River contractions typically occur as a result of either natural restraints (e.g. landslides, debris accu¬mulations, longitudinal bars, confluences) or hydraulic works (e.g. bridge embankments, lateral banks, spur dikes). In case of subcritical flows, the flow velocity increases through the contrac¬tion reach and scouring processes and bed degradation can develop. Straub in 1934 was probably the first to suggest a one-dimensional model for long contractions based on the DuBoys’ transport formula and the Manning’s equation. Many equations have been suggested afterwards, most of which were derived from Straub’s approach (e.g. Komura 1966; Gill 1981). More recently, Dey and Raikar (2005) considered long contractions with uniform and non-uniform sediments. They provided the experi¬mental data for 131 runs under clear-water scour. However, the available experimental data to sup¬port the existing predictive models are still limited and, more importantly, the majority of literature studies focuses on the maximum scour depth lacking a more detailed characterization of the bed morphology. Based on several experiments at laboratory scale, this paper aims to provide new insights on the spatial and temporal changes of the bed morphology with emphasis on: the local scour at inlet contraction, morphological features of the thalweg line that typically develops along the channel axis, and the potential bed degradation downstream of the contracted region.
I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.