Okayama Prefecture Dam

1905-Chiya Dam / Okayama Pref.

4.0
1905-Chiya Dam / Okayama Pref. Okayama Prefecture Dam
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Date of interview: Wednesday, February 18, 2015

On this day, we were all invited to see the Shin Naruha River Dam, and we stopped at the Senya Dam on the way there. It looks like a directly operated dam because of its gorgeous equipment, but it is a Okayama Prefecture-owned dam. The time was around 7:40 in the morning. We visited the dam in the sleet.

From the left bank

The most luxurious equipment is this. In addition to the 11 free overflow emergency flood discharges, there are also 11 free overflow flood discharges,crest gate(The station is fully equipped with four roller gates, two orifice gates, and two conduit gates for permanent flood discharge. In addition, there is one five-stage linear multistage selective intake system and one water discharge pipe.

Looking downstream from the left bank
Looking downstream from the left bank

The specifications of the flood control discharge system are as follows

discharge pipe

form (something takes)Circular buried steel pipe with square hood
DimensionsDrinking mouth W3.200mxH4.400m
Middle section Φ2.400mx Φ2.000m
number of articlestwo articles
flow rate (esp. water or electricity)100m3/sec
Completion dateMarch 1997
productionMitsui Engineering & Shipbuilding Co.

main gate

form (something takes)Jet Flow Gate
caliberΦ2000mm
number of gatestwo gates
Opening and closing speed0.1m/min
open/close systemHydraulic cylinder system
Completion dateMarch 1997
productionMitsui Engineering & Shipbuilding Co.

secondary gate

form (something takes)ring holowagate
caliberΦ2000mm
number of gatestwo gates
Opening and closing speed0.3m/min
open/close systemHydraulic cylinder system
Completion dateMarch 1997
productionMitsui Engineering & Shipbuilding Co.

This is the construction monument of the Senya Dam. It shows that the main body of the dam was constructed from March 1989 to June 1997, a period of eight years. The word "Heisei" sounds like a recent development, but it was a long time ago.

monument
monument

On the upstream side of the left bank, there is a magnificent building, which is a boatyard and a warehouse for storing patrol boats for the reservoir. An incline is also attached on the other side (reservoir side).

boathouse
boathouse

The top edge is open to automobile traffic.

View of the top edge from the left bank
View of the top edge from the left bank

The reservoir of the Senya Dam is named "Sensuiko (Thousand Water Lake).

Stone monument on the upstream side of the left bank
Stone monument on the upstream side of the left bank

There is another stone monument on the left bank with the river name "Takahashi River" engraved on it.

Another monument on the left bank
Another monument on the left bank

Looking at the upstream face, the facilities are so well equipped that it is hard to believe that it is a very prefectural dam.

Looking upstream from the left bank
Looking upstream from the left bank

There is a management office on the left bank. It also has an exhibition room, but it is too early in the morning and not open yet. I hear that the models and other exhibits are amazing, so I would like to visit again.

Senya Dam Management Office and Dam Exhibition Room
Senya Dam Management Office and Dam Exhibition Room

The font of "Chiya Dam" on the wall looks stylish, like Hotel Okura.

Senya Dam font
Senya Dam font

To the top

The mountains upstream were covered with a light overall snow cover and were white. The wind seemed to be strong.

View of the reservoir from the top
View of the reservoir from the top

The spare gate of the conduit gate can be seen in the middle of the top edge.

Conduit gate reserve gate
Conduit gate reserve gate

The preliminary gate specifications are as follows

form (something takes)Steel roller gate
Door body width, door body heightW3.700mxH4.620m
number of gatestwo gates
Opening and closing speed0.5m/min when hoisting, 1.0m/min when lowering
door weight32t
Completion dateMarch 1997
productionMitsui Engineering & Shipbuilding Co.

Downstream side is directly downstream in the middle.conduit gate(The design is a bit unusual in that it has a (jet flow gate) building. The notch in the middle of the sub-dam is not there to prevent water from the jet flow gate from hitting the sub-dam and damaging it...right?

Looking downstream from the top
Looking downstream from the top

The building will be a selective water intake facility.

Selective Water Intake Facility Building
Selective Water Intake Facility Building

The specifications for each are as follows

Intake gateWater control gateLower gate
form (something takes)Straight multi-step gate (5 steps)
(Water intake 5 m3/s)
Steel Slide GateSteel Slide Gate
Effective dimension3.5m wide by 38.5m high1.9m dia.1.9m dia.
number of gates(one) gate(one) gate(one) gate
Opening and closing speed0.3m/minRaise 0.5m/min
Lowering 1.0m/min
1.0m/min
door weight77.3 tons5.1ton1.8ton
Completion dateJune 1997June 1997June 1997
productionMitsubishi Heavy Industries, Ltd.Mitsubishi Heavy Industries, Ltd.Mitsubishi Heavy Industries, Ltd.

Go to the right bank.

We have reached the right bank. The rain has stopped, but the footing is a little bad. Two concrete structures can be seen on the upper part of the slope on the left bank, which may be the remains of the foundation of a cable crane.

View of the top edge from the right bank
View of the top edge from the right bank

The same was found on the upper right bank.

right bank (slope)
right bank (slope)

In terms of design and function, it still does not look very much like a prefectural dam. There are two pavilions with tongari roofs on the downstream side of the top edge, and the roofs of the boatyard and the administration office are of a uniform color, which is also nice.

Looking downstream from the right bank
Looking downstream from the right bank

The upstream side of the embankment soaking wet. It was early in the morning, but no one was around except for us. This kind of winter atmosphere is surprisingly nice, isn't it?

Looking upstream from the right end of the embankment
Looking upstream from the right end of the embankment

downstream

Moving downstream from the top end level, we can see the conduit gate (jet flow gate) building. The downstream side is quite close to the embankment. It is quite a large building.

Conduit gate (jet flow gate) building
Conduit gate (jet flow gate) building

Notched, visible from the top edge.sub-damI'm not sure if this is a good idea or not. If you look closely, you can see that there are screened holes on both sides to allow water to drain out.

View of the sub-dam from the right bank
View of the sub-dam from the right bank

This is the Senya Dam intake and discharge facility building. The triangular glass roof eaves are a distinctive feature.

Senya Dam Intake and Discharge Facility Building
Senya Dam Intake and Discharge Facility Building

The specifications of the intake and discharge facilities are as follows

Main gate for discharge pipe

form (something takes)Jet Flow Gate
Effective dimension0.65m dia.
number of gates(one) gate
Opening and closing speed0.05m/min
weight12.8 tons
Years of construction completedJune 1997
productionMitsubishi Heavy Industries, Ltd.

Sub-gate for discharge pipe

form (something takes)Circular high pressure slide gate
Effective dimension0.65m dia.
number of gates(one) gate
Opening and closing speed0.1m/min
weight9.7 tons
Years of construction completedJune 1997
productionMitsubishi Heavy Industries, Ltd.

The orifice gate and discharge pipe used for the test flooding are installed as a monument in the plaza downstream. I had thought that the orifice gate would be used for the test flooding, but I was surprised to see a steel slide gate. It seems a waste to use the gate only for test flooding, but perhaps that is because the dam was constructed during the bubble period.

Orifice gate and discharge pipe for test waterlogging
Orifice gate and discharge pipe for test waterlogging

This is the Senya Power Plant (back side) of the Okayama Prefectural Bureau of Public Enterprises. For some reason, I did not take a proper picture of the exterior. The Senya Power Station is a dam-type power station that uses water from the irrigation discharge and can provide up to 3,000 kW of electricity.

Okayama Prefectural Bureau of Public Enterprises, Senya Power Station
Okayama Prefectural Bureau of Public Enterprises, Senya Power Station

From here, it is hard to believe that this is a prefectural dam. And it is huge.

Looking downstream from the Senya Power Station
Looking downstream from the Senya Power Station

Detailing begins downstream. The windlass room of the crest gate is well designed and built. The triangular roof overhanging the front of the top edge is the observation platform and is located on both the left and right banks. Below it is theorifice gateThe formwork is made up of a series of decorative forms. If you look closely, you can see the decorative formwork near the center and on the downstream face of the observation deck.

Around crest gate and orifice gate
Around crest gate and orifice gate

And a conduit gate (jet flow gate) at the bottom.

Conduit gate (jet flow gate)
Conduit gate (jet flow gate)

The Senya Dam was gorgeous in every way.

Downstream face of the Senya Dam embankment
Downstream face of the Senya Dam embankment

Senya Dam Specifications

LocationSugo, Niimi City, Okayama Prefecture
River NameTakahashi River, Takahashi River System
ObjectiveF (flood control, agricultural disaster prevention)
N (unspecified water, water for river maintenance)
W(Water for water supply)
I (industrial water)
P(Power generation)
ModelG(gravity-fed concrete dam)
Bank height97.5m
Bank length259m
Dam volume697,000 m3
Watershed Area88km2
Reservoir area111ha
Total storage capacity28,000,000 m3
Effective water storage capacity26,200,000 m3
Dam operatorOkayama prefecture (Chuugoku area)
Main body constructorObayashi Corporation, Kajima Corporation, Omoto Corporation
Year of launch1971
Year Completed1998
Name of Dam LakeSensui Lake

Other facilities/observations

Restrooms appear to be located in the administration office. The observation deck at the top end is marked as x because it is outside the definition of this site.

Parking lot
Toilet
Park×
PR Exhibition Hall
Fishing
Viewing platform×

Map around Senya Dam

Weather around Senya Dam

Accommodations that may be close to Senya Dam

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This article was written by.
Shin Jinma

Dam enthusiast who loves Momosuke Fukuzawa / Dampedia and Dam News administrator / Certified Dammeister (01-018) by the Japan Dam Foundation / Started selling discharge caution goods.https://shop.dampedia.com

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