Hydrodynamics of flow through double layer rigid vegetation

Vegetation in riparian environment varies in size from grass to shrubs to trees. A double layer approach, with an array of short and tall acrylic dowels, is employed here to simulate such an environment. The focus of the present work is to study the response of the flow as it travels through a double layer arrangement for a variety of conditions. For this purpose, instantaneous measurements of velocity were collected using a one dimensional laser Doppler velocimeter at multiple locations to create velocity and turbulence intensity profiles. The results indicate that velocity is nearly constant within the short and tall dowel array and increases significantly at the top of the arrays. The velocity profile behind a dowel is characterized by multiple inflection points and velocity spikes near the bed, especially for locations directly behind a tall dowel, where a bulge in the velocity at the top of the short dowel array is present, followed by a significant drop in velocity. The region immediately behind a tall dowel, where the highest turbulence intensities are found, is very unstable, especially at the dowel boundaries, where significant mass and momentum exchange occurs. The better known case of submerged single layer flow is included for comparison. (C) 2009 Elsevier B.V. All rights reserved.