Once used for turning turbines, washing and bathing, the Ichikigawa river was destroyed in an earthquake in 1972, but has been restored to the condition you see below. Rapid urbanization led to a deterioration in water quality, but after the installation of sewage treatment facilities, a volunteer Ichikigawa City Beautification group was established to help preserve the town’s symbolic river for future generations. With input from this society, we built a fish ladder in Aichi prefecture by placing stone over existing structures.
The natural stone riverbanks of the Ichikigawa river have been washed down to the bedrock in spots from flooding, and in many places are worn through completely. Since these rocks create the walls of the fish ladder, we adopted Tosazumi piling to use rubble to fill in the gaps. This method of piling, a construction technique unique to Aichi Prefecture, creates overhang from stone, and we brought masons from Aichi to oversee the process.
When we created the plans for this fishway, we intended to take sediment from deep pools on the downstream part of the fishway and create sandbars by piling it along the left bank, thus making low water meanders, riffles and pools. Erosion points have resulted in the sandbars changing location, but the meanders remain, and so we have hopes for the future of this element. In addition, the shallows created by the meander have become new freshwater goby spawning grounds.
To investigate the results of the fish ladder, we installed a fixed shore net at the upper edge of the furthest upstream pool to catch fish that come upstream. The results showed that we were unable to find the targeted Ayu, but we could confirm that light and dark chub fry, freshwater goby and other demersal fish and migratory fish, as well as aquatic creatures like mitten crabs, were climbing the fish ladder. We could also confirm the inhabitation of fish like light and dark chub through dive observation.
When building the Ichikigawa River fishway, we intended to use erosion and sedimentation as well as the direct creation of riffles, pools, and rock shelter to create space for inhabitation and spawning for area aquatic creatures. Our company plans to carry out continuous monitoring, and provide a (proposed) O&M scheme based on ecological considerations for local volunteer groups who carry out river beautification activities.
