Sediment Size Effects in Acoustic Doppler Velocimeter-Derived Estimates of Suspended Sediment Concentration

Mehmet Öztürk

doi:10.3390/w9070529

Abstract

Backscatter output from a 10 MHz acoustic Doppler velocimeter (ADV) was used to quantify suspended sediment concentrations in a laboratory setting using sand-sized particles. The experiments included (a) well-sorted sand samples ranging in size from 0.112 to 0.420 mm, obtained by the sieving of construction sand, (b) different, known mixtures of these well-sorted fractions, and (c) sieved natural beach sand with median sizes ranging from 0.112 to 0.325 mm. The tested concentrations ranged from 25 to 3000 mg•L−1. The backscatter output was empirically related to concentration and sediment size, and when non-dimensionalized by acoustic wavelength, a dimensionless sediment size gradation coefficient. Size-dependent upper and lower bounds on measurable concentrations were also established empirically. The range of measurable conditions is broad enough to make the approach useful for sand sizes and concentrations commonly encountered in nature. A new method is proposed to determine concentrations in cases of mixed-size sediment suspensions when only calibration data for well-sorted constituent sands are available. This approach could potentially allow better estimates when the suspended load is derived from but is not fully representative of the bed material, and when the size characteristics of the suspended material are varying in time over the period of interest. Differences in results between the construction and beach sands suggest that sediment shape may also need to be considered, and point to the importance of calibrating to sediments encountered at the site of interest.

Highlights

The transport of suspended sediment is an important issue in many problems related to agriculture, environment, and engineering [1,2,3]
It is possible that another parameter, investigate the feasibility of estimating suspended sediment concentration using the backscatter notsignal measured such as velocimeter
(1) well-sorted sands obtained by sieving construction sand, (2) well-sorted sands obtained by sieving

Summary

Introduction

The transport of suspended sediment is an important issue in many problems related to agriculture, environment, and engineering [1,2,3]. In some environments and events, sediment kept in suspension by hydrodynamic processes accounts for the majority of the sediment transported past a location of interest. Both sands and finer material may be transported in suspension, depending on the magnitude of the energy in the flow, among other factors. The quantification of suspended sediment concentration (SSC) has been done in one of two ways, classified here as direct and surrogate methods. Direct methods, employing water sampling bottles or submersible pumps, tend to be labor-intensive and in some cases not representative due to the spatial and temporal variability of the suspended sediment concentration in the water column.

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Conclusion