An Integrated Approach to Assess Sediment Stability in River Ecology for Contamination Control

Knowing the stability of the contaminated sediment under different river discharges is critical for assessing its impact on the surrounding environment and downstream water quality. However, determining sediment stability in the field presents a challenge because it is difficult to measure the bed shear stress (BSS) directly, which is a crucial factor in determining sediment erosion. In addition, numerous indirect methods are subject to significant uncertainties. To enhance the reliability of sediment erodibility assessments, verify the results obtained, and examine the sediment stability under extreme river flow rates, unlike most similar studies that use only one or two methods, a comprehensive approach with the development of new techniques and devices was employed in this study. This included (1) estimating sediment BSS from flow velocity vertical profiles obtained by the deployed acoustical instruments based on the widely applied law of the wall; (2) using an open channel flume with a particle imaging velocimetry system in the laboratory to determine the sediment critical bed shear stress (CBSS) at the different depths from collected sediment samples; (3) using a newly developed portable in situ flume indirectly to measure sediment CBSS in the field; (4) developing a long-term standalone underwater camera system to monitor the sediment movements under different river flow rates and verifying results obtained by other applied methods; and (5) using a three-dimensional hydrodynamic model to investigate sediment stability under extreme river discharge conditions. The possible measurement errors occurring in various applied methods were discussed. According to this study, widely used and established methods, along with well-controlled laboratory environments, can still produce large uncertainties. Sediment stability studies should employ an integrated approach, such as the combination of field measurements, laboratory assessments, and on-site direct monitoring, to verify the obtained results directly or indirectly. A more comprehensive study can be developed in the future based on the findings of this study.