Sediment pulse 発生後における土砂の波状移動と分級現象

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Understanding how sediment supply from lateral source influences on sediment distribution along a channel reach is a key issue for preliminary surveying of sediment disaster. Sediment pulse formed by storm-induced sediment supply from lateral source was investigated for four years after 2003 storm at Kita-iwanai-ninosawa Creek located in a headwater catchment of Tokachi River, Eastern Hokkaido, Japan. Cross-section measuring and sediment sampling were conducted on site, and the relationship between longitudinal changes in sediment volume transformed to a sediment mass curve and grain size distribution was examined. In this paper, the ratio of sediment delivery magnitude (M) against quasi-stream power (Ps) was employed as an efficiency index (M/PS) of sediment transfer. The result is as follows : 1) Although storm-induced sediment pulse formed by quite lots of sediment input is not identified by deference in grain size, sediment pulses gradually reproduced by low-water flow after storm event have characteristics of grain size distribution. 2) Magnitude of sediment delivery with large materials (>75 mm) decreases downstream because of their short travel distance even by flooding. However, selective transport of smaller materials by low-water flow increases the magnitude of sediment delivery. 3) Comparing sediment mass curves, the wave peak by largemagnitude flooding is higher than that by small-magnitude flooding, and the wave length by large-magnitude flooding is shorter than that by small-magnitude flooding. 5) The efficiency index (M/PS) of sediment transfer yielded by storm induced sediment supply is quite high, but it gradually decreases with time after the initial sediment supply.
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Sediment pulse 発生後における土砂の波状移動と分級現象

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