An Open Channel Flow Experimental and Theoretical Study of Resistance and Turbulent Characterization over Flexible Vegetated Linings

Hydraulic engineers and scientists working on river restoration recognize the needfor a deeper understanding of natural streams as a complex and dynamicsystem, which involves not only abiotic elements (flow, sediments) but alsobiotic or biological components. From this point of view, the role played byriverine vegetation in river dynamics and flow conditions becomesessential. Hydro-mechanic interaction between flow and flexible plantscovering a river bed is studied in this paper and some previous works arediscussed. Experimental tests and measurements of turbulence on the flow in anopen channelwere performed using plastic plants seeded in a gravel bed. Characterization of flowresistance (friction factors) due to vegetation flexible roughness fordifferent plant densities was attained; furthermore, measuring detailedturbulent velocityprofiles within and above submerged and flexed stems allowed us to distinguishdifferent turbulent regimes. Some interesting relationships wereobtained between the velocity field and the deflected height of the plants, suchas a linear fit between the non-dimensional flexural parameter and the relativedeflection of the plants. Turbulent stresses weremeasured showing two different regions: above and inside the vegetationdomain. The spectral interaction between the plant oscillations, their wakes and theturbulence at different heights, forces strongly anisotropic Reynolds tensors andin order to clarify turbulent processes and their complexstructure, theoretical concepts (Taylor, Kolmogorov's K41) and several dataanalysis (autocorrelation functions, integral scales) were applied.