Author(s): Takeshi Okabe; Yasuo Anase; Mahito Kamada
Linked Author(s):
Keywords: Willow community; Condition of establishment; Hydrogeomorphic process; Data analysis; Shallow-water simulation
Abstract: The relationship between establishment of willow communities and hydrogeomorphic process is investigated from ecological and hydraulic points of view. The study site is a downstream reach of the Yoshino River, Shikoku, Japan, where three alternate bars of similar configuration have formed over the past five decades. Salix chaenomeloides and Salix grasilistyla communities have been successively established since the early1970s. Their establishment is found clearly restricted in both time and place due to colonization trait and mobility of bed material of the willow communities. With regard to the mobility of the bed material, it is clarified that the colonization niche is restricted to areas where annual maximum dimensionless tractive force of the bed material is around 0.06 during two or three years after their generation. The geomorphologic process at the study site appears to be considerably affected by expansion and growth of the willow communities. The bed level of alternate bars has been aggraded year after year mainly along their outer edges fringed by the growing willow communities. On the contrary, beds of low-water stream have been degraded so much as to potentially damage bank-protection works at some places. Typical changes in flow pattern and distribution of sediment mobility between the early and present stages of establishment of the willow communities are also demonstrated based on two-dimensional shallow open-channel flow simulations.
Year: 2001