Author(s): Yoshiya Igarashi; Norio Tanaka
Linked Author(s): Norio Tanaka
Keywords: Tsunami run-up in a river; Water level in front of forest; Effect on opposite bank; Density of inland forest; Depth of moat
Abstract: A hybrid defense system by embankment and coastal forest is planned at shores in Hokkaido Prefecture after the Great East Japan tsunami. However, even though the defense system placed at the shore protect coastal land, the tsunami has a possibility to flood coastal areas through openings at river mouths. Flood defense forest can reduce the damage not only by river floods but by the tsunami inundation from a river. However, it has the risk of increasing the water depth and/or fluid force at opposite side of a small-width river because of the reflection induced by the forest. On the other hand, a moat in front of the forest can reduce water level in front of the forest. Flume experiments were conducted for investigating the effect of hybrid forest along a river, forest model (FM) and moat model (MM), against tsunami inundation. When FM is dense and the angle between FM and a river model is large, FM generates a hydraulic jump and increases the water depth in front of FM. A small-depth MM in front of FM decreases the water level in the front of the FM, however, for a large-depth MM, the water depth at MM and on opposite side of the river channel becomes large. Disadvantageous conditions have been clarified in relation to the density of FM, the angle between FM and river, and the depth of MM.
Year: 2018