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

摘要

Hydraulic engineers and scientists working on river restoration recognize the need for a deeper understanding of natural streams as a complex and dynamic system, which involves not only abiotic elements (flow, sediments) but also biotic or biological components. From this point of view, the role played by riverine vegetation in river dynamics and flow conditions becomes essential. Hydro-mechanic interaction between flow and flexible plants covering a river bed is studied in this paper and some previous works are discussed. Experimental tests and measurements of turbulence on the flow in an open channel were performed using plastic plants seeded in a gravel bed. Characterization of flow resistance (friction factors) due to vegetation flexible roughness for different plant densities was attained; furthermore, measuring detailed turbulent velocity profiles within and above submerged and flexed stems allowed us to distinguish different turbulent regimes. Some interesting relationships were obtained between the velocity field and the deflected height of the plants, such as a linear fit between the non-dimensional flexural parameter and the relative deflection of the plants. Turbulent stresses were measured showing two different regions: above and inside the vegetation domain. The spectral interaction between the plant oscillations, their wakes and the turbulence at different heights, forces strongly anisotropic Reynolds tensors and in order to clarify turbulent processes and their complex structure, theoretical concepts (Taylor, Kolmogorov's K41) and several data analysis (autocorrelation functions, integral scales) were applied.