Abstract

Settling columns are used to determine required parameters for stagnant water in sedimentation study. The most common parameter is sediment fall velocity. Extensive studies have been conducted in the past to determine fall velocity for non-cohesive sediments but less is done for cohesive sediments. Water with different concentration of cohesive sediment were allowed to settle in a 3.0 meter height and 0.30 meter diameter this study Samples of water and sediment mixture were taken at different depths of the column and relative diagrams were constructed in order to estimate fall velocity of the cohesive sediments based on the McLaughlin's differential equations. At the beginning of the settlement, particles at low flow depths accelerate faster and reach higher velocity as result of flocculation. Depend on level of concentration; the process of flocculation thus maximum fall velocity at a point is reduced gradually as flow depth increases. The turning point from acceleration to deceleration of particles appears sooner and at lower velocity as result of slowing flocculation down at deeper points.

Keywords: cohesive sediment, fall velocity, concentration, flocculation