We have been always aware of the danger of living near a river but Typhoon no. 19 that happened 2 weeks ago triggered my interest to visit this flood prevention system.
We did a quick google check and realised that they conduct free study tours every Tuesday and Thursday, with 2 sessions per day (morning and afternoon), so an appointment was reserved via telephone. Unfortunately, the tour is only conducted in Japanese.
Be prepared to spend around 1.5 hours in this facility, but I totally enjoyed myself. Probably it was also because my previous job in Singapore covers such study tours at this kind of government-related facilities too.
Introduction – 5 minutes
Presentation – 20 minutes
Live Demonstration & Control Room Visit – 15-20 minutes
Tunnel Tour – 20-25 minutes
Q&A – 10 minutes
The presentation starts with a short video that features the flooding that occurred in 1991 around Nakano area, which causes great damage to the neighbourhood.
Urbanisation is listed as one of the main causes of river flooding and how usual solutions like widening the river banks will not solve the issue easily. Due to the high density of nearby housing, roads and rail tracks, widening the river banks didn’t seem like a feasible option.
I think the below comparisation of the same bridge area really illustrates the dangers of river flooding and how quickly things can change without a good system in place.
After the presentation, we moved to the 2nd floor of the facility where they showed us a live demoｎstration of how the system is triggered to open its gate to allow floodwater to flow into the underground tunnel and kept in the reservoir.
I was impressed how they made efforts to make sure the way the huge amount of water drop from ground level to underground 43 metres will not cause noise and vibration to the surrounding residential area.
Central Control Room
We then moved over to the central control room which is the actual place they will monitor the water levels, and control the water gates.
Depending on the level of warning from the Japan Meteorological Agency, the staff will need to come to this control room and be prepared to manage the situation, but usually, it will be 2-3 people called back regardless of the day and time. The guide made a joke that he doesn’t think he will need to demonstrate the part on how to use the control panel today.
Main highlight : Tunnel Tour!
Moving over to the next building where we can finally descend to the tunnel level via the elevator which can only take 9 people at one time. Apparently, when they have study tours with primary school kids, they need to use the stairs which is equivalent to 11 floors of a building.
We were gathered at the pump room which already has a faint sewage odour. Those who are sensitive to smells are recommended to wear a mask. We were also warned beforehand that there will be water puddles in the tunnel and also some water may drop from the ceiling, and there will be some areas we need to move around narrow passageways so we should be wearing clothes that you can move around easily.
A brief explanation of the “drop shaft” and “retention pond” was given. It was really easy to understand when we imagine it’s a waterfall from 40 metres coming down, and the bottom of the pond will be damaged without any water to “cushion” the impact, thus the “retention pond”.
After this, we were asked to move across the tunnel for 150 metres before reaching the actual point where we can see the reservoir. There were around 4-5 accompanying staff who were carrying torchlights to guide the way.
The Underground Reservoir
We finally reached the underground reservoir which is of course emptied of water by this time. It was such a vast tunnel of darkness, that I feel as if I am in a sci-fi movie set.
Total water storage capacity : 540,000 cubic metres
Phase 1 : 240,000 cubic metres (Finished works in 1998)
Phase 2 : 300,000 cubic metres (Finished works in 2008)
Length of tunnel : 4.5 km (Phase 1 : 2km, Phase 2, 2.5km)
Diameter of tunnel : 12.5m
Water collection points : 3 (Phase 1 : Kanda River, Phase 2 : Zenpukuji River, Myoshoji River)
Well, guess what? It costs 1000 billion JPY to build this system.
We asked about the amount of water that was stored in the reservoir from Typhoon no. 19, and apparently it was 90% full. OMG! We were fortunate that our area is not flooded, all thanks to this system.
It’s actually pretty scary to see that there are a lot of cracks in the reservoir walls, but the staff assured that they are closely monitoring this.
Experience the “Dark”
There was a “fun” moment where the staff switched off all the lights so that we can experience the total darkness of the tunnel. It was like for 2 seconds, and we were a group of 22 “old people” so no screaming around… I can imagine when it was the primary school kids tour, it must be so funny.
Moving back up to ground level and we saw the area where they have the elevator to move vehicles or maintenance trucks to the tunnel level.
Overall, it has been a very insightful and highly educational trip. It’s kind of personal discovery when you visit a facility that is so important to keep you and your property safe from flooding caused by heavy rain or typhoons which have been pretty rampant these days.