Flow Characterization in a Vegetated Marsh Environment.

Turbulence;Marsh;Particle Image Velocimetry;Artificial Marsh;Civil and Environmental Engineering;Engineering;Environmental Engineering

Morgan, Jenahvive KellyKatopodes, Nikolaos D. ;

University of Michigan

关键词: Turbulence;    Marsh;    Particle Image Velocimetry;    Artificial Marsh;    Civil and Environmental Engineering;    Engineering;    Environmental Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/99882/jenah_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Marsh environments provide a multitude of beneficial functions in natural ecosystems, from flood storage, trapping of contaminated sediments, improved water quality, and creating protected habitat for aquatic species.However, marshes are at risk due to land development, lake level fluctuations related to climate change, misguided shoreline protection measures, etc. As a consequence, the need for artificial marshes has been growing.Thus far, artificial marshes have not performed as well as natural marshes, a potential culprit is the lack of understanding of the local hydrology and flow characteristics.This work focuses on quantifying these parameters in both field and laboratory experiments in order to fully assess the effect of vegetation on flow through a marsh.The field experiments were performed in the Huron River, MI where three different softstem bulrush colonies were investigated.Underwater Particle Image Velocimetry (PIV) was used for the first time in a natural marsh to determine flow structure for different stem densities.The data reveal a relationship between the reed density of the bulrush patches and the wake turbulence downstream of the bulrush.The average spacing between reeds was found to dictate the size of eddies or flow structures observed in these environments.To further the investigation of the effect of vegetation on flow, laboratory experiments were performed using arrays of vertically aligned cylinders, 0.64 cm in diameter, in a variety of flow configurations (alternating and random placement of rods), in a re-circulating water tunnel.Particle Image Velocimetry (PIV) was used to determine flow characteristics at different velocities from 2.5 to 15 cm/s.Different stem densities (50 to 400 stems/m2) were tested depending on the geometry.Similarly to the field experiments, the spacing between rods controlled the eddy size.In both the laboratory and field experiments, transverse vorticity (i.e. vorticity at a given downstream distance evaluated across the region of interest) was most revealing in terms of eddy size and strength.This parameter should be included in future design studies of artificial marshes to improve marsh performance when considering the important physical features of the flow in vegetated aquatic environments.