A device to allow fish or other animals to overcome obstacles such as weirs, dams, sluices or hatches in rivers and other waterways. The device is in the form of a bunch of tubes in which water momentum in the outer tube A and inner tube B are equal by virtue of their equal cross-sectional areas and velocities. The outer tube water flow is reversed and brought in to opposition to the water in the inner tube by a scoop E. At the juncture of the two flows the axial water velocity is reduced to zero. The water velocity in the inner tubes is greatly reduced thus enabling the fish to swim comfortable through the tubes to the upper waters. The water velocity at the outlet C is determined solely by the vertical height of the orifice tube and is thus independent of the obstacle height and upstream water level G.
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