The measurement of sand transport in two inlets of Venice lagoon, Italy

Amos, C.L., Villatoro, M., Helsby, R., Thompson, C.E.L., Zaggia, L., Umgiesser, G., Venturini, V., Are, D., Sutherland, T.F., Mazzoldi, A. and Rizzetto, F. (2010) The measurement of sand transport in two inlets of Venice lagoon, Italy. Estuarine, Coastal and Shelf Science, 87 (2), 225-236. (doi:10.1016/j.ecss.2009.05.016).

Abstract

Sand transport in Lido and Chioggia inlets was measured using modified Helley–Smith sand traps equipped with 60-micron nets. The traps had an efficiency of about 4% only but provided enough material for analysis. Very fine sand (0.07 < d < 0.11 mm) only was collected in the traps. Transport of sand was greatest in the bottom 10% of the water column and followed a Rouse profile. Sand extended to a height of about 4 m above the bed during peak flows corresponding to the estimated thickness of the boundary layer; and observed in synoptic ADCP profiles. The sand in the benthic boundary layer was largely inorganic (>95%); above this layer, organic content varied widely and was greatest near the surface. The movability number Ws/U* showed a linear relationship to dimensionless grain diameter (D*): (Ws/U*)=(D*/10); D* < 10. Sand concentration in suspension was simulated by a mean Rouse parameter of ?2.01 ± 0.66 (Lido inlet) and ?0.82 ± 0.27 (Chioggia inlet). The ? parameter (Hill et al., 1988) was correlated with D* and movability number in the form: ?=2.07?2.03D*+59(Ws/U*)2 (r2 = 0.42). Von Karman's constant was back-calculated from a Law of the Wall relationship as a test on the accuracy of U* estimates; a mean value of 0.37 ± 0.1 (compared to the accepted value of 0.41) suggest U* was accurate to within 10%. The constant of proportionality (? = 3.54 × 10?4) between reference concentration (Ca) and normalized excess bed shear stress was in line with the published literature.

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Contributors

Author: C.E.L. Thompson

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