Causes and mechanisms of the disappearance of braided channel patterns (the example of the Białka River, Western Carpathians)

Abstract

The channels of multi-threaded (braided) rivers occur commonly in areas that fulfill certain conditions such as substantial influx of bed material and gradients large enough to create significant energy of flowing water. Natural conditions favoring the formation of multithreaded channels are present in the Carpathians in Poland in Podhale – a large basin located in the piedmont area of the high-mountain Tatra massif. The area had experienced glaciation in the Pleistocene. Yet the 20th century – and especially its second half – was a period of rapid and irreversible elimination of braided channels across the region. The Białka is considered to be the last braided river in the Carpathians in Poland. Many parameters like: structure (morphologic reach sequence), degree of braiding (BI index, W/D) and also a number of hydrodynamic ones (unit stream power, critical stress, shear stress, others) were investigated in order to assess a current stage of development of the Białka river channel. The Białka river channel appears to be a complex system with a differentiated structure. Its channel system is a mosaic of different types described by the following sequence: straight-sinuous-braided. It represents an intermediate type that is somewhere between a single- and a multi-threaded channel. Future evolution of the Białka river channel appears to include further degradation and transformation into a poorer channel ecosystem.