Confluences between a pipeline and a channel are commonly found in urban drainage networks. The mechanisms of sediment transport and the coherent structure within the confluence zone remain ambiguous. The hydro-morpho-sedimentary processes at pipe and channel confluences, which are influenced by discharge ratios, are investigated using a laboratory-scale confluence. The pipe current compresses and diverts downstream upon entering the main channel, creating a scour hole that carries sediment downstream. Coarser sediment deposits first, forming the slope of the downstream boundary of the scour hole (D50 = 60.31 μm) and the inner bar (D50 = 62.67 μm). Finer sediments are then deposited in the outer bar (D50 = 53.12 μm), resulting in a bed morphology consisting of the scour hole, outer and inner bars, and corridor. The penetration of the pipe current causes redistribution of the main channel flow, creating two shear layers. The height of the bar is directly related to the intensity of turbulence. Within the range of discharge ratios from 0.06 to 0.09, the shear layers and bars are displaced toward the outer bank by a distance of approximately one pipe diameter (0.05 m). Turbulence in this area is not isotropic, with power-law relations for streamwise and lateral velocity having an exponent of approximately −5/3. Conversely, the separation zone deviates from this pattern. Overall, this study highlights the significant influence of the bed morphology in modifying the flow structure compared to channel confluences and jets into crossflow, which are important in drainage engineering designs and fluvial studies.

Planform evolution and terrestrial habitat health of two representative mid-channel bars (Baishazhou bar and Tianxingzhou bar) in the urban reach of the Middle Yangtze River in Wuhan City have not been understood under the combined influences of natural forcing and human activities. Using dry-season Landsat imagery (1989–2020), hydrological records from the Hankou gauging station (1990–2019), and field surveys, we quantified bar-morphology changes and examined the mechanisms underlying their differentiated scouring. We also developed an indicator system to evaluate terrestrial habitat health on mid-channel bars. Indicator weights were determined using a combined weighting approach integrating the Analytic Hierarchy Process and the entropy weight method. Since the Three Gorges Dam began operation, the runoff in the Wuhan reach has decreased only slightly (6.72%), whereas sediment load decreased sharply (69.88%), causing net scouring of both bars. Baishazhou bar, in a straight anabranching reach, lost 43.83% of its area (1989–2020), with erosion concentrated at the head and main channel margin and caving. Tianxingzhou bar, in a mildly curved reach, had moderate shrinkage (26.33%, 1992–2022) as revetments curbed head/right margin retreat. Both bars were “very healthy” in natural attributes, with the Baishazhou bar showing longer water–land ecotone exposure (217 d) and higher vegetation cover (92%). Socially, Baishazhou bar was “sub-healthy” due to unprotected shrinkage, and Tianxingzhou bar was “unhealthy” due to area loss and low permeability of hard works. Overall, both bars were “healthy”. These findings provide a basis for ecological conservation and habitat restoration of bar wetlands.