Using ADV for suspended sediment concentration and settling velocity measurements in large shallow lakes

Abstract

Sediment resuspension plays an important role to provide nutrient release for algal growth in large shallow lakes. The settling velocity (w s ) is the key parameter for understanding the suspended sediment transport. In this paper, acoustic Doppler velocimeter (ADV) and optical backscatter sensor (OBS) instruments were used to measure in situ velocities and suspended sediment concentration (SSC) simultaneously without affecting the ambient turbulence in the bottom layer of Lake Taihu. The results showed that (1) ADV echo intensity (EI) could be transferred into SSC successfully by using a simple logarithmic relationship with a strong correlation of 0.87. (2) Three methods from a balance of settling and diffusive flux gradients for calculating settling velocities were applied, including Reynolds concentration flux, estimation of eddy diffusivity using the von-Karman Prandtl equation, and Kwon's power equation. The average settling velocity during the observation period was 0.11mm/s for Lake Taihu. (3) The fitted power function, w s = 1.85 × 10-3 C 1.04, could be used to estimate w s according to SSC. (4) Settling velocity changes with SSC, vertical velocities, and wind speed, which describes suspended sediment instantaneous and continuous motions. This paper provides an effective approach for estimating the settling velocity, provides a reference value of settling velocity for hydrodynamic model, and supports a better understanding of sediment transport process and nutrient release in large shallow lakes.