Sedimentation Some Basic Considerations

This force will pull the particle downward —that is, Fne, will have the same sign as g — if p2 Pi, and the particle is said to sediment. If, on the other hand, p, p2, then the particles will move upward, which is called creaming. 

Since the net force of gravity and the viscous force are equal under stationary state conditions, Equations (1) and (2) may be equated to give 

The stationary state is quite rapidly achieved, so Equation (3) describes the velocity of a settling particle during much of its fall. This velocity is known as the stationary settling velocity. 

It assumes that the bulk density of the pure components applies to the settling units (i.e., no solvation). 

It permits the evaluation of v for a situation in which the mass-to-friction-factor ratio (m/f) is known. 

---

All this basic information has set the stage for bioremediation as an inexpensive and effective approach for cleaning contaminated soils, waters, and sediments. Considerable efforts are currently underway to develop the necessary field application techniques that make this a wholesale commercial reality. However, the complexities of the biodegradation processes involved make the efforts challenging if not, in some cases, frustrating. This is especially true for larger-scale field studies because increased variability and heterogeneity Cause difficulties in data interpretation. 

Coasts undergoing erosion display two basic elements of the coastal profile, namely, the cliff and the bench or platform. In any theoretical consideration of the evolution of a coastal profile, it is assumed that the coast is newly uplifted above sea level. After some time, a wave-cut notch may be excavated, and its formation intensifies marine erosion in this narrow zone. The development of a notch varies according to the nature of the rock in which excavation is proceeding, for example, it may be present if the sediments are unconsolidated or if the bedding planes dip seawards. Where a notch develops, it gives rise to a bench, and the material above is undermined and collapses to form a cliff face. 

---