Author(s): H. J. Biggs; V. I. Nikora; C. N. Gibbins; S. M. Cameron; K. Papadopoulos; S. Fraser; M. Stewart; D. Vettori; M. Savio; D. R. Green; D. M. Hicks
Linked Author(s): Davide Vettori
Keywords: No Keywords
Abstract: Aquatic plants such as macrophytes and bryophytes inhabit many of the river systems around the world. They are primary producers that provide a 3D substrate matrix for invertebrates and small fish, but at high levels of instream biomass they can have a significant impact on flow conveyance and sediment transport. Investigation of flow interactions with aquatic vegetation is challenging however, due to the wide range of scales that these interactions occur over. For example, flow interactions with large patches are not a summation of flow interactions with stems and leaves (due to clumping and reconfiguration), which makes extrapolation of small scale laboratory studies to real vegetation in natural channels problematic. This issue is further enhanced by the lack of data on the size distribution of natural vegetation patches. To address these knowledge gaps, two field studies were undertaken: one of patch characteristics and the other of fluid velocities around patches. In the former, over 1,000 Ranunculus penicillatus patches were surveyed in the River Urie (North East Scotland) using an unmanned aerial vehicle. This survey revealed that natural R. penicillatus patches at the end of summer have mean planform area of 1.32 m2, mean length of 2.95 m, mean aspect ratio of 5.63, over 1,000 m of total stem length and over 15,000 leaves. These average natural patches are 2-3 orders of magnitude larger than laboratory replicas by biomass. In the second field study, flow interactions with a natural patch of the macrophyte R. penicillatus were investigated using high resolution stereoscopic field Particle Image Velocimetry (PIV). The macrophyte patch caused substantial changes to velocity distributions and turbulence in its wake. Flow fields were highly three dimensional and log profiles did not occur in the wake of the macrophyte patch.
Year: 2018