New system to predict real-time flood levels in central Tokyo
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During a bout of torrential rain, having a good idea of how severe the flooding might be could significantly help reduce damage and, in severe conditions, help people escape to safety.
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This is the hope of researchers at Waseda University and the University of Tokyo who devised a system that predicts estimated flood levels in real time for a 20-minute period in the event of a torrential downpour or other natural disaster.
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A trial run is being eyed for late next month for the system, which will cover all 23 wards of the capital.
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The forecast system is expected to help residents evacuate quickly and allow operators of underground facilities to implement countermeasures against inundation.
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The researchers said at a news conference on May 20 that data on the width and inclination of roads expected to be flooded as well as the size and length of sewerage systems will be provided by the Tokyo metropolitan government under the new mechanism.
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The information will be combined with land ministry radar observation network data to measure rainfall per 250-meter square every minute and information from the Japan Meteorological Agency’s monitoring system to predict rainfall for up to 30 minutes.
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Based on analysis of such data, flood levels for a 20-minute period at five-minute intervals will be forecast and shown on the science and technology ministry-affiliated website. Flood depths will also be displayed in different colors, such as blue for 10 centimeters and red for 80 cm or more.
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Rainwater is discharged in urban areas through underground sewers to rivers and flood-control reservoirs. But when rainfall from typhoons and torrential rain exceed the drainage capacity, there is a risk of undrained water flowing into underground shopping complexes and underpasses.
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Masato Sekine, a river engineering professor at Waseda University’s Faculty of Science and Engineering who was involved in the development of the system, said it will prove useful for management of such infrastructure and other sites.
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“As the estimate will be refreshed in real time, I would like it to be used for taking countermeasures, such as people evacuating to higher places and underground facility operators setting up watertight barriers beforehand,” Sekine said.
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He also said the flood level forecast can be introduced for other urban zones if data on sewers and roads is available.
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The system will be tested on the technology ministry’s data analysis system site at (http://www.diasjp.net/).
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INSUFFICIENT DRAINAGE
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An increasing number of floods resulting from insufficient drainage during torrential downpours and typhoons have been reported in Japan.
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Damage caused by such flooding accounted for 700 billion yen ($6.36 billion) of 1.7 trillion yen in damage from inundation cases throughout the country between 2007 and 2016, according to statistics.
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Also, flood damage owing to insufficient sewerage systems totaled 400 billion yen over the five-year period through 2015 in municipalities other than prefectural capitals and other major cities with near-prefecture-level authority, 1.6 times that of the five-year period through 2010.
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The land ministry conducts an annual study of whether drainage infrastructure in previously flood-affected regions and elsewhere can deal with a heavy rainfall amount that might occur once every five years. The findings show that the drainage capacity was not sufficient in 42 percent of the surveyed area totaling 843,000 hectares across the nation at the end of fiscal 2017.
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