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A study of the hydraulic parameters and ecological significance of braided rivers under flow variations

One‐dimensional numerical simulations based on the actual braided‐channel geometry in the middle reaches of the Yarlung Tsangpo River can be used to calculate the characteristics of braided channels in terms of their branching conditions and hydraulic parameters. Numerical modeling in the study area showed that a higher number of branches at fish‐spawning grounds may provide more suitable habitats for local organisms to survive. During most of the year, the distributions of the flow velocity and water depth in the higher‐branching channels were significantly lower than those in the lower‐branching channels. The hydromorphological index of diversity (HMID) of higher‐branching channels was higher than that of lower‐branching channels during all water periods, which showed the higher habitat heterogeneity of higher‐branching channels. The Froude numbers of higher‐branching channels ranged from 0.1 to 0.3, and the stable flow regime partially explained why higher‐branching channels are important habitats for fish‐spawning and nurseries. The lower flow velocities and water depths in the higher‐branching channels may have met the hydraulic habitat conditions for the survival of juvenile fish. This article analyses the characteristics of the hydraulic parameters and the ecological significance of braided river channels and provides theoretical support for the protection of fish habitats in braided rivers.