TURBIDITY AND SUSPENDED SEDIMENT ASSOCIATED WITH BEACH NOURISHMENT DREDGING

Daniel M. Hanes

Abstract


A field observation program was carried out to measure natural and maninduced fluctuations in suspended sediment and turbidity in connections with a beach nourishment project. The project was carried out at Longboat Key, on the west coast of Florida. The analysis of the manual turbidity, sedimentation, and wave data revealed several significant facts concerning the differences between the hard bottom sites and control sites and the interactive dynamics between these three phenomena. The sedimentation measurements indicate that the sand sedimentation rates are highly variable, particularly with time. In contrast, the fines sedimentation rates are relatively less variable with respect to both location and time. It is evident from the examination of the sedimentation data that the sand sedimentation rates at the hard bottom sites were approximately 2.5 times higher than those of the control sites. The statistical analysis indicated that there is less than a 10% probability that this difference is due to chance. In contrast, there were no significant differences in fines sedimentation rates between the hard bottom and control sites. The manual turbidity measurements indicate high variability in space and time. Based on approximately 15 measurement dates, following nourishment the hard bottom sites experienced approximately 50% less turbidity than the control sites. The variations in sand sedimentation rates are believed to be directly related to the hydrodynamic forces resulting primarily from waves. The wave height was approximately 33 % greater at the hard bottom sites.

Keywords


dredging; beach nourishment; suspended sediment; turbidity

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