Current Continuity and Restoration of Process for Fish Habitat in Decreased Discharge

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River environment is characterized as dynamic properties in which cycles of destruction and restoration through fluctuations in discharge, and typical river environment is maintained and formed by fluctuations in discharge ranging from low water to high water. It is estimated that causes of the changes of habitats and thriving state of fauna and flora based on observed data in the Neo-River where includes a irrigative distribution problem. Also, how morphological structure on gravel bars is changing under influence of human disturbances is discussed by comparing the aerial photograph data for forty years. As a result, macro and micro morphology scale related to habitats and thriving state of fauna and flora are defined. It is occurred partially to flow discontinuity zone in the site using temperature data logging system. It is pointed out that flow discontinuity impacts through river ecological system.The "nature-oriented river works exhibition" has been constructed at downstream reach … More for three hundreds meters in the Shin-Sakai River branch of the Kiso River. The foot-protection works are using of natural materials and the porous concrete blocks, and the traditional nature-oriented method such as the well-stabilized riprap with wooden-framed-cobbles are constructed experimentally. This study has been conducted to investigate characteristics of fish habitats using by topographical survey, hydraulic measurement and fish trappings. As results of the field observation and estimation, it is pointed out as follows. The topography of upstream reach from the calvert is monotonous horizontal river line with a gently bottom slope. It is pointed out that fish habitat have diversified flow distributions caused by complicated topography and vegetation cover. The nektonic fishes inhabited mainly in the slope side section and preferred to riffle and pool, while the benthonic inhabited mainly in the paddy field section and were closely related with riparian plants, submerged plants.Settlement and upstream migration in the Japanese mitten crab (Eriocheir japonica) was investigated in the Seseragi-fishway in the Nagara estuary barrage. Megalopa larvae settled and metamorphosed to crab stage in the upper tidal zone in the Seseragi-fishway. Settlement of megalopa larvae occurred mainly in early summer (June) and early winter (December). Their upstream migration to the freshwater area began in July and August. The majority of larvae that settled in winter did not survive and metamorphose to the crab stage due to low water temperatures. Thus, the growth and upstream migration of the Japanese mitten crab seemed to be strongly influenced by water temperature in the estuary. This mode of settlement with two peaks in summer and early winter reflected the temporal pattern of reproduction observed in the sea. In this study, it is clarified that the Seseragi-fishway have a function of settlement and upstream migration for supplement of decreased estuary zone. Less