Remembering 3/11
Tokyo Prioritizes Tackling Floods Before the Next Big One
Thirteen years after 3.11, Tokyo is reinforcing its disaster preparedness. We look at how the city is preventing floods and redeveloping coastal communities.
In December 2022, the Tokyo Metropolitan Government (TMG) launched the Tokyo Resilience Project (TRP). A year later, in December 2023, it announced an upgrade to the project. TRP aims to strengthen Tokyo against floods, storms, earthquakes, power supply disruptions, and infectious diseases.
Over the next decade, the TMG will spend approximately ￥7 trillion JPY ($47.3 billion USD) on urban resilience infrastructure and technology.
Taking Action
2024 marks the 13th anniversary of the Great East Japan Earthquake and tsunami that devastated Northeast Japan. Almost 20,000 people lost their lives, and thousands had to leave their homes and temporarily or permanently relocate. As the recent Noto Peninsula earthquake demonstrated, earthquakes and natural disasters still threaten the safety and well-being of people in Japan.
In addition to earthquakes, rising sea levels and more frequent storms due to climate change constitute a further threat. According to the Intergovernmental Panel on Climate Change (IPCC), a global average temperature rise of 2°C could be catastrophic. In its 6th Assessment Report, the IPCC found that rainfall would increase 1.1 times. It also estimated that sea levels would rise by 0.6 meters.
Situated on the central east coast of Honshu, the Tokyo metropolitan area is particularly vulnerable to storm surges and flooding. As part of the TRP, the TMG has devoted considerable energy and resources to constructing floodgates and surge barriers.
JAPAN Forward recently visited the Bureau of Port and Harbor's Storm Surge Management Center in Tatsumi, Tokyo. During a tour of the center's facilities, we gained insight into the TMG's impressive storm and flood preparedness measures.
Dealing With Geography
From 1910 to 1970, groundwater pumping and natural gas drilling around Tokyo Bay caused land to subside. As a result, the elevation of the eastern area of Tokyo's 23 wards is quite low. This means that 40% of the 23 wards (approximately 255 square kilometers) would be flooded in the case of a large typhoon. Twenty percent of the 23 wards (approximately 124 square kilometers) are below sea level. These "zero-meter areas" are home to some 1.4 million Tokyoites.
The Port of Tokyo sits deep inside Tokyo Bay, making it relatively safe from tsunamis. However, its location means it is prone to flooding. When winds drive the sea up against the shore, it has nowhere to go, causing the sea level to rise.
To reduce the risk of flooding, Tokyo has an expansive system of coastal protection facilities. Floodgates, land locks, and tidal embankments form a line of defense against the encroaching tide during storms and typhoons. This remarkable disaster and risk reduction infrastructure spans about 50 km and stands five to eight meters above sea level.
Facilities include 16 floodgates, 33 land locks, and four drainage pump stations. In addition, there are 38.6 km of outer tide embankments, 20.6 km of waterside land tide embankments, and 45.8 km of inner levees. Without these facilities, Tokyo would experience daily floods, and storm-surge flooding would be more widespread.
Floodgates and Land Locks
At the Storm Surge Management Center, staff operate and maintain Tokyo's 16 floodgates daily. Built on canals, the floodgates are typically kept open so as not to interfere with marine traffic or dam up adjacent rivers.
Land locks are built on roads and are usually left open as bridges for pedestrians and vehicles. In the event of a natural disaster, the Center shuts the floodgates and land locks. Along with Tokyo's seawalls, this prevents flood damage to inland areas.
Center staff generally operate the floodgates by remote control. They constantly monitor video and signals from other facilities to swiftly and effectively respond to any situation.
Since 2015, a second storm surge management center in Konan has been managing floodgates and facilities on the west side of the Sumida River. Normally, the Tatsumi facility functions as the headquarters. If an earthquake or typhoon puts one center out of operation, the other center becomes the effective headquarters. Should both centers become remotely inoperable, staff will go to the facilities to run them manually.
Drainage Pump Stations
Once the floodgates are closed during a typhoon, they serve as partitions to stem water flow from canals. They also prevent too much water flowing from rivers to the sea. While this mitigates the issue of flooding due to sea level rise, it can cause inland water levels to rise. Therefore, the Center uses drainage pump stations to drain accumulating inland water. The Bureau of Port and Harbor's four drainage pump stations contain a total of 14 pumps. These stations are located in Tokyo's Tatsumi, Sunamachi, Hamarikyu, and Shibaura districts.
Each station has three to four pumps, which vary in size and capacity. However, a pump with a pipe diameter of 2.3 meters can drain approximately 12 tons of water per second. In other words, a single drainage pump could fill an entire 25-meter swimming pool with water in about 18 seconds. If all pumps worked simultaneously, it would only take five to six seconds.
Improving Waterfront Spaces
Tokyo's tidal levees prevent seawater floods during storm surges and tsunamis. They are not just practical, however. In designing these levees, the TMG carefully considered how best to incorporate them into riverside green spaces.
Along the Harumi Canal Line, the TMG integrated a levee into a park to create a scenic promenade. Elsewhere, a gently sloping levee along the Tastumi Canal Line blends almost seamlessly into the surrounding greenery.
Between these tidal levees and floodgates are inner levees. These levees prevent flooding, coastal erosion, and earthquake-induced ground deformation. The TMG constructs these levees in front of existing barriers to seismically reinforce them.
A Tokyo Canal Renaissance Project
Besides these coastal projects, the TMG has also been working with communities to set up vibrant districts along Tokyo's canals. This project is called the Canal Renaissance Project.
Previously, only port-related businesses could receive permission to work and operate along the waterfront. By easing these restrictions, the TMG aims to develop more attractive areas along the canals and promote tourism in Tokyo.
Communities in these areas receive financial support and assistance from the TMG in promoting their initiatives. Designated areas include Shibaura, Shinagawa, Tennozu, Asashio, Katsushima, Hamakawa Samezu, and Toyosu.
Even after 13 years, the March 11 earthquake remains fresh in the hearts and minds of many Japanese people. Japan will always have to contend with natural disasters. However, the TMG's robust and constantly developing network of storm surge barriers and floodgates is heartening.
Furthermore, its Canal Renaissance Project offers a glimpse of a future where communities can prosper where they once lived in fear.
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Author: Daniel Manning
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