滋賀県犬上川河口部の掘削凹地を埋積した土砂の堆積過程

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The river-mouth delta of the Inukami River, which flows into the Biwa Lake, had been dredged in 1992 and 1993. The shoreline survey showed that the tip of the right bank has drastically retreated. As of now, about 10 years after the dredging, new topography (channel bar, mound and spit) has formed. The new topography was investigated, and its sedimentary processes (river flood or wave) was tried to determine from grain-size distribution and pebble flatness. The sediment of channel bar consisted of single layer composed of cobble-gravelly sand. The sediment of mound had several alternate layers; one was composed of medium-coarse sand, the other was pebble-gravelly sand. The spit sediment consisted of two types of sediment, and one was mainly composed of pebble, and the other was composed of alternate medium-coarse sand and pebble. Grain-size analysis for sandy sediments sampled at the mound revealed that the skewness was minus, showing that the sand was transported by waves and longshore currents of the lake. The pebbles were classified into two groups: average flatness of about 2.0 and that lower than 1.8. The maximum and mode of former was flatter than those of the latter. Flatter pebbles were considered to be transported by wave and the others were by river. However, the difference was not significant, and this determination was not conclusive. Measurement of coastal current revealed that strong northwestern wind drove southwest-ward current at around the right bank of the river mouth and southeast-ward current at the northeast beach, and these currents move sediment at the tip of the right bank into the river-mouth area and the northeast beach. Mound and spit were mainly affected by waves.
日本地形学連合の論文
2004-04-25

滋賀県犬上川河口部の掘削凹地を埋積した土砂の堆積過程

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