Proceedings of ninth International Conference on Hydro-Science andof ICHE2010,
Engineering (ICHE 2010), IITProceedings
Madras, Chennai,
India. IIT Madras, Aug 2-5,2010
PROPAGATIONAND
DEFORMATIONOFFLOODFLOW HYDROGRAPHS
2 - 5 August 2010

IN RIVER WITH A SERIES OF SMALL HYDROPOWER DAMSPROPAGATION AND DEFORMATION OF FLOOD FLOW HYDROGRAPHSIN RIVER WITH A SERIES OF SMALL HYDROPOWER DAMS

Yoshiharu TAKEMURA1 and Shoji FUKUOKA2

Abstract: A series of small hydropower dams have been constructed along gorge sections ofriver in Japan. It is important to study propagation characteristics of flood flow associatedwith the hydropower dams which will be usable for the future flood control management. At
first, we show the effects of the gate operation of small hydropower dams on flood
propagation speed and deformation of discharge hydrographs from observed data in thegorge section of the Agano River. Secondary, we evaluate the storage function of thesereservoirs by using the unsteady one dimensional flow analysis which has developed toconsider the effects of the gate operation.
Keywords: flood propagation; hydropower dam; gate operation; gorge; reservoir;
discharge hydrograph ; flood control project

INTRODUCTION
Frequency and scale of floods are predicted to increase due to the global warming in Japan.
So, the measures for adaptation strategies of flood control against the global warming are
required. Because a storage facility is the most confidential measures to protect people’s life
and their property against flood disasters, it is important to use existing storage facilities
effectively for flood control management.
As a result of modern development of water resources, a series of small hydropower dams
have been constructed along gorge sections of river in Japan. In some rivers, total length of
the reservoirs occupies a large part of the gorge section. Therefore, it will be important to use
these hydropower dams for future flood control management. The above requires us tounderstand the effects of small hydropower dams on flood propagation and to evaluate thestorage function of these reservoirs.
Flood propagation in reservoirs was studied intensively in 1950’s from 1970’s (e.g. Yano &Adachi 1956, Akimoto & Maruoka 1968 and Ozaki & Akimoto 1979). As indicated by thesestudies, flood propagation in reservoirs is affected by gate operation of the dams. Ozaki &1 Department of Civil Engineering, Graduate Student of Science and Engineering, Chuo University, 1-13-27,
Kasuga, Bunkyo-ku, Tokyo, Japan, Email: yoshiharu@civil.chuo-u.ac.jp.
2 Research and Development Initiative, Chuo University, 1-13-27, Kasuga, Bunkyo-ku, Tokyo, Japan, Email:sfuku@tamacc.chuo-u.ac.jp.

1Proceedings of ICHE2010, IIT Madras, Aug 2-5,2010
PROPAGATION AND DEFORMATION OF FLOOD FLOW HYDROGRAPHSIN RIVER WITH A SERIES OF SMALL HYDROPOWER DAMS

Akimoto (1979) illustrated the propagation characteristics of flood flow in a reservoir under
the different gate operations. But, because of the lack of field observed data, most of thesestudies were carried out by experimental channels. So the study based on field observed data
is required for the further understanding. Mitkova et al. (2005) investigated the effects of aseries of small hydropower dams on flood propagation in the Danube River by thehydrological flood routing model. However, because flood propagation is a dynamic
phenomenon, the hydrological flood routing model is not enough to explain the storage
phenomena in reservoirs associated with gate operation of the dams.
The Agano River has a gorge section which continued about 70 km long between the Aizu
Basin and Niigata Plane as shown in Figure 1. In this section, six small hydropower dams areconstructed and the distance of individual dams is about 10 km long (see Figure 2). The
objectives of this study are to understand the effects of the gate operation of smallhydropower dams on flood propagation and to evaluate the storage function of the gorge
section of the Agano River. First, we examine the effects of the gate operation of smallhydropower dams on flood propagation speed and discharge hydrographs based on observed
data which obtained in the reservoirs at 1982 flood, 2002 flood and 2004 flood. Next, toevaluate the storage function of small hydropower dams, we develop the unsteady one
dimensional flow analysis to consider the effects of the gate operation and apply the model tothe gorge section of the Agano River.
GORGE SECTION OF THE AGANO RIVER AND GATE OPERATION OF SMALLHYDROPOWER DAM
Figure 2 is the outline of the section studied. In this section, river width varies from 50 m to
200 m and small hydropower dams, as shown in Figure 3, are constructed continuously along
the river. Table 1 indicates the hydraulic and topographic conditions of these dams. The
Niigata Plane: Hydro power dam
Agano River

Section studied

Kanose dam (65.7km)
Toyomi dam (78.5km)

FLOW

Kaminojiri dam (92.0km)
Aizu BasinYamasato dam (101.8km)

Agekawa dam (51.3km)

Shingo dam (108.8km)

Fig.2 Outline of section studied.

Fig.1 Agano River basin.

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Proceedings of ICHE2010, IIT Madras, Aug 2-5,2010
PROPAGATION AND DEFORMATION OF FLOOD FLOW HYDROGRAPHSIN RIVER WITH A SERIES OF SMALL HYDROPOWER DAMS

Fig.3 Kanose dam.
Table 1 Hydraulic and topographic conditions of hydropower dams.

Elevation (T.P. m)

Dam name
Stora ge capacity
Hight
Normal water laevel
Spare stage
Elevation of dam crest

Shingo da m Yamasato dam Kaminojiri dam Toyomi dam Kanose dam Agekawa dam
22,720 m3
7,591 m3
12,370 m3
18,667 m3
16,525 m3
13,748 m3
27.5 m22.5 m30.0 m34.2 m32.6 m19.0 m161.8 m140.8 m125.5 m105.5 m78.1 m50.5 m160.3 m140.3 m125.0 m104.5 m77.6 m43.5 m152.0 m133.0 m118.0 m95.5 m68.7 m38.5 m

180
160
140
120
100
80
Agekawa dam
60
40
20
50

55

Shingo dam
Kaminojiri dam Yamasato dam: Normal water level
Toyomi dam
Kanose dam

60

65

70

75
80
85
90
Longitudinal distance (km)

95

100

105

110

Fig.4 Longitudinal profiles of section studied and normal water level.
height of these dams is 20 m to 30 m. Figure 4 shows the longitudinal profiles of the section
studied and normal water level (the water level for electricity generation) of the dams. And
water level is observed at just upstream of the dam body in each reservoir shown in Figure 2.
The gate operation of small hydropower dams during flood is illustrated in Figure 5.
Individual dams have the reference discharge for the gate operation called “flood discharge”.
In this section, flood discharge is 3000(m3/s) at all the dams. If inflow discharge of thereservoir is increasing due to flood and predicted to exceed the flood discharge, the waterlevel in the reservoir is lowered to spare stage (pre-lowered water level against flood). Afterthe inflow discharge becomes larger than the flood discharge, there are two different gate
operations. If the inflow discharge is smaller than the capability of the outflow discharge of3

Proceedings of ICHE2010, IIT Madras, Aug 2-5,2010
PROPAGATION AND DEFORMATION OF FLOOD FLOW HYDROGRAPHSIN RIVER WITH A SERIES OF SMALL HYDROPOWER DAMS

Inflow discharge is smaller than flood discharge(reference discharge for gate operation.
Reduce the water level in dam
reservoir.

Floodgate

Spare stage (pre-lowered water level
against flood).

Inflow discharge exceeds flood discharge
Inflow discharge is smaller than capabilityof outflow discharge of flood gate

Inflow discharge is bigger than capabilityof outflow discharge of flood gate
Floodgate

Floodgate

Spare stage

Spare stage

Free flow operation
Floodgate are full opened and outflow
discharge is not regulated .

Constant water level operation
Maintain a constant water level just
upstream of a dam body.

Fig.5. Sketch of gate operation of small hydropower dam.
the dam, the water level just upstream of the dam body is maintained at spare stage. When the
inflow discharge becomes larger than the capability, the flood gates are full opened. In thiscase, flood flow in the reservoir is no longer regulated. In this paper, we call the former
operation “constant water level operation” and the latter “free flow operation”.
EFFECT OF GATE OPERATION OF SMALL HYDROPOWER DAM ON FLOOD
PROPAGATION
For the section shown in Figure 2, large floods in 1982, 2002 and 2004 are investigated inthis paper. Figure 6 shows the outflow discharge hydrographs from the hydropower dams inthese floods. The duration of the free flow operation are indicated by arrows in Figure 6. The
free flow operation was conducted (i.e. flood gates were full opened) at Kaminojiri dam (92.0km) and Agekawa dam (51.3 km) in all the floods. In the duration of the free flow operation,
deformation of the discharge hydrographs is emphasized between Yamasato dam (101.8 km)
and Kaminojiri dam (92.0 km), Kanose dam (65.7 km) and Agekawa dam (51.3 km).
However, deformation of the outflow discharge hydrographs is relatively small between

4Proceedings of ICHE2010, IIT Madras, Aug 2-5,2010
PROPAGATION AND DEFORMATION OF FLOOD FLOW HYDROGRAPHSIN RIVER WITH A SERIES OF SMALL HYDROPOWER DAMS

Shingo dam(108.8km)
Yamsato dam(101.8km)
Kaminojiri dam(92.0km)

6000

Free flow operation(Kaminojiri dam)

Outflow discharge(m3/s)

Outflow discharge(m3/s)

6000
5000
4000
(Flood discharge)

3000
2000

Duration of free flow operation

1000

Toyomi dam(78.5km)
Kanose dam(65.7km)
Agekawa dam(51.3km)

Solid line : Free flow operation
Broken line : Constant water level operation

Free flow operation(Agekawa dam)

5000
4000
3000

(Flood discharge)

2000
Duration of free flow operation

1000

Solid line : Free flow operation
Broken line : Constant water level operation

0

0
18:00

0:00

6:00

12:00

18:00

18:00

0:00

(a)

Outflow discharge(m 3/s)

Outflow discharge(m 3/s)

Free flow operation(Kaminojiri dam)

5000
4000

(Flood discharge)

3000
2000

Duration of free flow operation
Solid line : Free flow operation
Broken line : Constant water level operation

0:00

6:00
Time(hour)

12:00

6000
Free flow operation(Agekawa dam)

5000
4000
3000

(Flood discharge)

2000
Duration of free flow operation

1000

Solid line : Free flow operation
Broken line : Constant water level operation

0

0

(b)

18:00

18:00

0:00

7000
Free flow operation(Kaminojiri dam)

18:00

5000
4000
(Flood discharge)

3000

Free flow operation(Agekawa dam)

6000
Outflow discharge(m3/s)

6000

Duration of free flow operation

1000

12:00

Toyomi dam(78.5km)
Kanose dam(65.7km)
Agekawa dam(51.3km)

7000
Outflow discharge(m3/s)

6:00
Time(hour)

2002 flood (left : Shingo dam～Toyomi dam , right : Toyomi dam～Agekawa dam).
Shingo dam(108.8km)
Yamasato dam(101.8km)
Kaminojiri dam(92.0km)

2000

18:00

Toyomi dam(78.5km)
Kanose dam(65.7km)
Agekawa dam(51.3km)

6000

18:00

12:00

1982 flood (left : Shingo dam～Kaminojiri dam , right : Toyomi dam～Agekawa dam).
Shingo dam(108.8km)
Yamasato dam(101.8km)
Kaminojiri dam(92.0km)

1000

6:00
Time(hour)Time(hour)

Solid line : Free flow operation
Broken line : Constant water level operation

5000
4000
(Flood discharge)

3000
2000

Duration of free flow operation

1000

Solid line : Free flow operation
Broken line : Constant water level operation

0

0
6:00

12:00

18:00

0:00

6:00

12:00

Time(hour)

(c)

6:00

12:00

18:00

0:00

6:00

Time(hour)2004 flood (left : Shingo dam～Toyomi dam , right : Toyomi dam～Agekawa dam)

Fig.6. Discharge hydrographs of hydropower dams in 1982, 2002 and 2004.

5

12:00

Proceedings of ICHE2010, IIT Madras, Aug 2-5,2010
PROPAGATION AND DEFORMATION OF FLOOD FLOW HYDROGRAPHSIN RIVER WITH A SERIES OF SMALL HYDROPOWER DAMS

Table 2. Flood propagation speed in 2002, 2004 floods.
CASE1
Section Studied
Distance
Flood propagation time
Flood propagation speed

2002 flood
2004 flood
2002 flood
2004 flood

CASE2

Shingo dam(108.8km)～
Agekawa dam(51.3km)

Shingo dam(108.8km)～
Toyomi dam(78.5km)

Shingo dam(108.8km)～
Kanose dam（65.7km)

57.5 km
220 min
230 min4.36 m/s
4.17 m/s

30.3 km
100 min
110 min5.05 m/s
4.59 m/s

43.1 km
150 min4.79 m/s

Shingo dam (108.8 km) and Yamasato dam (101.8 km), Toyomidam (78.5 km) and
Kanosedam (65.7 km).
Next, we investigate the effects of these gate operations on flood propagation speed inreservoirs in 2002 and 2004 floods. The flood propagation speed is examined in the section
long as possible, because it is difficult to examine in short section. The flood propagation
speeds in each section are indicated in Table 2. In Table 2, CASE 1 indicates the flood
propagation speed in the section which includes both Kaminojiri dam (92.0 km) andAgekawa dam (51.3 km) (i.e. include two dams conducted free flow operation). CASE 2
indicate the speed in the section which includes Kaminojiri dam (92.0 km) and doesn’t
include Agekawa dam (51.3km) (i.e. include one dam conducted free flow oeperation). Floodpropagation speed in each section indicated in Table 2 is calculated by the following process.
First, we examine the time lag of the occurrence of a maximum discharge between the upper
end and lower end of each section from the time series data of the outflow discharge andrecord of the gate operation. And we define the time lag as the flood propagation time in eachsection. Also, because it is difficult to determine a maximum discharge at Kanose dam (65.7km) in 2004 flood from the data, the flood propagation time and flood propagation speed
between Shingo dam (108.8 km) and Kanose dam (65.7 km) in 2004 flood are excluded fromthis investigation (diagonal lines are drawn in Table 2). As shown in Table 2, flood
propagation speed of CASE 1 is smaller than that of CASE 2. It means that the free flow
operation delays flood propagation in the reservoirs compare with the constant water level
operation.
UNSTEADY ONE DIMENSIONAL FLOW ANALYSIS IN THE RIVER WITHSERIES OF HYDROPOWER DAMS
To evaluate the storage function of the gorge section of the Agano River, we develop theunsteady one dimensional flow analysis to consider the effects of the gate operation of smallhydropower dams and apply the model to the 2004 flood in the section shown in Figure 7.
The section-integrated continuity and momentum equation are shown as equation (1) andequation (2), respectively. And equation (3) is the force acting on a dam body and flood gates6Proceedings of ICHE2010, IIT Madras, Aug 2-5,2010
PROPAGATION AND DEFORMATION OF FLOOD FLOW HYDROGRAPHSIN RIVER WITH A SERIES OF SMALL HYDROPOWER DAMS

as defined in Figure 8.
A Q

0
t x

(1)

 Q
QV
H
n 2V 2  gA gA 4 / 3

t
x
x
R






Q
QV
n 2V 2
F
1

2


 
B  gh  dy  gA 4 / 3 
 t
x

x  2Rx  xi 



xx

(2)

i

1
1

F  K P  B  g ( H  H u ) 2  g ( H 2  ( H  H d ) 2 ) dy
2
2



(3)

Where A = cross-sectional area, V = section-averaged velocity, Q = discharge, H = waterlevel, h = water depth, R = wetted perimeter, B = river width on water surface,  = water
density, g = gravity acceleration, n = Manning’s roughness coefficient, F = force acting on
dam body and flood gates, xi = position of dam body.
The derivation of equation (2) and (3) are shown in Figure 8. First, we assume that river bed
is flat and set the control volume as Figure 8. Equation (2) is derived from the assumption ofhydrostatic pressure distribution and uniform velocity in cross sections. The force acting on a
dam body and flood gates are given by hydrostatic pressure distribution and dimensionlessparameter Kp as shown in Figure 8. Kp means the deviation of pressure distribution fromhydrostatic pressure distribution on the dam body and flood gates. Where P = pressure, Hd =elevation of dam crest, Hu = bottom elevation of flood gates.
The calculation process is shown in Figure 9. Upstream and downstream boundary
conditions are given by the time series data of the outflow discharge from Shingo dam (108.8km) and observed water level just upstream of Toyomi dam body, respectively. Dimension
less parameter Kp is adjusted as the calculated water level correspond to the observed waterlevel at the points indicated by open dots in Figure 7. In this study, Kp varies from 1.0 to 1.35
during flood. And, we give the Manning’s roughness coefficient 0.04 uniformly in the section
shown in Figure 7.
：water level observation
Toyomi dam(78.5km)flow
Shingo dam(108.8km)
Kaminojiri dam(92.0km)Yamasato dam(101.8km)

Fig.7 Plan form of section analyzed and observed points of water level7

Proceedings of ICHE2010, IIT Madras, Aug 2-5,2010
PROPAGATION AND DEFORMATION OF FLOOD FLOW HYDROGRAPHSIN RIVER WITH A SERIES OF SMALL HYDROPOWER DAMS

Control volume flood gateflow

・Outflow discharge data
・Gate operation record
・Observed water levelYdam body: velocity(plan view)
Control volume
flood gate

Roughness distributionX: water level

flow

Boundary conditonF

Equation of continuity

P
P
Z

Time series data
・Upstream discharge
・Downstream water level
・Gate opening ratio
・Water level near dam body
Topography data
・Cross-section

Water level near dam body

Hu H

F

Equation of motion

HdX
river bed
(longitudinal view)

Adjustment of Kp

Result of analysis

dam body

Fig.8 Concept of analysis forflow over the dam.

Fig.9 Flowchart of the analysis.

RESULTS OF ANALYSIS AND DISCUSSION

Figure 10 shows the observed and calculated outflow discharge hydrographs from thehydropower dams in 2004 flood. In Figure 10, the calculated outflow discharge becomes
smaller than the observed discharge during the flood. It is the main reason that the lateral
inflow in the section shown in Figure 7 is neglected in this analysis. However, deformation of
the calculated discharge hydrographs are relatively large between Yamasato dam (101.8 km)
and Kaminojiri dam (92.0 km) in the duration of free flow operation indicated by allows in
Figure 10 and relatively small in the other duration. This tendency agrees with that of theobserved discharge hydrographs shown in Figure 6.
Figure 11 shows the temporal changes of the calculated water level profiles in the reservoirs
in the rising-discharge phase. In the reservoirs with constant water level operation (Yamasato
dam (101.8 km) and Tyomi dam (78.5 km)), the water level is rising as discharge increase in
the upstream part of the reservoirs, but remained almost constant at the downstream as shownin Figure 11. So, flood flow is stored only in the upstream part of the reservoirs with constantwater level operation. On the other hands, in the reservoir with free flow operation(Kaminojiri dam (92.0 km)), the water level profiles become relatively mild due to thebackwater effects of the dam body and change almost in parallel as shown in Figure 11. This
indicates that the storage volume of flood flow in the reservoir with the free flow operation islarger than that with the constant water level operation.

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Proceedings of ICHE2010, IIT Madras, Aug 2-5,2010
PROPAGATION AND DEFORMATION OF FLOOD FLOW HYDROGRAPHSIN RIVER WITH A SERIES OF SMALL HYDROPOWER DAMS

Table 3 is the attenuation ratio of the maximum discharge in each reservoir. The attenuation
ratio is defined the ratio of the attenuation of a maximum discharge in each reservoir to the
maximum discharge of Shingo dam. As shown in Table 3, the attenuation ratio in Yamasato
dam (101.8 km) and Kanose dam (78.5 km) is only about 0.1 %. On the other hand, theObserved outflow discharge (Shingo dam 108.8km)
Observed outflow discharge (Yamasato dam 101.8km)
Observed outflow discharge (Kaminojiri dam 92.0km)
Observed outflow discharge (Toyomi dam 78.5km)

Caluculated outflow discharge (Shingo dam 108.8km)
Caluculated outflow discharge (Yamasato dam 101.8km)
Caluculated outflow discharge (Kaminojiri dam 92.0km)
Caluculated outflow discharge (Toyomi dam 78.5km)

6000

Free flow operation(Kaminojiri dam)

outflow discharge(m3/s)

5000
4000

(Flood discharge)

3000
2000

Duration of free flow operation

1000
0
6:00

12:00

18:00
0:00
Time (hour)

6:00

12:00

Fig.10 Observed and calculated outflow discharge hydrographs.

Elevation (T.P.m)

Constant water level operation(Toyomi dam reservoir)

Constant water level operation
Free flow operation(Kaminojiri dam reservoir) (Yamasato dam reservoir)

150

2hour

140

4hour

130

6hour

120

8hour

dam body
110

10hourdam body
100
90
80

12houraverage river bed

dam body
78.5
83.5

average elevationof river bed
88.5

93.5
98.5
Longitudinal distance(km)

103.5

108.5

Fig.11 Temporal changes of water level profiles in reservoirs.
Table 3. Attenuation Ratio of maximum discharge in reservoirs.
Attenuaton ratio of maximum discharge
Yamasato dam(101.8km)
Kaminojiri dam(92.0km)
Toyomi dam(78.5km)
Constant water level
Free flow
Constant water level
0.1
1.46
0.14

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Proceedings of ICHE2010, IIT Madras, Aug 2-5,2010
PROPAGATION AND DEFORMATION OF FLOOD FLOW HYDROGRAPHSIN RIVER WITH A SERIES OF SMALL HYDROPOWER DAMS

attenuation ratio in Kaminojiri dam (92.0 km) reaches about 1.46 %. Because the effects ofthese hydropower dams are integrated and propagate to downstream, it is important toconsider the effective use of the hydropower dams.
CONCLUSIONS

There are two different gate operations for small hydropower dam during flood. We
investigated the flood propagation in the reservoirs associated with these gate operations. The
primary conclusions are indicated below.
1 It was shown that the free flow operation delays the flood propagation and deforms thedischarge hydrographs in the reservoirs compare with the constant water level operation fromthe observed data in the large floods in the gorge section of the Agano River.
2 We investigated the effect of the gate operation of small hydropower dams on temporalchanges of longitudinal water level profiles and the attenuation ratio of a maximum discharge
in the reservoirs by using the unsteady one dimensional flow analysis method which had
developed to consider the gate operations.
References
Akimoto, T, Maruoka, K, 1968, proceedings of the Japanese conference of hydraulics, 12,
43-48.
Ozaki, Y, Akimoto, M, 1979, On the behavior of flood wave passing through a reservoir,
proceedings of the Japanese conference of hydraulics, 23, 27-33.
Yano, K, Adachi S, 1956, Experimental study of the propagation of flood wave throughreservoir, deserter prevention research institute bulletin memorial issue of fifth anniversary,
211-219.
Mitkova ,V, Pekarova, P, Miklanek, P, Pekar, J. 2005. Analysis of flood propagation change
in the Kienstock-Bratislava of Danube River, Hydrological Sciences Journal 50(4): 655668.

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