Abstract
To elucidate source areas of leaf-litter that enters river streams, a new model was developed for predicting leaflitter dispersion. This model simulates falling-leaf motion based on physical parameters such as riparian forest wind data, leaf-falling velocity, and tree-crown central height. The new model was applied in two lowland riparian forests to two willow trees. The model estimates fitted in well with the observed willow-leaf dispersion data, except for the vicinity of tree crown. Thus, we considered the new model as more effective than the existing models describing leaf-litter dispersion. Then, the leaf-litter dispersion of two riparian buffer strips was estimated using the new model. It was assumed that each tree belongs to the same species with equal height as other trees and equal distance from the other trees. The strip width had almost no effect on leaf-litter supply for the stream channel because the trees near stream banks had a strong leaf-litter supply into the streams. The riparian forest strips in upwind parts of the streams supplied more litter to the stream channels than the downwind strips. Thus, the upwind strips were considered more important for leaf-litter supply into the streams. Furthermore, the channel form was also considered to influence the leaf-litter supply into the streams. A highly meandering channel located in the same valley as a straight channel probably receives more litter than the latter. However, in a riparian forest with low tree density, the effect of channel form was lesser.
