Technical Assessment of River Training Impact on the Raba River Bed Stability on the Selected Longitudinal Section

摘要

Short assessment and prediction of movement of selected sections of the Raba river in Southern Poland, using existing, historical sources is presented in this paper. It has been done to the most practicable extent, with regard to the river training structures as groynes and revetments stability structures. The old maps (almost non-existent) and/or aerial photographs of the selected areas and the archival projects of technical Raba river channel regulation were complemented with specific stream power and bed shear stress. In the 8.2 km long study area four specific sections has been studied in the current paper. The general trends over the last fifty years has been artificial narrowing of the active channel width with uniform riverbed longitudinal slope. The current studies lead to conclude that the narrowed river channel tends to restore its previous state. However, throughout each analyzed section the channel-forming processes are varied, mostly related to restoring the local natural longitudinal slope. In Section-1 the process of sediment deposition was observed and it continues till now. In Section-2 the channel-forming processes were carried out with high intensity with tendency to rebuilt its previous braided course. Currently this tendency is continuing. The third Section seems to be the most stable after river training works. In Section-4 the process of high erosion especially of the left bank in observed. The results of analysis lead to conclude that more comprehensive investigation is needed of the whole 8.2-km long reach to assess the river state.