ON SITE EVIDENCE OF GRASSES, SHRUBS AND TREES IN REDUCING FLOW VELOCITY NEAR RIVERBANKS
There is lack of sufficient understanding on the complex interaction of vegetation with river flow velocity under field condition. A field experiment was undertaken in an open earth channel by diverting a river in Southwest Ethiopia, Jimma area, 380 km from Addis Ababa. Six plant species were installed in the open channel and 3D velocities were measured within the vegetation and bare treatments by using 10 MHz Acoustic Doppler Velocimeter (ADV). The results revealed that vegetation increased secondary flow significantly compared with the bare treatment. For instance, the percentage of depth averaged free stream lateral velocity (Vy) relative to free streamwise velocity (Vx) was 29.3% in the grass, 44% in the leafy tree branches and 18.9% in the bare treatment. Likewise, the percentage of average free stream vertical velocity (Vz) relative to free stream Vx was 29% in the grass, 3.5% in the tree branches, 11.55% in the shrub, 6.8% in the bare and 2.8% in the leafless-branchless stems. Flexible vegetation such as grasses, leafy tree branches and shrubs can effectively minimize riverbank erosion in-situ and siltation ex-situ compared with rigid stems and non-vegetated channels.
Ayalew Legass (Primary Presenter/Author), KU Leuven, firstname.lastname@example.org;
Moise Ndekezi ( Co-Presenter/Co-Author), University of Rwanda, 2. Department of Civil, Environmental and Geomatic Engineering, email@example.com;
Jean Poesen ( Co-Presenter/Co-Author), KU Leuven, Department of Earth and Environmental Sciences, firstname.lastname@example.org;
Bart Muys ( Co-Presenter/Co-Author), KU Leuven, Department of Earth and Environmental Sciences, email@example.com;
Jan Diels ( Co-Presenter/Co-Author), KU Leuven, firstname.lastname@example.org;