Abstract
This study presents a methodology for improving the efficiency of Baptist and Stone and Shen models in predicting the global water flow resistance of a reclamation channel partly vegetated by rigid and emergent riparian plants. The results of the two resistance models are compared with the measurements collected during an experimental campaign conducted in a reclamation channel colonized by Common reed (Phragmites australis (Cav.) Trin. ex Steud.). Experimental vegetative Chézy’s flow resistance coefficients have been retrieved from the analysis of instantaneous flow velocity measurements, acquired by means of a downlooking 3-component acoustic Doppler velocimeter (ADV) located at the channel upstream cross section, and by water level measurements obtained through four piezometers distributed along the reclamation channel. The main morphometrical vegetation features (i.e., stem diameters and heights, and bed surface density) have been measured at six cross sections of the vegetated reclamation channel. Following the theoretical assumptions of the divided channel method (DCM), three sub-sections have been delineated in the reference cross section to represent the impact of the partial vegetation cover on the cross sectional variability of the flow field, as observed with the ADV measurements. The global vegetative Chézy’s flow resistance coefficients have been then computed by combining each resistance model with four different composite cross section methods, respectively suggested by Colebatch, Horton, Pavlovskii, and Yen. The comparative analysis between the modeled and the experimental vegetative Chézy’s coefficients has been performed by computing the relative prediction error (εr, expressed in %) under two flow rate regimes. Stone and Shen model combined with the Horton composite cross section method provides vegetative Chézy’s coefficients with the lowest εr.
Highlights
The present study aims at evaluating the efficiency of Bp and S&S resistance models [8,9] by exploiting experimental data retrieved from field hydrodynamic and vegetative measurements, realized by Errico et al [1] within an abandoned vegetated reclamation channel located in northern Tuscany (Italy)
It is easy to observe that the cross sectional riparian vegetation distributions, synthetically expressed by λ, resulted to be very similar for all the six examined cross sections and it was assumed to be homogeneous along the entire reclamation channel, as already highlighted in Errico et al [1]
Both experimental and modeled Cr retrieved at just the acoustic Doppler velocimeter (ADV) cross section have been assumed to be representative of the conditions of the entire partly vegetated reclamation channel
Summary
The presence of backwater in manmade reclamation channels enhances the growth of riparian vegetation, promoting the expansion of aquatic and terrestrial habitats and improving water quality [1,2].In this context, the analysis of the real-scale interaction between riparian plants and water flow in vegetated channels can provide relevant hints to the administrators of land reclamation areas, aboutGeosciences 2020, 10, 47; doi:10.3390/geosciences10020047 www.mdpi.com/journal/geosciencesGeosciences 2020, 10, 47 the most useful approaches to be followed when managing the riparian vegetation, which can ensure the conveyance capacity of the channel with limited impacts on the natural habitats [1].One of the most challenging tasks when programming the management of riparian vegetation in reclamation channels is the definition of simple and accurate models for assessing the global flow resistance coefficients (e.g., the vegetative Chèzy flow resistance coefficient Cr [3,4], the Manning’s n hydraulic roughness coefficient [5], the vegetative Darcy-Weisbach’s friction factor f” [6]). The presence of backwater in manmade reclamation channels enhances the growth of riparian vegetation, promoting the expansion of aquatic and terrestrial habitats and improving water quality [1,2]. In this context, the analysis of the real-scale interaction between riparian plants and water flow in vegetated channels can provide relevant hints to the administrators of land reclamation areas, about. The Baptist et al [8] and the Stone and Shen [9] resistance models (hereinafter referred to as Bp and S&S [8,9]) have been validated for real riparian vegetation, considering both emergent and submerged vegetative conditions, depending on the ratio between the water level (h) and the plants height above the vegetated channel bottom (hv )
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