| " Bur cucumbers which are annual weeds have grown thickly in Chikuma River since 1994. We presumed thatthis phenomenon is accelerated by large floods that may spread the seeds of them. We have estimated the critical tractive force of seeds by a waterway experiment and analyzed the places where transported seeds can accumulate along the river and the destruction force of bur cucumber colonies by numerical simulation. Consequently, critical tractive force(τ*) of the seed was determined as 0.04. When the friction speed (u*) that works at the river bed exceeds about 17cm/s, the destruction of bur cucumber colonies seem to begin. However, bur cucumber colonies are not destroyed when they are accompanied with false acasia even if the friction speed exceeds that level." |
