Laboratory Measurements of Flow and Turbulence in Discontinuous Distributions of Ligulate Seagrass |
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Authors: | Antonino Maltese Eleanor Cox Andrew M. Folkard Giuseppe Ciraolo Goffredo La Loggia Giovambattista Lombardo |
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Affiliation: | 1Graduate Research Assistant, Dipartimento di Ingegneria Idraulica ed Applicazioni Ambientali, Univ. di Palermo, Viale delle Scienze, 90128 Palermo, Italy (corresponding author). E-mail: maltese@idra.unipa.it 2Graduate Research Assistant, Dipartimento di Ingegneria Idraulica ed Applicazioni Ambientali, Univ. di Palermo, Viale delle Scienze, 90128 Palermo, Italy. 3Lecturer, Dept. of Geography, Univ. of Lancaster, Lancaster, LA1 4YB, U.K. 4Researcher, Dipartimento di Ingegneria Idraulica ed Applicazioni Ambientali, Univ. di Palermo, Viale delle Scienze, 90128 Palermo, Italy. 5Professor, Dipartimento di Ingegneria Idraulica ed Applicazioni Ambientali, Univ. di Palermo, Viale delle Scienze, 90128 Palermo, Italy. 6Graduate Student, Dipartimento di Ingegneria Idraulica ed Applicazioni Ambientali, Univ. di Palermo, Viale delle Scienze, 90128 Palermo, Italy.
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Abstract: | Turbulent flow characteristics were investigated in laboratory flume studies of a ligulate plant canopy interrupted by a gap representing discontinuities observed in seagrass prairies. The reliability of velocity measurements obtained using an acoustic Doppler velocimeter within the canopy was shown using specifically designed experiments. In relatively fast flow (mean velocity 5.5?cm?s?1), the mean flow profile was logarithmic above the canopy, had an inflection point near its top, and uniformly low values within it. Within the gap, a recirculation cell formed. Reynolds stress maxima were approximately coincident with the mean flow inflection point. Quadrant analysis revealed an ejection-dominated upper layer, a sweep-dominated region around the top of the canopy and within the gap, and no dominant quadrant within the canopy. In slower flow (mean velocity 1.7?cm?s?1) the plants were quasiemergent and the flow fields more uniform. Sweeps similarly dominated the region near the top of the canopy and within the gap. In both flows, autocorrelation of longitudinal velocity fluctuations showed a Lagrangian time scale maximum at the downstream end of the gap. |
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Keywords: | Aquatic plants Turbulent flow Velocity Reynolds stress |
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