2008 Volume 14 Pages 421-424
In the upper Chikugo River, the so-called “Ohyama River,” decrease of the flow rate due to intake for electric power stations by dams has made the riverine environment worse. To improve it, water volume discharged from Ohyamagawa Dam has been increased to 4.5m3/s in a period from the end of March to the beginning of October and to 1.8m3/s in the remaining term since 2002. In this study, we intend to evaluate the influence of instream flow change on hydraulic situation and riverine ecosystem, and find the appropriate flow regime. We carried out fortnightly sampling of attached algae mainly from spring to summer in 2007. As a result of this research, we conclude as follows: 1) The temporal change of chlorophyll-a was similar. 2) During a period with no disturbance by flush, chlorophyll-a increased monotonically and reduced after showing maximal value. The maximal value depends on the amount of solar radiation. 3) It needs longer time for growth of attached algae under initial condition with no algae than with a certain amount of algae. The amount of attached algae depends primarily on flow regime.
