Flow-induced forces on free-floating macrophytes |
| |
Authors: | Maureen Downing-Kunz Mark Stacey |
| |
Institution: | (1) Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720, USA |
| |
Abstract: | Free-floating macrophytes have buoyant petioles and unanchored roots; certain species are highly invasive, owing to characteristics
such as high growth rates and the formation of dense floating mats that drift on wind and water currents. Water hyacinth (Eichhornia crassipes) is one example; its invasion of tropical and subtropical freshwater systems worldwide harms native ecosystems and impedes
human activities. This research examines flow-induced forces and biomechanical properties of E. crassipes to better understand flow interactions and transport mechanisms. Drag forces were measured in a flume and a wind tunnel for
varying approach velocities and raft configurations; from this data, drag coefficients in water (C
Dw) and air (C
Da) were developed. Over similar Reynolds number (Re
b
) regimes, C
Dw decrease as Re
b
increases while C
D
a
are invariant. For the same raft tested in air and water, water drag exceeds air drag and the value of C
Dw approaches C
Da at high Re
b
. Force–velocity relationships indicate root canopies reconfigure by streamlining in higher flow velocities while leaf canopies
do not. Root canopy streamlining is further explained through biomechanical testing: we found the major vegetative structures
of E. crassipes (roots, stolons, and petioles) have similar moduli of elasticity but second moments of area are three orders of magnitude
smaller in roots compared to stolons or petioles, leading to significantly lower flexural rigidity in roots than in stolons
or petioles. Flow interactions with the root canopy differ for an individual plant compared to a raft assemblage. Laboratory
results suggest that water currents are the dominant mechanism for E. crassipes dispersal. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|