Study on the critical velocity of sediment incipient motion in saline water based on Hangzhou Bay field investigation

The critical condition of sediment incipient motion (SIM) is one of the most pivotal and fundamental topics for the mechanics of sediment transport in offshore areas. The flocculation of fine sediment exerts a complex influence on SIM, particularly in bay areas where the water salinity varies. This paper analyzes data measured in Hangzhou Bay with 50 observation points from 2005 to 2019. The objective is to ascertain the effect of salinity on the critical velocity of SIM (uc), figure out the calculation error of traditional equations for uc in saline water and improve the calculation accuracy of uc. Results indicate that the calculation error rate of traditional uc equations escalates with the increased clay content of bottom sediment and water salinity. An improved uc equation in saline water environment is constructed with the consideration of clay content and salinity based on a traditional equation. The improved equation is fitted through measured data and validated with the experimental data. The accuracy of the improved equation significantly increases compared to traditional equations in the area with clay content over 15% and salinity over 12‰.