Effect of wave-current interactions on sediment resuspension in large shallow Lake Taihu, China.

Abstract

The disturbance of the water-sediment interface by wind-driven currents and waves plays a critical role in sediment resuspension and internal nutrient release in large, shallow lakes. This study analyzed the effects of the interactions between wind-induced currents an1d waves on the driving mechanism of sediment resuspension in Lake Taihu, the third largest freshwater lake in China, using acoustic and optic techniques to collect long-term, high-frequency, synchronous in situ measurements of wind, currents, waves, and suspended solid concentrations (SSCs). The results suggested that water turbidity started to increase at wind speeds of approximately 4m/s and significantly increased when wind speeds exceeded 6m/s. In most cases, wind-induced waves were the main energy source for changes in turbidity. Wave-generated shear stress contributed more than 95% to sediment resuspension and that only in weak wind conditions (<4m/s) did the lake bottom shear stresses generated by currents and waves contributed equally. The relationship between SSC and bottom shear stress generated by wave was established by fitting the observed results. The processes of sediment dynamics were divided into four stages (A through D) according to three shear-stress thresholds. In stage A, SSC remained stable (about 45mg/L) and τw was less than 0.02N/m2. In stage B, the sediment bed was starting to be activated (SSC 45∼60mg/L) and τw was in the range of 0.02∼0.07N/m2. In stage C, a medium amount of sediment was suspended (SSC 60∼150mg/L) and τw ranged from 0.07 to 0.3N/m2. In stage D, large amount of sediment was suspended (SSC 150∼300mg/L) and τw was larger than 0.3N/m2. The findings of this paper reveal the driving mechanism of sediment resuspension, which may further help to evaluate internal nutrient release in large shallow Lake Taihu.