Hydrodynamics of Partly Vegetated Channels: New Approaches for Flow Discharge Prediction and Sustainable Development

Vegetation is a fundamental component of riverine ecosystems, playing various valuable physical, ecological, and biological roles. Consequently, the presence of vegetation and its interaction with the flow alters the mean velocity and turbulent flow field, which has implications for flow resistance, water conveyance, and the transport of mass and energy. The proper understanding of these vegetation-influenced processes is essential for solving the existing and future river management challenges concerning both societal needs and ecosystem requirements. In the first part of this thesis, we attempt to experimentally investigate the flow turbulence structure in a partly vegetated channel. To achieve this objective, various configurations were carried out, varying the contraction and aspect ratios. The contraction ratio is defined as the ratio of the width of the vegetated (obstructed) area to the width of the unvegetated (unobstructed) area, while the aspect ratio is the ratio of the flow depth to the width of the unvegetated area. The experiments were conducted in a very large channel at the Coastal Engineering Laboratory of the Department of Civil, Environmental, Building Engineering and Chemistry at the Polytechnic University of Bari, Italy. Extensive measurements of flow velocities were conducted vertically and transversally, both within and outside the vegetated area for each configuration. The instantaneous three flow velocity components were accurately measured using a 3D-Acoustic Doppler Velocimeter (ADV)-Vectrino system at high frequency. Flow behaviors through the vegetated area, at the interface, and in the unobstructed area were analyzed by time-averaged velocities, turbulence intensity, correlation properties, and spectral analysis. Experimental results showed the development of three distinct characteristic flow zones: i) a vegetated area of low streamwise velocity, high turbulence intensities, dominant inward interactions, and more intense power spectrum, ii) a shear layer zone of increasing streamwise velocity, more enhanced transverse flow motion, exponential decrease in turbulence intensities, and frequent ejection and/or outward interaction events, and iii) a free-stream zone of higher and almost constant streamwise velocity, lower turbulence intensities, frequent sweep and/or inward interaction events, and less intense streamwise power spectrum. The findings of this study provided further insights into the flow dynamics in these characteristic flow zones. In the second part, this thesis provides new insights into predicting the flow discharges of partly vegetated channels with emergent vegetation by adapting the Interacting Dividing Channel Method (IDCM) and applying it to a curved interface plane. The total and zonal discharges of the partly vegetated channel were predicted using the IDCM method and validated against the experimental results of this study, as well as data from previous studies in the literature. The IDCM method, considering lateral momentum transfer in terms of apparent shear stress at the curved interface plane, showed better performance than diagonal and vertical interfaces. In the comparison of IDCM and Divided Channel Method (DCM), the IDCM method with a curved interface plane performed significantly better than the DCM method with curved, diagonal and vertical divisional planes.