Advances in River Sediment Research – Fukuoka et al. (eds)© 2013 Taylor & Francis Group, London, ISBN 978-1-138-00062-9

Roles of disturbance in structuring geomorphology for riverine animalcommunities
M.K. Choi
Ph.D. Student, Water Resources Research Center, Disaster Prevention Research Institute, Kyoto University,Kyoto, Japan

Y. Takemon
Associate Professor, Water Resources Research Center, Disaster Prevention Research Institute, Kyoto University,Kyoto, Japan

T. SumiProfessor, Water Resources Research Center, Disaster Prevention Research Institute, Kyoto University,Kyoto, Japan

ABSTRACT: Local species diversity is maximized when ecological disturbance is the intermediate
disturbance. However, artificial impacts such as dam, excavation and levee caused decreasing dynamism andactivity of sediment and biological habitats, and thereby biodiversity by disturbance less than intermediate.
This paper aims at showing the effects of decreasing disturbance on changes of landscapes and geomorphic
habitat diversity. Hierarchical structure of aquatic habitats in the lower reaches of the Kizu River, a tributaryof the Yodo River, central Japan, was investigated using the aerial photos taken in 1948, 1961, 1971, mid 70 s,
1979, 1990, 2002, 2008, 2010 and 2012. Results of the landscape changes showed that water surface and bareland significantly decreased with increasing bushland and woodland. Average channel width, braided index
and shoreline index as geomorphic parameter decreased gradually. According to changes of landscapes andgeomorphic parameters, habitat diversity increased gradually between 1948 and 2012. Increase of habitat
diversity during the period indicated that the increase of vegetation area contributed to raising habitat diversity to some extent. Therefore, vegetation expansion derived from stabilization of flow regimes and reduction
in sediment dynamics fascinated the environmental heterogenety in there 60 years in the Kizu River.
1INTRODUCTION

2Artificial impacts such as dam, excavation and weircaused blocking the upstream sediment supply
and fundamental fluvial hydrology (Williams andWolman, 1984; Grant et al., 2003). Thus, rivers lost
biological dynamism and continuity of the upperand lower sides by decrease of disturbance.
The intermediate disturbance hypothesis statesthat local species diversity is maximized when
ecological disturbance is neither too rare nor toofrequent (Connell, 1978). This hypothesis suggeststhat maximum diversity is found at intermediatelevels of natural disturbance.
This paper aims to show the effects of decreasing disturbance on changes of landscapes andgeomorphic parameters with habitat diversity byaerial photos in the Kizu River.
Habitat diversity is useful predictor of species
diversity, because the number of habitats in a regionis almost always positively correlated with thenumber of species inhabiting (Joaquin et al., 2009).

STUDY SITE

The study area was established in the lower reaches(0^26 km) of the Kizu River, a tributary of theYodo River in central Japan.
Sediment and discharge of the Kizu River
were influenced by 5 dams; Takayama Dam(1969), Syourenzi Dam (1970), Murou Dam (1974),
Nunome Dam (1992), Hinachi Dam (1999)(Fig. 1). Sediment supply and discharges decreased
and riverbed degraded after construction of dams
and sand excavation from 1958 to 1963.
The Kizu River has been so called as a typical sand river, because it is strongly influenced
by granite in upper stream of Kizu River basin.
In 1965, an estimated 100,578 m3/y of sediment
discharge decreased about 80% in 2010 (Fig. 2).
The average of annual peak discharges after
construction of Takayama Dam (1970) also
decreased (Fig. 3).The riverbed of the Kizu River
had degraded from minimum 0.8 m to maximum
4.9 m with decrease of sediment discharge and1701

Figure 4. The riverbed degradation of the Kizu River
0~23.2 km between 1965 to 2012 (Yodogawa River
Breau, 2012).

annual peak discharges during about 60 years(Fig. 4). Floodplain is dominated by vegetationand stabilized with reduction of channel width(Fig. 6).

Figure 1.

A map of the Kizu River basin.

3METHODS

To examine longer term patterns of riverbed geomorphology on the Kizu River, the orthorectified
and georeferenced aerial photographs that comprise
information on terrain topography and x-y coordinate have been collected among usable data fromthe Yodogawa River Bureau. We compiled sequential aerial photos from 1948, 1961, 1971, mid 70 s
(1974^1978), 1979, 1990, 2002, 2008, 2010 and 2013.
In order to minimize errors, all data overlaid according to coordinate and quantitatively calculated areaof landscapes and habitats using ArcGIS (ESRI). Allparameters calculated and classified per 1 km unit.
Figure 2. Changes of sediment discharge between 1965
and 2010 (Yodogawa River Breau, 2012).

3.1

Landscape parameters

Landscape parameter was classified into water surface, bareland, bushland, woodland, cleared-land.
Cleared-land was defined as using land (e.g., farm,playground and bamboo forest) or empty space bytree cutting.
3.2

Figure 3. Annual peak discharge in Inooka observatoryfrom 1956 to 2012. The average annual peak discharge
calculated per 13 years. Average value between 1956 and1968 is value before construction of Takayama Dam(Yodogawa River Breau, 2012).

Geomorphic parameters

Channel width was estimated by the average width ofactive channel (low flow channel and islandbars) bytransects spaced 250 m apart in 1 km unit. Braided
index was calculated as total channel length (sumof mid-channel lengths of all channels, divided bylength of the widest channel’s mid-line; Friend andSinha, 1993). Shoreline index was determined asvalue of total aquatic area (water surface in channel
and aquatic habitat on the floodplain) to total lengthof shoreline. Shoreline index is important for ecology
since it reflects the amount of shallow and low velocity
habitats (Bowen et al., 2003) for many riverine species

1702including softshell turtles (Plummer, 1997; Moll andMoll, 2004), riverine fishes (Scheidegger and Bain,
1995; Johnson and Jennings, 1998).
3.3

Aquatic habitat

Aquatic habitat was classified into lotic and lentic
ecosystem depending on spatial size of animals andtheir home rages. As guided by the classification criteria in Table 1, Aquatic habitat type composed lotic(riffle, deep-slow) and lentic (bar-head wando, bartail wando, active pond, terrace pond). Deep-slow
does not show in this study, because it was difficult
to calculate the number (it was estimated total areaof water surface in main channel except riffle.).
Habitat diversity was estimated as richness
index and diversity index. Habitat richness wasdefined as total number of aquatic habitats; riffle,
bar-head wando, bar-tail wando, active pond, terrace pond. According to definition of habitat richness, it has value from minimum 0 to maximum 5.
Habitat diversity was calculated by ShannonWiener index.

3.4 Statistical analysis
Annualized rates of change in channel were compared using a one-way ANOVA. Correlation analysis and regression analysis was used to examine
relations of habitat diversity to landscape andgeomorphology.
4RESULTS

4.1 LandscapeLandscape in the lower reaches of Kizu River
showed significant changes between 1948 and2012. Aerial photo showed marks of sand excavation in 1961 and woodland developed on floodplain in 1971 (Fig. 5). They probably were reflectedby the lack of large floods in preceding years, aswell as a corresponding reduction in the frequencyof disturbance.
Bareland area decreased about 70% from 1961
to 2008, and increased between 2008 and 2012

RDiversity £ pi log pii 1

R = richness, pi = proportional abundance of
the ith type.
Table 1. Definitions of classification of aquatic habitat
based on aerial photographs in the Kizu River.
Habitat type
Lotic
Riffle (RF)Deep-Slow (DF)

LenticBar-Head
Wando (HW)
Bar-Tail
Wando (TW)Active Pond(AP)Terrace Pond(TP)Definition

Area of high current flow withrough water surface rowing
locating point of bars
Area of slow deep flow with smoothwater surface locating between
riffles
Channel blocked by bare/vegetation deposits with upstream
connection
Channel blocked by bare/vegetation deposits withdownstream connection
Side pool in active channel
Permanent or temporary
standing stagnant water on barelandSide pool on terrace at abandoned
channelPermanent or temporary standing
stagnant water on wood/bush land

Figure 5. Historical changes of the Kizu Riverlandscapes in 3~4 km.

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slightly. Although area of water surface decreased
gradually since 1948, they increased between 2010
and 2012 (Fig. 6).
The decrease in bareland and water surface
resulted from the expansion of vegetation area(bush wood). Expansion of woodland and bushland marked since 1961 due to sand excavation andconstruction of Takayama Dam. However, bushland
decreased about 20% from 2008 to 2012 and woodland decreased about 28% in 2012 compare to 2010
by management of wood cutting in 2011 and 2012.
4.2

Geomorphic parameters

By 1948, the active channel had narrowed by theaccretion of islands and stabilization of mobilebars. Average channel width significantly decreased

from 170.6 m in 1948 to 97.7 m in 2012. Increaseof channel width in 2012 was reflected by detachment of bareland from floodplain (Fig. 7.a).
Braided index decreased gradually from 2.23 in1948 to 1.39 in 2012 (Fig. 7.b). Shoreline also
decreased gradually from 31.3 in 1948 to 18.4 in2012 (Fig. 7.c). Decrease of shoreline index in 2010
resulted of increase of the area of water surface
and disappearance of multiple channels.
4.3

Aquatic habitat

The Number of RF decreased about 50% from113 in 1948 to 54 in 2012, in spite of increase
between 1961 and mid 40’. The number of HW
remained between 7 and 20 without significant
changes since 1961. The number of TW increased
gradually from 12 to 39 during about 60 years. The
number of AP decreased until 2002 and increased
between 2002 and 2010. The number of TP
increased from 1948 to 2012, especially between
2008 and 2012. The number of TW and TP among
5 habitat type only increased gradually during
about 60 years (Fig. 8).
Habitat richness and diversity showed similar results on the Kizu River. Habitat richness
increased from 2.61 to 3.84 and diversity index also
increased from 0.73 to 1.12 (Fig. 9).

Figure 6. Changes of landscape in the Kizu Riverbetween 1948 and 2012.

Figure 8. Changes of abundance of aquatic habitat
between 1948 and 2012. Abundance represents total
number of the habitats in 26 km reaches.

Figure 7. Changes of average channel width (a),braided index (b) and shoreline index (c) in the Kizu
River between 1948 and 2012. Error bars indicated oSD.

Figure 9. Changes of habitat richness and diversity
index between 1948 and 2012. Error bars indicated oSD.

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55.1

DISCUSSION
Relations of habitat to landscapeand geomorphology

Number of riffle was positively correlated highgeomorphic parameters (e.g., channel width, braidedindex) than landscapes. This result showed numberof riffle decreased with decreasing channel widthand braided index in the Kizu River (Fig. 10.a).
Number of HW was not significantly
correlated with changes of landscapes andgeomorphic parameters. The ratio of vegetation(bushland woodland) in channel showed positive
correlation with TW and TP, and negative withAP (Fig. 10.b, 10.c). This indicated number of
TP and TW increased with vegetation expansion.
In contrast, AP decreased with vegetation expansion and decrease of bareland (vegetation ratio
and bareland ratio have negative correlation.
coeffient = 0.83, P  0.001).
Habitat richness and diversity had positive correlation with the ratio of vegetation in channel(richness r  0.24 and P  0.001, diversity r  0.16
and P  0.01) and negative correlation with theratio of bareland (richness r  0.22 and P  0.001,
diversity r  0.14 and P  0.01).
Habitat richness and diversity increased withincrease of vegetation similar to TW and TP. This
result was explained by Table 2. Correlation witheach habitat and habitat diversity showed thehighest coefficient with HW and TW. RF and AP
distributed most of the reaches, whereas TW and
HW low a density. Therefore, habitat richness anddiversity will be influenced by existence of TWand HW. In addition, TP were positively influenced by vegetation expansion contributed highhabitat diversity.
Habitat diversity had negative correlation or
low correlation with RF.
Habitat richness and diversity index showedsmall difference with vegetation. Habitat richness
index had more high correlation with vegetation
than diversity. However, Habitat richness anddiversity index had high correlations with vegetation than each wood land and bushland (Table 3).
5.2 Relations of disturbance to geomorphology
Flow and sediment modification has resulted in
the expansion of vegetation and loss of the initialchannel width. Since the 1960s, the width of thechannel has stabilized, vegetation has trapped sediments, and woodland had developed. Vegetation
expansion was related to species diversity lived onvegetation area positively, on the other hand, theycaused decreasing discharge capacity and increasing stabilized bars (..).

Figure 10. Regression analysis of each abundance ofhabitat to landscape and geomorphology. Correlationof abundance of (a) RF and braided index (b) TW andvegetation ratio in channel (c) AP and vegetation ratio inchannel (b) TP and vegetation ratio in channel.

In this study, the abundance of aquatic habitatand habitat diversity increased with expansion ofvegetation. It indicated that the increase of vegetation area contributed to raising habitat diversity tosome extent. Therefore, the stability of flow regimes

1705

Table 2. Correlations of habitat richness and diversity
index to abundance of habitat.
Richness
Habitat
RFHW
TW
AP
TP

Diversity

r

Pr

0.3
0.001
0.001
0.001
0.001

0.063
0.505
0.539
0.291
0.312

P
0.123
0.447
0.515
0.231
0.128

0.05
0.001
0.001
0.001
0.04

Table 3. Correlations of habitat richness and diversity
index to vegetation area in channel.
Richness

Diversity

Landscaper

Pr

PWoodBushVeg (wood0.209
0.216
0.241

0.001
0.001
0.001

0.136
0.144
0.160

0.03
0.02
0.01bush)

and reduction in sediment dynamics fascinated theenvironmental heterogenety in there 60 years in theKizu River.
6CONCLUSION

In the Kizu River, bareland area decreased about
70% from 1961 to 2008, and bushland area andwoodland area significantly increased between
1961 and 2012. The average of channel width andbraided index gradually decreased between 1948
and 2010 and shoreline index decreased until 1979.
The changes of landscapes and geomorphic parameters were influenced by construction of dams andsand excavation from 1958 to 1963. As aquatic
habitat, TP and TW increased with decrease of RF
and AP between 1948 and 2012. At a same time,
habitat richness and diversity increased gradually.
The habitat richness and diversity during the period
indicated that the increase of vegetation area contributed to raising habitat diversity to some extent.
Although size and frequency of disturbance in theKizu River had decreased, it influenced positiveeffect in terms of geomorphic habitat structure.
ACKNOWLEDGMENTS
This study was conducted in a research project“Developmentofriver-bed
management

techniques for river environments” supported by
the Japanese Ministry of Land, infrastructure,Transport and Tourism.
We would like to thank Ikeda and Nishii inASIA AIR Survey CO.LTD for providing historical aerial photos; we also express our sincere
appreciations to the Ministry of Land, infrastructure, Transport and Tourism as they provided thehistorical hydraulic data.
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