Abstract
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.
Highlights
Case coefficient a for E. canadensis varied from 2.22 to 10.32 depending on the measurement date
The highest value was observed on 16 August 2016, which coincided with the highest biomechanical properties of the plant at this time [35]
(6)) were presented, which may help properly calculate the drag forces (Equation (1)). These calculations were used to estimate the relationship between the diameter of a stem and its flexural rigidity using examples from three freshwater macrophyte species: E. canadensis, P. pectinatus, and P. crispus
Summary
Aquatic plants that grow in rivers significantly affect hydrological conditions, e.g., [1,2,3,4,5].Estimations of hydraulic resistance [4,6,7], stream restoration [8,9,10], investigations of invasive aquatic plant colonization [11,12], and development of theoretical approaches for linking ecological, biomechanical, and hydrodynamic descriptions [1,2,13] play important roles in the development of the ecological management of vegetated channels, both separately and as components of aquaticWater 2018, 10, 540; doi:10.3390/w10050540 www.mdpi.com/journal/waterWater 2018, 10, x FOR PEER REVIEW interfaces. Aquatic plants that grow in rivers significantly affect hydrological conditions, e.g., [1,2,3,4,5]. The interaction mechanisms between plants and flow structures may be considered on multiple interconnected scales, individualplant, plant, plant patch, or plant multiple interconnected scales,such suchasasleaf, leaf, stem, stem, individual plant patch, or plant patchpatch mosaic scales [1,14]. Theseinteractions interactions depend depend on and mechanical properties of of mosaic scales. These on the thegeometry geometry and mechanical properties aquatic macrophytes. The comprehensive knowledge knowledge ofofthese consists of three groups aquatic macrophytes [1].[1]. The comprehensive theseinterplays interplays consists of three groups of plant characteristics plantmorphology morphology characteristics; plant material characteristics; of plant characteristics [1]:[1]:
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