林道路面におけるリル侵食の形状変化 (II)

Abstract

前回の調査では, 林道路面上に半ば形成されていた水跡 (リル) に着目して, その発達の様子を夏から秋に掛けて調査した。今回は, 路面を一度ブルドーザーで削新たに路面を造成した段階から, どのようにリルが形成され, 発達してゆくのかを積雪期を含む約10ヶ月間に渡って調査した。

In the previous report, the changes of shape and development of the rill in the beginning stage of erosion on the forest road surface were investigated for about 5 months from early in summer to late in autumn. In this report the same investigation was performed on the new made surface of which rill already made were smoothed out by bulldozer, for about 10 months including snow lay season (the period was from June to next April). The area of investigation was about 30 meter lengths and the measured points were located at intervals of about 5 meters (see Fig. 1). The measurement results are shown in Fig. 2 measured point by point. Each figure has 6 broken lines, and these lines show the temporal changes of the cross section of road surface and rill corresponding to increase of the thickness of line individually. From these figures the following tendencies were observed. 1) In June the unevenness of road surface stood out from other months in consequence of remaining of traces of wheel tire and so on, but in July most of these traces were worn out, and in September the profile of the present surface had already formed. Hereafter no remarkable changes of the profile were observed in spite of not a little rainfall. 2) During the investigation of 10 months, the maximum depth of rill erosion was 60-65mm at NO.6 of measured point, and at other points the orders of erosion were about 25 to 50mm. 3) Snow lay and melting of the snow had not much influence on the rill erosion, however, if examined in detail in figures it was generally observed that the roughness of road surface and rill were smoothed and had made more even in next April.