Study on Change in River Landscape in Alluvial Fun Rivers and Its Restoration

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The aim of the project is to establish the method to predict and evaluate the change in river landscape in alluvial fun rivers where both sediment supply and peak discharge of floods have been decreased due to dam constructions. First, several individual topics observed in the rivers have been investigated using field data, flume experiments and numerical simulations. Second, the synthesized processes including the response of trees in a river to the change of the geomorphology have been discussed in order to seek proper restoration method of the rivers. The results have been summarized as below :1. Comparison between two rivers -The Tedori River and The Abe RiverThe changes in geomorphology and vegetated area in the Tedori River and those in the Abe River have been compared using survey data and aerial photographs. The two rivers have almost same drainage area and bed-slope in an alluvial reach. The Tedori River has a large dam, but the Abe River does not. The results show that the de … More crease of the peak discharge in floods causes the thriving of vegetation in a channel.2. Processes of geomorphology and growth of vegetated areaThe following processes are investigated in detail.(1) Sediment transport process in a channel with vegetated area(2) Patterns of growing vegetation area concerned to ground water level and deposited bed-material(3) Flood damage and/or advantage on vegetationThese investigations have emphasized the importance of the interaction among vegetation, geomorphology and water regime.3. Modeling of vegetation dynamics due to decrease of peak discharge in floodsThe effect of the decrease of peak discharge in floods on the growth of vegetation has been modeled in order to evaluate the changing landscape due to dam constructions. The model has successfully predicted the thriving of vegetation in the Terori River, and it would be one of powerful tools to discuss the change in river landscape.4. Evaluation method of changing habitatThe IFIM/PHABSIM method has been modified by adding the idea for synthesis of several different life-stages of a fish species. The method has also been cooperated with sediment transport model in order to discuss the effects of the change in geomorphology and vegetation pattern on the habitat.5. Toward restorationThe environmentally sound and cost-effective methods for the restoration of the rivers have been discussed base on the results shown in the above. Less