Japan's G-CANS (Metropolitan Area Outer Underground Discharge Channel) is the world's largest underground flood control system. It safeguards Tokyo from heavy rains and storms. Could it be an effective model for countries like India? Yes, though its cost and construction present significant challenges.
What is G-CANS?
Constructed from 1992 to 2006 at a cost of $2.6 billion (approximately ₹21,000 crores), G-CANS is located in Kasukabe, Saitama Prefecture, near Tokyo. It comprises a network of tunnels extending 6.3 km at a depth of 50 meters.
Read More:
Source: aajtak
The system aims to prevent Tokyo from flooding by collecting excess water from its rivers, such as the Edogawa River. Capable of managing a once-in-200-years flood, it has been utilized over 200 times, averting $430 million in damages. It protects over 10 million Tokyo residents and 100 square kilometers of area.
How does G-CANS work?
G-CANS comprises 5 massive silos, tunnels, a large storage tank, and pumps, collectively known as the underground temple. Here's a step-by-step breakdown...
Read More:
Source: aajtak
Water Collection (Silos):
During floods, excess water from nearby rivers flows into 5 large silos via overflow channels. Each silo stands 65 meters tall and 32 meters wide – large enough to house the Statue of Liberty. These silos connect to the rivers and send water down into tunnels 50 meters deep.
Tunnel Transport:
From the silos, water travels through 6.3 kilometers of 10-meter-diameter tunnels, 50 meters below the city. This system allows water to flow swiftly due to gravity, minimizing city impact.
Read More:
Source: aajtak
Storage Tank (Underground Temple):
Water from the tunnels gathers in a huge central tank, known as the underground temple. This tank is 25.4 meters tall, 177 meters long, and 78 meters wide, housing 59 columns, each weighing 500 tons. Water is temporarily held here, pressure controlled, with a capacity of 67,000 cubic meters of water – akin to an Olympic swimming pool.
Water Extraction (Pumps):
Once flood levels decrease, four massive turbines (each with the power of a Boeing 737 engine at 14,000 horsepower) activate. These pumps can send 200 cubic meters (about 53,000 gallons) of water per second into the Edogawa River, heading towards Tokyo Bay. There are 78 pumps overall, each with a capacity of 10 MW, capable of emptying a 25-meter swimming pool in 12 seconds.
Read More:
Source: aajtak
This system is earthquake-resistant, an essential feature for Japan.
Is G-CANS an Excellent Flood Prevention Model?
Yes, G-CANS presents an impressive flood management model. In densely populated cities like Tokyo, it operates without surface disruption. As climate change leads to more frequent flooding, G-CANS offers inspiration. Smaller versions could be developed for cities like Mumbai and Delhi. However, challenges exist...
Cost: ₹21,000 crores – a hurdle for less affluent nations.
Construction: Requires geological stability and space. Easier in earthquake-prone areas like Japan, but tough elsewhere.
Maintenance: Cleaning tunnels and pumps is costly.
Source: aajtak
Where floods annually affect millions in India, a G-CANS-like system could prove useful for cities like Mumbai or Chennai. Starting small, with tunnels and pumping stations, is advisable.
