The variation of local scour pattern around representative natural vegetation elements.

Oral Yagci, Vasileios Kitsikoudis, Furkan Celic, Can Hodoglu, V.S.Ozgur Kirca, Manousos Valyrakis, Zaide Duran, Sinasi Kaya

Tuesday 30 june 2015

12:00 - 12:15h at Africa (level 0)

Themes: (T) Water engineering, (ST) Experimental facilities and instrumentation

Parallel session: 5F. Engineering - Instrumentation

It is a well-known fact that in riverine corridors the existing strong bilateral relationship between geomorphological and ecological processes determines the dynamics of self-adjustment process. Today it is commonly adopted that the level of this two-way interaction dictates the dynamics and self-adjustment potential of the river. From this motivation, a series of flume experiments were undertaken to further understand the scour pattern around the different forms of representative vegetation elements when exposed to steady flow conditions. The laboratory experiments were conducted in a flume, which has a length of 26 m, width of 0.98 m, depth of 0.85 m, and the bed was layered with coarse sand. Three different kinds of representative vegetation elements were tested, namely natural plants, a group of hexagonal cylinders, and a solid cylinder. For comparison purposes, at the beginning of each experiment the fully flat bottom was scanned. Newly released Vectrino II (i.e. Vectrino profiler), which is capable of measuring instantaneous 3D velocity profile near the bottom, was utilized for the velocity measurements around the obstacles. With the utilization of Vectrino II, the time-scale of the scour process downstream of the element was determined and it was decided whether equilibrium conditions are attained. Subsequently, velocity profile measurements were taken close to bed, downstream of the vegetation element, and along the centerline of the flume (i.e. over the scour and deposition zone). Finally, the final form of the bottom was digitally scanned by 3D Leica laser scanner. The preliminary findings clearly denote that the deformed velocity distributions due to different elements markedly affect the erosion patterns. Since each of the elements has distinguished anatomy, the generated horseshoe vortex, lee-wake vortices, and downflow characteristics were unique; hence, the scour/deposition patterns around the obstacle were different.