A nature restoration project has been conducted in the Oku River in the northern part of Okinawa Main Island. The purpose of this project is to restore the habitat of Ryukyu-ayu, which is extinct in the wild in Okinawa Main Island. The removal of drop structure and the restoration of pool by withdrawing the river bank were conducted to prevent the water leak as subsoil water and revive the structure of riffle and pool. The restoration for fish habitat was indicated by the results of investigation on fish and riverbed forms. These river improvements were evaluated in terms of bed deformation using numerical simulation. The results of numerical simulation indicate that the removal of drop structure induces the change of the longitudinal profile into original one, and the restored pool maintains the function as a pool over the next ten years.
