Impact of channel regulation on tributary main-stem interactions in the Vsetínská Bečva River

River confluences represent an integral component of the fluvial system, with the potential to disrupt downstream longitudinal trends in the main river through inputs of water, sediments, and other materials, such as woody debris. These various inputs at confluence zones result in a high degree of morphological and, consequently, ecological diversity. This study examines the potential relationship between the spatial characteristics of the catchment and the parameters of the confluence hydrodynamic zones (CHZs). A total of 15 tributaries and their adjacent CHZs were selected for analysis along a 50 km reach of the Vsetínská Bečva River in the Javorníky and Hostýn-Vsetín Mountains in the Czech part of the Outer Western Carpathians. The Vsetínská Bečva River is highly channelized, with the majority of channelization efforts involving riverbank stabilization, weirs, or grade control structures. The study hypothesized a correlation between the spatial arrangement of the channel, as indicated by the channel width symmetry ratio, and the angle between the tributary and main-stem river, and the increased morphological activity, evidenced by changes in average bed depth at the CHZs. The correlation coefficient (r) and p significance were employed to describe the relationships among the parameters. The results indicated a significant correlation between channel width and the catchment area symmetry ratio (r = 0.747, p = 0.001), likely influenced by channel regulation works (e.g., channel shape or size), which are often artificially adjusted to accommodate local hydrological conditions and flood discharges for flood protection. A significant inverse correlation between channel width symmetry ratio and average main-stem channel depth was also found (r = -0.584, p = 0.022).