| Our research and many present studies pointed out the important functions of debris feeding mammals inhabiting on river terrace. The debris on river terraces has important functions feeding the mammals that are high lank aspect indicator of the river ecosystem. The results indicated conservation of debris has important roles for inhabiting high lank aspect indicator and the direction of river ecosystem on river terraces. However, almost present studies mainly focused on the function from view point of behavioral ecology, few studies research on hydraulic formation process of the debris from view point of river engineering.Therefore, we studied on hydraulic formation process of debris on river terrace in the Kitagawa river flowing in south part of Japan. Firstly we conducted fields survey from 2002 to 2011 and recorded the position of debris and their utilization by the middle mammals. Secondly, using 2D hydraulic simulation, we simulated current velocity condition and consider the hydraulic formation process of the debris on the simulation data. In the results, we clarified the following phenomena. (1)Meandering of the channel enhanced gradient of water surface between main channel and sub channel in floods, and the gradient and high current velocity due to the gradient flowed the organic matters that are composed of the debris into the river terraces. (2)Trees such as willows filtered the organic matters and form the debris. (3)Despite the high current velocity, areas where trees vegetate could trapped many organic matters. Results in (2) and (3) indicated importance of the tree to forming the debris. Although wood expansions cause decreased the capacity of flow, in the other hands the woods have important ecological functions. The results indicated that management wood expansion in the river in diverse view points. |
