Scour Morphology Downstream of Log-Frame Deflectors in Series

Stream deflectors are grade-control structures of common use to control riverbed evolution, stabilize channel alignment, protect stream banks, and rebuild the natural habitat. Among them, log-frame deflectors consist of a triangular log frame filled with rocks. Log-frame deflectors, constructed either singly or in series in low gradient meandering streams, divert base flows toward the center of the channel. Under certain hydraulic conditions, they modify both the depth and velocity of flow, resulting in scour pool formation and fish habitat improvement. The main purpose of the current study is to analyze the effect of the distance between log-frame deflectors on the scour morphology, when installed in series. Therefore, experimental tests have been carried out in a horizontal channel and in clear water conditions at the hydraulic laboratory of the University of Pisa. Results show that the meandering process in rivers is deeply influenced by the distance between log-frame deflectors, when located at both left and right river banks. Furthermore, scour characteristics and morphologies downstream of log-frame deflectors have been analyzed, resulting in useful suggestions for a correct design of such structure typology.