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Vegetation is one of the key factors in river management where environmental aspects as well as flood protection should be taken into consideration. Because of this, numerous studies have been done including experiments and hydrodynamic modelling. Because most of experimental studies were made in indoor laboratory flumes with artificial trees, there are still limitations in transfer of their result to actual channels. REC (River Experiment Center) of Korea has been operating three real-scale, nature-like outdoor experimental channels. In a straight channel, several 4x2 m actual willow patches were planted and have been grown last three years for studies on flow vegetation interaction. A set of intensive flow measurement was made around the first upstream willow patch using ADVs together with measurement of vegetation properties. The experiments were made under several different depth conditions simulating snow-melt and flash-flood. Distribution of flow around and through the patch was characterized along with vertical profiles. The results of the experiment enhance understanding on interaction of flow and actual vegetation in a natural channel and may also provide information on flow resistance used for hydrodynamic modelling and validation.

This study carried out experiments to investigate the effects of vegetation patches of rooted willows on the flow pattern. Stream-scale experiments on vegetated flows were performed for various hydraulic conditions: emergent and submerged conditions of vegetation. Vegetation patches were arranged by alternative bar formation and the flows in vegetated and non-vegetated sections were compared. Three-dimensional flow velocity was measured by ADV (Acoustic Doppler Velocimeter) and ADCP (Acoustic Doppler Current Profiler). Vertical, cross-sectional, and longitudinal velocity distributions were provided for different hydraulic conditions at various points. Flow velocities through the sparse patch were similar to those of non-vegetation area for low flow condition of emergent vegetation. Dense and submerged vegetation produced more complicated and non-uniform flows over the cross-sections of vegetation patches.