Effect of Salinity on Suspended Cohesive Sediments

Experiments are conducted in an annular flume to determine the effect of salinity on the evolution of the suspended sediment concentration (SSC) of four cohesive sediments (alumina, kaolin, Rhine river mud and silica) with different degrees of salinity. A turbidity sensor is placed at mid flow depth to record the variation of turbidity. These turbidity values are converted to the corresponding SSC. The obtained time variation of the SSC is approximated as an exponential decay function. The flocculation and settling processes of alumina are enhanced with salinity. Alumina attained the highest settling velocity in 35 g/l salinity. The deposition of kaolin increased with an increase in the degree of salinity and quickly reached a steady state concentration (Ceq). The settling velocity of kaolin is positively correlated to the degree of salinity. The deposition of Rhine mud is significantly decreased with salinity. Similarly, silica deposits faster with zero salinity than in saline water. The settling velocity of silica showed identical behavior in saline water irrespective of degree of salinity. In the presence of salinity, kaolin and silica attained the highest and lowest overall settling velocities, respectively. Deposition rate increases with an increase in the initial suspended sediment concentration (Co), which affects the ratio of Ceq/Co in the presence of salinity.