On the Case of Surface Erosion on the Steep Forest Road

1988

S. 198-207

10 Abb., 4 Tab., 5 Lit. Ang.

Unselbständiges Werk

200012651

In this report, we referred to surface erosion, especially to rill erosion generated on the steep grade forest road, taking up a case ofsteep primary road passable with 4WD car only. 13.9% was the mean road gradient of the investigated route. To analyze factors that had affected generation and cross-sectional scale of the erosion, we used the Hayashi's Quantification, 1, 2, and the multiple regression analysis. The results we've got are as follows: As road gradient increased, the road surface tended to be subject to roll erosion. That is to say, generative frequency of rill erosion had positive correlation to road gradient. (see Fig 4, 5). As to less than about 20% gradient, it is true that the same relation as above was recognized between (cross-sectional)scale of rill erosion and road gradient, but this relation wasn't true of every case with more than the gradient, or rather, even negative correlation was recognized between them. (see Fig. 6, 7). The cause of this result is presumed that on the earth road surface with steeper gradient than about 20%, traffic cars should smooth shape of rill by wheelslip or skid. Both generative frequency and scale of rill seemed to decrease when the road was covered by crowns of trees which lined it on side. (see Table 2, 4). Finally, we wish to make extra remark: almost all along the investigated route, logs and crushed rocks were buried under or into the road surfaces to reinforce them. Besides the way of surface drainage that cross section of road surface is slightly inclined down to bank slope (of course it must be stabilized) so as not to concentrate runoff of rill, we consider that these manners are very effective to restrain surface erosion on the forest road.