top < Outline of the Nagaragawa Estuary Barrage < Fishways < Naturally Shaped Fishway

Outline of the Nagaragawa Estuary Barrage

Naturally Shaped Fishway

The naturally shaped fishway is about 320 m long and 15 m wide (including a water surface of 3 m in width) provided on the overflow levee on the right bank of the estuary barrage. A stream resembling a natural brook was created to allow a wide range of fish to travel upstream. The channel is given a gentle slope, and cobblestones and other natural stones are placed in it. Rapids and pools are arranged alternately to diversify the depth and the velocity. The channel was made to meander, and resting places and shelters for fish were formed. At the exit (upstream end) of the naturally shaped way, four roof weirs made of rubber cloth were provided to deal with a change in the water level on the upstream side. This fishway is proving effective in aiding the upstream movement of many types of fish, including benthic fish, fish with low swimming capacity, shrimps, crabs, and ayu (strong-swimming fish).

The naturally shaped fishway viewed
The naturally shaped fishway viewed
from the upstream side

Ayu swimming upstream over the naturally shaped fishway
Ayu swimming upstream over the naturally shaped fishway

A rubber cloth roof weir(upstream section of shallow fishway)
A rubber cloth roof weir
(upstream section of shallow fishway)