Author(s): Tadaharu Ishikawa; Hiroshi Senoo
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Keywords: Discontinuous levee system; Early modern age; Hydraulic function; Numerical flow simulation
Abstract: Before the middle of 19th century, discontinuous levee system was commonly adopted in Japan to control river inundations. In this study, the construction process and hydraulic function of the discontinuous levees which were gradually developed on the Kurobe Alluvial Fan during the late 17th and early 19th centuries were investigated being based on old map analysis and numerical flow simulations. The distortion of pictorial map drawn in 1875 was corrected from comparison with the modern map of 1910, and the levee layout in the former was determined. The result clarified that the early fragmentary levees were integrated to the large levee system in the early 19th century and that the early levees were placed mainly on the two sections where the river tended to change its course due to the long-term geomorphological movement; one was near the fan top, and the other was around “the geomorphological nodal point” on the middle of slope of the dissected alluvial fan. The results of numerical flow simulation for the levee arrangement in the early 19 th century clarified that an exceeding flood was diverted to the old river channels beside the main channel through “simple levee openings” upstream from the geomorphological nodal point and that a part of diverted flow was returned to the main channel through “funnel-shape levee openings” located on the lower river reach. This fact suggests that the civil engineers of those days knew the geomorphological characteristics of the alluvial fan.
Year: 2020