国土交通省 関東地方整備局 江戸川河川事務所
江戸川河川事務所ホーム > 事務所の取り組み > 首都圏外郭放水路 > Overview of Facilities > About the Metropolitan Outer Area Underground Discharge Channel

事務所の取り組み

  • 首都圏外郭放水路

    Overview of Facilities

    About the Metropolitan Outer Area Underground Discharge Channel

    Language日本語English簡体中文繁体中文

    One of the world's largest underground discharge channels at 50 meters below ground.

    “Sairyu no Kawa”-The Metropolitan Outer Area Underground Discharge Channel

    “Sairyu no Kawa”-The Metropolitan Outer Area Underground Discharge Channel “Sairyu no Kawa”-The Metropolitan Outer Area Underground Discharge Channel

    The Metropolitan Outer Area Underground Discharge Channel is an underground river constructed to prevent flood damage by draining the water from small and medium-sized rivers---such as the Nakagawa River, the Kuramatsu River, the Ootoshi-Furutone River, No.18 water channel, and the Koumatsu River---directly into the Edogawa River.
    The basins of the Nakagawa and Ayase Rivers are surrounded by large rivers such as the Tone, Edogawa, and Arakawa.
    This area has suffered flood damage many times because the land is shaped like a bowl , which makes it easy for water to accumulate. The slopes of the rivers are also gentle, making it difficult for water to flow out into the sea. So, when there is heavy rainfall, the water level is slow to fall. Furthermore, in recent years, the rapid progress of urbanization has made it harder for rainwater to penetrate the ground, so instead it flows directly into the river itself, making it easier for floods to occur.
    The completion of the Metropolitan Outer Area Underground Discharge Channel has drastically decreased the number of houses flooded in the surrounding areas and the area of flooding, thereby greatly reducing the damage from the floods that have assailed the river basin for many years.

    Overall configuration diagram

    First, the inflow facilities and the banks, which take in flood water from all the rivers. Next, the Pressure-Adjusting Water Tank, which lessens the force of the water in the underground space, ensuring a smooth flow. Finally, the drainage facility and the drainage pipe, which drain the flood waters underground.

    Overall configuration diagram Overall configuration diagram
    • No.5 bank (State of inflow)
    • Showa Drainage Pump Station / No.2 Bank / No.1 Bank / No.4 Bank (Overflow levee)
    • No.3 bank (State of inflow)
    • Pressure-adjusting water tank
国土交通省 関東地方整備局 江戸川河川事務所
〒278-0005 千葉県野田市宮崎134 電話:04(7125)7311