EXAMINING THE MECHANISM OF WOOD ACCUMULATION AND EXPORT IN TERAUCHI DAM CATCHMENT

Abstract

 Woody debis sometimes has negative effect to our lives. For example, woody debris can damage the construction, and it can stop the gate of dams to move. Furthermore, it is said that the amount of woody debris will increase in the future because these days forest in Japan is getting dead and guerilla heavy rain happens increasingly. Theofore, it is important to understand the mechanism of woody debris and know the characterristics of wood accumulation and export in catchment scale. Komori et al. constructed the wood export model assuming that there were 2 types of wood export, flood flow-type and base flow-type. They assumed that flood flow-type export could happen as woods were recruited when it rained heavily, and base flow-type export could happen under the nomal condition. And they adapted the model to the dam catchments which belonged to Kitakami-river, in Iwate prefecture.

 The objectives of this study were : (1) to adapt the model to Terauchi dam catchment, where large amout of wood recruited because of the heavy rain in Northen Kyusyu in 2017 and understand the mechanism of wood export at that time ; (2) to compare the result in Terauchi dam catchment to that in the dam catchments belonging to Kitakami-river. As a result, calculated amount of wood export was almost accurate, so it meant that the characteristics of the wood accumulation and export in Terauchi dam catchment could be explained by flood flow-type and base flow-type. Moreover, it was revealed that the heavy rain event in 2012 might affect the large wood export in 2017. And also it seems that in Terauchi dam catchment, accumulated wood can be easily transported without heavy rain event, comparing with the catchments which belong to Kitakami-river.