432
diffracted
waves
14 Tides and Waves on Vegetated Coasts
Fig. 14.9: Wave movement across a platform reef
approaching
wave
rays
wave period are assumed to be 3.65 m and 6.8 s, respectively. At the reef
front, wave height gradually decreases due to bottom friction. Wave height
oscillations observed at the reef front are due to reflection from the reef. At
the reef edge, waves start to break and their height constantly decreases.
Coral reefs are obviously three-dimensional structures when investigating refraction and diffraction (Massel, 1993b,1996a). Waves, which may be either
swell or sea generated in the ocean outside the reef, approach the reef from
various directions. Refraction and diffraction occur over the steep outer slope
of the reef. The refraction mechanism is compounded by the diffraction of waves
around the reef into its lee area. At the reef edge waves eventually break and
considerable energy is dissipated. This process continues as the broken waves
propagate over the reef surface. One of the geomorphological consequences of
wave action on such structures is coral cay formation (Gourlay, 1988). Coral
cays are the deposits of coral sand, mostly at the lee side of the reef platform
with respect to the predominant wind direction (see Fig. 14.9).
The maximum possible wave height over water of constant depth was discussed in Chap. 4. In particular, theoretical proof and experimental evidence
demonstrated that the ratio of maximum wave height to water depth is smaller
than 0.8 which is often used in oceanographic and engineering practice. Similar
behaviour is observed for waves propagating over the reef top. Coral reefs grow
to about the mean low tide level, and in their mature form, are planar reefs
with extremely flat, solid and quite smoothly cemented surfaces. However, at
high tide, depth-limited waves are able to propagate across the reef top. In
the GBR region, tide ranges may be as great as 3 to 4 m, and water depths of
2 m to 3 m over the reefs at high tide are common. During the passage of a
cyclone storm surge, these depths could increase by 0.3 m to 0.5 m, or much
more, depending upon the intensity and path of the cyclone (Massel, 1996a).
diffracted
waves
14 Tides and Waves on Vegetated Coasts
Fig. 14.9: Wave movement across a platform reef
approaching
wave
rays
wave period are assumed to be 3.65 m and 6.8 s, respectively. At the reef
front, wave height gradually decreases due to bottom friction. Wave height
oscillations observed at the reef front are due to reflection from the reef. At
the reef edge, waves start to break and their height constantly decreases.
Coral reefs are obviously three-dimensional structures when investigating refraction and diffraction (Massel, 1993b,1996a). Waves, which may be either
swell or sea generated in the ocean outside the reef, approach the reef from
various directions. Refraction and diffraction occur over the steep outer slope
of the reef. The refraction mechanism is compounded by the diffraction of waves
around the reef into its lee area. At the reef edge waves eventually break and
considerable energy is dissipated. This process continues as the broken waves
propagate over the reef surface. One of the geomorphological consequences of
wave action on such structures is coral cay formation (Gourlay, 1988). Coral
cays are the deposits of coral sand, mostly at the lee side of the reef platform
with respect to the predominant wind direction (see Fig. 14.9).
The maximum possible wave height over water of constant depth was discussed in Chap. 4. In particular, theoretical proof and experimental evidence
demonstrated that the ratio of maximum wave height to water depth is smaller
than 0.8 which is often used in oceanographic and engineering practice. Similar
behaviour is observed for waves propagating over the reef top. Coral reefs grow
to about the mean low tide level, and in their mature form, are planar reefs
with extremely flat, solid and quite smoothly cemented surfaces. However, at
high tide, depth-limited waves are able to propagate across the reef top. In
the GBR region, tide ranges may be as great as 3 to 4 m, and water depths of
2 m to 3 m over the reefs at high tide are common. During the passage of a
cyclone storm surge, these depths could increase by 0.3 m to 0.5 m, or much
more, depending upon the intensity and path of the cyclone (Massel, 1996a).