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Coastal Engineering: Theory and Practice
Boundary layer
séparation
Fig. 7.2 Flow streamlines around the cylinder.
diameter of the obstruction. Flow velocity and sédiment characteristics
[Melville, 1975]. In cohesive sédiments, the extent and depth of the scour
are controlled by the size of the horseshoe vortex. Some sédiment déposition
may occur in the wake région of the flow. Erosion of cohesive soil occurs
when the fluid shear is sufficient to overcome the tensile strength and the
submerged weight of the bed materials.
7.2.2 Fluid mechanism of scour
The foregoing aspects give a base for an understanding of the complicated
flow field in the vicinity of the obstruction. The processes that develops
scour due to pure wave action are found to be different from those associated with steady current. Depending upon the environmental forces, the
processes that develop scour are grouped into the following.
(i) Scour due to steady current
(ii) Scour due to the wave action
(iii) Scour due to simultaneous action of waves and current