Assessment of flood risk management in lowland Tokyo areas in the seventeenth century by numerical flow simulations

Tadaharu Ishikawa, Ryosuke Akoh

Research output: Contribution to journalArticle

Abstract

Numerical simulations using the shallow water model on an unstructured triangular mesh system were conducted to elucidate the hydraulic functions of the Nihon levee system, which was built in the seventeenth century to protect the city of Edo (present-day Tokyo) against flooding. Because numerical data related to the topography and hydrology of that era do not exist, simulation conditions were inferred from records from the beginning of twentieth century and recent GIS elevation data and flood records. In the simulation results, floodwaters spread over the floodplain surrounded by the levee system, and the inundation areas expanded gradually through a canal to rice paddies in the adjacent river basin. Furthermore, the rise in the water level induced by the levee system produced a steeper water surface slope in the downstream channel, causing a high-rate discharge to Tokyo Bay, where the water level was practically constant. These results suggest that the river engineering of Japan in the seventeenth century was based on a levee design technique with the aim not of restraining floodwaters with levees but of generating water head differences to divert flood flow from urban areas.

Original languageEnglish
JournalEnvironmental Fluid Mechanics
DOIs
Publication statusAccepted/In press - Jan 1 2018

Fingerprint

seventeenth century
levee
Flow simulation
Risk management
Water levels
Water
Rivers
simulation
Levees
water level
Hydrology
Canals
river engineering
Catchments
Geographic information systems
Topography
Hydraulics
twentieth century
canal
floodplain

Keywords

  • Early modern period
  • Historic flood control strategy
  • Levee system design
  • Shallow water model

ASJC Scopus subject areas

  • Environmental Chemistry
  • Water Science and Technology

Cite this

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abstract = "Numerical simulations using the shallow water model on an unstructured triangular mesh system were conducted to elucidate the hydraulic functions of the Nihon levee system, which was built in the seventeenth century to protect the city of Edo (present-day Tokyo) against flooding. Because numerical data related to the topography and hydrology of that era do not exist, simulation conditions were inferred from records from the beginning of twentieth century and recent GIS elevation data and flood records. In the simulation results, floodwaters spread over the floodplain surrounded by the levee system, and the inundation areas expanded gradually through a canal to rice paddies in the adjacent river basin. Furthermore, the rise in the water level induced by the levee system produced a steeper water surface slope in the downstream channel, causing a high-rate discharge to Tokyo Bay, where the water level was practically constant. These results suggest that the river engineering of Japan in the seventeenth century was based on a levee design technique with the aim not of restraining floodwaters with levees but of generating water head differences to divert flood flow from urban areas.",
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N2 - Numerical simulations using the shallow water model on an unstructured triangular mesh system were conducted to elucidate the hydraulic functions of the Nihon levee system, which was built in the seventeenth century to protect the city of Edo (present-day Tokyo) against flooding. Because numerical data related to the topography and hydrology of that era do not exist, simulation conditions were inferred from records from the beginning of twentieth century and recent GIS elevation data and flood records. In the simulation results, floodwaters spread over the floodplain surrounded by the levee system, and the inundation areas expanded gradually through a canal to rice paddies in the adjacent river basin. Furthermore, the rise in the water level induced by the levee system produced a steeper water surface slope in the downstream channel, causing a high-rate discharge to Tokyo Bay, where the water level was practically constant. These results suggest that the river engineering of Japan in the seventeenth century was based on a levee design technique with the aim not of restraining floodwaters with levees but of generating water head differences to divert flood flow from urban areas.

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