Coppice at River Banks - Properties, Hydraulic Action and Behavior

摘要

The department of Soil Bioengineering and Landscape Construction at the University of Agricultural Sciences Vienna investigates material properties of riparian wood (i.e. bending behaviour, flexibility, pulling-out resistance, capability to develop adventitious roots) and their influence on hydraulic parameters. By means of a unique test flume located at the Wien river the discharge - waterlevel relation, the flow velocity, the influence of the vegetated bank are observed during artificial floodings. It is shown that the plants flexibility decreases significantly with a basal diameter higher than 40 mm. The plants resistance against pulling out is much higher than the drag force applied by the water (Oplatka, 1998). Thus, both the mechanical failure of single plants and the instability of the bank is due to erosion of soil material. Beside that, the plants' influence on the flow velocity become visible. At a high discharge rate, flexible willows are submerged and thus they reduce the flow velocity less than assumed. For practical application these results mean, that hydraulically smooth bioengineering constructions made of shrubby, flexible tree species' that grow densely and remain flexible for several years are highly suitable for protection measures.