HYDRAULIC MODEL EXPERIMENT ON EFFICIENCY OF INUNDATION SEDIMENT TRAPPING BY INLAND FLOOD-RESTRAINING FOREST BELTS

The effects and functions of sediment capture with inland flood-restraining forest belts were demonstrated in a 1/100-scale hydraulic model experiment in this study. The 3-cm-square lattice wooden model used consisted of an inundation area featuring forest belts with widths of 0.1 – 0.4 m in an open channel, and measured 3.05 mm in diameter. The sediment was mixed silica sand (Nos. 5 – 8) with a dry density of 1.43 g/cm3 and set as a natural-dried volume of 4.9 × 10-3m3 in front of the inundation area. The ratios of sediment mass passing through the forest section were 77% for non-forest, 62% for the 0.1- and 0.2-m belt widths, 64% for 0.3 m and 61% for 0.4 m. The median sediment particle size d50 became smaller as the sediment passed through the forest belts. Values of the index representing sediment sorting d84/d16 didn’t show a specific trend. These results suggest that the presence of inland flood-restraining forest belts especially contributes to reduction of sediment mass derived from inundation.