Spatial and temporal variability of the morphodynamics of a regulated mountain river

For more than 30 years, the lower section of the Bialy Dunajec river (Poland) has been regulated by grade control structures (GCSs). Despite the short length of the section and the uniform method of regulation, varying dy-namics have been observed in the longitudinal profile. The study aimed to identify the morphometric parameters of the channel and the hydraulic parameters of the flow that determine this variability, to establish whether the variability in the morphodynamics of a regulated river can be predicted in the longitudinal profile and over time. The novelty of this study is that it recognizes not only the variations in the morphology of the regulated river in the longitudinal profile and cross-sections but also the changing flow dynamics over the last 60 years. For this purpose, archival designing projects were used in this study, from which five different flow models were pre -pared. Using these models, adjustments of the river to the changes made were reconstructed. The study showed that the stream power, which is often used to predict fluvial processes in natural channels, was not useful while evaluating the regulated river, where both sediment supply and lateral connectivity with the valley are severely limited. The varying dynamics of the river depended on the morphometrical parameters of the channel, espe-cially depth and the W/d ratio. The magnitude of erosion was also positively correlated with the distance be-tween GCSs. Interestingly, varying morphodynamics in the river showed similarities to those before regulation. Formerly erosive sections showed a tendency toward erosion, and the braiding depositional section showed a tendency toward lateral erosion and deposition. The river is unstable and the hydraulic structures are destroyed at low flows, contrary to the design assumptions. A key factor that seems to complicate the predictability of the processes in regulated rivers is the supply of debris, which is not only severely limited but also spatially and temporally variable.

Automated summary

This study aimed to determine the morphometric parameters of the channel and the hydraulic parameters of the flow in order to predict the variability in the morphodynamics of a regulated river. The study found that the dynamics of the river varied depending on the morphometric parameters of the channel and the distance between GCSs. Interestingly, the varying morphodynamics showed similarities to those before regulation.