Estimation of ship-induced sediment resuspension in intertidal waterways based on field measurements at the Hooghly River, India

The estimation of the sediment flux due to individual ship movement is necessary to identify adverse effects on the river banks in tidally-driven waterways. The separation of each wake event due to ship propagation from the tides is cumbersome. The present study focuses on the study of the ship waves on the sediment resuspension in intertidal waterways through a field survey. The time-frequency analysis proved to be an effective tool for separating the high-frequency ship waves from the tides. The ship-generated SSC was estimated by using the backscattering intensity from the acoustic sensors after proper calibration. The individual effect of each ship wake event on the sediment resuspension was estimated by filtering the ship-generated SSC from the total SSC by using a moving average filter. The overall contribution of the ship waves during the survey tenure was 24.66% with respect to the ambient SSC. The approximate amount of sediment flux by ship waves in a calendar year could be 1.46 * 106g/m2. Finally, a new empirical equation to predict the sediment flux from the depth Froude number is proposed, which could be used in long-term analysis of SSC after proper calibration and validation.

Automated summary

This study investigated the impact of ship waves on sediment resuspension in tidal-driven waterways through a field survey. Time-frequency analysis was proven to be an effective tool for separating high-frequency ship waves from tides. Ship-generated suspended sediment concentration (SSC) was estimated using backscattering intensity from acoustic sensors after calibration. The individual effect of each ship wake event on sediment resuspension was estimated by filtering the ship-generated SSC. The contribution of ship waves to the ambient SSC during the survey tenure was approximately 24.66%, and the estimated sediment flux by ship waves in a calendar year could be 1.46 * 106g/m^2. Finally, a new empirical equation to predict sediment flux based on the depth Froude number is proposed for long-term SSC analysis after calibration and validation.