北海道の源頭部流域における扇状地の年輪年代解析に基づく土砂流出パターンの推定

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This study examines the pattern of episodic sediment yield and relationship to catchment morphology within 13 steep and credible headwater catchments in the Hidaka Mountain Range, Hokkaido. The history of episodic sediment yield of each catchment was dendrochronogically reconstructed from the sequence of sediment accumulated on debris fans at catchment outlets. The timing of fan growth was then compared with landslide distributions and rainfall records for the past 40 years, to determine the connectivity between slope and channel processes as well as the sensitivity of catchments for episodic sediment production in response to rainfall events. Based on mode of fan deposition, the study catchments were subdivided into two groups: L (5 catchments) and H (8 catchments). In the former group, fan growth occurred only in years when the rainfall intensity exceeded 300 mm day^<-1>, while in the latter group, fans underwent notable sediment accumulation in years even when the maximum daily rainfall was less than 200 mm. While the timing of fan growth in both groups did not necessarily coincide with the occurrence of landslides, the connectivity between hillslope and fluvial processes were more apparent in Group H. The size and channel slope of catchments within Group L were >0.1-1.0 km^2 and <0.20〜0.30 m m^<-1>, respectively: which is in agreement with catchments where fluvial transport is the dominant sediment delivery process. Our results indicate that catchment size and channel slope can be used to estimate catchment response to rainfall events of various magnitudes even in landslide prone regions.
2012-01-25

北海道の源頭部流域における扇状地の年輪年代解析に基づく土砂流出パターンの推定

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