Abstract
We researched geomorphic quantities on micro landforms at our study area damaged by overland flood due to the typhoon no.0514 in the Miyazaki Plain. Many micro landforms can be classified in the downstream area of Ooyodo River and Honjo River. The study area adjacent to both rivers was classified into the landforms such as dike, slightly elevated area, lowland and river bed from the interpretation of shade maps made by 5mDEM. The geomorphic quantities of the landforms are average height and relative height to water level calculated by using 5mDEM. The characteristics of the longitudinal profiles on both geomorphic quantities were discussed.
In the profiles, some sections become convex curve caused by aggradations in elevation of micro landforms. The form of convex curves in the profiles on relative height is clearer than that in the profiles on average height. In the profiles on relative height, we can identify large convex curves with approximately 5 km wavelength and small ones with approximately 1 km wavelength. The areas with the maximum value in the large convex curves are close to the river mouth to the main river and the sea, the flection of the rivers, and the bottleneck section. Such areas in the small convex curves are close to the confluence of tributaries. Such areas of the landforms outside of the dike are located downstream those of the landforms inside of the dike. At the areas, it is considered that water velocity decreases, sediment accumulates, and flood level is easy to go up. In the inundated area, the relative height of landforms increases outside of the dike and it decreases inside of the dike. In the non-inundated area, the height of them decreases outside of the dike and it increases inside of the dike. Therefore, the relative height difference between lowland and river bed from the each profiles, we can distinguish the sections where are easy to be inundated by overland flood and where are hard to be inundated.
Consequently, in this study, we clarified that it is easy for us to recognize the vulnerable area for inundation from the analysis of geomorphic quantities on micro landforms.
