143
Landform Conservation and Flood Control:
the Issue of the Chitose Diversion Channel
Project in Hokkaido, Japan
Blackwell Science Asia
YUGO ONO, Graduate School of Environmental Earth Science, Hokkaido University, Japan.
Abstract
Landform conservation is the main task of geomorphology in the 21st Century.
Since landforms provide the templates for the development of wildlife habitats,
landform change is likely to cause habitat loss, inducing a reduction of biodiversity. From the viewpoint of ‘geomorphic species’, specific landforms such as
natural rivers, tidal flats and coral reefs are endangered species in the Japanese
islands. To avoid the further destruction of natural rivers, environmentally appropriate flood control plans are necessary.
The analysis of the Chitose Diversion Channel project in Hokkaido,
Japan, revealed that (1) the construction of this diversion channel has caused
not only environmental problems but also serious social conflicts relating to
habitats within and beyond the drainage basin; (2) excavation of a deep channel
changed the groundwater supply which previously supported a natural river
system, and (3) selection of a very high discharge value as the target of flood
control was the main reason for planning this project. From a landform conservation perspective, the method adopted in Japan is unsuitable because it
does not incorporate the scientific procedure necessary for selecting the ‘best’
peak discharge corresponding to the target rainfall with a certain recurrence
period. An alternative flood control plan, combining the selection of a lower
peak discharge, construction of retention pools and the restoration of meandering river channels is proposed to avoid the further destruction of natural
rivers.
KEY WORDS geomorphic species; flood control; nature conservation; river
environment; floodplain management; retention pool
Introduction
Conservation of biodiversity and the global
environment are the main issues for humanity
in the 21st century. Ecology and biology are
believed to be the major disciplines in considering biodiversity; and climatology and energy-
related technology are increasingly concerned
with global warming issues. What about geomorphology? Is geomorphology not related to
the global environment? Is geomorphology as
a discipline not responsible for environmental
conservation?
Australian Geographical Studies • July 2002 • 40(2):143–154
144
Raising these questions emphasises the
importance of geomorphology, not only for
environmental conservation but also for future
biodiversity maintenance, because it is the form
of the land itself that composes and supports the
habitats which are required by all creatures, both
animals and plants (Ono, 1992). Therefore, if
any individual landform is changed and the
habitat destroyed, creatures cannot survive, even
if conservation measures are biologically introduced. For example, river fish cannot survive if
their spawning habitat, comprised of riffle-andpool structures, is destroyed (examples: Hoopes,
1972; Lanka et al., 1987; Fukushima, 1994).
Recent studies have made clear the important
role of riparian forests in maintaining riffleand-pool structures by supplying coarse woody
debris (CWD) to the river bed (Keller and
Swanson, 1979; Murphy and Koski, 1989;
Nakamura and Swanson, 1993). Since riparian
forests stand on flood plains, river terraces and
valley sides, conservation of these landforms
which support the riparian ecosystems is necessary in order to maintain the biodiversity of fish
and related aquatic insects. These ideas led me
in 1992 to propose the new concept named ‘geomorphic species’ (Ono, 1992). A geomorphic
species is defined as an individual landform
such as flood plain, river terrace and alluvial
fan. On a smaller scale, each riffle and pool
comprises a basic unit of geomorphic species.
On a larger scale, we can regard the natural
river or meandering river as one geomorphic
species.
By analysing the actual condition of the landforms of the Japanese islands, Ono (1992)
pointed out that several geomorphic features
such as natural rivers, natural coasts (especially
sandy beaches), tidal flats and coral reefs are
endangered. An important task of geomorphology in the 21st century, therefore, is to ensure
the worldwide survival of these endangered geomorphic species. Without suitable landform conservation many habitats, which are supported by
these geomorphic species, are being lost with
the consequent diminution of both biodiversity
and global environmental quality.
Australian Geographical Studies
The Chitose Diversion Channel Project is an
example of geomorphic species conservation.
As each geomorphic species is endangered by
human actions such as flood control, disaster
prevention, construction and developmental
works, alternative actions which both conserve
the geomorphic species and sufficiently meet
the human requirements are needed. In the case
of the Chitose Diversion Channel Project flood
control is the major human requirement.
This paper points out some of the methodological problems involved in preparing a flood
control strategy in Japan, and proposes an alternative which allows for both flood control and
landform conservation.
The Chitose Diversion Channel Project
The Chitose Diversion Channel Project (Figure 1) was the biggest public works project
involving large-scale landform modification
undertaken in Japan since 1982. The estimated
budget totalled at least 500 billion Yen (US$400
million), with 20 years allocated for the construction period. The project was planned by
the Hokkaido Development Agency, which is a
national agency involved in the management of
river works. The project plan was approved by
Cabinet in 1983 following endorsement by the
National River Work Committee. In Japan, as a
rule, once a project has Cabinet’s endorsement
to proceed it cannot be stopped. However, the
Chitose Diversion Channel Project was abandoned in 1999 as a result of a very strong citizen
movement against its completion. Therefore,
this project has a special symbolic meaning for
the Japanese people as it was the first largescale, national public works project to be
stopped by citizen action (Ono, 1999).
The Chitose River is a tributary of the Ishikari
River, the longest river (328 km) in Hokkaido.
The Chitose River joins the Ishikari near the
town of Ebetsu and flows into the Sea of Japan.
The purpose of the Chitose Diversion Channel
Project was to divert the Chitose River (when in
flood) into the Pacific Ocean via a long, flood
control channel (named the Chitose Diversion
Channel). This channel, approximately 40 km
© Institute of Australian Geographers 2002
Landform Conservation and Flood Control
145
Figure 1 Plan of the flood control channel of the Chitose River (Hokkaido Development Agency, 1994).
A, B and C: locations of controlling gates;
blank: alluvial plain;
dotted: Shikotsu pyroclastic flow and hills;
oblique lines: mountains and volcano;
triangles: main peaks.
long and between 200 and 400 m wide, would
connect the middle reach of the Chitose to the
Pacific coast (Figures 1 and 2).
The project involved the construction of three
big ‘water gates’ at the junction of the Chitose
and Ishikari (point A in Figure 1), at the entrance
to the diversion channel (point B) and at the
mouth of the diversion channel (point C). At
times of normal flow, the gate at point A would
be opened whilst the gates at points B and C
would be closed, in order to connect the Chitose
© Institute of Australian Geographers 2002
to the Ishikari, allowing neither river water nor
sea water to enter the diversion channel. The
diversion channel would become a long ditch
with standing water about 3 m deep. During a
flood the gate at A would be closed, whilst the
gates at B and C would be opened so that the
Chitose, then separated from the Ishikari by
the gate, would flow inversely (as indicated by
an arrow in Figure 1) in the middle and lower
reaches and, through the diversion channel, into
the Pacific Ocean.
146
Figure 2
Australian Geographical Studies
Birds eye view of the Chitose Drainage Basin (after the Hokkaido Development Agency, 1994).
Basic problems of the Chitose Diversion
Channel
As shown in Figures 1 and 2, the Chitose Diversion Channel would evacuate the flood water of
the Chitose into the Pacific Ocean across the
natural divide between the Chitose and the
Bibi rivers. This in-valley divide was formed
by pyroclastic flows which erupted from the
Shikotsu volcano 42 000 years BP, creating a
caldera lake known as the Shikotsu. The aim
of the Chitose Diversion Channel was to shift
flood water control from the drainage basin of
the Chitose to that of the Abira-Bibi. Since the
farmers living in the Abira drainage basin would
suffer as a result of the division of their agricul-
tural land through the excavation of a large
diversion channel, they were naturally opposed
to the construction plan.
The Bibi is a very small river which dissects
the volcanic plateau formed by the pyroclastic
flow. The river water is fed by many springs at
the foot of the dissected plateau. The importance of the Bibi lies in its well-preserved natural environment which provides an important
migration corridor for the brown bear and other
endangered wildlife; and in the fact that the
water of the Bibi feeds Lake Utonai, the fourth
Ramsar site and the first wildlife bird sanctuary
created through NGO (non-government organisation) actions. As can be seen in Figure 3 the
© Institute of Australian Geographers 2002
Landform Conservation and Flood Control
147
Figure 3 Topographical and geological sections through the Bibi and the Chitose Diversion Channel (after Hokkaido
Development Agency, 1994).
T: Tertiary
As and FM: middle to late Pleistocene
Spfl1-3: Shikotsu pumice Flow deposits 1-3
En Ta: tephra from Mt.Eniwa and Tarumae volcanoes
A: alluvial deposits
B: river deposits in the Bibi valley
Chitose Diversion Channel has been excavated
deep into the original landform. This caused
most of the groundwater previously emerging
in the valley of the Bibi and around the foot
of the volcanic plateau to be diverted to the
diversion channel, decreasing the flow of the
Bibi and drying up Lake Utonai. As a result
the Wild Bird Society and other NGOs for
nature conservation began a movement against
the construction of the diversion channel. In 1993
the 5th Conference of the Ramsar Convention
at Kushiro, Eastern Hokkaido, provided a good
occasion for these and other environment© Institute of Australian Geographers 2002
alists to appeal this issue both nationally and
internationally.
The strongest movement against the construction of the Chitose Diversion Channel was led
by the fishermen who cultivate shellfish offshore
in the Pacific Ocean. These cultivated marine
shellfish are undoubtedly killed by the highly
turbid floodwater evacuated by the diversion
channel into the Pacific Ocean.
These issues gave rise to an effective and sustained movement against the planned Chitose
Diversion Channel. However, from geomorphological and hydrogeomorphological points of
148
Figure 4
Australian Geographical Studies
Extent of the 1981 flood of the Ishikari and Chitose rivers (after the Hokkaido Development Agency, 1994).
view it is necessary to understand the reasoning
behind the planning of such a large project.
For this purpose, it is necessary to analyse the
method adopted by the engineers who designed
the Chitose Diversion Channel project, which
was proposed soon after the historically largest
flood of the Ishikari in 1981.
The 1981 flood
The 1981 flood occurred between the 4th and
7th of August, 1981 (Figure 4). The total precipitation of 282 mm in three days (Figure 5), with
a recurrence interval estimated at 200 years
(Figure 6), was an historical record in the
Ishikari drainage basin. Figure 4 illustrates the
area inundated by this flood. Most of the inundated area is lowland from which water could
not drain due to the raised water levels of the
Ishikari and Chitose rivers. Since the land surface is very low-lying in the middle and lower
reaches of these two rivers, many pumping stations had been constructed. These pumps functioned efficiently during the flood. However, as
a result of the raised the water level of the rivers,
pumping had to cease because it was contributing to over-bank flooding. On the other hand,
inundation by the over-bank flood was limited.
These facts suggest that river work to reduce
lowland inundation should be a priority in this
area.
© Institute of Australian Geographers 2002
Landform Conservation and Flood Control
149
Figure 5 Annual maximum precipitation (three days mean) in the Ishikari River between 1926 and 1998 (after the Hokkaido
Development Agency, 1994).
Figure 6 Evaluation of recurrence period of heavy rain in
the Ishikari Drainage Basin (after the Hokkaido Development
Agency, 1994).
© Institute of Australian Geographers 2002
Methodological problems of flood control
planning
Flood Control Plans in Japan are designed to
prevent inundation of lowlands, caused by heavy
rainfalls with recurrence periods of more than
20 years. However, the estimated recurrence
period increases with river size and importance.
For the Ishikari it is 150 years, and for the Chitose it is 100 years. The three days rainfall with
a recurrence period of 150 years was calculated at 260 mm, using the same method used
to evaluate the recurrence period of rainfall
(Figure 6). On the basis of this rainfall (260 mm
in three days), a peak discharge of the Ishikari
was calculated by using a precipitation/runoff
model covering the whole drainage basin.
The Hokkaido Development Agency, which is
responsible for the flood control work in
Hokkaido, concluded that the peak discharge
of the Ishikari corresponding to rainfall with a
recurrence period of 150 years (260 mm in three
days) is 18 000 m3 s−1.
Figure 7 compares this peak discharge and
the hydrograph of the Ishikari with those of
the 1981 and 1976 floods. It is clear that the
150
Australian Geographical Studies
Figure 7 Comparison of the estimated peak discharge of
the Ishikari for the designed precipitation of 260 mm in
three days, corresponding to the rainfall with a 150-year
recurrence period, and the peak discharges of the 1981 and
1976 floods (after Hokkaido Development Agency, 1994).
estimated peak discharge for the 150 year rainfall
is much higher than that of the 1981 flood, which
corresponded with rainfall with a recurrence
period of 200 years (282 mm in three days).
Table I
1994).
This unreasonable result was induced by the
methodological problem involved in the estimation of peak discharge. Table I indicates the
results of seven calculations by the Hokkadio
Development Agency of peak discharge of the
Ishikari corresponding to 150-year rainfall. For
all calculations, the total rainfall of 260 mm in
three days is given, but its distribution is different in each calculation. In the case of the 1981
flood the rainfall had two peaks, while in the
1976 flood there was only one, but higher
peak (Figure 8). The method used by the
Hokkaido Development Agency to calculate
peak discharge postulates that a 260 mm in
three days precipitation can occur with any
rainfall pattern which has occurred in the past
(but with a far smaller precipitation, as indicated in Table I).
Since the precipitation pattern differs with
each rainfall event, the calculated peak discharge corresponding to the same precipitation
(260 mm in three days) shows a wide range,
from 11 400 m3 s−1 to 18 000 m3 s−1. All these
values are possible ones, and all correspond to
the 150-year rainfall; however, the Hokkaido
Development Agency adopted only the maximum value (18 000 m3 s−1) as the estimated peak
discharge for the 150-year rainfall. The Chitose
Diversion Channel is closely linked to this
very high peak discharge, because such a high
Calculated peak discharges of the Ishikari River for future heavy rainfalls (after Hokkaido Development Agency,
No.
Rainfall pattern
Total
precipitation
(mm/3days)
Enlargement
ratio
1
Aug.1981
282.2
1.00
2
Aug.1975
173.0
1.50
3
Aug.1973
113.6
2.29
4
Aug.1966
109.9
2.37
5
Sep.1965
107.0
2.43
6
Aug.1962
133.0
1.96
7
July.1961
151.5
1.72
Planned
Precipitation
(mm/3days)
282.2





 260





Calculated Peak
Discharge (m3/s)
Recurrence
Time
14 400
200years
18 000
150years
16 400
11 400
12 500
17 600
16 100
© Institute of Australian Geographers 2002
Landform Conservation and Flood Control
Figure 8
1994).
151
Precipitation pattern of the 1981 flood (A) and the 1975 flood (B) of the Ishikari. (Hokkaido Development Agency,
discharge inevitably needs an evacuation of
flood water out of the drainage basin, since it is
impossible to let it flow in the river channel.
Proposal of the alternative
To avoid the need to construct the Chitose
Diversion Channel, which is causing serious
environmental destruction and social conflict
especially between within-basin inhabitants and
those living beyond the basin, an alternative is
needed. First, the choice of the highest estimated peak discharge should be re-examined.
Since the historical peak discharge was
12 000 m3 s−1, which was caused by rainfall with
a recurrence period of 200 years, it is reasonable
to adopt a value of around 12 000 m3 s−1 for
the peak discharge for the 150-year rainfall.
Because the inhabitants are asking for their area
to be safe even if a flood with the historical
maximum discharge occurs, they would find it
difficult to accept a lower value. A higher value
than 12 000 m3 s−1 may not be necessary, since
the 1981 rainfall has a recurrence period of
200 years which is greater than the expected
© Institute of Australian Geographers 2002
recurrence period (150 years). However, as this
peak discharge actually occurred in 1981, it
will be better to adopt a discharge higher than
12 000 m3 s−1 for the inhabitants’ safety.
Therefore, a peak discharge between 120 000
m3 s−1 and 18 000 m3 s−1 should be chosen as the
target for flood control. The decision should be
made following discussions involving a representative of the inhabitants, a specialist in flood
control, a geomorphologist, an hydrogeomorphologist, an ecologist and a social scientist.
The final decision should be arrived at from
the point of view of the estimation of the most
probable precipitation-runoff model, probability
analysis of precipitation and flood, ecological
loss by flood control, and cost-benefit. Only
after discussions involving these various viewpoints should the most suitable peak discharge
value for the target of flood control be chosen.
Second, river work in order to minimise flood
damage should be proposed. Geomorphologically, the risk of flooding in the Chitose drainage
basin increases through a higher peak discharge
at the junction of the Ishikari and Chitose. The
152
Australian Geographical Studies
Figure 9 Former river channel of the Ishikari River (after Science and Technology Agency, 1960).
increase of the peak discharge is caused by the
straightening of the channel of the Ishikari. As
illustrated in Figure 9, the channel of the Ishikari
meandered extensively prior to, and was continuously straightened during, the 20th century, with
almost 100 km being straightened in the middle
reach. Therefore, restoration of a meandering
channel in the middle reach could decrease the
peak discharge and reduce the water level at the
junction of the Ishikari and the Chitose.
For this purpose, construction of large retention pools in the former meander belt is useful
both for flood control and to reduce water level
downstream. In the Chitose drainage basin,
retention pools are also effective for flood control and the reduction of flood damage. Figure 10 shows the altitudinal distribution of the
Chitose drainage basin. Lowlands below 7.5 m
have suffered from frequent inundation in the
past. On the basis of this Figure, a pattern of
selective retention pool construction in the area
below 7.5 m can be designed to reduce the area
inundated by floods. Since retention pools are
effectively used as paddy fields, farmers can agree,
provided they receive sufficient compensation
(rental fee income or purchase of land, and the
right of continuous cultivation), to the modification of their farmland to a retention pool.
© Institute of Australian Geographers 2002
Landform Conservation and Flood Control
153
landforms and related ecosystems of the river can
be changed by implementing these alternatives.
Conclusion
Landform conservation is an important task for
geomorphology in the 21st century. For the conservation of natural rivers, which are already an
endangered geomorphic species in Japan, more
suitable flood control plans which provide for
the preservation of natural river landforms are
needed urgently. The analysis of the Chitose
Diversion Channel project revealed that the most
important problem lies in the method used to
determine the peak discharge of the target flood
with a recurrence period of 150 years. Since the
calculation of peak discharge depends on the
artificial enlargement of precipitation with different temporal patterns, the results have a wide
range and are difficult to evaluate. The evaluation
is only possible by combining various viewpoints
such as flood control, geomorphology, hydrogeomorphology, ecology and social science as
well as the views of the inhabitants. The most
suitable peak discharge for the flood control
plan should be chosen after multi-disciplinary
discussion and evaluation. To reduce the peak
discharge value, alternatives including restoration of meandering channel patterns and construction of retention pools are proposed.
Correspondence: Dr Yugo Ono, Graduate School of Environmental Earth Science, Hokkaido University, 060-0810
Sapporo, Japan. E-mail: [email protected]
Figure 10 Altitude distribution of the Chitose Drainage
Basin and the proposed retention pools (after the Hokkaido
Development Agency, 1994).
By coupling these alternatives, flood control
of the Ishikari and the Chitose can be achieved
without damaging the natural river ecosystem of
the Bibi-Lake Utonai. Furthermore, these alternatives will serve to restore the meander river
ecosystem of the Ishikari itself. Flood control
works which have usually destroyed the natural
© Institute of Australian Geographers 2002
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Huchen (Hucho perri) in the Sarufutsu, Northern
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Hokkaido Development Agency, 1994: Technical Report on
the Chitose Diversion Channel Project. (J)
Hoopes, D.T., 1972: Selection of spawning habitat by Stokeye Salmon in small streams. Fishery Bulletin 70, 447–
458.
Keller, E.A. and Swanson, F.J., 1979: Effects of large
organic material on channel form and fluvial processes.
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Lanka, R.P., Hubert, W.A. and Wesche, T.A., 1987: Relations to geomorphology of stream habitat and trout standing stock in a small Rocky Mountain stream. Transactions
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Murphy, M.L. and Koski, K.V., 1989: Input and depletion of
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Australian Geographical Studies
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© Institute of Australian Geographers 2002