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Effect of Forest Harvesting on Hydrogeomorphic Processes in Steep Terrain of Central Japan
Citation:
Imaizumi, F. AND R. C. SIDLE. Effect of Forest Harvesting on Hydrogeomorphic Processes in Steep Terrain of Central Japan. Geomorphology. Elsevier BV, AMSTERDAM, Netherlands, 169-170:109-122, (2012).
Impact/Purpose:
see description
Description:
Forest harvesting activities affect various hydrogeomorphic processes in forest terrain, including increases in occurrence of mass movements (i.e., landslides and debris flows), and changes in sediment transport rate in channels. Thus, the influence of harvesting on these processes needs to be assessed to protect aquatic ecosystems. In steep terrain with frequent mass movement, relationships between rainfall magnitude and frequency of mass movements associated with forest harvesting are needed to develop improved strategies for disaster prevention. We examined the effects of forest harvesting on the frequency of mass movements in the steep Sanko catchment (central Japan) using aerial photographs for six different years covering 1976 to 2003. We also investigated the spatial distribution of sediment stored in the system as well as sediment transport rate in selected subcatchments by field surveys. Landslides occur during moderate rainfall events (return period of daily rainfall < 10 years) in younger forests (< 25 years after harvesting), whereas the threshold magnitude of rainfall for landslides is higher in older forests (> 25 years after harvesting). The occurrence of mass movements substantially altered the volume of sediment storage in the channel that links sediment supply from hillslopes with sediment yield downstream. However, the volume and spatial distribution of sediment deposits in headwater channels were not clearly related to forest age because of the redistribution and evacuation of sediment by debris flows. Bedload transport rate was highly affected by sediment storage volume, whereas suspended sediment concentration was affected by the area of exposed sediment along channels that was carved by debris flows. Thus, the effect of harvesting on hydrogeomorphic processes cannot be estimated simply by the elapsed time after forest harvesting; rainfall magnitude and the history of mass movements need to be considered to better understand these linkages.
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Effect of Forest Harvesting on Hydrogeomorphic Processes in Steep Terrain of Central Japan