Journal of the Japan Society of Erosion Control Engineering, Vol.59,No.6,2007

Fundamental study on sediment yield due to freeze and thaw process
\Field observation on bare slope in Tanakami Mountains and its numerical simulation\

Daizo TSUTSUMI, Masaharu FUJITA, Motohiro ITO, Hiroyuki TESHIMA,Toyoaki SAWADA,
Ken'ichiro KOSUGI and Takahisa MIZUYAMA



Abstract

A detailed field observation was conducted to elucidate mechanisms of freeze and thaw process and following sediment yield on a bare slope in Tanakami Mountains, southern part of Shiga Prefecture. During the observation period (December 2004 ] April 2005), air, surface and subsurface (10, 25, 50 cm depth) temperatures were continuously measured with 10 min interval. The sediment which was yielded on the bedrock was collected and weighted once in a week from a plot area (plot 1). For another plot area (plot 2), the sediment was left on the bedrock until the end of observation period. From the observation results, it was indicated that the freeze and thaw cycle occurred repeatedly, and the frozen zone (temperature 0 ) reached to the depth of 10 cm. The sediment yield occurred due to the active freeze and thaw process, and stopped at the end of the observation period when the freeze and thaw cycle also stopped (April, 2005). Total amounts of the sediment yield on plot 1 and 2 were 108 and 44 kg/m2/year respectively. This difference indicates that the sediment cover on the bedrock surface mitigated the effect of freeze and thaw process. These observed results were simulated by simplified thermal conductivity analysis method. Comparison between observed and simulated results suggested that multiple experiences of the freeze and thaw cycles are necessary for the bedrock to become sediment. It was confirmed that the estimation of the sediment yield due to freeze and thaw process is possible by this numerical simulation method.

Key words:Sediment yield, Freeze and thaw, Thermal conductivity calculation, Model simulation
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