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4-2. Removal of the Arase Dam: Japan’s First Attempt toDismantle a Hydroelectric Dam and Restore the Original River
Environment
Overview of Arase Dam
The Arase Dam, built exclusively for hydroelectric power
generation, had an annual power output of 74.66 million
kWh (kilowatt per hour). Completed in 1955, the dam islocated about 15 km from the estuary of the Kuma River(mainstream length 115 km, watershed area 1,880 km2) as
it flows past Sakamoto Town (formerly Sakamoto Village),
Yatsushiro City, in southern Kumamoto Prefecture. The
Arase Dam is a concrete gravity dam consisting of eightgates, having a height of 25 m, a total length of 210.8 m,
Arase Dam.
a total reservoir storage capacity of 10.14 million m 3,
and a submerged area of 123 ha. It is the oldest of theprefecture-operated hydroelectric dams constructed according to Kumamoto Prefecture’s Kuma River
Comprehensive Development Plan.
The removal of the Arase Dam has been beset with twists and turns. The first decision for the removal
was made by the Prefecture Council and the Prefectural Governor in 2003 due to lobbying fromfisher-folks and local residents, only to have the decision frozen in 2008 when a new governor cameinto office. In 2010, however, when it became clear that the procedure to renew water rights could not
be done without the agreement of the fishing co-op, the final decision to remove the dam was madeand work to dismantle the dam began in 20121.

Changes in Environment and Lifestyle in the Kuma River Watershed
Brought about by the Dam
Three dams have been constructed on the Kuma River mainstream, the construction of all three
being pursued intensively over a period of a few years in the late 1950s. These are, in order from theestuary, the Arase Dam (completed in 1955), the Setoishi Dam (completed in 1958), and the Ichifusa
Dam (completed in 1959). The construction of these dams had serious impacts on the Kuma River
environment.
Prior to the construction of the Kuma River dams, catches of ayu fish (Plecoglossus altivelis altivelis)
were extremely large. A river fish, the ayu is one of the most popular Japanese freshwater fish. The
Kawabe River, a tributary of the Kuma River, was particularly well known for the “shaku ayu,” alarge ayu reaching over 30 cm in length, providing livelihoods for professional river fisher-folks andattracting large numbers of angling enthusiasts. The ayu made great contributions to the economy of
the Kuma River watershed, including the inns and local restaurants that catered to the anglers. It isreported that at a time when the average salary for white collar workers in Japan was about 8,000 yen
per month, 10,000 yen could be made in a day by catching and selling ayu fry.

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At the construction site of the Arase Dam in Sakamoto Village, five to six tons of ayu could be
harvested in the two months of the “ochi ayu”2 season. This fishing was carried out by around 280
people in 30 households, but the number of people involved is reported to have fallen to just 16 in thefive years following the completion of the Arase Dam, and to a mere two by 20003. The ayu spawn in
the river in the fall, and the eggs flow down the river to hatch in the vicinity of the estuary. The ayu
fry then swim back up the river in the spring. Large structures that obstruct the flow of water, such as
dams, become serious obstacles hindering the movement of the ayu.
In addition to ayu, eels, donko (a kind of fish, Odontobutis obscura) and gane (a kind of crab,
Eriocheir japonica) could also be caught before the dam was constructed. The donko and gane, caught
using handmade implements, were consumed by local families, and it is said that children would sellthem to adults if they caught a lot of them4. It appears that these creatures also virtually disappeared
within a few years following the construction of the dam.
Since the Kuma River is also the only major river flowing into the Yatsushiro Sea, the freshwater andnutrients from the river are vitally important for the ecology of this almost totally landlocked sea. The
estuary of the Kuma River has tidal flats of about 1,000 hectares, and before the dam was constructed,
the flats were so ecologically rich that even a child could fill a bucket with prawns5.
After the construction of the dam, the biota of the flats changed. The return of the ayu to the upstream
waters was obstructed, and the tidal flats became muddy and difficult to walk on due to a reduction in
the amount of sand flowing down the river. Since the ayu were of significant importance to the local
economy, the fishing co-op began a project to collect ayu fry taken from a fishway of a weir locatedin the lowest regions of the Kuma River, and then transported them by truck to release the fry in
upstream areas. It cost them 50 million yen (approximately USD 500,000) per year to do this. Whilea fishway was constructed on the Arase Dam in 1998, only a very small number of ayu were able topass it, and according to the observation of local fisher-folks, the dam reservoir at the top end of the
fishway was almost completely still. Even if the ayu were able to swim up the fishway, they were notable to swim further upstream from there.
The dam also distressed local residents with its noises and vibrations, deterioration of water quality,
and unpleasant smell. In the former Sakamoto Village, people were living in homes built close to
the river to make it easy to fetch water for daily life. There were floods before the dam was built,
but people coexisted with the floods by moving their household belongings to the upper floor before
the floods arrived, and going out to catch ayu or collect river sand during flood times. However, thedamage to these private houses was extremely severe after completion of the Arase Dam because thewater level rose very rapidly when water was released. Silt that built up in the dam lake behind thedam flowed downstream when water was released. The houses that were flooded became inundatedwith silt, making it impossible for the people to coexist with the floods.

The Process up to the Decision to Remove the Dam
There were several twists and turns in the story up to the point when the final decision was made toremove the dam. In the former Sakamoto Village, where the dam is situated, the Sakamoto Village
River Fisher-folks’ Union began activities targeted at revitalization of the Kuma River in 2001, a
couple years before the renewal of water rights was due in March 2003. An Association to Consider<4-2>2

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the Arase Dam that encompassed a wider range of the local residents was established, thus givingorganization to the calls for the removal of the dam as the consensus of the residents. In September
2002, the Sakamoto Village Council submitted a written opinion to Kumamoto Prefecture demanding
suspension of the use of the dam. The prefecture then announced that it would limit the renewal of
the water rights of the Arase Dam to seven years and begin the work of dismantling the dam in April
2010. This was the first time an official decision was made to dismantle a hydroelectric dam, not onlyin Japan but in the whole of Asia. The prefecture then continued deliberations on the methods and soon to be used to dismantle the dam by establishing an Arase Dam Measures Investigation Committee
consisting of academic experts, related organizations and representatives of the local residents.
The process was proceeding smoothly until Governor Kabashima was inaugurated in 2008. It wasannounced that the plan to decommission the dam had been withdrawn for economic reasons, among
which was the estimated 10 billion yen (approximately USD 100 million) cost to dismantle the dam.
When in January 2010 it became clear that the procedure for the renewal of water rights, due toexpire in March of that year, could not be completed on time6, dam removal once again became thepolicy espoused by the prefecture. At the end of March 2010, power generation at the Arase Dam was
terminated and all the gates were fully opened on April 1st.

The State of River Restoration in the First Year after Opening the Gates
A year and a half after the gates opened, the revival of the Kuma River had become apparent to the
local people who had been continually observing the river. According to Ms. Shoko Tsuru, Vice
Chairperson of the Kumamoto Nature Interpreter’s Association, the changes seen thus far in the river
can be described as follows:
1) Change in water quality: Water downstream from the dam that was turbid before the gates wereopened, has shown a remarkable change, becoming clear and blue following the opening of thegates. Water turbidity after rain also clears more rapidly;
2) The appearance of rapids and pools: Before construction of the dam, there were rapids andpools in about 20 locations above and below the dam site, resulting in a self-purifying effecttaking place through the creation of turbulence in the river flow. After the construction of the dam,these rapids and pools were lost due to inundation upstream and a reduction in the supply of earthand sand downstream. They have reappeared after the gates were opened;
3) Kuma River fish: It has not been possible to ascertain the state of restoration of fish thus far;4) Kuma River estuary tidal flats: It is reported that after the gates were opened the amount of sandflowing down the river increased. The muddiness of the Yatsushiro Sea tidal flats was therefore
reduced and they have become easier to walk on. The numbers of creatures that inhabit the sandy
areas by digging holes in the sand, such as anajako (a kind of prawn, Upogebia major) andhamaguri (common orient clam, Meretrix lusoria), appear to have increased, but since the numberof people collecting these has also increased it has not been possible to ascertain precise numbers;5) Green laver (aonori) in the vicinity of the estuary: Although these grew to only about 50 cm inlength before the gates were opened, they now extend to about two meters. The colors are now
more vivid than before and fade less easily;6) Fisheries in the Yatsushiro Sea: The seaweed bed in the vicinity of the Kuma River estuary has
revived. Very soon after the gates were opened, large catches of the brachiopod midorishamisengai(Lingula anatina) became possible for the first time in 30 years, and veined rapa whelk (akanishi)
and razor clam (mategai) have also increased. Eels, which no one had tried to catch for many years<4-2>3<Nature and Our Future: The Mekong Basin and Japan>

due to their absence from the environment, reappeared after the gates were opened and foundtheir way onto the market last year;
7) Removal of the dam and revival of the sea: Since the gates were opened, it appears that thewater in the estuary and even the sea has become cleaner. The Kuma River has a great impact
on the Yatsushiro Sea and removal of both the Arase and Setoishi dams will have a good effecton the revival of the sea and tidal flats environments. When a dam is present, accumulated silt
flows downstream when water is released. Following the opening of the gates, the amount ofwood flotsam and jetsam floating downstream increased, resulting in the negative impact of torn
nets. This is probably because the mountain forests in the upstream areas are not being properly
cared for. It is hoped that if the tidal flats are restored, more young people are able to make a livingfrom fishing.

Toward a Revival of the Entire Watershed
As noted above, the decommissioning of the Arase Dam is the first case of its kind in Asia. The
impacts of decommissioning on the Kuma River and the Yatsushiro Sea, however, will remain
limited as long as the Setoishi Dam, located 10km upstream of the Arase Dam, continues operation.
When both of these dams are removed, the Kuma River will become a Class A river with no largescale dam all the way upstream to the Ichifusa Dam, close to the border with Miyazaki Prefecture,
and a magnificent revival of the ecology and environment of the river and sea, as well as biologicalresources, is anticipated.
The 50-year term of the Setoishi Dam water rights will also expire in 2014. The local fishing co-op
has refused to recognize the renewal of water rights and a resolution aimed at removal of the dam
has made the dam’s decommissioning a possibility. However, since the Setoishi Dam is located on
the outskirts of both Ashikita Town and Kuma Village, there is no resident community that suffers
direct damage from the dam, as in the former Sakamoto Village, and because 70% of the ayu caught
downstream are released upstream of the Setoishi Dam, the number of ayu harvested from the river
has been maintained. For these reasons, the intense activities by residents to demand the removal ofthe dam as seen at the Arase Dam have not occurred in the case of the Setoishi Dam. Nevertheless,up to now, when water was released from the Setoishi Dam, the Arase Dam played the role of a
supplementary dam, adjusting the water volume. The Setoishi Dam has thus relied on the Arase Dam
to some extent, creating a necessity for the operation of the Setoishi Dam to be reviewed when the
Arase Dam is removed.
Even though the removal of the Setoishi Dam may not come about, if hydroelectric power generation
is suspended and the gates opened, albeit temporarily, the flow will be restored and sand and earth will
be supplied to the lower reaches. Thus it is said that by altering the operation of the Setoishi Dam togive increased consideration to ecology and nature, revival of the Kuma River and the Yatsushiro Sea
can be enhanced7. From now onwards, the focus of the revival of the Kuma River and the Yatsushiro
Sea will move to the Setoishi Dam and whether or not it is possible to remove the Setoishi Dam oralter its mode of operation.

Recommendations: Multifaceted Monitoring Should be Conducted
The removal of the Arase Dam is an extremely important case when considering methods for the
future revival of the natural environment of Japan’s rivers, on which a large number of dilapidated<4-2>
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dams exist. To really understand the environmental impacts of decommissioning the Arase Dam, it isnecessary to carefully monitor the environment prior to, during, and after dismantling the dam. Precise
monitoring also provides valuable information regarding necessary conditions to enable a smoothenvironmental revival. However, the Arase Dam is the property of Kumamoto Prefecture, and there isvery little nationwide interest in its removal. Multifaceted monitoring surveys by specialists have notbeen carried out. Inquiries to the official responsible for biodiversity-related matters at the Ministry of
the Environment revealed that the Ministry is simply not aware of the Arase Dam.
Kumamoto Prefecture has set up a Specialist Follow-up Committee on the Arase Dam Removal,
which is proceeding with deliberations to “implement the dam removal safely and with consideration
for the environment while evaluating and verifying the results of monitoring surveys on water control
and the environment with respect to the removal of the Arase Dam.” The scope of this committee
however, is limited to monitoring in the Arase Dam removal impact assessment zone, downstream
only as far as the Yohai Weir, which does not include the estuary tidal flats or the Yatsushiro Sea. If
this situation remains unchanged, the only comprehensive survey will be the observations that havebeen continuously conducted by local citizens’ organizations active in opposing the Kawabe River
Dam and demanding the removal of the Arase Dam.
As noted above, the removal of the Arase Dam will have a huge impact on the ecology of the tidal
flats and the Yatsushiro Sea, and the fisher-folks who depend on the marine resources. Considering theimportance of the Arase Dam removal as a case of natural restoration and Asia’s first dam removal,
we feel strongly that a monitoring survey that includes the Yatsushiro Sea should be conducted andthe results made public.
References
Corporate Agency of Kumamoto Prefecture. Kumamoto Prefecture Specialist Follow-up Committee on the Arase Dam Removal(in Japanese).
http://www.pref.kumamoto.jp/site/kigyoukyoku-hp/ (Last accessed on April 20, 2012)
Corporate Agency of Kumamoto Prefecture. Removal of the Awase River Dam (in Japanese).
http://www.arasedamtekkyo.hinokuni-net.jp/ (Last accessed on September 18, 2013)
Kimoto Seiko et al. 2011. Revive! The Clear Flow of the Kuma River: The Struggle of Fisherfolk against the Kawabe River Dam andthe Arase Dam (in Japanese).

Sayoko Iinuma (Global Environmental Forum)

1. To view pictures of the project site, visit: http://www.arase-dam.jp/shinchoku/index.html
2. Ayu that swim downstream to spawn in the fall
3. According to the morning edition of the Kumamoto Nichinichi Shimbun Newspaper of October 27, 2002
4. From a hearing with Mr. Seiko Kimoto (Chairman of the Sakamoto Village River Fisher-folks’ Union) conducted on October 23, 2011
5. From a hearing with Ms. Shoko Tsuru on October 23, 2011
6. Since water cannot be used for power generation unless the water rights are renewed, the continued existence of the dam became
untenable.
7. From a hearing with Ms. Shoko Tsuru on October 23, 2011<4-2>
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