Propeller Jet–Induced Suspended-Sediment Concentration

Abstract

When subjected to a strong swirling jet flow induced by a rotating ship’s propeller, the bed of a waterway may undergo significant changes. These changes will not only cause instability to quay structures and damage the protection work of the beds/banks of rivers and canals, but also resuspend the bed sediment. The latter likely will pollute the water column and affect the aquatic life. In this study, the propeller-jet velocity and sediment-concentration profiles downstream of a propeller are measured using an acoustic Doppler velocity profiler and a suction device, respectively. The estimates obtained by using formulas for the axial velocity and four published methods for calculating the reference near-bed concentration of suspended sediment are compared with the experimental data. Moreover, the behavior underlying the temporal and spatial variations in seabed scour and sediment suspension is also investigated. A new set of equations for estimating the sediment concentration profiles is developed. The new equations generally yield reasonably good estimates of the reference concentration and Rouse number at the measurement locations within the scour hole and on the deposition mound. The proposed modified Rouse equation produces reasonable predictions that are consistent with the experimental data.