Protect Shibuya at the "valley bottom" from heavy rainfall! Start of operation of "rainwater storage facility" under Shibuya Station
In preparation for heavy rain and large typhoons, the "Shibuya Station East Exit Rainwater Storage Facility" will be installed in the basement of Shibuya Station, which is undergoing redevelopment, and will be in service from August 31, 2020.
Shibuya Station, which is surrounded by slopes such as Dogenzaka and Miyamasuzaka, is located in the center of the surviving landform, suitable for a "valley". The elevation difference between Shibuya Station and Omotesando Station is about 22 meters.▲3D area around Shibuya Station (Courtesy of Tokyu Corporation)
GINZA LINE /Shibuya Station platform is connected to the 3rd floor of SHIBUYA SCRAMBLE SQUARE even though it is a subway, you can see that the area around the station is extremely low.
▲Purple line = Udagawa (underdrain) Gray = Shibuya river (underdrain) Blue = Shibuya river
Furthermore, around Shibuya Station, there are two large rivers, the Shibuya River and the Udagawa River. The Shibuya River runs under the footpaths of Cat Street, Miyashita Park and SHIBUYA SCRAMBLE SQUARE, and you can look out along the SHIBUYA STREAM.▲ In the autumn of 2018, we constructed a promenade along the Shibuya River and transformed it into a waterfront space where pedestrians can walk easily.
On the other hand, Udagawa flows under the current Udagawa Dori and goes from Udagawa Koban to Inokashira Dori. Furthermore, it passes through the JR YAMANOTE LINE under the guard between Seibu A and B, and joins the Shibuya River under Miyashita Park. At present, it is completely underdrained, so even if you walk in the city of Shibuya, you will hardly notice it, but in reality, Shibuya is a "river town."
▲Under the Inokashira street, the underdrained Udagawa flows. The reason why there are no underground passages in Seibu A and B is that the river is influential.
Therefore, once every heavy rainfall, the river overflowed with water and flooded the entire city. What is new to my memory is that the heavy rainfall in August 1999 and July 2015 caused water to flow into the subway premises and the Shibuya underground shopping area, causing flooding.
In recent years, heavy rainfall of 50 mm and 100 mm per hour is not uncommon, and it has been one of the issues that must be solved in Shibuya, where flood damage has been occurring for a long time. However, railways and buildings are generally densely populated in large cities, and retrofitting storage facilities is quite difficult. However, in the case of Shibuya, it was also the timing of a large-scale redevelopment work around the station called "once every 100 years", so as part of the land readjustment project, "rainwater storage facility (store rainwater The plan to efficiently develop a large pool) has proceeded smoothly.
It has been almost 10 years since the construction work started in February 2011, and finally the maintenance will be completed on August 31st. According to a person involved in the construction, the safety is ensured because "it is a limited land between the railway and the river, and it is necessary to continue the construction without stopping the station used by many people" It took a while for the construction work.
Where is the rainwater storage facility located in Shibuya?(Upper photo) The city of Shibuya seen from Shibuya Hikarie. The new home that grows straight vertically is GINZA LINE. (Photo below) Shibuya Station East Exit Basement Square. The Shibuya River flows in the part where the picture of the wave is drawn.
At the ground level at the Shibuya Station East Exit, you can see the SHIBUYA SCRAMBLE SQUARE East Building and the GINZA LINE New Platform, but the "Shibuya Station East Exit Square" has started operation in November last year. There is a storage facility about 25 meters below this underground plaza.▲Shibuya station east exit side underground construction cross section (provided by Shibuya station block land readjustment project co-executor)
The underground plaza is on the second basement, and the storage tank for rainwater is equivalent to the fourth floor. The area is about 45 meters north-south and 22 meters east-west, and the volume is about 4,000 cubic meters. If you compare it to a pool at an elementary school, you can temporarily store rainwater equivalent to about 9 pools.
Watch the video below to see how rainwater is stored.
▲Shibuya Station east exit rainwater storage facility inflow video (Courtesy of Shibuya Station block land readjustment project joint operator)
In the video above, the inside of the water storage facility where rainwater was flowing in was released for media coverage before it began full-scale operation, so I would like to introduce some of the situations.▲ Inside the water tank. Rainwater comes in from a large pipe in the center.
▲ Inside the water tank. It is divided into several blocks, and when the amount of rainwater increases, water flows into each block in order.
So how much rain will this facility actually operate?
If more than 51 mm of rain falls per hour, it will flow into the rainwater storage facility through five intake points installed in existing manholes such as Miyamasuzaka, Meiji Dori, and National Route 246. .. It can handle up to 75 mm of precipitation per hour.
▲The pipe with a vertical slit (left) is a device for measuring the amount of stored water, the two pipes in the center are drainage pipes for draining the accumulated rainwater to the sewage, and the thick pipe on the right is a pipe for collecting rainwater.
Rainwater coming from each intake point in Shibuya flows down from the thick pipe on the right side of the above photo. A technology called "drop shaft" is adopted for this pipe, and the inside is a spiral water channel. It is said that it plays the role of preventing the deterioration of the bottom of the facility by reducing the force of rainwater that falls vigorously as much as possible. The silver pipe with the vertical slit on the far left is a measuring instrument to check the extent to which the water is stored.▲A pump for discharging water is installed at the roots of the two pipes in the center.
In addition, the black thin pipe in the center is a pipe that drains rainwater to the sewer main line in about 48 hours using the pump at the root after the weather has recovered. It is necessary to carefully drain the wastewater while checking the drainage of sewage and rivers, and it takes about 2 days to drain about 4000 tons.
By the way, around Shibuya Station, there is now the "East Exit Rainwater Storage Facility" that was announced this time, as well as the "Jinnan Storage Pipe," which started operation in FY2018. The “Jinnan Reservoir”, which is mainly responsible for rainwater protection on the side of the park, is not a pool type like the east exit, but a device that temporarily fills the ground with a large pipe to store rainwater. It has a water storage capacity of about 4,000 tons, and with the opening of the East Exit rainwater storage facility, facilities for storing up to about 8,000 tons of rainwater around Shibuya Station have been set up. Of course, it is not uncommon to see a heavy rainfall of 100 mm/hour or more than 200 mm/hour in recent years. However, it is important in preventing the paralysis of urban functions and inundation of subways and underground malls, and reducing damage as much as possible.
When it comes to large-scale redevelopment work at Shibuya Station, we tend to focus on new commercial facilities on the ground level, but it is truly unsung hero. You can see that it supports the town development of Shibuya in places where you cannot see it.
Editorial department · Fuji Itakashi
Shibuya registrar. In addition to Shibuya of Culture information, seasonal news and topics, it will spell write that feel every day.