Author(s): Norio Tanaka; Yusuke Shirono; Toshimitsu Takagi
Linked Author(s): Norio Tanaka
Keywords: Wind-blown sand; Required width of vegetation; Sand deposition; Carex kobomugi
Abstract: Wind tunnel experiments and numerical analysis were conducted for elucidating the relationship between the density of Carex kobomugi Ohwi, one of the most common species growing on sand dunes in Japan, and the required vegetation width of vegetation for depositing wind-blown sands against the prevailing wind direction. Flow around C. kobomugi and a colony model was investigated to clarify the wind-blown sand deposition mechanism. By the presence of colony-type roughness, local scouring around the plants and sand deposition behind it was occurred with dry sand condition. In field observation, the scour was not observed, therefore the experiment of fixed bed with blown-sand was conducted and sand deposition amount was measured. Sand deposition amount with fixed bed became larger than that with local scouring. The effect of the spacing of colonies on the amount of sand deposition around them was investigated and represented as a function of the colony spacing. The calculated required width was about 100 m at Ryuyo Beach, Japan. The width corresponds to the length from the edge to the point at which no sand deposition was observed behind a C. kobomugi colony in prevailing wind direction. The required width of the vegetated region increases greatly with increasing the shear friction velocity and the colony-spacing.