Field-derived relationships between fish habitat distribution and flow-sediment conditions in fluctuating backwater zone of the Three Gorges Reservoir

The habitats of mountain river were excessively disturbed by various anthropogenic stressors with the development of social economy and increasing of population. To improve the geomorphological and ecological conditions of these habitats, restoration measures have been widely taken. Before any river restoration, there must be an understanding of the fish habitat requirement. The aim of this study was to gain an understanding of the relationships between hydraulic characteristics and fish assemblage in fluctuating backwater zone of the Three Gorges Reservoir and provide a scientific basis for protection and restoration of river habitats. To achieve this aim, three steps were taken. Firstly, a description of the characteristics of fish assemblage patterns in space and time was presented based on two hydroacoustic field surveys. Then the hydrodynamic model was used to numerically simulate the hydrodynamic conditions during the investigation period. Finally, evaluation of the hydrodynamic requirements of fish habitat was conducted on the basis of the relationship between the fish assemble and hydrodynamic conditions. The results showed that fish swarm preferred to gather and distribute in the deep pools with a depth of more than 20 m. Taking both hydrodynamic conditions and sediment transport into consideration, the minimum and maximum velocities of fish habitat requirement in the study area was 0.6 m/s and 1.2 m/s, respectively.