Abstract
Accurate estimation of flow resistance because of vegetation is important for river management tasks. In the last decade or so, a new measurement technique using an airborne laser bathymetry (ALB) with a green laser has remarkably developed in the discipline of river engineering. This effective technique efficiently enables us to conduct high-resolution measurements of both the planar river bathymetry including the underwater bed profile and vegetation height for long river reaches. Flow resistance because of vegetation in rivers generally depends on the vegetation species. Therefore, we can expect the accuracy improvement of flooded river analysis, provided we readily obtain the spatial distribution data of vegetation species establishing in targeted rivers.
For this paper, we developed a methodology to determine the vegetation species (herbaceous plants, woody plants and bamboo trees) in the lower Asahi River, focusing on the spatial distribution of ALB point cloud data. Using these results, we estimated hydraulic parameters relating to flow resistance. Then, we examined the validation of the methodology by comparing results of numerical simulations of flood flows using the parameters with observations. Results showed that the simulated results using the present data are relatively consistent with observations for both the longitudinal water level and the distributary discharge into the Hyakken River, compared with the results using the conventional data.
