EFFECTS OF SLOPE ATTACHED TO WEIR ON MIGRATION RATE IN POOLAND-WEIR FISHWAY

Abstract

A slope with 45 degree against a horizontal line was attached on the first weir in a pool-and-weir fishway, which is located beside of a large weir in the Onga River, to allow fishes migration. The observation of migrating fishes at the fishway with a digital video camera and velocity measurements with a 3-D electromagnetic current meter were carried out after the improvement. It was found that the migration rate near the side wall is larger than that at the central region of the fishway, because instantaneous velocity near the side wall is smaller than that at the central region of the fishway, irrespective of that the time averaged velocity of both regions are almost same and also the eddy scale around the fish is larger than the body length of the migrating fishes.