| In the lower reaches of the Mukawa River，the following events were reported as the behavior of SS during floods1)2)：Suspended solids (SS) supplied to flood flows in the upper reaches accumulate on downstream riverbanks and flood plains．SS accumulated on riverbanks and flood plains are supplied to the water in the next flood．At the same time，SS are transported to the lower reaches and accumulates on a certain downstream places．SS are transported from the upper reaches to the sea by repeating thisprocess．SS accumulated along river channels are considered to contribute greatly to the concentration of SS during floods．[*]However，the behavior of SS in an upstrem mountainous basin，which is considered to be a supply area of SS，has not been well recognized．We measured SS during the flood in July 1999 at Kosei Bridgeover the Pankeshuru River which is located at the uppermost area fo the Mukawa River．As a result，we found the behavior of SS at Kosei Bridge was different from that in the lower reaches and production of SS in an upstream mountainous basin was strongly related to the surface-subsurface runoff component during floodss． |
