Abstract
In Inaho area of cold, light snowfall Tokachi district, investigations were carried out for influences of soil freezing on soil erosion which is a marked characteristic in this district.
As a result of this, it revealed about the soil erosion in the snowmelt period that eroded damage occurred much more in slopes incidental to the upland field of reclaimed fields than in the upland field itself. Following findings were obtained for this characteristic.
(1) A rill erosion occurs due to a drain overflowing its diversion ditch incapable of keeping its sufficient sectional area to flow down the drain in the snowmelt period, because the snowfall in the winter time covers the sectional area of the diversion ditch.
(2) In a period when, with a soil in the slope frozen in the winter, the frozen soil layer still stays in the snowmelt time, seepage water causes a surface plane slip and a seepage slip in the middle of slope, because it flows down in this frozen layer making it a quasi-river bed.
(3) Due to such an imperfection of soil erosion protection works as a shortage of drainage, diversion ditch, etc., along the tractor passage in the reclaimed field, a rill erosion is caused by a surface run-off water which originally is to pass through its drainage canal to the outside of this district, but runs off in the slope.
Also concerning the dangerousness of soil erosion due to its slop aspect, it revealed that a period in which a frozen layer remains in the soil layer of a slope facing the north is longer than that in a slope facing the south in the snowmelt time, and its snow coverage remains much there due to the sun shade, therefore, the dangerousness is highly expected.
