Installation of Bamboo Gabions as a Groin to Create Fish and Invertebrate Habitats in the Kizu River, Japan

Groins are usually installed to prevent bank erosion and levee damages. In Japan, gabions made by bamboo and gravels, called bamboo gabions in this paper, have been used traditionally in the construction works of rivers, however they are not frequently used recently due to the cost and high efforts of their production. Many rivers in Japan and world are now facing environmental problems associated with channel degradation or aggradation. The Kizu River, which flows north in Kyoto Prefecture, Japan, is a granite sandy river, and invertebrate and fish species were originally poor due to the fine bed materials and very flat and uniform topography. Due to constructions of dams upstream, beds became coarser and species richness became higher in the river during several decades. However, river managers are planning to sluice of sediments through the reservoir outlet to prevent over-degradation of the channel, which can induce re-appearance of fine and simple bed conditions unsuitable for river biota. Thus, we should take any measures to keep and improve more preferable condition. In the floodplain and riverside area, bamboo forest has been expanding due to reduction in flood disturbance and harvesting. The local residents and municipality are now seeking to better utilize bamboo again to stop expansion of the bamboo forest.This paper main objectives are to: 1) focus on the specific features of bamboo gabions, which fit in nature and ecosystem, from views of maintaining suitable river habitats and well-utilizing bamboos; 2) examine the effect of bamboo gabions as groin on riverine invertebrate and fish habitats, we installed the gabions and monitored the changes in bed topography, bed materials and animal community in a lower reach of the Kizu River.