Author(s): Mona Mahmoud Mostafa; Hassan Safi H. Ahmed; Gamal Abozied Abd El-Raheem; Nashaat Abdllah Ali; Akihiro Tominaga
Linked Author(s): Akihiro Tominaga
Keywords: Flow Pattern; Water Surface; Groyne Permeability; Compound Channels
Abstract: Presented here are the results of an experimental study on the flow characteristics around compound channel floodplain groynes with various permeability and relative length. Both the permeable and impermeable groynes are considered to clarify the influences of single floodplain groyne on flow structure, velocity, and water surface. A channel consisting of a main channel and one floodplain with flat and fixed bed was used. The width of floodplain is the same as the main channel width. Pile groyne models with three different relative lengths relative to floodplain width (Lr), 0. 5, 0. 75, and 1. 0, with three different permeability values (P% = (area of water crossing the groyne/total projected area of groyne) *100) 40, 60, 80% plus an impermeable groyne were used and installed in the floodplain with single arrangement. The 3D flow velocities at both of the horizontal plane above floodplain bed by 0. 25 of floodplain water depth (hf) and at the main channel centerline in the vertical plane were measured using an Acoustic Doppler Veloci-meter (16 MHz Micro-ADV). The flow pattern around groynes was analyzed in both the horizontal and vertical planes. The results show that, for permeable groynes as the permeability increased the groyne length has limited influence on the flow structure. For the horizontal plane maximum and tip velocities were decreased while the minimum velocities were increased as the permeability increased. Empirical formulas to describe these relations depending on the groyne relative length and permeability were suggested. The influence of permeable groynes installation in the compound channel has insignificant effect on the main channel flow while the impermeable groynes affect greatly the main channel flow structure. Both the groyne permeability and length ratio have obvious effects on the floodplain water depth.
Year: 2013