If stability of the bank revetments are secured by only the herbaceous plants, not only the expenditure in constructing the artificial banks are reduced, but also the vitality of the stream ecosystem is restored. The effect of herbaceous plant roots on reinforcing the bank stability are examined quantitatively.
Three kinds of herbaceous species with different forms of roots were selected for the analysis. The plant species used were, Flame Grass(Miscanthus sinensis var. purpurascens), Curled Dock(Rumex crispus L.) and Green Bristlegrass(Setaria viridis L.). The soil samples including herbaceous roots was collected in the fields, and these samples were used for the direct shear test.
The results of direct shear test between soil samples including roots and roots-removed samples were compared, and it proves to be effective in reinforcing the bank revetments by herbaceous plant roots. The amount of increased shear stress by herbaceous plant roots proves to be the largest in Flame Grass(Miscanthus sinensis var. purpurascens), which is about 73%.
Soil was removed from the samples and only the roots were collected after the direct shear test. The root volume and root hair weight were measured. From the results of the increased shear force versus the root volume and root hair weight, it was proved to be shear forces increased as the root volume and root hair weight were increased.
The Stoloniferous/rhizomatous root type among the three kinds of species in Flame Grass(Miscanthus sinensis var. purpurascens) was the most effective species in reinforcing the banks.