Estimation of Vegetation Removal by Aerial Photograph Analysis and Flood Flow Simulation

This study purposes to estimate the spatial distribution of vegetation removal on a gravel bed and braided river, called the Tenryu in Central Japan. Aerial photograph and flood flow simulation are used to observe the vegetation change. Frequent changes of river width, bed level, bar areas indicate that it is an active river geomorphologically. High magnitudes of flood flow have direct impacts on bar area changes and vegetation dynamics. High discharge and less vegetation in the bar area produced extensive land erosion in the year 1990. High annual flood flow promotes vegetation removal and low flood flow in the preceding year accelerates vegetation invasion. Numerical simulation of flood flow can estimate the spatial conditions of vegetation wash out or vegetation remaining with minor misjudgment. Inclusion of sediment transport equation in the simulation may reduce the misjudgment during computation.