Turbulent Flow through Random Vegetation on a Rough Bed

Abstract

River vegetation radically modifies the flow field and turbulence characteristics. To analyze the vegetation effects on the flow, most scientific studies are based on laboratory tests or numerical simulations with vegetation stems on smooth beds. Nevertheless, in this manner, the effects of bed sediments are neglected. The aim of this paper is to experimentally investigate the effects of bed sediments in a vegetated channel and, in consideration of that, comparative experiments of velocity measures, performed with an Acoustic Doppler Velocimeter (ADV) profiler, were carried out in a laboratory flume with different uniform bed sediment sizes and the same pattern of randomly arranged emergent rigid vegetation. To better comprehend the time-averaged flow conditions, the time-averaged velocity was explored. Subsequently, the analysis was focused on the energetic characteristics of the flow field with the determination of the Turbulent Kinetic Energy (TKE) and its components, as well as of the energy spectra of the velocity components immediately downstream of a vegetation element. The results show that both the vegetation and bed roughness surface deeply affect the turbulence characteristics. Furthermore, it was revealed that the roughness influence becomes predominant as the grain size becomes larger.

Shear layer over floodplain vegetation with a view on bending and streamlining effects

“…The heterogeneous spatial distribution of plant material results in complex spatially variable velocity field. Consequently, the flow has to be analyzed in a spatially averaged sense, adopting a horizontal averaging scheme over a specific spatial scale [55,56]. The flow description should be based on a double averaging methodology (DAM) [57], in which flow properties are averaged both in time and space.…”

Flow Hydrodynamic in Open Channels: A Constantly Evolving Topic

“…In [42], the authors aimed to experimentally investigate the effects of bed sediments on flow in a vegetated channel. Since in previous laboratory studies, most of the experiments were conducted in vegetated channels with smooth beds, the effect of bed sediment was certainly neglected.…”

“…The SI, entitled "Flow Hydrodynamic in Open Channels: Interaction with Natural or Man-Made Structures", comprises eleven original articles [37][38][39][40][41][42][43][44][45][46][47] and two reviews [48,49] on flow hydrodynamic structures in open channel flows.…”

Simulation of Accelerated Subcritical Flow Profiles in an Open Channel with Emergent Rigid Vegetation

“…where the constants c 1 , c 2 and c 3 were determined with the Matlab software (The Math-Works, Inc., Natick, Middlesex County, MA, USA). Having obtained the average flow profiles, Wang et al [1] computed the local drag coefficient C D by means of Equation (8). They observed a non-monotonic pattern of the drag coefficient C D versus the stem Reynolds number Re D * ; indeed, the C D increases from the inlet (low Re D * ), reaching a peak value, and then decreases toward the outlet (high Re D * ).…”

“…In relation to the river ecosystem, aquatic plants can improve water quality by producing oxygen, consume excess nutrients, decrease the suspended solids, provide a habitat for aquatic animals by creating low-flow areas and prevent fertilizers and pollutants from reaching the watercourses [6][7][8][9]. Projects for the renaturalization and rehabilitation of watercourses are currently underway worldwide [10][11][12][13][14].…”