- Second trial.Assume that Ru1.8 m. The average slope is
(1.82.56)/(9.0 5 6 5.6)4.36/25.6≈0.17.
1.0160.17(1.38/76.5)^ 1/21.78 m. (equation (15.21))
Worked Example 15.3
An embankment at 10 m OD along an east-facing bay is to be protected
against erosion and flooding. The table below gives fetches, wind speeds,
and refraction coefficients for obtaining design wave heights:
Direction
N NE E SE S
Fetch (km) 400 250 100 80 60
Design wind speed (km h^1 ) 075 075 050 50 75
Refraction coefficient, Kr 000.2 000.35 000.8 00.7 00.3
(a) Provide a hydraulic design of sea wall protecting the embankment.
The maximum still-water level is 3.5 m OD, the depth of water being
3.5 m.
Solution
The wave heights and periods are calculated using the JONSWAP spec-
trum for fetch-limited sea (equation (14.55)), given in the table on p. 667.
Choose 2.17 m as the significant wave height for the design, the
significant wave period being 8.16 s.
Consider the sea wall profile shown in Fig. 15.16. Two layers of rough
quarry stone will form the cover layer. The density of quarry stone is
Ru
1.38
Fig. 15.16 Sea wall profile adopted (Worked example 15.3)
666 COASTAL ENGINEERING
