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Open AccessArticle

On the Relationship between Aquatic Plant Stem Characteristics and Drag Force: Is a Modeling Application Possible?

1
Institute of Geophysics, Polish Academy of Sciences, Księcia Janusza 64, 01-452 Warsaw, Poland
2
Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawińskiego 5a, 02-106 Warsaw, Poland
*
Author to whom correspondence should be addressed.
Water 2018, 10(5), 540; https://doi.org/10.3390/w10050540
Received: 22 March 2018 / Revised: 13 April 2018 / Accepted: 20 April 2018 / Published: 24 April 2018
This paper presents a basic model that shows the relationship between the diameter of a stem and its flexural rigidity. The model was developed from experimental measurements of biomechanical traits (i.e., tensile and bending traits like maximum forces, stresses, moduli of elasticity, flexural rigidity, strain) of three freshwater macrophyte species (Elodea canadensis Michx., Potamogeton pectinatus L., and P. crispus L.), reflecting the seasonal changes in plant biomechanics throughout the vegetative season. These were obtained with the use of a bench-top testing machine in 2016 and 2017. The presented calculations are based on the ratio of drag-to-bending forces, in which the flexural rigidity plays a key role. The proposed model has the form EI = adb, and two approaches based on a regression analysis were applied to determine the parameters of the model—a and b. In the first method, the parameters were identified separately for each day of measurement, while in the second method, the coefficient b was calculated for all data from all days as a unified number for individual plants. The results suggest that coefficient b may provide information about the proportion of changes in drag forces depending on plant stiffness. The values of this coefficient were associated with the shape of the stem cross-section. The more circular the cross-section, the closer the value of the parameter was to 1. The parameter values were 1.60 for E. canadensis, 1.98 for P. pectinatus, and 2.46 for P. crispus. Moreover, this value also depended on the density of the cross-section structure. Most of the results showed that with an increase in stem diameter, the ratio between the drag and bending forces decreased, which led to fewer differences between these two forces. The model application may be introduced in many laboratory measurements of flow–biota interactions as well as in aquatic plant management applications. The implementation of these results in control methods for hydrophytes may help in mitigating floods caused by increases to a river channel’s resistance due to the occurrence of plants. View Full-Text
Keywords: aquatic plants; biomechanics; drag force; hydrodynamics; flow–biota interactions; hydrological processes aquatic plants; biomechanics; drag force; hydrodynamics; flow–biota interactions; hydrological processes
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Łoboda, A.M.; Karpiński, M.; Bialik, R.J. On the Relationship between Aquatic Plant Stem Characteristics and Drag Force: Is a Modeling Application Possible? Water 2018, 10, 540.

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