京都大学防災研究所年報 第 58 号 B 平成 27 年 6 月
Annuals of Disas. Prev. Res. Inst., Kyoto Univ., No. 58 B, 2015

Estimation of Habitat Potential for Ayu Fish by Analyzing Riffle Geomorphology
in the Yodo River System

Koji MISHIMA(1), Yasuhiro TAKEMON, Souhei KOBAYASHI and Tetsuya SUMI
(1) Graduate School of Engineering, Kyoto University
Synopsis
Riffle is an important habitat for various lotic animals and its geomorphic variations bear
the faunal biodiversity in stream ecosystems. In the present paper, we classified the riffle
geomorphology and estimated the habitat potential for Ayu fish, Plecoglossus altivelis(Osmeridae) in the Kizu, Uji, Katsura and Kamo River, in the Yodo River System. Riffle
geomorphology was classified into five types based only on plan view pictures: i.e.,Traverse type, Widely Diverge type, Narrowly Diverge type, Converge type andArtificial type. Composition and abundance of theses riffle types were distinctively
different among the four rivers. Based on these differences, the potential population of
Ayu fish was estimated to be 526131 in Katsura River, 688,795 in Kizu River, 176,365
in Kamo River, and 356,005 in Uji River.
Keywords: riffle, geomorphology, habitat potential, Plecoglossus altivelis

1
Introduction
1.1 Background
Many rivers in developed countries have been undervarious human impacts such as channelization,straightening and confinement by sediment control
works and dam construction. These river channel
alternations have led to deterioration of biologicalhabitats. The ecological sustainable management isdesirable in rivers, and this management requires thesuitable methods for assess the river situations.
Thomson et al said quantity and quality of habitats are
critical elements of ecological conditions to develop
methods for environmental assessment and to identify
an appropriate target image (Thomson, et al., 2001).
Thus, methodological development of habitat
qualification is feasible for the assessment andprediction of river ecosystem. Tamai (2004) alsomentioned that quantification of habitat suitability is
the important task for river environmental management.
1.2

Importance of riffle as habitat

Aquatic habitats in rivers have been classified into
riffle, pool, backwater, secondary channel etc. anddifferent geomorphic habitats may serve for feeding(deep-slow), resting (backwater), or spawning (gravelbars) for fish and invertebrates (Takemon, 2007).
Riffles tend to support higher species diversity andbiomass of benthic invertebrates than the others, andthus are important as food-producing areas for fishes.
Riffles are also important as spawning sites as well for
fishes such as Ayu fish, Plecoglossus altivelis and Dark
chub, Nipponocypris temmincki (Mizuno et al. 1958;
Katano, 1990; Gordon et al., 2004). Thus, Nakajima, elal. (2011) examined that riffles with gravel bed
deposited in relatively recent time were the suitable forspawning redd of Ayu fish. Kobayashi et al. (2011)
evaluated invertebrate habitat suitability by historicalchanges of riffle types using aerial photos and fieldsurvey data.
1.3 Estimation of Ayu fish abundance per habitat
types― 424 ―

Relations of Ayu fish density to stream habitat
structures were investigated by various researchers.
Takahashi, et al. (2009) reviewed studies on habitat
quantification for Ayu fish conducted in various rivers,
including his own studies on potential densities of Ayu
fish in various types of aquatic habitats (Takahashi andTaniguchi, 2012: Takahashi, et al., 2012). There have

The study sites were established in four rivers in the
Yodo River System (Table 1). The study area of Kizu
River located in the lower reaches (0-26 km). The
largest flood event occurred in 1953 and reached almost
6,000m3/s. the peak discharge decreased to about
3,000m3/s after the dam construction. The annual meandischarge is about 25m3/s and high discharge is about

been known as the methods multiplying the habitat
density estimated from the size of bed rock, fromproductivity of algae, from the area of each bed
morphology in Takatsugawa, and counting the numberof Ayu fishes live per unit area at site (Aizawa andNakagawa, 2008). The common concept of thesemethods is using an index of potential densities of Ayu
fish in the particular habitat type. A total number of
Ayu fish in a particular reaches of a river would bepossible to be estimated by multiplying total area of
habitat types with the Ayu fish density of each habitat
type.

43 m3/s. The annual mean sediment transportation tothis reach was estimated to be about 100,000 m3/yearin the last 30 years. The channel width of the study area
was 300–500 m and fine bed materials smaller than
16mm dominated with a mean grain size of 4.27
cm13)14). The length of the sandbar wave was about 2
km (1,848 m). Due to sediment reduction resulting
from the dam construction and sand excavation
between 1958 and 1963, riverbed degradation was
accelerated and had been continued in the lower reach(0 – 10 km) until now (Ashida et al., 2008).
Study site of Katsura River was established in thelower reaches (0 - 18 km). The largest flood event
occurred in 1953 and reached almost 2,700m3/s,
whereas intensity of peak discharge decreased by 2,400
m3/s after dam construction15). The annual meandischarge is about 30 m3/s and high discharge is about
45 m3/s 16). The annual mean sediment discharge to thisstudy site was estimated to be about 1,961m3/year. The
channel width of the study area was 300 – 400 m andrelatively coarse bed materials (> 16 mm) dominatedwith a mean grain size of 20 mm17). The length of thesandbar wave was about 1.5 km (1662 m). After Segi
dam was constructed in the upstream, 1940,

1.4 Objectives of this study
Purpose of this study is to quantify abundance of theriffle habitat and other suitable bed morphology for
Ayu fish to develop methods for estimation of habitat
potential for the fish. In order to achieve the purpose,several riffle types were classified by geomorphic
characteristics, and distributions in four rivers of Kizu,
Katsura, Kamo, and Uji in the Yodo River basin.
Moreover, various geomorphological characteristics
within the Yodo River basin were considered as theparameter for determining the development of riffles.
The developed method in this study is expected to be
adopted for future river management.
Table 1 Hydraulic and physical parameter of the four
rivers studied

2
Method
2.1 Study site

downstream side (0 – 12 km) continue to occur river
bed degradation, on the other hand, upper part (12 – 18km) was in a trend of river bed aggradation, and bed
material in the middle part (7 – 12 km) were coarsened.
For Kamo river study was conducted in the range of
13
km
from
Kamo-ohashi-bridgeto
Hazukashibashi-bridge. The largest flood event
occurred in 1959 and reached almost 715 m3/s18). The
annual mean discharge is about 5 m3/s 19). The channel
width of the study site was about 50 m and the length ofsandbar wave was about 500 m (549 m).
At last, the study site of Uji River was set in thelower reaches 0 - 14 km, from the point where Katsura,
Kizu, and Uji River join to KEIJI BY-PASS. The
largest flood event occurred in 1953 and reached about
1,780 m3/s. The annual mean discharge is about 137― 425 ―

m3/s and high discharge is 189m3/s. The annual
sediment discharge in the study site was estimated to beabout 2,290m3/year17). The channel width of the study
area was about 100 m. riverbed degradation has been
lasting continuing for a long time and bed materials isin a trend of coarsening. The channel width was about
100 m (102 m) and the sandbar wave length was about

4 types by geomorphic characteristics, wide diverge,
narrow diverge, traverse, and converge, and definedthem according to Kobayashi & Takemon (2013)(Fig.1).
Riffles of wide diverge type cross the bar front
diagonally or in a nearly parallel angle and diverge, in
addition, development of the bar front is not obvious.
Narrow diverge types also cross the bar front

1 km (1008 m).

diagonally or nearly parallel. Comparing to the former,
this type is less diverged and the development of thebar front is strong. Riffles of traverse type cross the bar
front by nearly right angles or similar angles and theflow width is wider. Riffles of converge type cross thebar front similarly, and the flow width is narrow in theriffle. The direction of flow changes significantly
before crossing the sand bars for traverse and converge
types, while it changes little for diverge types. In
addition, abrupt decrease in water width is more
apparent for traverse and converge types. According to
the previous study, types of riffles in this study aredefined as follows. Firstly riffles develop near andupstream side of the bar front. Riffles are classified into
5 types, traverse, wide diverge, narrow diverge,
converge, and the artificial type. Traverse type is ariffle with the stream line deflected twice sharply where
it cross the bar front. In addition water width is wide.
The upper boundary is the line where the stream line
start to be deflected and the lower boundary is thesecond place of deflection. Wide diverge (D1) typecrossing the sand bar front diagonally or in a nearlyparallel with slightly narrowed water width compared
to upstream and downstream. Narrow diverge (D2) type

2.2 Materials and Methods
Aerial photos of the study sites in 1990 and 2000
were used and processed into digital data using Arc
GIS version 10.1. After that, riffle area, water surface
area of rivers, channel width, and sandbar length which
is rounded to the nearest to the whole number for
simplification. In addition each river was divided into
units based on the sand bar wave length of each river
reaches, in order to compare not only within rivers but
also among rivers. It enables to compare them in astandardized condition for several hydraulic parameter
like water discharge. Values of hydraulic or physicalparameters of rivers, water discharge, channel slope,and sediment discharge were cited from the data
published by Ministry of Land, Infrastructure, andTransportation and Tourism17). For estimation of theamount of Ayu fish, the mean density for each bed
morphology was set based on previous studies9)10)11).
Takahashi classified bed morphology into 6 types, rapid
riffle, flat riffle, pool, A, and B and below dykes, andestimated the value of habitat density as shown in left
half of Table.212). In this study more detailed
classification for riffle types were defined and thehabitat density for those types as shown in the right halfof Table 2.
Table 2 Habitat density of previous studies and thevalue for use habitat suitability estimation

2.3

Classification of riffle

Kobayashi & Takemon (2013) classified riffles into

is a riffle crossing the sand bar front diagonally or in anearly parallel manner with well narrowed water widthcompared to upstream and downstream. For these two
types the upper boundary is defined where the channel
width gets narrowed compared to the upper stream, andthe lower boundary is where the channel width getswider. Converge type is a riffle with a stream line
curved with a narrow channel width. The upperboundary is defined as where the stream line starts tocurve and the channel width gets narrowed, on the other
hand the lower boundary is where stream line starts tocurve to the opposite direction and the channel width
gets wider. Artificial type is a riffle developed below
dykes constructed for river management.
Pool and slow A was determined based on therelation to riffles. Pool is defined as a part with slow

― 426 ―

flow developed in downstream of the traverse type
riffle and artificial type Slow A is defined as a channel
with relatively fast flow, which is developed indownstream of narrow diverge type and riffle
developed in downstream of traverse type. And then therest of the river bed are classified as slow B.

Fig. 1 Examples of the four types of riffles. See
text for their definition.
2.4 Analysis
For standardization riffle area ratio was calculated,which is the value of each riffle area divided by thewater surface area in each unit. The temporal change ofthe mean of area ratio in the rivers were investigated
and they were compared between those rivers. In
addition the difference of area ratio among the units of
one of the rivers were investigated with the physicalparameters.
3
Results
3.1 Distribution of each riffle type in each rivers
Sandbar wave length of Kizu River was about 2 km
(1,843m) therefore the length of unit is 2 km each.
Total riffle area of traverse type area reached up to
51,000 ㎡ in the study reaches in 1990. Fig. 2 shows
the number of riffles in each unit for Kizu River. In
1990, the number of riffles was 51 in total. Kizu River
has the most abundant number of riffles in the four
rivers. In some units there were a several riffles,
especially unit of 22 - 24km has 5 riffles. A total of 22
riffles of traverse type were counted in almost all units
except for 10 to 12km section and 24 to 26km section.
Most abundant area for traverse type in Kizu River was
14 to 16km section the riffle area ratio to total section

area reaches 0.09, which is the second largest value ofall the rivers of this study site, and additionally there
were two units of 2 – 4 km and 20 - 22 km, which hadlarge area of traverse type riffles. Wide diverge typealso had limited distribution ranged 4 - 8km and 12 14km, and 16 - 20km section, compared with othertypes in Kizu River, the abundance of riffles of wide
diverge type was on the low side, but compared withthis type of other rivers, it was the largest of all (Fig.2).
Wide diverge type was totally about 14,000 ㎡ in 1990
and the maximum value was about 0.026 in the unit of
12 – 14 km. About Narrow diverge type there were no
riffles of this type in 12 - 20km sections. Number ofriffles was the largest of four rivers and concentrates on
4 - 6km section. The total area of narrow diverge typewas about 18,000 ㎡ in 1990 and the maximum value
for one unit was 0.048 in the unit of 24 - 26 km.
Distribution of converge type is limited in 4 - 6km, 14 16km, 18 - 20km, and 22 - 24km sections. This type
had no unit in which more than one riffle exists. The
total riffle area was about 12,000 ㎡ in 1990.
Maximum value of the area ratio of riffle to unit water
surface area was about 0.017. Although converge type
was less than the other types, upstream part of 18 – 20km, 22 – 24km section had more riffle area of converge
type. On the whole, although all the riffle typeabundantly existed, converge type and wide diverge
type were relatively scarce distribution, but all the units
had plural riffles, so, on the whole, it can be said there
were a variety of bed morphology. Compared with theother for rivers’, all the type of riffles except for wide
diverge type in Kizu River had the largest area ratio totheir section area if the four rivers and wide diverge
type had the second largest area following Kastura river.
It could be thought that Kizu River such kind of riffle
abundance and the change in time were caused by thefrequent occurrence of sediment transportation.

Fig. 2 Longitudinal distribution of riffles in Kizu River― 427 ―

Next, Katsura River had 28 riffles in total, 11 of
traverse type, 4 of wide diverge type, 11 of narrow
diverge type, and 2 of converge type as shown in
Figure 2. In Katura River traverse type riffles had wide
distribution although stepping-stonelike empty units
existed (1.5 – 4.5km, 7.5 - 9km, 12 - 13.5km, and 16.5 18km sections) (Fig. 3). Especially, in each units of 0 -various types of riffles compared to the middle reaches.
This might be caused by the formation of backwater inthe upstream of the weirs. The most abundant unit foreach riffle types was located either the bottom part (0 3 km) or upper part (15 – 18 km), it could be said there
was a deviation in riffle distribution.

1.5km, 10.5 - 12km, and 15 – 16.5km there were threeor more traverse type riffles. The total area of traverse
type riffles was about 11,000 ㎡ in 1990, and the mostabundant unit for this type of riffle was the part of 15 –16.5 km, and its area ratio to water surface area in theunit was about 0.044. For traverse types in Katsura
River was the second most abundance in the four rivers.
Considering the number of riffle was not small though
the ratio was in a small side compared with that type ofother rivers, the size of each riffles was small. 5 rifflesof wide diverge type were counted, and two of themeach were developed in 3 – 4.5km, and 16.5 – 18km
units and the other was develop in 10.5 – 12km unit.
Furthermore in the unit of 3 - 4.5km there were only
wide diverge type riffles. The total area of wide diverge
type was about 12,000 ㎡ in 1990, and the mostabundance part was the unit of 16.5 - 18 km and thevalue of area ratio of riffles to unit water surface area
was 0.083. For narrow diverge type, totally 4 riffles
were developed in 1990. Two of them were in 10.5 –12 km unit and one of them was in 4.5 – 6km and theother was in 6 – 7.5km. Total area of narrow diverge
types was about 7,200 ㎡ of area. The maximum valueof the area ratio of riffles to unit water surface was

In the Kamo River there were many weirs.
Numbers of riffles of each type were not so many: i.e.,
8 riffles of traverse type, 2 of wide diverge type, 2 ofnarrow diverge type, and 3 of converge type in 1990.
For traverse type riffles were concentrated in 5 – 7.5
km section, and this type dominated in Kamo River(Fig. 4). total area of traverse type riffles was 4,000 ㎡
in 1990, and the maximum ratio of riffle area to thewater surface area in the unit reached up to 0.1 in 5.5 –6 km reaches. This was the largest value in all the study
area. One each of wide diverge type was developed in 3
– 3.5 km unit and 7 – 7.5 km unit. Wide diverge type
was totally about 750 ㎡ in 1990. The maximum valueof riffle area ratio to the unit water surface was about

about 0.0028 in the unit of 4.5 – 6 km. Compare withother types, the area of narrow diverge type was small.
Moreover the number of them itself was small. The
number of converge types were counted up to 9 riffles.
Three of them were located in 0 - 3km section and theother in 13.5 - 16.5km section, respectively. Converge
type had totally about 10,000 ㎡ in 1990 and the
maximum value of area ratio of riffles to unit water
surface was about 0.016 in the unit of 1.5 – 3 km.
Opposed to such abundance of upper part and bottom
part, there were no riffles in the middle part of the river(3 – 13.5km). Compare with the other rivers, Katsura
River could be mentioned that abundant distribution ofwide diverge types and converge type and scarce
distribution of narrow diverge types were characteristic,
and upper and lower reaches of the river had relatively

0.031, whose location was in the unit of 3 - 3.5 km.
Similarly one each of narrow diverge type wasdeveloped in 0 – 0.5 km unit and 11 -11.5 km unit.
Total area of narrow diverge type was about 550 ㎡ in
total (1990). The riffle density was the most in 0 – 0.5
km section, and the ratio of riffle area to water surface
area was 0.045. For converge type were developed in
2.5-4 and 4 – 4.5 km units. There was only a few rifflesof converge type, whose area was at most 500 ㎡ in
1990, but the peak value of the area ratio to the water
surface area in the unit through the study reaches was
about 0.031 in the unit of 3.5 – 5 km. As a whole Kamo
River had biased distribution. Traverse types andconverge types were concentrated in the middle reachesof the river. Sections of 0.5 – 2.5 km and 8.5 – 12 km
there were almost no riffles other than artificial type. It

Fig. 3 Longitudinal distribution of riffles in KatsuraRiver― 428 ―

could be thought the channelization and drop structure
effected the formation of riffles. In the Kamo River
Overall, Kamo River had a small number of riffles but
most of them were large for the water surface of theunit.

Fig. 5 Longitudinal distribution of riffles in Uji River
3.2 Comparison of distribution of riffle types andtheir temporal change

Fig. 4 Longitudinal distribution of riffles in KamoRiver
Uji River had the least number of riffles in four
rivers. Three of traverse type, three of wide diverge
type, and three of narrow diverge type, and two of
converge type were counted respectively, but artificial
type was not found in this river. In the study site of Uji
River, the total riffle area was about 15,000 ㎡. Rifflesof traverse type were developed in 6 – 12 km section,
and was totally about 4,000 ㎡ and the maximum valueof the area ratio of riffles to the water surface in the unit
was about 0.021 in the unit of 11 – 12 km (Fig.5). Widediverge was in 10 - 13 km sections, total area of wide
diverge type was about 7,400 ㎡. The peak value of thearea ratio of riffles to unit surface was about 0.052 in
12 – 13 km unit. wide diverge type accounted for thelargest of total riffle area in Uji River Narrow diverge
type existed in 6km, 9 – 10 km, and 12 km sections.
The total area of the type was about 2,400 ㎡, and thedensest unit of narrow diverge type riffles was 8 – 9 km
unit and the area ratio of riffle to water surface wasabout 0.015. Converge types in 12 – 13 km sections.
This type was very slight amount of area, and thelargest value of area ratio of riffles to unit water surface
was about 0.01.As a whole, it could be said that 12 – 13
km section had abundant riffle distribution and 0 – 5
km section was not the environment suitable forforming riffles. This scarce distribution was thought tobe caused by the poor sediment transportation due todams in the upstream. The character of Uji River wasvery little amount of riffle for unit water surface area
and that there was no riffle in the downstream (0 – 5
km section).

Fig.6 shows the mean value of riffle area summed up
within a unit divided by the unit water surface area foreach river with their standard deviations. Comparedwith the other rivers, for all the type of riffles except for
wide diverge type and artificial type, Kizu river had thelargest area ratio to their section area of the four rivers
and wide diverge type had the second largest area
following Kastura river in 1990. In Katsura River wide
diverge types were developed very much compared tothat of other rivers. Contrary to that narrow diverge
type were slightly developed in the river. In the Kamo
River, riffles of traverse types were much developed
and those artificial types were also abundant, whereas
those of the other types were not developed well. For
Uji River the area ratio of riffles are smaller than otherrivers. Only wide diverge types were well developed asmuch as Kizu River. For the other types of the Uji
River the area ratios were low. For the secular change
the area ratio did not change very much in most ofcases. However, area ratio decreased or increased verymuch in several cases. Converge type in Kamo River
increased much and narrow diverge type of Kizu Riverand converge type in Katsura River oppositely
decreased.

― 429 ―

It could be said each riffle type had the largest area
ratio at a certain channel width and slope. For Katsura
River, traverse type was estimated to have the peak area
ratio around 180 – 200 m of channel width and 0.0025– 0.003 of channel slope. Wide and narrow diverge
type and converge type were also estimated 100 – 120m, 170 – 190 m, and 140 – 160 m of channel width and,
0.0025 -0.0027, 0.0001 – 0.0003, and 0.0023 – 0.0025
of channel slope, respectively. The other rivers had thepeak value at a similar value of slope other for traverse
type and converge type other than Kizu River.
Compared with the other rivers, Kizu River had thepeak value of area ratio at much more gentle slope thenthe other rivers. In Kizu River traverse type had thepeak around 0.0006 – 0.0008 of the channel slope andconverge type is 0.0005 – 0.0007 of channel slope.

Fig. 6 Comparison of abundance of riffle with rivers
3.3 Relations
betweenrifflegeomorphological parameters

types

and

Fig.7 and 8 show the relations of riffle abundance tothe channel width and channel slope. Channel slope hadsome links to the distribution of area of riffles. For
channel width wide diverge type of Kizu River of 1990
and Uji River and converge type of Uji River increased
and decreased similarly to the channel width inlongitudinal change. For channel slope traverse andnarrow diverge type of Kizu River and traverse type ofUji River also increased or decrease similarly tochannel slope, although the phase of traverse type of
Kizu River was deviated.
Some types of riffles showed a peak value of theriffle area ratio around a particular value of channel

Fig.7 Relations of riffle area ratio to the channel width
in the four rivers studied.

width and channel slope, especially those of traverse
type and narrow diverge type with channel width, andthose of wide diverge type and narrow diverge type forcannel slope. Correlation between channel width andtwo types of traverse and narrow diverge type wasdownward convex around 100m of channel width.
Moreover the transition of mean area ratio of narrow
diverge type in ten years also showed positive
correlation especially more than 100 m of channel
width. On the other hand, while correlation between
area ratio and channel slope of narrow diverge type was
upward convex between 0.0015 and 0.002. The
transition in time between mean area ratios of narrow
diverge showed a little bit similar correlation to it, andfor converge type the two comparisons show a similarcorrelation in the range of more than 0.0008.

Fig. 8 Relations of riffle area ratio to the bed slope in
the four rivers studied.

― 430 ―

3.4 Estimating potential of population of Ayu fish
Table 3 and Fig.9 show the estimated potential
density of Ayu fish for each river based on theestimated values for each type of habitats. The plottedvalues indicate the mean of the potential density in two
years. Among the four rivers, the Kizu River and theKamo River had relatively high potential density. But
largely it could be said potential densities of thoserivers were around 0.35 fishes/ ㎡ . By the way,
Takatsugawa and Gohnokawa, which are known as
natural rivers are 1.26 and 0.66 fish/m2. Compared withthese values, the habitat potential of each studied rivers
are much lower.
Table 3 estimated potential density for habitat
suitability of ayu

Figure 9 Estimation of habitat suitability in mean value
case
4Discussion

From the result of significant correlations between
riffle area ratio and parameters, we can make a proposalof a method for the river management. For better riverenvironment, changing the channel slope and channel
width into those to increase the riffle types suitable to
Ayu fish. In the case of Katsura River, because thepresent mean channel width and slope are 154 m and0.0015, respectively, it can be predicted that decreasechannel width and increase bed slope leads to increase
traverse and converge types. For Kizu River it isthought that the channel width should be narrowed andthe channel slope should be slightly gentler as the
habitat for Ayu fish. An example of the specificmethods to change those physical parameter may beelimination of weirs in the Katsura River. The
elimination of weirs is expected to make the channel
slope steeper in the section.
In this study, the abundance of riffles of each typeper unit area was related to physical and hydraulicparameters of each river. These interrelationship can beuses for the environmental river management
particularly for increasing the potential of population of
Ayu fish. In order to apply the method in practicalmanner, there are still several study subjects remained
to be investigated. One is to verifying the riffles
definition. Whether the definition of riffle in this study
is truly valid for the actual riffles should be confirmedby field survey for actual physical parameter like water
depth and maximum bed material size. Another is toverify the validity of potential of population of Ayu fish.
Verification work is also needed for this problem
because in this study data of other river of previous
studies are used. The other is to examine the otherparameters contributing to the formation of riffles. In
this study correlations to channel width and channel
slope were found but only these two parameters did not
dominate the determination of riffle development.
Therefore further analysis is needed about otherhydraulic and physical parameter. Numericalsimulation of riverbed evaluation is also required forthe validity.
5

Conclusion

Numbers and areas of five type of riffles were
estimated for Katsura River, Kizu River, Kamo Riverand Uji River. Katsura River had many wide diverge
and artificial types and few riffles are developed in
middle part of the river. In the Kizu River there werethe most abundance of riffles, especially traverse type.
In the Kamo River traverse type riffles dominatesconcentrating on middle part of study site. At last in the
Uji River there are the least abundance of riffles,
especially no riffles in lower part. This is applicable toother organisms than Ayu fish. The potential populationof the fish was estimated to be 526131 in Katsura River,
688,795 in Kizu River, 176,365 in Kamo River, and356,005 in Uji River. However, further consideration― 431 ―

and verification will be needed for practical use.
Correlation are confirmed between development ofriffle and geomorphological parameters, width and bed
slope. There seems to be a suitable value for
maximization of riffle, however channel width and bed
slope are not only the parameters for dominating theformation of riffles.
6

Acknowledgements

We would like to express much thanks to thefollowing prople who helped me greatly for writing thisthesis. Firstly, I sincerely express the great thank formy supervisor Prof. Dr. Tetsuya Sumi and also Assoc.
Prof. Dr. Yasuhiro Takemon. In addition I would like tosay thanks to Yodogawa River Office in the Ministry ofLand, Infrastructure, Transport, & Tourisms and River
deputy of Kyoto Prefecture for supplying river data andaerial photo. Finally, I deeply thank all my laboratory
members, especially Dr. Choi Mikyoung for helping
data analysis and Mr. Kazuki Terada for advising forwriting.
7

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(Received 11 June 2015)