

1.4

110

― 828 ―

9

4days/yrTurbid w ater
below the dam
Dam
Clear water inthe reservoir

Turbid w aterentering reservoir

Photo 4 Turbidity current passing through (Morrisand Fan, 1998)
In Grimsel reservoir (Photo 5), in Switzerland,
an ongoing design project consists of heightening
the two existing dams by 23 m (Spitallamm ArchDam 114 m; Seeuferegg Gravity Dam 42 m). The
excavation and demolition works necessary for theplanned heightening generate approximately
150'000 m3 of rock material. This large amount ofmaterials has to be stored somewhere near theconstruction site. This led to the idea of building
some kind of obstacle in the form of a submerged
embankment dam to prevent sediment deposition
due to the turbidity currents in the area near theintake structures. A case study is presented toinvestigate the occurrence and impact of turbidity
currents on the reservoir sedimentation and to checkthe efficiency of such submerged obstacles to retain
the sediments (Oehy 2003).

Photo 5 Grimsel reservoir (1909 m.a.s.l., 108 m3)(Bühler, J., 2009)

The release of sediment laden water throughpower intakes and turbines is a promisingpossibility to manage the long term problem of thesedimentation process in reservoirs. In order to get
the suspended sediments entrained into the power
intake, they need to be in suspension right in frontof the water intake. At Laboratory of HydraulicConstruction (LCH), Swiss Federal Institute ofTechnology (EPFL), Jenzer (2009), experimentallyinvestigates an innovative technique to keep theturbid water in suspension (Fig.9). Therefore an
upward flow to lift the sediments and to maintainthem in suspension is required. Jenzer (2009) tested
several series to provide attractive methods whichallow these processes using a minimum of externalenergy by making use of the affluxes of watertransfer tunnels feeding the reservoir. The water of
the transfer tunnels is caught and introduced into jet
nozzles fixed at a definite position in the reservoir
close to the power intake.

penstock
Water jets

Fig. 9 Schematic view of the water jets supplied by
the feeding pipe coming from water transfer tunnels(LCH, EPFL, Switzerland, Jenzer, 2009)
In addition, as countermeasures for long-term
turbid water discharge problem, selective
withdrawal works are installed at many dams. And,in Katagiri dam at Tenryu River, curtain wall isinstalled in front of a non-gate outlet conduit todischarge water from the bottom layer of reservoir.
Discharge of fine-grained sediment using thesefacilities can also be classified in density current
venting. Furthermore, Flood mitigation dam (FMD)
is a gateless outlet dam designed only for the
purpose of flood control which provides long-termand efficient protection against floods. Its bottom
outlets are installed at the original river bed tofacilitate the sediment transport during flood andflush out the deposited sediment at the end of flood.

― 829 ―

In USA flood mitigation dams are called “Drydam”, in Europe “flood retention basins”,(“Hochwasserrückhaltebecken” in German), in
Japan “in stream flood control dam” (Ryusuigata
dam, Japanese), others “flood mitigation dam”.
Therefore, FMD have less influence on reservoir
sedimentation than a storage dam. FMD is one ofgood solutions in dam engineering for sustainable
management of reservoirs, downstream riverenvironment, and sediment transport. FMD is
expected as environmentally friendly, since almost
all incoming sediment during flood periods can passthrough dam bottom outlets that designed at theoriginal river bed level and there will be fewer
impacts to downstream river environment.
Kantoush and Sumi (2010) have classified FMD
based on outlet arrangement: 1) installing
regulating gates in bottom outlets or not and 2)
securing continuity of the river through theseoutlets or not. Photos 6 and 7 present two examplesof FMD from Europe, Ligistbach dam in Austria
and Orden dam in Switzerland, respectively.
Because of geographical conditions, there is large
difference between both dams.

Photo 6 Flood mitigation dam of Ligistbach, Styria,
Austria

Photo 7 Flood retention basin of Orden dam,
Switzerland

Another example of from Japan is Masudagawa
dam, is shown in Photo 8. Silts are installed forflushing sediment from the stilling basin andachieve fish passage functions. The stilling basin of
Masudagawa dam dissipates the energy by
hydraulic jump type equipped with an endsill toobtain appropriate tailwater depth. This type ofenergy dissipater is the most widely used in Japan
where downstream water depth is usually small.
The width of the stilling basin was designed
according to the width of the downstream river.

Photo 8 Masudagawa flood mitigation dam,
Shimane Prefecture, Japan
In response, a future research project isestablished to study updated planning, designingand operating of flood retention dams. In the frame
work of a research project, the FMD individualized
and characterized for three parts, inlet upstream ofthe dam, outlets, and stilling basin with downstream
reach of the dam. The approach appeared efficient
to help flow and sediment practitioners, andecologists work together, and find technicalsolutions complying with both flood mitigation andbiodiversity preservation requirements. The effectsof the geometry will be investigated with systematic
physical experiments, numerical simulation, andfield data. This will allow identifying the optimal
stilling basin shape of the flood mitigation dam thatdissipate more energy, minimizes the deposition
and reduces the number of horizontal recirculation
cells. The results will help to understand theinfluence of geometry on the flow stability,
sediment deposition and flushing process in order todesign the stilling basin geometry. The predictionof sediment profile lies in the prediction of flow
pattern and, in turn, sediment deposits were able tochange the flow structure.

― 830 ―

(3) Sediment removal accumulated in reservoirs
Basically, there are two types of systems foraccumulated sediment removal from reservoirs:[1] Hydraulically: This comprises sedimentflushing, siphoning (HSRS) and redistribution of
the sediment inside the reservoir. Hydraulicflushing involves the opening of bottom outlet tocompletely empty the reservoir and allow stream
flow to scour a flushing channel. Basically, there
are two types of flushing operations with, andwithout drawdown, and optional techniques can beused with the complete drawn flushing as shown in
Fig.10 (Kantoush et al., 2010).
Types of Sediment Flushing in Reservoirs
With Drawdown

Without Drawdown

More effects along and across the basin (flushing channel)

Very local effects (flushing cone)Floodseasonemptying

Dam outlets are
opened for very
short time

PartialComplete

Nonflood Under pressure
Seasonminimum
emptying operation level

Free flowoverspillway

Fig. 10 Classification
techniquesofAdditional techniqueswith complete drawdown

Auxiliary
channelMechanically

Lateral,Longitudinal, andin both directions

Bulldozers topush deposits
into flushingchannelsediment

flushing[2] Mechanically: This approach is regarded asa last resort in case sediment is accumulated inreservoirs in spite of various efforts being done: 1)
mechanically excavating sediment accumulated in
the upstream region of reservoirs, and 2) dredging
sediment accumulated at the middle anddownstream regions. As for excavation anddredging techniques, it is important that theremoved sediment should be treated properly andreused.
On the other hand, sediment flushing is atechnique to restore tractive force in a reservoir
beyond its critical force by means of drawdown ofreservoir level, and flush the deposits thoughbottom outlets in the dam body with inflow water,
mainly in an open channel flow condition, to thedownstream of dam.
When the amount of sediment inflow issignificantly large, man-powered techniques suchas excavation and dredging are hard to be adopted
because of problems involving transportation anddump site. In such a case, however, sedimentflushing can be a permanent measure if conditions
are met. Traditionally in Japan, sediment flushingfacilities such as flushing sluices and outlets were
installed at small-scale hydroelectric dams or weirs
for the purpose of discharging sediment depositedin the vicinity of intake. In contrast, at
Dashidaira-Unazuki dams in the Kurobe River,where a large amount of sediment is discharged,
and sediment flushing is implemented incoordination of upstream and downstream dams
(coordinated sediment flushing). The effects of
sediment flushing in the Kurobe River should be
evaluated. The suitable condition to perform theflushing operation is the taking place of a natural
flood more than a constant scale.

Table 2 Comparison of sediment flushing dams in the Japan and Europe
InitialDam
Name of Dam

Country

Storage

Height Capacity
(m)

(CAP)
(Mm3)

Mean
AnnualSediment
Inflow(MAS)(Mm3)

1/(MeanAnnualReservoir

Runoff)

Life (=（=CAP

CAP/ MAS)/MAR)

Average
Flushing
Discharge(m3/s）

Flushing Flushing
Duration Frequency（hrs）(1/ yr)Dashidaira

Japan

76.7

9.01

0.62

0.00674

14.5

200

36

1

Unazuki

Japan

97

24.7

0.96

0.014

25.7

300

48

1

Gebidem

Switzerland

113

9

0.5

0.021

18.0

10

45

1

VerboisSwitzerland

32

15

0.33

0.00144

45.5

600

36

3

Barenburg

Switzerland

64

1.7

0.02

0.000473

85.0

90

20

5

Ferrera

Switzerland

28

0.23

0.008

0.00018

28.8

80

12

5

Genissiat

France

104

53

0.73

0.00467

72.6

600

36

3

Gmund

Austria

37

0.93

0.07

0.00465

13.3

6

168

N.A.

― 831 ―

360
350
normal waterlevel 343m

Elevation （EL.m）

340
330

spillway
325m

320

July 2008, after flushing
July 2009, after flushing310

May 2009, before flushing

August 2004, after flushing300

May 2004, before flushing290

December 1994

Dashidaira dam
280
-500
-0

Original river bed in 1985

(a)

500

1,000

1,500

2,000

2,500

3,000

sediment flushing of Dashidaira dam and a tributary
river. The flushing efficiency calculated from thewater consumption including the discharge during
drawdown and the sediment volume flushed out isabout 2%. For this reason, it can be estimated that
sediment flushing by using a natural flood
discharge in the rainy season is executed regardlessof the previous year's amount of sedimentation toprevent the sediment from changing in quality inthe reservoir every year, and in that case while
doing an enough dilution.

Distance from dam（m）

5.

280
270
Equilibrium sedimentation profile

Elevation（EL.ｍ）

260

Case studies of sediment replenishment
technique at Nunome Dam Japan and
Sylvenstein Germany

December 2003
250

normal water level 245m

240spillway 231m
230

Sept. 2009, after flushing
May 2009, before flushing

224

220

August 2004, after flushing
May 2004, before flushing

210

Original river bed, December 1999

Unazuki dam
200-1,000

(b)

0-

1,000

2,000

3,000

4,000

5,000

Distance from dam (ｍ）

Fig. 11 Actual field longitudinal bed profiles
variations in time along (a) Dashidaira reservoir;(b) Unazuki reservoir (Sumi and Iguchi, 2005)
The previous and present longitudinal sedimentprofiles of Dashidaira and Unazuki dams are shownin Figs.11(a) and 11(b), respectively. Dashidaira
dam was constructed fourteen years before Unazuki
dam. Therefore, the Dashidaira Dam is currently at
an equilibrium state in terms of its sediment, andthe quantity of passing through is approximately
one million cubic meters yearly.
However, sediment is still being accumulated at
the Unazuki Dam. While the majority of sedimentsof grain size larger than 2 mm are trapped at thereservoir, about 70% of the sediment that has grain
size smaller than 2 mm, is sluiced. High sedimentdeposition is formed in May 2004 within
Dashidaira reservoir as shown in Fig. 11(a).
Afterward in August 2004, by continuous sedimentflushing another bed profile is formed. Longitudinal
profiles before and after flushing in 2009 are shownin Figure 11(a). On the other hand in Figure 11(b),the sedimentation in Unazuki dam progresses
mainly by the coarse sediment inflow from both

In Japan, it is common practice to remove
accumulated coarse sediment by excavation anddredging, and to make effective use of the removed
sediment. Sediment replenishment method is one of
new measures of sediment management. In thismethod, trapped sediment is periodically excavatedand then transported to be placed temporarily
downstream of the dam. In a manner decided
according to the sediment transport capacity of thechannel and the environmental conditions.
Therefore, the sediment is returned to the channel
downstream in the natural flooding processes. The
procedure of the experiments consists of four steps:(1) extracting mechanically the accumulated
sediment at check dam; (2) transporting it by truck
to downstream river; (3) placing the sediment withspecific geometry (Fig.12), and (4) monitoring flow,
sediment, and environmental parameters.
5.1 Sediment Replenishment Projects in Japan
Large Japanese rivers are often trained to a large
extent, to maintain services such as navigation,hydropower generation and flood defense. Okano etal., (2004) summarized sediment replenishment
projects in Japanese Rivers, such as Tenryu,
Ota-kine, Abukuma, Ara, Oi, Naka, Kuzuryu, Yodo,
Kanna, and Tone, have been conducted by
Minis-try of Land, Infrastructure and Transport(MLIT). Kantoush et al. (2010) investigated themorphological evolution and corresponding flow
field during replenishment experiments in Uda
River, Japan. Sediment treatment system is applied― 832 ―

by Sumi et al. (2009), to produce appropriate grain
sized material with less turbidity.

P laced sed imen tg eo m et ry

F lood st age
N orm al s tage

Fig. 12 Concept of sediment replenishment andplaced sediment geometry on the bank of Nunome
River.
Sediment transport and associated channel bed
mobility are recognized as key processes forcreating and maintaining physical habitats, aquaticand riparian ecosystems. In Japan, sediment
replenishment projects are undertaking withdifferent configurations and characteristics of
sediment and discharges. Fig.13 summarizes factorsthat influence the sediment replenishment research.
These factors are classified in six groups as shownin Fig.13.

5.2 Field experiment for sediment replenishment
in Nunome River
Yodo River (Yodo-gawa) system is 75 km in
length, located in the central part of Japan. There
are five completed dams in the Kizu River System,
Nunome, Shourenji, Hinachi, Takayama, andMurou dams. Nunome dam is a gravity dam forflood control and water supply, completed on 1994,
16 years ago. The test site is placed by the Japan
Water Agency (JWA) on the left side bank of
Nunome River (Fig.14). The sediment is located in
the down-stream reach at 300 m from the Nunome
dam. Planning, design, implementation andlongterm monitoring of tests are guided by JWA.
Fig.14 shows the location map of the placed
sediment and reservoir shape.
Nunome Dam

Location of
500 m 3 placed
sediment

Nunomereservoir

Factors of Sediment Replenishment
Sediment
PhysicalCharacteristics

Flow PhysicalCharacteristics

River PhysicalCharacteristics

Replenishment
Characteristics

Monitoring
Characteristics

Economics
Characteristics

Porosity anddensity

Flood flow
discharges (Floodhydrographs)

Initial bed
morphology andslopesPlaced sedimentvolume andgeometry shape

Water quality(turbidity, Ph,temperature,

Excavation andsediment
treatment costs

Sediment type andcohesion

Flow water depths

Bed material size,
gradation andpermeability

Submerged or
partial or unsubmerged state

Environmental (fishspecies, stream
invertebrates,
algae)

Transportation cost

Grain size
distribution, andpercentage of finesediment

Flow duration
curve andfrequency

Sediment rating
curve (suspended
and bed loads)

Locations andplacement
arrangement along
the river

Flow field andvertical velocity
profilesTreatment of
excavated anddredged sediment

Flow patterns andvelocity profiles

River bankvegetation

Frequency of
feeding per year
and season

Cross sectional
survey and precise
surveying of riffles
and pools

Erosion rate andtype (side bank orvortex types)

Volume of Trapped
sediment inreservoirs

Indirect (side bankfeeding) or direct(in river) feeding
methodVisual inspection
and grain size
analysis

Sediment source

Check dam
Check damFeeding cost

Monitoring cost

Fig 14 Map of Nunome reservoir, dam, and placed
sediment. Photo of geometry and check dam.

Project benefits

Fig. 13 Main groups of sediment replenishment
characteristics and managing factors.
Several significant gaps in the scientificunderstanding of these processes remain,
particularly concerning how riverbed deposition
and geometry are influenced by variability in waterand sediment release. Sediment replenishment
scenarios may, induce undesirable morphologicaland ecological consequences as well as significant
channel adjustments that can result in failure of therestoration project itself. That is, it is necessary tobetter understand reversibility, direction and timescale of changes, and the sustainability ofreplenishment intervention before is implemented.

5.3 Results of Replenishment DS of Nunome
Dam
The evolving of bed topography and grain size
distribution is monitored, along with water surface,velocities and rate of sediment transport at thedownstream end of the Nunome River. Fig.15
shows the remained sediment of 2008 and during
the heavy rain with peak discharge of 81 m3/s.
When the discharge exceeds 8m3/s, the erosion
starts and about 40 m3 of sediments are trans-ported.
Figure 8 shows the photos of field tests phases. Allof the remained sediments are removed, and thennew dredge sediments are placed. To understand theprocess of erosion and deposition of the placed
sediment during flood, series of pictures are taken
at different time and discharges are shown in Fig.16.

― 833 ―

The erosion at the base of the placed sedimentcauses the sand mass of placed sediment bank toslide downward and deposit. Deposited sand massis then eroded due to water flow. Deposition occurs
when the bottom shear stress is less than the critical
shear stress. Only sediment with sufficient shear
strengths to withstand the highly disruptive shear
stresses in the near bed region is deposited andadheres to the bed. The erosion region developed
from a straight bank line into the alcove shaped as
seen in Fig.16 (b). At the peak discharge the waterlevel increased at 11h50 produces a greater erosion
area and the water submerges the placed sedimentas shown in Fig.16(c).

placed sediment remains as shown in Fig.16(d). By
using satellite imagery and aerial photos a map of
Nunome River in 2009 is constructed for 1 km
below the dam. The river channel, island, point bars,
and vegetation area are identified and distinguishedby color as shown in Figure 10. The downstream
reach of the dam, first 150 m from dam,
experienced the greatest change in channel structure
and loss of bars and islands.
9:30
Q=9.46m3/s

(c)

13：00
Q=5.71m3/s

(b)

Ｂ=30ｍ

Ｈ=0.7ｍ

Ｈ=5ｍ

11：50
Q=15.36m3/s

Sediment volume 500m3

(a)

(d)
100m3 のうち約 40m

Remained sediment from 2008
Before 2009 Flood

Discharge 81 m3/s
Allsediment
erodedDuring Flood （8-10-2009）

Fig. 16 Processes of erosion and deposition of theplaced sediment during flood

Normal stage

Fig. 15 Evolution of sediment replenishment
experiment
The peak discharge is lasted for two hours andpermits a deeper cut in the inner side bank. With
peak flow, the eroded volumes increased in therange of 45 percent. Reduction of flood discharge
reduces the erosion rate, therefore 50 m3 of the

The surface flow area in the first reach is greaterthan the bars and vegetation areas. Between fourthand seventh cross sections, 300 m from dam, reachexhibits variable patterns of channel change andintermediate in loss of island and vegetation. The
reach after cross section 7, has a small sand bars,
islands, and riparian vegetations.
Deposition and vegetation after
replenishment over point sand bar

Stilling basin

Location of placed sediment (yellow area)

Point bar and vegetation
Stream flow

Under water
deposition
Newly formed sand bar after
sediment replenishment

Fig. 17 Processes of erosion and deposition of the placed sediment during flood― 834 ―

The replenishment processes are efficient torestore the bed load transport and the associatedhabited by coupling reintroduction with floodplain
habitat restoration. In Fig.17 along the Nunome
River, several cross sections are identified to survey
after replenishment. Newly depositions over sandbars and in the river channel are shown in Fig.17.
Moreover, a completely new sand bar is formed
after 600 m from dam. With the field experiments
the processes are directly visible, and will be usedfor validation of numerical models.
The effects of sediment replenishment areinvestigated for cross section bed deposition, flow
velocity, grain size distribution, water quality andorganisms. Eleven monitoring points are shown in
Fig.18. The distribution of river bed materials areanalyzed by visually determining the sizes of river
bed material in quadrate of 1 to 2 m in dimensions
and preparing a two dimensional map, whichenabled changes in distribution before and after
sediment replenishment to be compared.
Fig.18 shows bed material size in three different
monitoring times and 10 observation points along
the river. By comparing Fig.18(a) and 18(b), a
significant riverbed changes can be identified fromcross sectional surveys, and visual inspections suchas at section No. 1 and No. 11.
＞20cm

5～20cm＜5cm

Nunome Dam

No 4
No 19

(b)
No 9

No 8
8.2 kmNo 11

Percentage of bed grain size(a)Placed sedimentat 0.3 km
No 13
No 1 at 0.6 km
No 16
No 2
No 3

Monitoring section on 18-12-2008 before flood

Monitoring section on 5-8-2009 after flood(c)

Monitoring section on 28-10-2009 after flood

Fig. 18 Variations of river bed material size at 10
cross sections along the Nunome River
After 600 m from the dam the survey at point
No. 1 shows that the rate of gravel of less than 50

cm in-creased after natural flood, grace to thereplenishment. Similar sediment grain sizes arefound at point No 11 after 8200 m from dam point.
Before sediment replenishment in point No 1 andNo 11, the material is coarser gravel than in the
middle points No 4 and No 19 (Fig.18(a)). Afterflood, the fine material content of the channel
deposits strongly increased. The sedimentdeposition in point No 1 and No 11 after
replenishment consist of a nearly continuous layerof fine sand, but no change occurs from No 2 to No
9 (Fig.18(b)). But after second flood where anotherplaced sediment conducted, the bed material istransported and much of the coarsest sediment is
supplied to point No 1, and No 11 (Fig.18 (c)).
5.4 Sediment Replenishment in Isare River
Germany(1) ALPRESERV projectIn the frame of an international establishedproject called Sustainable Sediment Management of
Alpine Reservoirs considering ecological andeconomical aspects ALPRESERV. Within the EU
Interreg IIIB project, ALPRESERV 17 project
partners from 5 alpine countries worked together todevelop and evaluate a sustainable sedimentmanagement
andeconomic
issues,andde-sedimentation options. The project aims on awise management of sediments on basis ofexperiences gained on national level to establish
trans-national guidelines taking into account the EU
Water
Framework
Directive
andspatialdevelopment needs to preserve existing reservoirs
and to avoid uncontrolled exploitation by
constructing new storage capacity.
As flood protection is a major task and of highpublic interest trans-national strategies are needed
to implement a sustainable management aiming ona dynamic balance to avoid reservoir sedimentation
as well as degradation processes of rivers in theperi-alpine belt to reduce the risk of floods and to
avoid severe damages to infrastructure and private
property. Accumulation in reservoirs reduces
valuable morphological processes of rivers
downstream affecting biologic diversity andecologic dynamics.
As achievement a comprehensive guidelines on
sedimentation processes in the Alpine region for― 835 ―

enhanced training of water authorities, local
administrations and private businesses.
Seven typical Alpine reservoirs were selected
for pilot projects ranging from a high region facility
directly influenced by glacier activity down toperi-alpine belt river reservoirs to cover mostsedimentation problems in the Alpine region. The
activities are focused on different strategies totransfer or remove sediments in a larger scale
taking into consideration the fragile environment of
the Alps. Immediate information of local authorities
and all relevant interest groups (inhabitants,
fishermen, land owners) can reduce disputes
significantly. Experiences of how to encourage
locals to join the planning process will be sharedwithin the partnership and published asrecommendations to administrations and reservoir
owners.

(2) Reuse and deposition of sediments
Technical measures are mostly using different
dredging techniques (Photo 9) to either relocate thematerial into the downstream section or deposit it
outside of the water body. All options, especially
technical measures, encounter additional problems
in the alpine environment compared to lowland
applications. The specific conditions described in
ALPRESERV project affect time, duration andcosts of sediment removal.
For example, Lake Margaritze, a small artificial
reservoir in the Austrian Grossglockner region at analtitude of 2.000 m (6.560 ft), is accessible by apaved road. It needs more than 15 truck loads tocarry a small water injection dredger, disassembled
in parts, to the site. 6 – 8 weeks are necessary toassemble the equipment at the lake before it isoperational.

Photo 9 Excavation activities in reservoirs: Suction dredger and floating pipeline at the pilot action
Margaritze (left) and conventional hydraulic excavator at Sylvenstein (right) (ALPRESERV project).

Photo 10 Gravel replenishment into Isar at the Oberfohringer Wehr: Transport of excavated material by truckand deposition in the river bed as depots (left) and naturally distributed gravel material after minor flood
events after 3 months (right) (ALPRESERV project)
Due to climatic conditions transportation to the lake
is limited to spring time, while disassembling andtransport downhill has to be finished before thefreezing period. Thus operation is limited to thesummer months. Beside logistic difficulties(preparation, operation, supply) and resulting costs― 836 ―

administrative issues have to be taken into
consideration, too. As alpine regions are sensitiveenvironments high elevated areas are often
protected as National Parks resulting in restrictions
to minimize the impacts of technical measures likenoise, exhaust, possible contamination, etc. One
good example had been replenishment of more than
100.000 m3 of gravel material in the river ISar at
the Oberfhringer Wehr (Photo 10). A further
example of sediment replenishment is documented
for pilot action Forni in the ALPRESERV
publication.
6.

Conclusions

Various integrated management strategies ofwater and sediment incorporation to preserve riverenvironments downstream of dams in Japan arepresented. Water management measures arepresented as “Flexible Dam Operation” andinstream flow which discharge rate is defined tomaintain habitats of river biota, water quality in theeach studied section of the rivers depending on eachseason. For sediment management measures arereservoir flushing, sediment replenishment, bypass
tunnel, and flood mitigation dams are discussed.
The present problem for maintaining river
health is to determine the adaptive range of theriver system to the flow and sediment regimes,
which is the basic of all the measure. In detail, it isnecessary to find out flow and sediment release
which can meet demands of various functions basedon data of hydrology, water quality, ecosystem, etc.
Furthermore, the integrated management measurefor flow and sediment should be researched further,which means how to realize the reasonable andorder exploitation and how to regulate and control
reasonably by large hydropower project. The
sediment flushing of the Kurobe River is extremely
important from both sides of the sustainable
management of dam reservoir and the securing of
the sediment mobility in the sediment routing
system. By replenishing sand at different locationsof the Nunome and Managwa Rivers within thedownstream reaches, the replenishment may direct
future supplements for a more widespread dispersalof suitable sand for fish spawning.
Reservoir sedimentation management in Japanis entering a new era. Although there still technicalproblems to be solved, we believe that theimportance of pursuing sediment management will
increasingly grow. Assessing issues, depending oneach case, of dam security, sustainable managementof water resources and sediment management in asediment transport system, we have to draw up aneffective sediment management plan with a limited
budget and take specific action. Needless to say, ofcourse, our best endeavors should be exerted tominimize negative environmental impacts involved
in sediment management.
Reservoir sedimentation problem has been achallenging issue for many countries all over theworld, however only a limited number of countries
have been actively playing roles in reservoir
sedimentation management. Under the present
situation, for those countries which haveprogressively developed various techniques andpossess example cases, key questions are not to put
off dealing with this problem but to makecontinuous effort of further developing techniques
and putting them into practice, and to widely share
the resulting information and knowledge with every
country in need of them.
Acknowledgements
The first author gratefully acknowledges the
Swiss National Fund for Science (SNSF),
Switzerland, which provided fellowship funding tostay at Kyoto University.
References
ALPRESERV project, http://www.alpreserv.eu/.
Batalla, R.J. 2003. Sediment deficit in rivers causedby dams and instream gravel mining. A review
with examples from NE Spain. Cuaternario y
Geomorfología 17 (3–4):79–91.
Basson, G., (2009):General Reporter, ICOLD 2009,
Brasilia, Brazil.
Barsch, D., and Caine, N., (1984): The nature ofmountain geomorphology, Mountain Research andDevelopment, 4, pp. 287-298.
Boillat, J.-L., Oehy, Ch. and Schleiss, A., (2003):
Reservoir
sedimentation
management
in
Switzerland, 3rd World Water Forum, Japan, pp.

― 837 ―

143 – 158.
Bühler, J., (2009): Turbidity currents in an alpine
pumped-storage reservoir, International workshop
on the sediment management options for regulated
rivers, May 2009, Catalonia, Spain.
De Cesare, G. and Lafitte, R., (2007): Outline of thehistorical development regarding reservoir
sedimentation, 32nd IAHR Congress, Harmonizing
the Demands of Art and Nature in Hydraulics.
Fan, S., and Springer., F.E., (1993): Major
sedimentation issues at the federal energy
regulatory commission, In: Fan, S., Morris, G.
(Eds.), Notes on Sediment Management in
Reservoirs. Water Resources Publications,
Colorado, USA, 1–8.
Ikebuchi, S., Sumi, T., Kobayashi A., and Oomoto,I., (2007): Dams and environmental flows:
concept and implementation in Japan, 10th
International River Symposium, Brisbane.
Jacobsen, T., (1999): Sustainable reservoir
development: The challenge of reservoir
sedimentation, Conference Proc. Hydropower into
the next century, Gmunden, Austria, pp. 719–728.
Jenzer Althaus, J. M. I., (2009): Cyclonic
circulation created by water jets in reservoirs
allowing the release of fine sediments throughintakes, Proc. of the 33rd congress of IAHR, J. F.
Kennedy Student Paper Competition, Canada.
Kantoush, S. A., (2008): Experimental study on theinfluence of the geometry of shallow reservoirs on
flow patterns and sedimentation by suspended
sediments. Communication 37 of the Laboratoryof Hydraulic Constructions (LCH), Ed. A.
Schleiss and PhD Thesis, No 4048, École
Polytechnique Fédérale de Lausanne, Switzerland.
Kantoush, S. A. and Schleiss, A. J., (2009):
Channel formation in large shallow reservoirs
with different geometries during flushing, journalof environmental technology, 30(8): 855-863.
Kantoush, S. A., and Sumi, T., Kubota, A. andSuzuki., T., (2010): The impacts of sediment
replenishment below dams on flow behavior andbed morphology of river channel and river mouth,First International Conference, Alexandria, Egypt.
Kondolf, G.M., (1997): Hungry water: effects ofdams and gravel mining on river channels.
Environmental Management, 21(4): 533–551.
Kondolf, G.M., Matthews. W.V.G., (1993):

Management of coarse sediment in regulated
rivers of California, University of California,
Water Resources Center, Davis, CA.
Matsumoto, J., (1993): Global distribution of daily
maximum precipitation. Bulletin of the
Department of Geography, University of Tokyo
25, pp. 43–48.
Morris, G. L. and Fan, J., (1998): Reservoir
Sedimentation
Handbook:
DesignandManagement of Dam, Reservoirs and Watersheds
for Sustainable Use. McGraw-Hill Book Co., NewYork.
Morris, G. L., Annandale, G., Hotchkiss, R.,(2008): Reservoir Sedimentation. Chapt. 12 ofrevised Manual 54, Sedimentation Engineering,
Edited by Garcia M., ASCE Manuals and Reports
on Engineering Practice No. 110.
Okano, M., Kikui, M., Ishida, H. and Sumi. T.,(2004): Reservoir sedimentation management bycoarse sediment replenishment below dams,
proceedings of the ninth international symposium
on river sedimentation, Yichang, China,
1070-1078.
Oguchi, T., Saito, K., Kadomura, H. and Grossman,M., (2001): Fluvial geomorphoogy andpaleohydrology in Japan, Geomorphology 39, pp.
3–19.
Oguchi, T., (1996): Hill-slope failure and sedimentyield in Japanese regions with different storm
intensity. Bulletin of the Department ofGeography, University of Tokyo, 28, pp. 45–54.
Oehy, C., (2003): Effects of obstacles and jets on
reservoir sedimentation due to turbidity currents,
PhD thesis, No. 15, Swiss Federal Institute ofTechnology, Lausanne, Switzerland.
Poff, N.L., Allan, J.D., Bain, M.B., Karr, J.R.,
Prestegaard, K.L., Richter, B.D., Sparks, R.E. andStromberg. J.C., (1997): The natural flow regime:a paradigm for river conservation and restoration.
Bioscience 47(11):769–784.
Schleiss, A., De Cesare, G., Jenzer, J. (2008):
Reservoir
sedimentation
andsustainable
development, Presented in CHR Workshop
Erosion, Transport and Deposition of Sediments,
Berne, Switzerland.
Sumi, T. (2003): Reservoir sedimentation
management in Japan, The 3rd World Water
Forum, The 3rd World Water Forum,― 838 ―

Kyoto-Chiga-Osaka., Japan.
Sumi, T. (2000): Future perspective of reservoir
sediment management, Proc. of International
workshop on reservoir sedimentation management,
145-156.
Sumi, T., Murasaki, M., Fujinaga, K., Nagura, Y.
and Tamaki, H., (2004): Study on Measurement of
Erosion-Deposition
ProcessofReservoir
Sediment during Flushing Operation, Annual
Journal of Hydraulic Eng., Vol.48, 1147-1152.
Sumi, T., Murasaki, M., Nagura, Y., Tamaki, H.
and Imaki, 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.
Sumi, T. and Iguchi M., (2005): Technical

Feasibility Study of Sediment Flushing inReservoirs using the RESCON Model. Journal ofJapan Society of Dam Engineers, 15(2), 92-105.
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.
Sumi, T., Kobayshi, K., Yamaguchi, K. and Takata.
Y., (2009): Study on the applicability of the asset
management for reservoir sediment management.
International Congress on Large Dams, Brasilia,
Q.89-R.4.
Takahashi and Sakaguchi, (1976): Takahashi and Y.
Sakaguchi, Rivers in Japan. Kagaku 46 (1976), pp.
488–499 (in Japanese)

日本およびヨーロッパアルプスにおける河川形態および持続可能な貯水池土砂管理計画

Sameh KANTOUSH・角 哲也
京都大学防災研究所

要 旨ヨーロッパアルプス地域のダム貯水池は，流入河川がもたらす土砂の堆積作用によって，その持続可能性が著しく脅かされている。このような貯水池に対する土砂管理計画を，一般化された基準や方策で記述することはなかなか難しい。
本報では，日本とアルプス地域のダムにおける土砂堆積に伴うリスクを定義し，これを適切に計測することを目的としている。特に，総合土砂管理の導入によって，水資源の持続的利用，生物環境の保全，さらには，人間と自然の調和を図るために，健全な河川流域を如何に維持するかが最終的な目的である。土砂管理を成功させるためには，河川マネジ
メントから根本的に変える必要があり，これには，いくつかの対策の組み合わせにより，ダムを通過する水量と土砂量をバランスさせることが重要である。アルプスの大規模貯水池では，密度流が細粒土砂を高濃度で輸送する現象がしば
しば観察され，これを適切に制御することが求められる。

キーワード: アルプス貯水池，ダム堆砂，貯水池土砂管理，土砂管理計画，持続可能な貯水池，ダム影響― 839 ―