魚類の生息密度と多自然型河川工法に関する研究

Abstract

1) As a result of field investigations, it has cleared that concrete revetment river has less variety and smaller amounts of fish that normally inhabit rich aguatic plant habitats which in turn, slow the river flow, in comparison with a river of natural river bank (as time passed). And also, fish inhabit densities of concrete-revetment-river may be decreased about half in comparsion with un-improved/natural river which have aquatic plants, willow trees, rip-rap cobbles so on. 2) It could prove the importance of “uki-ishi-river-bed” (浮き石川床、unstable stream bed which is unsedimentary cobbles) for fish. Generally in the flood, lots of fish are flowed to down stream by flood because most fish can not resist the flow velocity at “shizumiishi- river-bed” (沈み石川床、stable stream bed which is sedimentary cobbles) which has not or cattail plants zone of river side. However, we could collect lots of fish using a casting cover nets from senter of river in flood at the Ta-river which is many uki-ishiriver-bed (because fish take refuge in to the uki-ishi-river-bed). 3) River improvement construction has promoted activity in construction of concrete revetment on the river side (which has come into wide use) in order to protect scouring caused by flood. However, river improvement producess an evil influence on the habitat of fish, due to the decreasing of rapids, pools and aguatic plants associated with these improvements. For the above reason, I carried out to improve the Construction “Method of Close-to Nature Type River” (多自然型河川工法) which is able to inhabit many kinds of fish according to rehabilitate inhabitable environment for fish.