Underground cities must be designed with possible flooding in mind

United Nations experts have issued a caution about the need to design underground spaces with natural disasters in mind, warning that water can travel along the interconnected labyrinths. Canadian cities such as Montreal and Toronto have extensive underground shopping networks in their downtown cores, partly to offer an escape from the weather. Crowded Asian cities are also making maximum use of underground space.
A release from the United Nations dated February 17 noted “The concentration of people and wealth in … underground spaces is expanding and merits careful examination…. Modelling a variety of catastrophic events is essential for building contingencies into underground infrastructure designs, during evacuations and the emergency containment and transport of flood waters, for example.”
Over two years ending in 2001, Tokyo had 17 incidents of underground flooding, mainly during monsoon and typhoon months. Despite extensive precautions people died in the incidents.
A concern is that underground space is usually mapped in relation to the buildings above ground, whereas subsurface maps would show connections along which water can flow a long way from its source.
Janos Bogardi, director of the UN University Institute for Environment and Human Security in Bonn, Germany, said: “It is essential to plan and construct underground space based on information such as connectivity and to design carefully all uncovered entrances to underground spaces.”
Underground disasters can threaten the stability of the buildings overhead, collapsing floors and compromising ventilation ducts.
The UN University is helping to build a computer system to simulate the impacts of natural disasters such as floods and tsunamis on towns and cities in Asia.