Settling Properties of Cohesive Sediments in Lakes and Reservoirs

Abstract

The fall velocity of fine particles was measured in a column of height 2.50 m and diameter of 0.30 m to model the settling properties of cohesive sediments in lakes and large reservoirs. In contrast to the traditional particle-size-based methods, an approach relying on time and depth variation of sediment concentration was employed to estimate the mean value of fall velocity at any depth and time. Particles at greater depths, particularly for the samples with a higher rate of sediment concentration, accelerated faster and remained at higher velocities for a longer duration owing to a higher rate of flocculation. As a particular property of cohesive sediments, particles for all concentrated samples and in all depths reached their maximum fall velocity at around the same time—15 min after the start of the tests. The low concentration samples reached higher maximum velocities because of the lower rates of hindering, but for a much lower duration in comparison to the higher concentrated samples. An empirical equation is developed to estimate the maximum fall velocity of particles for cohesive sediments where the ratio of flocculation to hindering is highest.