INFLUENCES OF RIVER CHANNEL PLANAR SHAPES ON CHARACTERISTICS
OF FISH HABITAT IN SMALL-MIDDLE SIZED STREAMSKazuaki

1,311,22OHTSUKI , Terutaka MORI , Keigo NAKAMURA and Yuichi KAYABA

1 Aqua Restoration Research Center, Public Works Research Institute Japan, Gifu, Japan. 2 Water Environment Research Group, PublicWorks Research Institute Japan, Ibaraki, Japan. 3 Dept. of Civil and Environmental Eng., University of Yamanashi, Yamanashi, Japan.

Abstract

Result 1. Influence on physical env.

- This study provides some patterns of hydroenvironment and fish fauna in bending and partialwidening reaches in small-middle sized rivers inJapan.

80- Dependency on each specific part in fish assemblages
are different. Percentage of fish species found inbended area is larger as fish species in the river isrich but that in widening reaches is opposite.

Methods

10080

KawauraHasamaRiffle6080Ishida80

60

402000204060

80 100

20

20

0080

0

20

40

40

40

20

20

60

160
140
120
100
80
60
40
20
0000

20

40

60

0

20

40

60

080

Daianji

Umetani 60

60

40

40

Pool

Itaya

60

40

40

100
80

60

80

20

40

2020006004080

120

Shizukuishi

Itaya
40

20020 40 60 80 100

0204020140
120
10080
60
40
20060

00160

80

60

4060

BND

140
120
100
80
60
40200Ijira

0.25

20 40 60 80 100

120

Ijira

Yukiya

100
80

0.2

60
40
20002040

60

80 100040120 160

0.0ഥ 𝐵𝐷𝑁 𝑜𝑟 𝑊𝐷𝑁 −➢ ∆𝑪𝑽 = σ/𝑥|
ഥ 𝑺𝑻𝑹
σ/𝑥|

-0.2
-0.2

0.0

0.2

0.4

Relationship between B/r and increase in diversity of water
depth and velocity➢Large plots found where
theCV
increase,suggesting that bend canincrease environmentalvariability.
➢Also, cases represent
large CV but small plot
(mild curve) or small CV
but large plot.

Result 2. Influence on fish assemblage
0.40.4- Monitoring flow condition (depth and velocity) andreach shapes and coverage with UAV were conducted.

0.3
0.2

0.2

- Fishes were collected with net in 30 minutes by 2people.
Bank condition
Blocks
Sediment
Vegetation

0.1

0.1

00

Daianji

KawauraHasamaItaya

MimizuBND

05

10
N1+N2WDN

0.3

150510N1+N215N1 : number of species
found in straight partN2 :Number of fish
species only inbended and widenedpart.

Percentage of species found only in river-plane changes in the appearance of straight and flatchanges. (left: bended part, right: widened part)➢Dependency of fish species on bended section increases inpoor condition (small N1+N2), but it on widened section
increase in rich condition (large N1+N2).
STR

BND

STR

BND

STR

Umetani

BND

BND

STR WDN

Ijira

0.6

0.6

0.4

0.4

0.2

0.2

0.0

0.0

-0.2

-0.2
-0.2

0.0

0.2

0.4

Circle sizecorresponded N1/ N1 +N2 , verticalaxis values inprevious figure.
-0.2

0.0

0.2

0.4

Relationship between diversity addition of water depth and velocity and specificity ofconfirmed fish species (left: bended part, right: widened part)➢Dependency of fish species has a relationship inincreasing variability in flow in bended part (left), but notin widened part (right).

WDN
STR

Ishida80➢Pool habitat are often found in BND part.
➢WDN part also bring riffle-pool habitat but not always.

N1 /(N1+N2)

BNDBND
WDN

0.4

Relationship of water depth velocity by location. The black, yellow, and green plots show the data for the straight, bended and widened
sections, respectively.

N1 /(N1+N2)

STR

B/r

0.6

080 100

WDN

Depth observed [cm]- 24 sites in 11 target rivers with a bed gradient of about
1/70 to 1/400 in Japan were surveyed (figure below).

Shin-sakai

Shin-sakai

6080- We found that bending part typically provide highdiversity in depth and velocity by creating pools, while
the widening part was uncertain in giving habitatdiversity.

STR

Velocity observed [cm/sec]

Shizukuishi

YukiyaConclusion- The pool is well formed in the curved part but not always in the widening part by sedimentation and plant invasion.
Standardized bend steepness (r/B) is potential indicator for pool forming.
- In case that If the original environment is monotonous in the widening area, the diversity of the flowing water
environment will increase greatly. the target riffle-pool environment may not be formed.

STR

WDN

STR

WDN

BND

STR
STR

STR

BND

Study Sites

WDNWDN- Comparing the fish fauna between the straight part and the flat part, it was found that the habitat created differs
between the curved part and the widened part, resulting in a difference in the reactivity of the inhabiting fish.