302
R.H. Charlier and Chr. P. De Meyer
Placement of a rock blanket with adequate bedding material seaward from the toe
of the structure will prevent erosion at the toe and will result in a more stable
structure.
For long-term effects, it is preferable to assume that the structure would have no
effect on reducing the erosion of the beach seaward of the wall. This erosion
would continue as if the wall were not there. Since the determination of scour can
only be approximate, general guides are usually adopted.
In fig. 37 the solid line represents an average existing profile ; a structure is to be
placed at point A in the fig.. Either the loss of beach width per year or the annual
volume loss of material over the beach area, which includes the profile, is known
from prior records. In the latter case, the annual volume loss may be converted to
an annual loss of beach width by the general rule : loss of 8 m 3 of beach material
is equivalent to loss of 1 m s of beach area on the berm (loss of 1 cubic yard of
beach material is equivalent to loss of 1 square foot of beach area on the berm).
This rule is applicable primarily at the ocean front. In shallow, protected bays,
the ratio of volume to area is usually much less.
IfB is at a waterdepth of 8 m (26 ft), E the point of slope break at about 2 m (6.5
ft), C the berm crest, n being the annual loss of beach width at the berm, then if
the structure in A is to last 50 years, in that time span the berm (in the absence of
a structure) will retreat 50 n to point D.
Analyses of profiles at eroding beaches allow to assume that the slope seaward of
8 m (25 ft) will remain nearly unchanged, the point of slope break E at about the
same elevation, the profile shoreward of the point of break in slope will remain
nearly unchanged.
To estimate the final depth at the wall a profile DF parallel to CE should be
drawn (D to elevation of E) and B and F connected. DFB will represent the
approximate profile 50 years hence if no structure is implanted. A ° approximates
the elevation of the receded beach at A.
R.H. Charlier and Chr. P. De Meyer
Placement of a rock blanket with adequate bedding material seaward from the toe
of the structure will prevent erosion at the toe and will result in a more stable
structure.
For long-term effects, it is preferable to assume that the structure would have no
effect on reducing the erosion of the beach seaward of the wall. This erosion
would continue as if the wall were not there. Since the determination of scour can
only be approximate, general guides are usually adopted.
In fig. 37 the solid line represents an average existing profile ; a structure is to be
placed at point A in the fig.. Either the loss of beach width per year or the annual
volume loss of material over the beach area, which includes the profile, is known
from prior records. In the latter case, the annual volume loss may be converted to
an annual loss of beach width by the general rule : loss of 8 m 3 of beach material
is equivalent to loss of 1 m s of beach area on the berm (loss of 1 cubic yard of
beach material is equivalent to loss of 1 square foot of beach area on the berm).
This rule is applicable primarily at the ocean front. In shallow, protected bays,
the ratio of volume to area is usually much less.
IfB is at a waterdepth of 8 m (26 ft), E the point of slope break at about 2 m (6.5
ft), C the berm crest, n being the annual loss of beach width at the berm, then if
the structure in A is to last 50 years, in that time span the berm (in the absence of
a structure) will retreat 50 n to point D.
Analyses of profiles at eroding beaches allow to assume that the slope seaward of
8 m (25 ft) will remain nearly unchanged, the point of slope break E at about the
same elevation, the profile shoreward of the point of break in slope will remain
nearly unchanged.
To estimate the final depth at the wall a profile DF parallel to CE should be
drawn (D to elevation of E) and B and F connected. DFB will represent the
approximate profile 50 years hence if no structure is implanted. A ° approximates
the elevation of the receded beach at A.