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 4 m/s and significantly increased when wind speeds exceeded 6 m/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 (<4 m/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 45 mg/L) and τ was less than 0.02 N/m. In stage B, the sediment bed was starting to be activated (SSC 45∼60 mg/L) and τ was in the range of 0.02∼0.07 N/m. In stage C, a medium amount of sediment was suspended (SSC 60∼150 mg/L) and τ ranged from 0.07 to 0.3 N/m. In stage D, large amount of sediment was suspended (SSC 150∼300 mg/L) and τ was larger than 0.3 N/m. 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.

Determination of the Downwelling Diffuse Attenuation Coefficient of Lake Water with the Sentinel-3A OLCI

“…As a shallow lake, the high dynamic ratio index (the square root of the surface area divided by the average depth, 25.6 km/m) of Lake Taihu indicates that winds are the main driving force for sediment resuspension. Wind-and wave-induced sediment resuspension will increase the SPM concentration in the water and thereby increase light attenuation in the water [52,67,68]. Several studies have demonstrated that the wind-induced resuspension is important in sediment related turbulence, the main driving factor for the spatial and temporal variations in K d for Lake Taihu [27,61,69].…”

“…This is because station S1 (located in central Lake Taihu) is more prone to wind effects, which can lead to sediment resuspension, whereas stations S2-S4 (located in the bay areas) are relatively closed, and the wind speed has an insignificant impact on sediment resuspension at these stations. In addition, the time delay for waves resulting from a change in the wind field varies between different waters, and the bay areas tend to stabilize before central Lake Taihu [68]. Figure 14b shows the spatial distribution of the maximum correlation coefficients.…”

High Temporal Resolution Monitoring of Suspended Matter Changes from GOCI Measurements in Lake Taihu

“…According to previous research [51][52][53], under normal circumstances, the suspended matter concentration in Lake Taihu is mainly affected by the resuspension of sediments. However, 60% of the flow into Lake Taihu comes from the Tiaoxi River [54], so when heavy rainfall occurs in the basin, a large amount of suspended matter that is carried by the river will be transported into the lake in a short period of time and thus increase the TSM concentration.…”

Waves-waves collide induced by different wind directions caused high exchanged in the water level at the open area Shallow Lake, China

“…The main dynamic steps considered to be the key of transporting solid particles and nutrients. Wind-induced waves are the forces which sediment re-suspension in shallow water bodies (Li et al, 2017;Qin et al, 2006;Stone, 2011;Wang et al, 2014). The changes in habitat of aquatic organisms may be attributed to a few storm events, waves-waves collide from different sources influence on transmission, nutrient and sediment transport (Barros, 2005;Davis et al, 1982;Mazumder and Ojha, 2007;Skilleter, 1996).…”

“…In addition, other research used numerical experiments to analyze the impact of hydrodynamic force on the sediment resuspension in lakes (Qin et al, 2004;You et al, 2007). Other researchers have worked on the impacts of currents and waves on sediment resuspension processes (Li et al, 2017;Pu et al, 2000). Observations on sediment dynamics resuspension were carried out in open-channels, rivers resuspension, and the results showed that it is primarily caused by current-induced shear stress (Jin and Ji, 2004;Li and Sheng, 2011).…”