Comparison of Vegetation Overgrowth Tendency in Several River Channels Using a Vegetation Dynamics Model

This paper examined and compared the tendency of vegetation overgrowth in several river channels of two river basins by using a vegetation dynamics model. The model employed a stochastic evaluation method for examining vegetation population states in a river cross section using an integrated model with Monte Carlo simulation. The integrated model consists of four processes as sub-models, i.e., vegetation population dynamics, flow discharge stochasticity, stream hydraulics, and channel geomorphology. The two river basins examined in this paper were Kako River and Takatsu River, in Japan, where many parts of the river channels have been well-vegetated during recent several decades. The optimal parameters of the vegetation dynamics model were determined in terms of flood impacts and plant physiology for applying it to the tendency analysis of several river channels in the two river basins. The results indicated stronger flood impact and weaker plant physiology of Takatsu River, resulting in that the tendency of vegetation overgrowth would be stronger in Kako River compared to Takatsu River. It also showed that the well-vegetated channels in both river basins would have smaller ratios of sandbar/channel widths. Moreover, predominant factors of vegetation overgrowth tendency were discussed with respect to the flood impact, plant physiology, as well as channel geomorphology in detail.