Nagara River
Estuary Barrage

History of flood control along the Nagara River
1 Ring-levee communities of waju
The Nagara River empties into Ise Bay through the downstream basin it has shaped together with the other two of the Kiso Three Rivers, namely the
Kiso River and Ibi River. The mesh-like pattern of intertwined streams has shifted during each flood.
In 1609, at the dawn of the Edo period (1603–1868), a great levee was constructed on the left bank of the Kiso River to protect the domain of Owari.
This nearly 50-km-long levee called okakoi zutsumi, literally a levee enclosure, served as a bulwark against other clans from western Japan as well
as floods. Unfortunately, the domain of Mino on the opposite side of the river suffered frequent flooding because of the restriction imposed to keep
their levees at least 91 cm lower than the levee enclosure of okakoi zutsumi, a fact that prompted further development of ring-levee communities
called waju.
Each waju community is encircled by a levee to protect settlements and farmland from floods. These ring levees, constructed by local residents, arewitnesses to united struggles of community members against the ever-present threat of flooding over their long history.

2 Horeki Flood Control Works
In the mid-Edo period, the ruling Tokugawa shogunate assigned so-called Horeki Flood Control Works to divert the courses of the Kiso ThreeRivers. The Shimazu clan duly fulfilled the duty by constructing the Aburajima cofferdam and other works between 1754 and 1755.

3 Improvement works
during the Meiji period(1868–1912)
In 1887, the fledging Government of Meiji
Japan embarked on major improvement
works with an ambitious plan tocompletely divert the Kiso Three Rivers.
The works lasted until 1912, and costed
about 12 percent of the national budget toshape the downstream basin close to what
it is today.

Sketch map of downstream basin(1755) and target sections of the
Horeki Flood Control Works

Distribution map of waju communities
before improvement works during the
Meiji periodPlan drawing of improvement works by
the Meiji government

4 Disasters in recent years
The improvement works during the Meiji period have considerably mitigated risks of flooding in the downstream basin of the Kiso Three Rivers.
Notwithstanding that, Typhoon Vera hit the Tokai Region in September 1959 and devastated the three prefectures of Gifu, Aichi, and Mie. Withother affected prefectures included, over five thousand people were killed or went missing. In August of the following year, Typhoons Virginia andWendy caused serious flooding damage, such as levee breaches on the Nagara River. Later, in June 1961, intense rainfall from a seasonal rain front
and Typhoon No. 6 caused yet another major flood that breached a levee along the Nagara River and inundated a vast area extending across thecities of Gifu, Ogaki, and beyond. These floods, including the one caused by Typhoon Vera, are known as the three major floods of the Showa
period (1926–1989).
Later, in September 1976, an unlucky
combination of a rain front and Typhoon
Fran caused a week of heavy rain that led
to major flooding of the Nagara River.
Consequent severe damage in various
parts of the basin included the collapse of
Ibi River
the right bank in the area lying beyond
Tokaido Shinkansen
Moribe in Anpachi, a part of Anpachi
District in Gifu Prefecture.

Levee breach

People crossing an inundated area on a boat
in September 1976 (Anpachi, Anpachi District,Gifu Prefecture)

NagaraRiver

AnpachiRing levee
WanouchiInundation following the collapse of the Nagara River’s right bank in the area lying beyond Moribe in Anpachi (Anpachi and Sunomata(today’s Sunomata in the city of Ogaki) in Anpachi District, Gifu Prefecture, September 1976)

Sound water resource development and prevention ofsalt damage induced by dredging
Dredging the Nagara River and preventing the associated seawater intrusion
Prior to construction of the estuary barrage and dredging works, a relatively elevated strip of the riverbed, known as the mound in the section
between roughly 14 and 18 km from the river mouth, had somehow managed to hold back seawater intrusion even when the river carried
little water.
Dredging carried out according to the plan to deepen the riverbed across the board would have let seawater advance to about 30 km from theriver mouth, further upstream of the mound that held it back. Resulting salination would thus render river water unfit for use in the hitherto
unaffected upstream areas. Over time, both groundwater and soil would suffer salt damage and become unfit for farming and significantly
limit other land use.
The Nagara River Estuary Barrage holds the tide back so that dredging works can be carried out while preventing salt damage. It has
desalinated the upstream area, which led to further water resource development.
Dredging works of the section with the mound began a day after the barrage was put into full service on July 6, 1995 and ended in July 1997.

Before barrage construction and dredging works
River mouthRiver mouth
LegendFresh
water
Saltwater

Water
intakeKatsuga Water Intake
Kita-Ise Industrial Water Intake 2

Shin-oe Water Intake

Kita-Ise Industrial Water Intake 1

Saltwater intrusion that would result from dredging works without barrage construction(water becomes unfit for intake and groundwater is contaminated by salt)

Katsuga Water Intake
Shin-oe Water Intake
Kita-Ise Industrial Water Intake 2
Kita-Ise Industrial Water Intake 1

Dredging works carried out after barrage construction to block saltwater

Katsuga Water Intake
Shin-oe Water Intake
Kita-Ise Industrial Water Intake
Intake for Kita-Chusei Water Works
Estuary barrage(blocks the tide) Intake for Nagara Water Conduit
River mouth

Dredged section in the Nagara River

Mound in the section 14–18 km upstreamof the river mouth

LegendDredged section

Distance fromthe river mouth

Mound exposed above the water at low water during a spring tide

Benefits of the Nagara River Estuary Barrage
1 Robust flood control

Reduced water level during flood

Construction of the Nagara River Estuary Barragebegan in fiscal year 1971. With understanding andsupport from local community members, such as
stakeholders in the fishery and farming sectors,
the permanent works were completed in fiscal
year 1994 for gate operation to begin in July 1995.
Subsequent dredging works of the section withthe mound that lasted until July 1997 hassignificantly improved the discharge capacity of
the river downstream when it swells. Operating
the barrage has reduced the risk of levee breaches
and proved very effective in flood control. For
instance, during major floods of the river above
the flood-watch water level in October 1998,
September 1999, September 2000, July 2002,
October 2004, and August 2014, the water level
was reduced by one to two meters compared to
the level that would have resulted without thebarrage.
During the flood of the Nagara River on August17, 2014 caused by heavy rain from a front thatremained over the area from August 14 to 18,
dredging works are estimated to have reduced thewater level by about 1.6 m at the Sunomata gauge
station 39.2 km upstream of the river mouthcompared to the level that would have resulted
before the works. As a result, the high water could
be safely conveyed downstream.

(Sunomata gauge station, 39.2 km upstream of the river mouth)

Reduced water level at peak flow

* T.P. is short for the mean sea level of Tokyo Bay (Tokyo Peil) that serves as the altitude reference point in Japan.

Design high-water level(T.P. + ca. 12.2 m)
Design water level without dredging works(T.P. + ca. 9.8 m)

Water level reduced by about 1.6 m
during the flood in August 2014
Ordinary water level(T.P. + ca. 1.5 m)

Actual water level during the flood in August 2014 (T.P.
+ ca. 8.2 m)

Reduction in water level during major floods
Date

Peak flow rate at theSunomata gauge station

Reduced peak water level at
the Sunomata gauge station

October 18, 1998

ca. 4,300 m3/s

ca. 1.2 m

September 15, 1999

ca. 5,900 m3/s

ca. 1.1 m

September 22, 1999

ca. 4,400 m3/s

ca. 1.3 m

September 12, 2000

ca. 4,900 m3/s

ca. 1.2 m

July 10, 2002

ca. 4,400 m3/s

ca. 1.6 m

October 21, 2004

ca. 8,000 m3/s

ca. 2.0 m

August 17, 2014ca. 4,100 m3/s

ca. 1.6 m

2 Better water use
Water use in the downstream part of the
Nagara River (as of January 2015)(1) New water supplies
The Nagara River Estuary Barrage desalinated upstream water, whichbecame available for water supplies and industrial use at a maximum volumeof 22.5 m3 per second.
In April 1998, intake of this newly developed source was initiated for the
Nagara Water Conduit and Kita-Chusei Water Works.

Nagara Water Conduit (2.86 m3/s)

Supplies added by the estuary
barrage
More reliable water intake fromexisting sources

Nagara River
Water Supply(irrigation)

Nagara River

Kita-Chusei Water Works (0.732 m3/s)

Water is taken in and supplied as municipal water to two cities in the
Chusei area in Mie Prefecture. The facility currently delivers industrial
water supplies in Kita-Ise.

Aichi
Prefecture

Mie
Prefecture

NagoyaCity

Total

Municipal
water

Kita-Ise Industrial
Water Supply(industrial)
Kita-Chusei
Water Works(municipal)

Top: Planned amount
Bottom: Ensured availability (during the second most severe drought in the last 20 years)

Fukuhara Water
Supply(irrigation)

Nagara Water
Conduit(municipal)
Nagara River
Estuary Barrage

Industrial
water
Total

Kiso River

Water is taken in and supplied as municipal water to four cities and fivetowns in the Chita Peninsula in Aichi Prefecture.

Breakdown of water use (maximum amount)

Water intake

Ise Bay

Nagashima in the city of Kuwana(municipal, irrigation, maintenance ofchannels)(2) More reliable water intake from existing sources
Prior to the full-fledged operation of the Nagara River Estuary Barrage, water intake from existing sources downstream of the mound was impededby contamination with saltwater intrusion induced by subsidence of the riverbed. Intake had remained particularly unstable for the Kita-Ise Industrial
Water Supply, even with the second intake constructed to cope with the problem. Once the barrage entered full service, water intake became morereliable as water upstream of the barrage was desalinated.
Kita-Ise Industrial Water Supply (2.951 m3/s)
Fukuhara Water Supply (0.256 m3/s)
Water supply to Nagashima in the city of Kuwana for irrigation, municipal use, and maintenance of channels (1.22 m3/s)
In the past, Nagara River Water Supply drawn from upstream of the mound used to be affected by the tide. However, more reliable intake became
possible because the full-fledged operation of the barrage stabilized the water level.
Nagara River Water Supply (8.78 m3/s) for irrigation in the cities of Hashima and Kaizu in Gifu Prefecture

Intake record of Kita-Ise Industrial Water Supply
Water became constantly
available for intake once thebarrage entered service

Water was unavailable for intake before
the barrage started operating(m3/d)

Monthly average ofthe daily water intake

Jan. 2015

Jan. 2014

Jan. 2013

Jan. 2012

Jan. 2011

Jan. 2010

Jan. 2009

Jan. 2008

Jan. 2007

Jan. 2006

Jan. 2005

Jan. 2004

Jan. 2003

Jan. 2002

Jan. 2001

Jan. 2000

Jan. 1999

Jan. 1998

Jan. 1997

Jan. 1996

Jan. 1995

Jan. 1994

Jan. 1993

Operation of the barrage since July 1995

(3) Greater capacity to cope with drought

Ise Bay

The Kiso River System was affected by drought when the amount of rainfall in July to August, 2000 fell nearly 40 percent lower than that of an
average year. Still, water supplies were not disrupted owing to new sources that became available for locations such as the Chusei area in Mie
Prefecture and the area serviced by Aichi Water Supply in Aichi Prefecture. This development was thanks to the Nagara River Estuary Barrage,
Agigawa Dam, and Misogawa Dam.
Were it not for water delivery from the Nagara River Estuary Barrage, the Mie prefectural government estimated that about 64,000 households or
180,000 residents in serviced municipalities in the Chusei area would have suffered disruption of supply for about three to eight hours a day.
Likewise, the water supply to about 1.25 million residents in the area serviced by Aichi Water Supply probably would have been curtailed or
disrupted because Makio Dam would have dried up without water delivered from the barrage or other sources.
Later, from spring to summer 2005,
Better water use during the drought of 2005
the amount of rainfall in the Chubu
region fell 20 to 40 percent below
Nagara River
Ibi Riverthat of an average year. Water stored
in dams in the Kiso River System
Kiso Riverwas drawn down at a faster pace thanduring the recent past’s most severe
drought year of 1994, which raised
Area serviced byconcerns about the potential impact
Aichi Water Supply
on water supplies. Fortunately, people
Additional area ofin the Chita Peninsula in Aichi
supply during drought in 2005
Prefecture were not forced to cut
Nagara River
water use thanks to reliable supply
Estuary Barrage
from the Nagara River Estuary
Additional area of supply during the drought
Barrage via the Nagara Waterof 2005 extending across five cities with an
Conduit.
approximate total population of 410,000
The unused portion of water supplied(excludes Kagiyamachi in the city of Tokai)
through the Nagara Water Conduit(0.66 m3/s) was delivered to a
Serviced area extending across four cities
and five towns in the Chita Peninsula, withneighboring area, usually served by
an approximate total population of
Aichi Water Supply, to make the best
430,000 as of 2005 (only Kagiyamachi isuse of the source developed by theserviced in the city of Tokai)
Nagara River Estuary Barrage. This
diversion has mitigated the impact ofdrought on the area served by Aichi
Area serviced by the Nagara
Water Conduit
Water Supply that happened to hostExpo 2005.
Area serviced by Aichi Water
SupplyServiced area extending across two cities of
the Chusei area, with an approximate total
population of 310,000 as of 2005 (only theformer towns of Mikumo and Ureshino areserviced in the city of Matsuzaka)

Additional area of supply during
the drought of 2005

Key environmental surveys conducted in relation to
the Nagara River Estuary Barrage
In the planning phase of constructing the Nagara River Estuary Barrage, a survey team known as KST studied resources in the estuarine region of theKiso Three Rivers. Later, various kinds of studies were conducted at each milestone marked by the beginning of important construction works. They
were aimed at keeping records of associated changes in the local environment and ensuring that adequate measures are taken as necessary. In fiscal
year 1994 when the permanent works were completed, another study was conducted while operating the barrage gates.
Status of environmental surveys
From fiscal year 1995, changes in the riverenvironment were monitored for five years to check theeffectiveness of conservation measures. The survey
primarily examined the following items, with advice
and recommendations from experts so as to conserve
the environment of the Nagara River while making
sure that the barrage fulfills its original purpose.
Disaster prevention• Measures against water infiltration into waju
ring-levee communities• Saltwater distribution
Water quality and bottom sediment
Ecosystem• Upstream and downstream migration of fish
• Habitat for plants, fish, shellfish, and otheranimals
This survey was publicly conducted with guidance andadvice from a committee of experts to monitor the
Nagara River Estuary Barrage. Each year, survey
results were published in an annual report on barrage
monitoring.
The monitoring committee held a total of twelve discussion sessions during the five years beginning in 1995. During their discussions, committee members
provided necessary guidance and advice on monitoring plans and barrage operation to the predecessors of the Japanese Ministry of Land, Infrastructure,
Transport and Tourism and the Japan Water Agency. Recommended activities included DO surveys and consideration of flushing operations to improve water
quality. The monitoring committee was deemed to have mostly fulfilled its original purpose and was disbanded in March 2000. As it wound up, the committee
indicated the immediate direction that should be taken on monitoring to keep the barrage operating reliably.
From fiscal year 2000 onward, monitoring continued in accordance with these recommendations through a follow-up survey. Findings were discussed among
members of a follow-up committee for managing dams and the like in the Chubu Region and those of its subordinate barrage working group.
The follow-up committee has deliberated on analysis and evaluation findings from follow-up surveys compiled in regular reports in fiscal years 2004, 2010,
and 2015. In the deliberations in fiscal year 2015—after 20 years of barrage operation—the committee acknowledged that the survey had been properly
conducted; that the barrage has properly fulfilled its intended purposes to control floods and enhance water use; and that the barrage is properly managed andoperated as demonstrated by the stable river environment in recent years after certain changes experienced soon before and after operation began.

Facilities for barrage operation
Overview[Location]
Left bank: Nagashimacho-Tokadomo, Kuwana,
Mie Prefecture
Right bank: Fukushima, Kuwana, Mie Prefecture
Information onhydrologicalfactors, water
quality, etc.

Road leading to
the city of Kuwana

Artificial
streamKiso River Downstream Office,run by MLIT

Rock-ramp
fishway
Lock gate(serving also as alock fishway)
Fishway with an
attraction channelon the right bank

Nagara River

Nagara River Estuary
Barrage Control Center

Artificial stream
Water gauge
Water temperature andconductivity meter
Automated water quality
monitoring equipment
Alarm (speaker)
Industrial television formonitoring

Overflowlevee

Rock-ramp
fishway

Gauge station

Adjustment
gate

Ibi River

Water temperature andconductivity meter

Upstream gauge
station for theright bankWater gauge
Water temperature and conductivity meterIndustrial television for monitoring

Upstream gauge
station for theleft bank

Adjustment Gate 10
Adjustment Gate 9
Adjustment Gate 8
Adjustment Gate 7
Adjustment Gate 6
Adjustment Gate 5
Adjustment Gate 4
Adjustment Gate 3

Adjustment Gate 2
Adjustment Gate 1

Water temperature andconductivity meter

Water
gauge
Industrial
televisionformonitoring

Lockfishway

Water gauge
Water temperature and conductivity meterIndustrial television for monitoring
Alarm (speaker)

Downstream gauge station
for the right bank

LegendLined flood
channelNagara River Estuary
Barrage Control Center

Water temperature andconductivity meter
Fishwayobservation room

Fishway with an
attraction channelon the left bankRoadleading to
NagoyaBarrage discharge control system
Multiplex radio system
Telemetry equipment anddischarge alarm
Data transmission equipment
Industrial television for monitoring

Aqua PlazaNagaraAqua Plaza Nagara, which serves as adisaster prevention museum

Downstream gauge
station for the left bankWater gauge
Water temperature andconductivity meter
Automated water quality
monitoring equipment(water temperature, pH,
DO, turbidity)

Lock gate (serving also as a lock fishway)

Strong-motion
seismograph

Lock fishway

Fishway with an attraction channel(on the left bank)

Gate operation
All gates of the Nagara River Estuary Barrage employ an environmentally sound double-roller design to perform both overflow and underflow
operations in a fine-tuned manner. These gates are operated in modes corresponding to different amounts of inflow and water levels on thedownstream side in ordinary times, against flooding, against flooding combined with a storm surge, and in anticipation of a storm surge. Anothertype of operation is carried out in response to a tsunami. Each operation is outlined as below.

Side view of an
adjustment gate

Modes of gate operation

Downstream
water level
Upstream side

Downstream side

Mean high tide during syzygy
at T.P. + 1.2 m
Mean tide level at T.P. + 0.2 m
Mean low water during syzygy
at T.P. − 0.9 m

During a storm surge (fully open)
In anticipation of a storm surge(fully open, overflow and underflow)

Upstream water level
T.P. + 1.3 m (upper limit at ordinary times)

In anticipationof flooding(underflow)

In ordinary times(overflow and underflow)

T.P. + 0.8 m (lower limit at ordinary times)

In anticipation of astorm surge(fully open, underflow)

Againstflooding(fully open)

Inflow to
barrage

1 Operation in ordinary times

Overflow

Underflow

Gate operation

In ordinary times, the river environment is conserved with a combination of
Downstream
Upstream Downstream
Upstream
overflow operation ( ) and underflow operation with raised lower stage gates
High
tide
High tide( ) to let water flow both over and under the gates and further down the river.
The water level upstream is kept as low as possible with a given inflow to
Low water
Low water
minimize the difference with the downstream level. In principle, it is kept up to
0.8 m above T.P., or the mean sea level of Tokyo Bay (Tokyo Peil), while theupper limit is assigned at T.P. + 1.3 m or the level 0.1 m higher than the meanhigh tide during syzygy at T.P. + 1.2 m.
Adjustment gates are operated with careful consideration to help fish move upstream or downstream. For instance, during an upstream migrationseason, priority is given to gates near both shores next to the fishways to lower the water level and thus lure fish into them.
As a way to safeguard its quality, upstream water is occasionally flushed, aside from being constantly sluiced in ordinary times. Since fiscal year
2011, the barrage has been operated even more flexibly to conserve and improve the river environment.

2 Operation against flooding

Kiso River

Nagara River

Ibi River

Upstream

Downstream

When a flood occurs, all gates (ten adjustment gates, as well as a few other lock gates and lock fishway gates) are lifted above the levee height sothey do not hamper the flow of flood water.
Overflow operation takes place by default until the inflow rate to the barrage reaches 200 m3/s. Once that threshold is crossed and further increase isanticipated, adjustment gates are lifted for underflow operation to prepare for full opening in response to flooding.
The operation to fully open all gates against flooding is
Gate operation
Reference point
prompted by measurement of the flow rate at a3
Inflowrate
tothebarrage
exceeds
800m/s
reference point upstream to allow enough time before
the inflow rate to the barrage reaches 800 m3/s. In thisGates fully
openedmanner, gates can be raised safely and reliably while
This operation iscarried out if any of the
avoiding sharp fluctuations in water levels bothconditions (1) throughupstream and downstream of the barrage.
(3) below does nothold or when the water
3
Once the inflow rate reaches 800 m /s, saltwater islevel at the Nagashima
Aburajima gauge
washed downstream and eliminates the risk of saltwater Saltwater
Fresh water
station exceeds T.P. +intrusion further upstream. Accordingly, all gates are
1.92 m.
fully opened ( ) and their bottom edges are kept higher
Operation to block saltwater intrusion
than the levee height (T.P. + 5.8 m) until the inflow rate
This operation is
3
subsides below 800 m /s.
(2) The downstream water level iscarried out tono less than T.P. + 0.5 m.
Any risks of saltwater intrusion induced by a particular(3) The inflow rate to prevent the risk ofthe barrage is less saltwater intrusion
downstream water level or other conditions can be(1) Rising tide(i.e., when all the
Nagara River Estuary Barragethan 1,400 m /s.
conditions (1) through(5.4 km from the river mouth)
stemmed by maintaining the operation to block the(3) hold), provided thatthe water level at the
intrusion without fully opening the gates ( ).
3

Saltwater

3 Operation against a storm surge

Fresh water

Nagashima Aburajima
gauge station is nohigher than T.P. +1.92 m.

When a storm surge occurs, all gates are lifted above the levee height in the same manner as against flooding so no gates hamper the river’s flow.
Gates are fully opened if the downstream water level exceeds T.P. + 1.2 m and is expected to rise beyond T.P. + 2.1 m to avoid sharp fluctuations inwater levels both upstream and downstream of the barrage. Once the downstream water level exceeds T.P. + 2.1 m, the bottom edges of all gates arelifted above the levee height (T.P. + 5.8 m).
Operation to block saltwater intrusion is maintained even with the downstream water level beyond T.P. + 1.2 m, as long as it is not expected to
exceed T.P. + 2.1 m.

4 Operation in response to a tsunami
When there is a tsunami warning for the coast of Ise Bay issued by the Japan Meteorological Agency combined with a tsunami height of 2 m or
greater measured at the Kamishima gauge station at the mouth of Ise Bay, which signals the advancement of a major tsunami wave from the sea into
the estuary, all gates are lifted above the levee height. The gates will therefore not hamper the flow of water.
Once the gates are fully open, a siren will sound or an announcement about an approaching tsunami will be made through speakers to prompt people
on boats, fishers, and other river users to evacuate the river. Relevant authorities will be notified of the response too, so patrols will take place toensure timely evacuation.