ISPIV2017

The 12th International Symposium on Particle Image Velocimetery
June 19 (Mon) – 21 (Wed), 2017 / Grand Hotel, Busan, Korea

Effects of Spanwise Width of Expansion Area in Open-channel Flow
on Resting Characteristics of Oikawa, Zacco platypus
Kouki Onitsuka1, Juichiro Akiyama2 and Kousuke Izumi2
1 Department of Civil Engineering, Kyushu Institute of Technology, Kitakyushu, Japan

onitsuka@civil.kyutech.jp
2 Department of Civil Engineering, Kyushu Institute of Technology, Kitakyushu, Japan

ABSTRACT
1. INTRODUCTIONConditions for fish to live in the river are to secure the flow of a river, water quality, feed, spawning ground, circular path,refuge, and to protect from natural enemies [1]. Even among them, this study focuses on securing the refuge. Fish has the redand ordinary muscle. Fish usually uses the red muscle and doesn’t use the ordinary muscle because fish gets tired [1]. However,when the flow velocity in a river increases and there is a risk of being preyed, fish uses the ordinary muscle, so it is importantto supply the refuge of low-velocity in order to rest. Some researchers investigated how to use the refuge for fish in such asfloods and the calm water. In the case of floods, it was confirmed that when water in a river rises, fishes take refuge in thewand [2]. Also, it is observed that when the artificial flood accrues in the experimental river, larva fish takes refuge in wand[3]. On the other hand, in the case of calm water, it was found that when there are concave areas such as the groyne, the wand,and the vegetation in a side riverbank, low velocity area occurs, so fishes use there as refuges and spawning ground [4-7].
Therefore, fishes rest in low velocity area in the river. However, hydraulic quantity such as velocity in low velocity area has
not been investigated. Also, suitable geometric shape of the rest area has not been investigated. In this study, resting
characteristics of Oikawa (Zacco platypus) with changing spanwise width of expansion area and the flow velocity wasresearched. Furthermore, deep pools and rapids are also resting area for fish, however, the purpose of this study is to research
resting characteristics of Oikawa which use the low velocity area caused by river structures such as groyne.
2. MATERIALS AND METHODS
Figure 1 shows the open-channel. It was designed as the following. Pool length (L) was 2.0m and width (B) was 0.8m. x
and z are the coordinates of the streamwise vertical and the spanwise directions, respectively. In expansion area, length ofstreamwise (Ls) is 1.2m and width is Bs. This channel is three areas composed of “upstream area”, “main channel”, and“expanded area”. “upstream area” is the area above main channel (-0.8<x<0.0m, 0<z<0.4m) , and “expanded area” is the areaof the right bank from main channel (0.0<x<1.2m, z<0m).
Table 1 shows experimental case. Flow velocity divided by averaged body length of Oikawa ( U m BL ) was set to fourpatterns within the range from 2 to 10 (1/s). Spanwise width of expansion area was set to three patterns within the range from0.2 to 0.4 (m). The depth of water in this open-channel was about 0.07m in all area. Also, the water temperature was about
20°C in all cases. The recording has been carried out 20 cases in each pattern and 240 cases in total. Averaged body length
was about 70mm. A circular wire net of 0.25m in diameter is set up the boundary line (x=1.0m) between main channel andexpanded area and 10 fishes are inserted. After it is confirmed that Oikawa settled down for 5~10s, the circular wire net istaken up. Further, trajectory of Oikawa was recorded for 120s with a digital video camera set up the upside of the openchannel. The number of pixel of the digital video camera is 1440×1080, and recording speed is 30fps. The swimming positionsof Oikawa were obtained with the aid of the digital video camera. Also, the velocity is measured by three dimensional
electromagnetic flowmeter in this open-channel.
3. RESULT AND DISCUSSION
The ground speed was defined as swimming speed of fish school to the ground and VE BL is that ground speed divided
by averaged body length of Oikawa. Figure 2 shows averaged ground speed of fish school ( VE BL ) in expanded area. When

Table 1 Experimental caseflow

top view

upstreamU m / BL (1/s)

z

B=0.40m

248100.2C02-2

C02-4

C02-8

C02-10

0.3

C03-2

C03-4

C03-8

C03-10

0.4

C04-2

C04-4

C04-8

C04-10main channel

initial position of fishx

Bs (m)

expanded area

Bs

Ls=1.2m
L=2.0mFigure 1 Open-channel
203

VE
BEL
V

35

Opsariichthys
platypus
Zacco
Platypus
Zacco
ZaccoPlatypus
Platypus

Um/Bl=0.5(1/s)
U
Um/Bl=0.5(1/s)
m BL  2(1/s)
Um/Bl=2.0(1/s)
Um/Bl=2.0(1/s)
Um BL  8(1/s)

Um/Bl=1.2(1/s)
U m B L  4(1/s)
Um/Bl=1.2(1/s)
Um/Bl=2.5(1/s)
U m BL  10(1/s)
Um/Bl=2.5(1/s)

BL2

Um/Bl=2.0(1/s)
Um/Bl=2.0(1/s)
Um BL  8(1/s)

Dz

Um/Bl=2.5(1/s)
U
Um/Bl=2.5(1/s)
m BL  10(1/s)

23
1.5

1.5
10
15
0.5

0

Zacco
Platypus
Opsariichthys
platypus
Zacco
Platypus
Zacco
Platypus
U
Um/Bl=0.5(1/s)
Um/Bl=1.2(1/s)
U
Um/Bl=0.5(1/s)
Um/Bl=1.2(1/s)
m B L  4(1/s)
m BL  2(1/s)

VE
Dx
BL200.230 BBsS(m)400.3(m) 0.4

Bs (cm)Figure 2 Averaged ground speed offish school in expanded area

10U m BL  10(1 /s)

62
140.51200

Zacco
Platypus
Opsariichthys
platypus

DGBL

20
20
0.2

30
30
0.3

4040
BBSs (m)(m) 0.4

Bs (cm)0200.230
0.4
0.3 BS (m) 40

BS (cm)Figure 3 Fish school length ratio
in expanded area

Figure 4 Averaged distance between theupstream wall at expanded areaand fish school
spanwise width of expanded area (Bs) or low velocity increases, ground speed of fish school in expanded area decreases. Thisis suspected that Oikawa rests in expanded area. Fish school length ratio ( Dx Dz ) is defined as that averaged fish school of x
direction divided by averaged fish school of y direction. Figure 3 shows fish school length ratio ( Dx Dz ) in expanded area.
In case of narrow expansion width, the form of fish school in expanded area is long and narrow form, however, when spanwise
width of expanded area increases, the form becomes nearly circular form. Figure 4 shows averaged distance between theupstream wall at expanded area and the center of gravity of fish school. With the increase of expansion width, fish school
rests in the downstream of expanded area. Therefore, it was found that when resting area or expansion width is narrow, it
requires enough long length of the flowing direction in low velocity area.
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