Visitation at Urayama dam and Takizawa dam
Hello everyone,
this is Zhang Zhaoyu a M1 student in the Kawasaki Lab. So glad to introduce you
the visitation we had on August 26th, 2022.
This is a visitation
organized by the Japan Society of Dam Engineers.
We visited two
dams located in the Arakawa River basin ( Urayama Dam and Takizawa Dam). We
learned basic information about these two dams and also watched how the work are
doing by the staff at the dams.
1.
The first one was Urayama Dam:
The dam height
of Urayama Dam is 156m and the dam length is 372m. the total water storage
capacity is 58 million m³ (of which 2 million m³ is the sediment accumulation
capacity), and it is a multi-purpose dam that regulates floods, provides water,
controls the river environment and generates electricity.
1.1 Flood control
The Urayama dam
takes the 100-year flood (1000m³/s) as the
design flood and has a flood regulation capacity of 23
million m³ during the flood season. When the design flood comes, the dam
is released at 110m³/s and the remaining water is stored in the reservoir.
In reality, the
largest flood was a record 420m³/s in 2019 when
Typhoon 19 came. Urayama dam has been used safely during floods so far.
1.2
Water suply
The Urayama dam can
provide 4.1m³/s water, of which 65% is provided
to Saitama, 29% to the Tokyo City, and the remaining 6% to the Chichibu area.
It is an important source of water supply for the Arakawa River basin.
1.3
Water environment
The Urayama dam
is often affected by the fact that the water becomes turbid after heavy
rainfall. Many businesses downstream (fisheries, factories, domestic water,
etc.) are affected. The management has taken a series of measures to solve this
problem. Like, the water intake is located about 6km
upstream of the dam and the entire pipeline is made of steel and reinforced plastic
pipes.
To prevent
insufficient oxygenation of the water in the reservoir, six supplemental air
devices have been installed upstream of the dam to ensure water quality.
There are also
devices to prevent driftwood.
1.4
Power generation
The Urayama dam
uses this water to generate electricity while releasing water downstream and
has a capacity of 5,000kw. At the time we
visited it, it’s running in 2.6 m³/s.
We can see that
there are two drainage holes here, one large and one small. The large one has a
drainage capacity of 40m³/s and the small one is
2m³/s. When we need to adjust the water release
in 0.1m³/s, it will be more convenient to use the small hole, and when we need
to release a large amount of water, it will be more convenient to use the large
hole.
2.
Takizawa dam
Takizawa dam has
a dam height of 132m, a dam length of 424m, and a total water storage capacity
of 63 million m³ (of which 5 million m³ is the sedimentation capacity)
Its function is basically the same as Urayama
dam.
2.1 Flood control
The Takizawa dam
has a 100-year flood level of 1850m³/s, of which
300m³/s will be released and the rest will be stored in the dam, corresponding
to a flood regulation capacity of 33 million m³ during the flood season.
The actual
maximum flood record is still Typhoon 19 in 2019, when the flood flow was 700m³/s. So far the operation of Takizawa dam in the
flood season is still safe.
2.2
water supply
The water supply
of Takizawa dam is very similar to that of Urayama dam. It provides 4.6m³/s of
water supply, 81% of which is supplied to Saitama and 29% to Tokyo.
2.3
Water quality
The water intake
facility is operated to draw water from a high turbidity layer during discharge,
and to preserve the fresh water layer. When there is no need to discharge, the
goal is to keep the water temperature when we take the water.
2.4
Power generation
Like Urayama
dam, Takizawa dam has a generation capacity of 3400kw.
At the time we
visited it, it’s running in 1.5m³/s.
3.
Spill way
The Urayama dam
has a common spillway (3m³/s) and two spillways for extraordinary periods
without gates (natural overflow).
The Takizawa dam
has a common water intake as well as three emergency spillways with arc gates,
which are operated by the winches inside the dam on both sides. These machines
are well maintained, and the workers also draw red lines on the screws to keep
an eye on the status of the machines.
4.
Dam Safety Monitoring
This device can
monitor the deformation of the dam.
There are also
equipments at the bottom of the dam to monitor the dam leakage
and lift pressure to ensure the stability
of the dam in several ways.
At the left bank
of Takizawa dam, a concrete revetment was made
to prevent soil erosion. Based on the color
difference of the revetment, we can also determine the long-term water level of
the dam.
5.
Sediment
The amount of
sediment in the watershed is relatively high because of typhoons and other
reasons. The sediment is used locally to fill the part washed away downstream
or carried to other places for other uses.
There are about 13000t sediment over this place.
This place was originally a reservoir, but because of Typhoon 19,
this reservoir was completely filled with sediment. We can still see some
concrete structures, but the former road and the appearance of the reservoir
are completely invisible.
At last
This visitation
was quite an experience. Dam management is now really digital. In the control
center of Takizawa Dam, we can observe the overall situation of the dam with
the naked eye, and at the same time, we can understand the parameters of the
dam in real time through various digital monitoring devices. The data is stored
in the computer, which is very useful for future management and research.
Learning about
these two dams on the Arakawa River Basin made me more aware of the role of
dams in stabilizing water supplies and preventing natural disasters such as
floods and droughts, and how hard our stable lives are to come by. All these
cannot be achieved without the efforts of the dam design department and the
management department.
