Structure Height
Waves breaking against a structure run up to an elevation above the Stillwater level (SWL) that
depends on the roughness and slope of the structure. Smooth concrete surfaces experience higher runup
than rough, stone slopes. If feasible, structures should be built high enough to preclude severe
overtopping. White spray does little damage, but solid jets of green water should be avoided. The
recommended height of structures above the Stillwater level is given in Table 4 for rough and smooth
inclined, stepped, and vertical structures. To use the table, determine which shape best characterizes the
structure. (Guidance is offered in the structure descriptions). The runup height R, is then given in terms
of the design wave height H, for various structure slopes, m.
The structure should be built to a height R, above the design water level to insure best
performance. For example, consider a rough-faced structure on a slope of 1 vertical on 2.5 horizontal
with a design wave height, H, of 3.0 feet. From the table, for a rough face with m = 2.5, R is 1.0 H.
Therefore, the runup height will be about one wave height or 3.0 feet above the design water level.
If it is impractical or undesirable to build the structures to the recommended height, a splash
apron should be provided at the top. Generally constructed of rock, it prevents the ground behind from
being eroded, and thus eventually undermining that portion of the structure.
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