ERDC/CHL CHETN-III-64
June 2002 (revised)
So the range of damage along the shore is quite large but still represents only minimal damage to
the structure.
The damaged armor layer profile shape can be analyzed in a similar fashion. The initial layer
thickness is
tr = 2Dn50 = 2(0.784 m) = 1.57 m
Then the means of the maximum eroded depth, minimum remaining cover depth, and maximum
eroded cross-shore length, respectively, would be given by Equations 9, 10, and 11 as follows:
E = 0.46 S 0.5 = 0.46(1.58)0.5 = 0.58
C = Co - 0.1 S = 1.57 - 0.1(1.58) = 1.41
L = 4.4 S 0.5 = 4.4(1.58)0.5 = 5.5
The mean dimensional eroded depth is de = Ē Dn50 = 0.58(0.784 m) = 0.45 m. The mean
dimensional minimum remaining cover depth is dc = CDn50 = 1.40(0.784 m) = 1.11 m, so there is
significant cover over the underlayer. Note that the initial thickness of the armor layer is not
uniform; so the maximum eroded depth may not occur in the same location as the location of
minimum remaining cover. In addition, the sum of E and C may not be equal to Co for the same
reason. The mean of the maximum eroded length or cross-shore eroded hole is le = 4.34 m. This
stone size was very well suited for this application if this was a design level storm.
If a storm of Nw = 5,000 waves were to strike the structure, then t = 5,000(10.8 s) = 54,000 s.
This represents a storm of a very long duration of 15 hr. The mean damage would increase to
1.605
(54, 000 s)0.25 = 2.20
S (t ) = 0 + 0.025
(10.8 s)0.25
This damage level is still quite acceptable for most situations.
CONCLUSIONS: This CHETN provides a method for computing damage on a rubble-mound
breakwater, revetment, or jetty trunk section stone armor layer that is exposed to depth-limited
breaking waves. The methods are useful in determining the expected life of new or damaged
structures and in developing life-cycle analyses. The empirical equations should be conservative
for most applications, but care should be exercised when applying outside of the tested
conditions, as described in this technical note.
ADDITIONAL INFORMATION: The author would like to thank Dr. Shamsul Chowdhury for
valuable technical assistance with editing this document. This CHETN was produced with
funding from the Navigation Systems R&D Program within the Prediction and Prevention of
7
Previous Page
