1st "Kamaguchi Water Gate"
Completed in 1936
(Maximum discharge 200m3/s)【 The history of Kamaguchi Water Gate】
31 rivers flow into Suwa Lake, and only the Tenryu River flows out. For this reason, Suwa Lake has
been repeatedly flooded since long ago.
Since the Edo period (1603-1867), work has been done to widen the outlet to the Tenryu River(Kamaguchi), and in the Taisho period (1912-1926), excavation work was done from Kamaguchi toabout 1.5 km downstream of the outlet.
Due to the continued flooding of Suwa Lake in the Showa period (1926-1989), the 1st"Kamaguchi
Water Gate" was constructed in 1932 to prevent the decrease in water level of Suwa Lake as theresult of excavation of the Tenryu River at the same time. However, flood damage continued tooccur after that, with major damage in 1950 and 1961.
In 1973, the flood control plan for the entire Tenryu River system was reviewed, and it was decided
to build 2nd "Kamaguchi Water Gate" with a large discharge capacity about 80 m upstream of the 1stCrrent（2nd）"Kamaguchi Water Gate"
Completed in 1988
(Maximum discharge 600m3/s)

Longitudinal section image of Suwa Lake

【The role of Kamaguchi Water Gate】

Suwa Lake

Water Level.

Tenryuu river※ The current Kamaguchi sluice gate was installedby digging down about 3m from lake bottom.

Management Water Level

High W.L. 2.2m
Operation
Tower

Normal W.L. 1.1m
Limited W.L. 0.75m(1) Flood control
In the future (after the Tenryu River revetment is completed),
1,000m3/s of flood control discharge(Max discharge 600m3/s)
will be implemented against 1,600 m3/s of design inflow at
Suwa Lake. For a while, considering the status of Tenryu River
improvemnt, Max discharge 430 m3/s will be implemented toprevent flood damage around the lake and downstream.
(2) Maintaining the normal function of running water
Replenish vested water supply for the downstream Tenryu
River coast.
For these purposes, the water level of Suwa Lake is managed
Operation Room for each gate

Right bank

Left bank

Low W.L. 0.5m
Normal times

Flood
No. 3 gate

Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec.

【Facilities of Kamaguchi Water Gate】

No. 2 gate

No. 4No. 3caisson

caissonNo. 2caisson

No. 1 gate

No. 1caisson<Total cost 10.2 billion yen>
Construction 1978～July,1988
・Foundation construction: 4 caissons
・3Gate（Upper:flap type, Lower:roller type）
・1boat-way(left bank side)・1 fish-way(Right bank side)

Management facilities
・Operation Tower (RC structure, 535.3 m2)
・Telemeters (7 rainfall stations, 9 water level stations)・Discharge warning device: Sirens and speakers 32 stations(33 km)3Floor Operation RoomControl equipment (Construction 1988～1993)
・Surroundings inprovement River park 16,400m2

Outline of Suwa Lake

Seen from the sky
Kamaguchi Water Gate759m(Ref.: Nagano City 362m, Matsumoto City 592m）
2Area
13.3km Circumference 15.9km
Max depth 7.2ｍ Average 4.7ｍ
Strage361,904,000m
CapacityStagnation
39days （Ref.：Biwa Lake 2,000days､Kasumigaura Lake 200days）
time
inflow river 31 (Class A river15､Law applicable river 5､Ordinary river 11)
Basin area 531.2km2
Normal water
759.145ｍ
level
Elevation

8th period

COD4.7mg/l total nitrogen 0.62mg/l
Maintain current level of total phosphorus, Transparency over1.3m

Target Water (2021 Quality COD5.5mg/ℓ total N 0.62mg/ℓ total P 0.041mg/ℓ Transparency1.2m)
Quality

Nagano Prefecture Suwa Constraction Office
Phone 0266-53-6000(representative)
E-mail:suwaken-ijikanri@pref.nagano.lg.jp〒392-8601 1644-10, 1-chome Kamikawa, Suwa

Kamaguchi Water Gate phone 0266-22-6866〒394-0044 1-9-5, Minato, Okaya