View the Whole Report - Center for Research in Water Resources ...

2. LITERATURE REVIEW
2.1 Introduction
Two strategies for minimizing the impact of stormwater runoff from construction
sites are erosion control and sediment control. Erosion control is a source management
method and usually is accomplished with slope coverings. These techniques include
temporary and permanent vegetation, plastic sheeting, straw and wood fiber mulches,
matting, netting, chemical stabilizers, or some combination of the above. Sediment
control may be considered as the second line of defense. Sedimentation ponds, post
sedimentation pond devices, and silt or sediment barriers reduce sediment loads
(Nawrocki and Pietrzak, 1976).
Sediment barriers are devices designed to diminish solids loading through short
term retention and/or velocity reduction and filtration. Silt fences and rock berms are
sediment barriers. Silt fences have been selected preferentially and installed widely
because of purported advantages attributed to these devices such as effectiveness for
durations greater than 6 months, stronger construction, greater ponding depth, minimum
removal efficiencies of 75%, easy assembly, and relatively low cost (Goldman et al.,
1986).
2.2 Sediment Removal Mechanisms
Sediment barriers capture eroded solids by sedimentation and filtration both of
which contribute to the overall efficiency of a system. The most important, cost effective,
and widespread treatment of suspended solids in water is by sedimentation. Gravity
separation of solids that have a specific gravity greater than water has been practiced for a
long time and is well understood. Stokes’ law, which is applied to calculate the settling
velocity of solid particles, is based upon the premises of laminar flow, no particle
interaction, and spherical particles. This relationship is valid for estimating the
approximate settling velocities and provides insight into factors affecting the
sedimentation of smaller particles, such as silts and clays (Kouwen, 1990).
5