Fish’ habitat area and habitat transition in a river under ordinary and flood flow

In the past, river management was mostly people-oriented (disaster prevention), focusing on development and utilization, and often neglecting the habitat of river organisms, which led to the destruction of river ecology. Moreover, in recent decades, river environment restoration has an area of focus, and the importance of environmental protection and ecological balance has gained popularity. The initial step in river restoration is to increase habitats, while concurrently understanding habitat distribution and habitat changes. Ordinary flow is generally very small, but during floods, river flow surges, and habitat changes become more apparent. In this study, Two-Dimension River Habitat Transition Model was developed and used to simulate the fish habitat of ordinary flow and flood flow in Zengwen river. The weighted usable area (WUA) and the percent usable area (PUA) suitable for fish survival under different flow discharge were quantified. In addition, the fish habitat distribution and habitat Transition under the ordinary flow and flood flow in Zengwen river were discussed. The simulation results indicated that the fish habitat distribution is within the main channel under ordinary discharge, while during floods, the river overflows to the floodplain, and the habitats of fish are mostly distributed over the flood plains on both sides of the main channel. Under this case, there are less fish habitats in the main channel indicating that as the amount of flow in the river increases, WUA increases, while PUA decreases.