Author(s): Naveed Anjum; Norio Tanaka
Linked Author(s): Norio Tanaka
Keywords: Tsunami; Coastal forest; Disaster reduction; Flow structure; Energy loss
Abstract: The disastrous events of tsunamis or floods in the past revealed the effectiveness of coastal forest. In tsunami mitigation strategies, interest in a multiple defense system is increasing rather than a single defense structure. This shift to a multiple defense system because the tsunami inundation could sufficiently be delayed and the overflow volume could be reduced compared to that of a single defense system. The previous research studies pointed out the limitation of land use in the coastal area, which is a major problem to construct a thick forest for tsunami mitigation. Thus, the present study conducted flume experiments to clarify the flow structure and energy loss through a forest with a gap, i.e. discontinuous forest model (DFM), under varying steady subcritical flows and varying gaps between the forest models. An experiment with continuous forest model (CFM) was also performed under the same flow conditions for the comparison purpose. The discontinuous forest, i.e. combination of upstream model (UM) and downstream model (DM), resulted in slightly larger backwater rise, i.e. 1-6%, upstream of the models due to higher flow resistance, as compared to that of continuous forest. Hence, due to double reflection (back movement of water wave due to backwater rise) and large resistance offered by DFM, the maximum loss of flow energy became higher, i.e. 37%, compared to that of CFM, i.e. 32%. The results demonstrate that this type of discontinuous forest with the appropriate configuration could be as effective as a continuous forest belt in mitigating the tsunami hazards.