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 26^th, 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.