How Japan Built a $2,4 Billion Underground River to Drink Up Floodwater
Structure Anatomy
1,093,138 views
Japan spent $2.4 billion building G-Cans, an underground flood control system beneath the Greater Tokyo area. When nearby rivers rise, five intake shafts draw in excess water. A massive tunnel carries it to a chamber that slows the flow, before four pumps drive it into the Edo River.
Why build this “underground river” instead of widening the rivers above? This documentary follows the problem, the construction, and what happens when a storm puts the system to work. It also explains the system’s limits: G-Cans helps protect a specific river basin, not all of Tokyo.
📌Timestamps
00:06 The $2.4 Billion Underground Flood Machine
01:27 Where G-Cans Is—and How It Works
02:43 Why Japan Built an Underground River
03:53 Mapping a Route Beneath the City
05:01 Excavating Five Giant Shafts
06:28 Building the Main Tunnel
07:45 Taming the Water in the Pressure Chamber
09:10 The Pumps That Send Water to the Edo River
10:35 What Happens When a Flood Arrives
11:20 G-Cans in Action
12:18 Maintenance After the Storm
13:10 What G-Cans Cannot Protect
14:24 The Engineering Behind the Underground River
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FYI: Kasukabe, Saitama is also the home of Crayon Shin-chan (anime character).
How Japan Built a $2,4 Billion Underground River to Drink Up Floodwater
Structure Anatomy
1,093,138 views
Japan spent $2.4 billion building G-Cans, an underground flood control system beneath the Greater Tokyo area. When nearby rivers rise, five intake shafts draw in excess water. A massive tunnel carries it to a chamber that slows the flow, before four pumps drive it into the Edo River.
Why build this “underground river” instead of widening the rivers above? This documentary follows the problem, the construction, and what happens when a storm puts the system to work. It also explains the system’s limits: G-Cans helps protect a specific river basin, not all of Tokyo.
📌Timestamps
00:06 The $2.4 Billion Underground Flood Machine
01:27 Where G-Cans Is—and How It Works
02:43 Why Japan Built an Underground River
03:53 Mapping a Route Beneath the City
05:01 Excavating Five Giant Shafts
06:28 Building the Main Tunnel
07:45 Taming the Water in the Pressure Chamber
09:10 The Pumps That Send Water to the Edo River
10:35 What Happens When a Flood Arrives
11:20 G-Cans in Action
12:18 Maintenance After the Storm
13:10 What G-Cans Cannot Protect
14:24 The Engineering Behind the Underground River