The 11th Pacific Symposium on Flow Visualization and Image Processing
1-3 December 2017,Kumamoto, JAPANEFFECTS OF BOULDERS LOCATIONS OVER POOL BED
IN POOL-AND-WEIR FISHWAY ON MIGRATION RATE OF ZACCO PLATYPUS
K. Onitsuka1, J. Akiyama1 and R. Ogata1
1Department of Civil and Architectural Engineering, Kyushu Institute of Technology
1-1 Sensuicho, Tobata-Ku, Kitakyushu 804-8550 Japan

ABSTRACT
It is important to keep suitable area by boulders in pooland-weir fishway to make the migration rate of fish high. In
this study, migrating behaviors of Zacco platypus in pooland-weir fishway were compared with locations of boulders
placed on the bottom of pool-and-weir fishway changed.
Migration behaviors of Zacco platypus were obtained withthe aid of two digital video cameras. It was found that
Zacco platypus migrates remarkably uses the space between
boulders when boulders were placed on the upper bottom inthe pool. It is because the velocity of space between
boulders is low compared to other space.

flow

x

zy

yHz

BLx

INTRODUCTION
Dam is constructed for the purpose of water control
and water utilization. However, dam blocks fish’s
migration that seeks to upstream. This is a problem for
migratory fishes in river. Therefore, fishway isconstructed in their rivers in order to comfort migration offishes. Nakamura (1995) has reported that the most of
fishway in Japan is pool-and-weir fishway. Pool-and-weirfishway has notch at the weir wall. Width of notch is
generally twenty or thirty percent of the weir wall’s one.
In calm river, over flow arise from only notch, so there ishigh velocity flow at point of fall. Sanz-Ronda et al.
(2015) have shown that fish’s swimming speed is roughlyclassified into two types: sustained speed and burst speed.
The latter causes fatigue. In case of migration at pool-andweir fishway, fish sometimes uses burst speed. Therefore,
it is necessary to keep resting area in the pool (seeNakamura, 1995). One of the method is an establishmentof boulders. In Aki-gawa River, it was confirmed thatboulders has affected kind and number of the migrated
fish (see Kaneko et al., 1997, Takasaki et al., 1999). Itwas confirmed that the large size boulders at bottom ofpool decreases the time for migrating (see Santos et al.,2013, Santos et al., 2014). Miyazono & Tomatsu (2003)
found that Salvelinus leucomaenis leucomaenis goes
through around boulder for migration. Onitsuka et al.
(2016) found that Zacco platypus swims between boulders.
Aoki et al. (2015) found that decrease of the crosssectional flow area hinders migration of Tribolodon
hakonensis.
It is necessary to investigate boulder’s effect on
migrating behaviors of Zacco platypus in the pool.
Besides, making suitable area in easy way is important. In
this study, migrating behaviors of Zacco platypus in pooland-weir fishway were compared with the locations ofboulders placed on the bottom of pool-and-weir fishwaychanged.

Figure 1, Pool-and-weir fishwayΔz(a)non(b)

alld=0.15m

(c)

lower

(d)

upper

Figure 2, Boulders location over pool bed
Table 1. Experimental caseQ(l/s)
13boulders area

nonall
lower
upper

noQ1
alQ1
loQ1
upQ1

noQ3
alQ3
loQ3
upQ3

5
noQ5
alQ5
loQ5
upQ5

The 11th Pacific Symposium on Flow Visualization and Image Processing
1-3 December 2017,Kumamoto, JAPAN

noQ1

1.0

alQ1
allQ1

1.0

doQ1
loQ1

1.0z
Bz
Bz
Bz
B

0.6

0.6

0.6

0.6

0.4

0.4

0.4

0.4

0.2

0.2

0.2

0.2

0.0

0.2

(a)

0.4

0.6

x L 1.00.0

noQ1

0.2

0.4

(b)

0.6

0.0

x L 1.0

0.2

alQ1

noQ5

1.0

0.0

0.0

0.0

0.0

alQ5
allQ5

1.0

upQ1

1.0x L 1.0

0.4

0.6

(c)

loQ1z
Bz
Bz
B

0.6

0.6

0.6

0.6

0.4

0.4

0.4

0.4

0.2

0.2

0.2

0.2

0.0

0.2

(e)

0.4

0.6noQ5x L 1.0

0.0
0.00.20.40.6(f)alQ5x L 1.00.20.4(g)x L 1.0

upQ1upQ5VV m s 0.6x L 1.0

loQ50.00.2

0.40.6(h)upQ5x L 1.0

0.60
0.60

0.30
0.30

000.6

0.0

0.0

VV (m/s)

0.0

0.4

1.0z
B

0.00.2(d)
doQ5
loQ5

1.00.0Figure 3. Flow velocity ( VV ) at the bottom of second pool in pool-and-weir fishway
EXPERIMENTAL SETUP AND CONDITION
Figure 1 shows pool-and-weir fishway. It is designed
following. Pool length (L) is 0.9m and width (B) is 0.8m.
The pool is connected in a staircase pattern. Thickness ofthe partition wall (Δx) is 0.2m, pool drop (Δy) is 0.15m andnotch width (Δz) is 0.16m. Height from the pool bottom to anotch bottom (H) is 0.3m. Pool number is in ascendingorder toward upstream. Figure. 2 shows location ofboulders which is inserted in second pool. In this study, theshape of boulder is a spherical (see Miyazono et al, 2005).
20 Zacco platypus average length B L =70mm are put into
the second pool. The locations of boulders are 4 patterns.
Table. 1 shows experimental cases. Discharge (Q) is set to3 patterns within the range from 1 to 5(l/s). Experiments are
performed 12 cases in total. After it is confirmed that theisolated Zacco platypus settled down, recording is beganwith the video camera from the left side wall and the upper
part of this fishway for 30 minutes. The number ofmigration and swimming position, was analyzed afterrecording. Further, the flow velocity VV was measured
using 3D electromagnetic velocity meter.

EXPERIMENTAL RESULTS AND ANALYSIS
Hydraulic properties at the bottom of pool
Figure 3 shows flow velocity VV at the bottom(y/h=0.25) of second pool in this pool-and-weir fishway
for 8 case (noQ1, alQ1, loQ1, upQ1, noQ5, alQ5, loQ5,upQ5).

0.5

nmN

nonall
lower

0.3

upper

0.2
0.1
01
3 Ql s  5
Figure 4, Migration rate of Zacco platypus
Figure 3 (a), (b) show that there are the uniform flowat the bottom of pool in the case noQ1 and there are thefast flow at some points on the bottom of pool in the case
alQ1. It is assumed that the placed boulders bring about
decrease of the cross sectional flow area. Figure 3 (d)shows that there are the fast flow nearby boulders at thebottom of pool in the case upQ1.
Figure 3 (f), (g) (h) show that there are the low
velocity flow area nearby boulders at the bottom of poolin the cases (alQ5, loQ5 or upQ5).
There are fast flow along the right side wall in eachlocation patterns of boulders at Q=5(l/s), so the area
( 0  x L  1.0 , 0  z B  0.2 ) is defined as high velocity
flow area.

The 11th Pacific Symposium on Flow Visualization and Image Processing
1-3 December 2017,Kumamoto, JAPAN
1.0

1.0

1.0

noQ1zBzBz
B

0.6

0.6

0.6

0.4

0.4

0.4

0.2

0.2

0.2

0

0
0

0.2

0.4

(a)

x L

0.6

0

1.0

0.2

noQ1

0.4

(b)

1.0

0x L

0.6

0

1.0

1.0z
B

0.6

0.6

0.6

0.4

0.4

0.4

0.2

0.2

0.2

0.2x L

0.4

0.6

(d)

alQ1

1.0

00

1.0

0.2

0.4(e)

x L

0.60z
B

0.6

0.6

0.6

0.4

0.4

0.4

0.2

0.2

0.2

0.2

x L

0.4

0.6(g)

loQ11.0

1.0

00.2

0.4

x L

0.6

01.0

loQ3

1.0upQ3z
B

0.6

0.6

0.6

0.4

0.4

0.4

0.2

0.2

0.2

0.20.4(j)

x L

0.6

upQ1

0.4

0.6

00.2

0.4(k)x L

1.0

upQ500

1.0

0.2

1.0z
B0

1.0(i) loQ5z
B0x L

doQ5
loQ500(h)upQ10.6

alQ5

1.0

doQ3
loQ3z
B00.4(f)zB00.2

alQ3

1.0

doQ1
loQ1

1.0

alQ5

01.0x L

0.6

noQ5

alQ3z
B00.4(c)z
B00.2

noQ3

1.0

alQ1

noQ5

noQ3x L

0.6

1.0

upQ300.2

0.4

0.6x L1.0(l) upQ5
n N

Figure 5, Projection chart of the existence rate
Migration rate of Zacco platypus
Migration rate was defined as following equation.
Migration rate =Number of fish that succeeded in migration nm(1)Number of fish that used to experiment N (  20)
Figure 4 shows the correlation between discharge Q (l/s)
and migration rate of Zacco platypus. The migration rate
shows higher values in the pattern upper than any othercase.
Change of the swimming properties in the pool
The horizontal section of the second pool is divided
into the x direction, y direction in the range of the interval
between 0.09m and 0.08m. The number of Zacco platypus

each area every 10 seconds is counted, and the average
number of Zacco platypus ( n ) is calculated. Figure 5
shows existence rate of Zacco platypus each case athorizontal section (x-z). Figure 5(a) shows that small valueof the existence rate ( n N ) spreads to the pool in the casenoQ1. Figure 5(d) shows that large value of the existencerate ( n N ) is dense on the center of second pool in thecase alQ1. Figure 5(g), (j) show results like figure 5(d).
The small existence rate ( n N ) is distributed to the upper
notch more in the case upQ1 than the case loQ1.
Figure 5(a)-(c) show that the existence rate ( n N ) is
distributed to the upper notch of second pool more on highThe 11th Pacific Symposium on Flow Visualization and Image Processing
1-3 December 2017,Kumamoto, JAPAN

44444

nonnon
all non
all

Rx
lower
all
Rz lower
lower
upper
BLL upper

BLRRx yBBLL

upper

22 2

22

1111100

01133 Ql s  55

1(a)x 3axis

(a)

non

non
non
all
all
lower
lower
upper
upper

44

nonRRx z
BBLL

all

lower
lower
upper
upper

22

1

10
13 Ql s  5051 (b) y axis
35Figure 6, Radius of fish school at x, y, z directions

00non
all

1(b) all(c) lower
Figure 7, Swimming frequency of Zacco platypus in y direction

discharge Q=5(l/s) than low discharge Q=1(l/s) in thepattern non. Figure 5(d)-(f) show that large value of theexistence rate ( n N ) is dense on the center of second pool
within the all discharge Q=1, 3, 5(l/s) in the pattern all.
Figure 5(g)-(i), (j)-(l) show that the distribution of theexistence rate ( n N ) spreads to x axis direction in thepatterns lower and upper when discharge is large (Q=3,5(l/s)).
Figure 6(a)-(c) show relations between radius of fish
school in x, y, z directions ( R x , R y , Rz ) divided byaverage length BL and discharge Q. Figure 6(a) showsthat the remarkable change of x radius ( Rx BL ) bychanging discharge is not observed in the pattern non. The
remarkable change of x radius ( Rx BL ) by the dischargechange is not observed in the pattern all and this x radius( Rx BL ) is lowest of the all patterns (non, all, lower,upper). The larger discharge Q (l/s) is, the higher the x
radius ( Rx BL ) is in the patterns lower and upper.
Figure 6(b), (c) show that the remarkable change of yand z radius ( R y BL , Rz BL ) by changing discharge is
not observed in the all patterns (non, all, lower, upper).
When discharge Q (l/s) is larger, the fish spreads to the xdirection, so fish gets less chance of swimming on highvelocity flow area in the patterns lower and upper.
Swimming level of Zacco platypus
Figure 7 shows swimming frequency of Zacco
platypus in y direction ( n y N ) for each boulders location

3 Ql s  51(c)z axis3(d)5upperpatterns. The frequency ( n y N ) above y/h=0.5 at
Q=5(l/s) is larger than Q=1, 3(l/s) in the pattern of non(Figure 7(a)), so increasing discharge raises swimming
level of Zacco platypus in this pattern. The frequency( n y N ) above the top of boulder at Q=1(l/s) is large, but
the frequency ( n y N ) under the top of boulder at Q=3,5(l/s) is large in the pattern all (Figure 7(b)). This result issuggested that Zacco platypus rests at the low velocity
area nearby boulder to avoid fast flow by increasing
discharge.
Increasing discharge raises the frequency ( n y N )above the top of boulder in the pattern of lower (Figure7(c)). The frequency ( n y N ) under the top of boulder at
each Q is large in the pattern of upper (Figure 7(d)), so
Zacco platypus swims between boulders in this pattern.
Change of migration route by boulders locations
Figure 8 shows the example of the 20 seconds
migration route in each case at horizontal section (x-z).
Boulders area is marked gray color. Fish migrates alongthe right side wall in the patterns non and lower. Thesemigration routes are within the high velocity flow area.
Fish migrates on oblique routes for the right side wall in
the patterns all and upper. Therefore, the migration routesof the patterns all and upper are shorter than the patterns
non and lower in the high velocity flow area( 0  x L  1.0 ，0  z B  0.2 ). Thus, it is that fish uses low velocity flow
area nearby boulders for migration in the patterns all andThe 11th Pacific Symposium on Flow Visualization and Image Processing
1-3 December 2017,Kumamoto, JAPAN

1.01

1.01

nononz
0.8
B

all
allz
0.8
B

1.01

downstream
lower

z
0.8
B

1
1.0

0.6

0.6

0.6

0.6
0.6

0.4

0.4

0.4

0.4
0.4

0.2

0.2

0.2

0.2
0.2

000

0.2

0.4
0.4

(a)

non

0.6

0.8
x L

1.0
1

000

0.2

0.4
0.4

0.6

0.8
x L

1.0
10

upstream
upperz
B

0.8

00

0.2
0.2

0.4
0.4

0.6
0.6

x L
0.8

1.0
100

00

0.2
0.2

0.4
0.4

0.6
0.6

0.8
x L

1.0
1

:boulders area(b)all(c)lower(d)upper

Figure 8, Migration routes at horizontal section (x-z)
0.7

upper. It was confirmed that Salvelinus leucomaenis
leucomaenis goes through around boulder for migration(2003). In this study, this experiment provide a similar
result.
The number of all data is NV =40 when the data isanalyzed 20s before migrating every 0.5s. The number ofdata for each flow velocity VV on passage points in 20s
before migrating nV is defined. The frequency
distribution every flow velocity on the migration routenV NV shows a most remarkable tendency within
discharge Q=5(l/s) than Q=1, 3(l/s) since the flow velocity
difference is largest on Q=5(l/s) in this study, so thedischarge Q=5(l/s) is adopted. Figure 9 shows thefrequency distribution every flow velocity on themigration route nV NV in the cases (noQ5，alQ5，loQ5,upQ5). In the cases (noQ5, loQ5), the frequency nV NV
has a maximum value on VV =0.25，0.3(m/s). In the cases(alQ5, upQ5), the frequency nV NV has a maximumvalue on VV =0.15 ， 0.1(m/s), so there are the more
frequency nV NV on the low velocity flow area in thecases (alQ5, upQ5) than cases (noQ5, loQ5). It is
understood that fish swims on a low VV area in the cases(alQ5, upQ5). Figure 3 (e)-(h) and Figure 8 show
migration routes of the patterns all and upper are shorter
than the patterns non and lower in the high velocity flowarea( 0  x L  1.0 ， 0  z B  0.2 ). Therefore, migratingon the oblique route for the right side wall gives a little
fatigue to fish. Thus, it is thought that migration rate hashigher value on the large discharge Q=3, 5(l/s) in thepattern upper than the patterns non and lower.

CONCLUSIONSIn this study, migrating behaviors of Zacco platypus in
pool-and-weir fishway were compared with the locationsof boulders placed on the bottom of pool-and-weirfishway changed. The knowledge that this study provided
is as follows.
(1) When boulders are placed on the bottom of all area inthe pool, Zacco platypus swims in a small area
nearby center of the pool.

nVNV

noQ5

0.5

loQ5alQ5

upQ5
0.4
0.3
0.2
0.10VV m0.45s  0.5
0.1 0.15 0.2 0.25 0.3 0.35 0.4

Figure 9, Frequency distribution every flow velocity
on the migration routes(2) When boulders are not placed on the bottom andplaced on the bottom of lower in the pool, Zacco
platypus migrates along the right side wall.
(3) When boulders are placed on the bottom of upper inthe pool, increasing discharge, Zacco platypus rests inthe low velocity flow area nearby boulders. Therefore,Zacco platypus migrates on oblique route for the rightside wall.
NOMENCLATURE
B pool width, m
L pool length, mH height from the pool bottom to a notch bottom, mΔx thickness of the partition wall, mΔy pool drop, mΔz notch width, mB L Zacco platypus average length, mVV flow velocity, m/s
Q discharge, l/s
n m number of fish that succeeded in migration
N number of fish that used to experimentn average number of Zacco platypus each area every 10
seconds was counted

The 11th Pacific Symposium on Flow Visualization and Image Processing
1-3 December 2017,Kumamoto, JAPANR x , R y , R z radius of fish school at x, y, z directions, mn y N swimming frequency of Zacco platypus in ydirection
NV number of all data analyzed 20s before migrating
every 0.5s
nV number of data for each flow velocity VV on passage
points in 20s before migrating

ACKNOWLEDGEMENTS
This study was supported by Grants-in-aid for
Scientific Research (17K06580) when the study conducts.
REFERENCES(1) Nakamura, S. (1995): “Gyodou no Hanashi”,
Sankaidou, pp. 42-49.
(2) Sanz-Ronda, F.J., Ruiz-Legazpi, J. Bravo-Córdoba, F.
J., Makrakis, S. and Castro-Santos, T. (2015):“Sprinting performance of two Iberian fish:
Luciobarbus bocagei and Pseudochondrostoma
duriense in an open channel flume”. EcologicalEngineering, Vol. 83, pp. 61-70.
(3) Kaneko, Y., Izumi, K., Tsuchiya, M. and Otake, Y.
(1997): “Hydraulic Characteristics and Ascending
Effectiveness of the Fishways in Akigawa River”.
Annual Journal of Hydraulic Engineering, Vol. 41,
pp. 265-270.
(4) Takasaki, T., Tsuchiya, M. and Otake, Y. (1999):“Efficiency of the Complex Style Fishways for Fish
Migration Behavior in Aki-gawa River”. Advances inRiver Engineering, Vol. 5, pp. 165-170.

(5) Santos, J.M., Branco, P., Silva, A.T., Katopodis, C.,
Pinheiro, A., Viseu, T. and Ferreira, T. (2013):“Effect of two flow regimes on the upstream
movements of the Iberian barbell (Luciobarbusbocagei) in an experimental pool-type fishway”.
Jounal of Applied Ichthyology, Vol. 29, pp. 425-430.
(6) Santos, J.M., Branco, P., Katopodis, C., Ferreira, T.
and Pinheiro, A.T. (2014): “Retrofitting pool-andweir fishways to improve passage performance ofbenthic fishes”. Ecological Engineering, Vol. 73, pp.
335-344.
(7) Miyazono, M., and Tomatsu, O. (2003):“Arrangement of Protruding Boulders in a SlantedFishway”. Jounal of the Japan Society of Erosion
Control Engineering, Vo56, No.1, pp. 3-12.
(8) Onitsuka, K., Akiyama, J., Shishido, A., Takamatsu,S., Kadota, Y. and Arisuda, T. (2016): “Effects ofBoulder over Pool Bed on Migration Rate in Pool-andweir Fishway”. Annual Jounal of HydraulicEngineering, Vol. 72, No.4, I_1135-I_1140.
(9) Aoki, M., Mukai, T., Kikuchi, Y. and Matsuki, K.
(2015): “On the Effect of the Fish Behavior on Gravel
Deposit in a Pool-and-weir-fishway”. Annual Jounalof Hydraulic Engineering, Vol. 71, No.4, I_1099I_1104.
(10) Miyazono, M., Takauji, T. and Tomatsu, O. (2005):“Hydraulic Chracteristics and Natatorial Action ofFish Around Boulders”. Jounal of the Japan Societyof Erosion Control Engineering, Vo57, No.5, pp. 1524.