Improved drag coefficient and settling velocity for carbonate sands

Amin Riazi,Tristan Salles,Umut Türker,Ana Vila-Concejo

doi:10.1038/s41598-020-65741-3

Amin Riazi, Tristan Salles + Show 2 more

Open Access

https://doi.org/10.1038/s41598-020-65741-3

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Abstract

Sediment transport calculations are used globally in the numerical models that coastal managers, scientists and engineers use to assess and forecast coastal change. Most of the existing sediment transport equations were defined based on experimental results using siliciclastic sands. Yet these equations are applied to all types of sand, including carbonate sands that have different characteristics and therefore, settling behaviour. A rigorous management of the transport of carbonate sand is essential for the present and future management of sedimentary features in coral reefs such as sandy beaches or reef islands. Here we present a new approach to estimating the drag coefficient of carbonate sands that considers both friction and pressure. Based on our new method, the calculated drag coefficients explain the great variability in settling velocities of carbonate sand observed in nature (from 0.025 m/s to 0.364 m/s in our database). Using our formula, we demonstrate that even small differences in the settling velocity obtained with the new drag coefficient can lead to substantial changes in sediment transport and call for an update of numerical models.

Highlights

Sediment transport calculations are used globally in the numerical models that coastal managers, scientists and engineers use to assess and forecast coastal change
Most sediment transport studies have focused on siliciclastic sands with many studies dedicated to analysing settling velocity and drag coefficients[5,6,7]
Researchers have acknowledged that the different shape and density of carbonate sands have important implications for the hydraulic properties that control sediment transport[9,10,11,12,13,14,15,16]; for example Smith and Cheung[15] demonstrated that irregular particles were more entrained under rough turbulent flow than regular particles with equivalent diameter

Summary

Introduction

Sediment transport calculations are used globally in the numerical models that coastal managers, scientists and engineers use to assess and forecast coastal change. By inserting Eq 7 in to Eq 1 we derived a new equation for settling velocity for carbonate sands (Eq 8) that considers both the shape of the particles, and α with our optimal value of 0.55.

Results

Conclusion