“Ever wonder how Tokyo avoids turning into a waterlogged mess?” Right here we are at the Reservoir Management Office. It is Tokyo’s first line of defense against floods. This office plays a crucial role in managing Tokyo’s intricate network of regulating reservoirs.
The Reservoir Management Office oversees 28 reservoirs on 12 rivers. These reservoirs protect Tokyo from devastating floods. Tokyo suffered greatly from flooding due to rapid urbanization. The city’s drainage basin lost its ability to retain water. In 1966, the Kanda River overflowed during Typhoon No. 4. This disaster flooded 403 hectares and inundated 9,000 homes.
To prevent future disasters, the Tokyo Metropolitan Government began improving rivers in the 1960s. These improvements aimed to handle heavy rainfall defined as 30 to 50 mm per hour. Widening rivers in urban areas proved difficult and time-consuming. The solution was to create regulating reservoirs. These reservoirs temporarily store rising water.
The first regulating reservoir was the Fujimiike Regulating Reservoir on the Shakujii River. After this initial success, Tokyo began installing reservoirs city-wide. Today, these reservoirs have a total storage volume of approximately 2.63 million cubic meters. That’s about 8,800 swimming pools in size.
Early reservoirs were built “in-ground”. These reservoirs were dug out of vacant land or parks near rivers. The stored water drains naturally. These areas can then be used as biotopes or even rice paddies. As land became scarce, Tokyo built “underground vault” and “underground tunnel” reservoirs.
Underground vault reservoirs are located beneath riverside parks. The areas above these vaults can be used as athletic grounds or residential areas. Underground tunnel reservoirs are built deep beneath roads. They can be built anywhere with water inlets and drainage outlets.
These reservoirs greatly reduced flood damage. However, Typhoon Hagibis in 2019 brought record-breaking rainfall. Seven rivers in Tokyo overflowed and caused damage. Flood control remains a top priority for the Tokyo Metropolitan Government. They continue to promote initiatives to prevent damage.
In 2019, the TMG started infrastructure tours of the Kanda River/Ring Road No. 7 Underground Regulating Reservoir. The tours aimed to educate residents about the benefits of regulating reservoirs. The tours became surprisingly popular. Over 6,000 people visited each year before the COVID-19 pandemic.
The TMG also distributes “IKE cards” to visitors. These cards describe each reservoir’s characteristics. The cards became popular on social media. These efforts increase awareness of regulating reservoirs and disaster preparedness. The Tokyo Metropolitan Government Bureau of Waterworks handles Tokyo’s water supply. They produce drinking water with advanced purification. They also supply tap water for industrial use without disinfection. The Bureau relies on the Tama River system for water. This includes managing water conservation forests and water quality. They also improve mountain trails. The Bureau even controls the temperature of water discharged from dams to protect downstream rivers.
So next time you see a park in Tokyo remember. It might just be holding back the floodwaters. The Reservoir Management Office is working tirelessly to keep Tokyo safe and dry.