The impact of channelization and flow regulation by dams and weirs on river habitats and landscape has been enormous. The most serious impact of river works in Japan, in order to meet the needs of flood protection and water resources, has been to lose a great variety of riverine plants. This has resulted in habitat loss for wildlife and reduced the ability of the river to carry out many of its natural functions, that is the control of local scouring in a levee, water purification and sediment storage. However, only few attempts have so far been made at the evaluation about progression characteristics of vegetation in channelized river and there is a necessity to consider of the potential opportunities for habitat enhancement and rehabilitation which may be undertaken during engineering works. This research attempts to evaluate the progression characteristics of in-channel vegetation in Tamagawa River by aerial photographs. The research has also shown the relationships between the progression characteristics of in-channel vegetation and the impact of the morphologic and hydraulic characteristics included by human impact on in-channel vegetation.

The maintenance flow discharge of the Ohyama River (upper Chikugo River) had been restricted to 1.5m 3 /s by a hydroelectric dam. To improve the river environment, the river administrator has changed it to 4.5m 3 /s in summer and to 1.8m 3 /s in winter. In this study, we aim at investigating the effects of discharge increase on epilithic biofilms composed of algae. We conducted sampling of attached algae every two weeks from March to July, 2006, at an impact reach increasing the disharge, at a control reach maintained a constant discharge, and at two reference reaches in upstream of the hydroelectric dam. Results of the field surveys show that chlorophyll-a at the impact reach is higher than one at the control reach. However, in case of controling flood disturbance by a dam, there is no difference in chlorophyll-a between the impact reach and the control reach, because attached algae is regulated by heterotrophic process.

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