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In support of the Trust proposal to construct an artificial reef
at Lyall Bay, ASR Ltd undertook
a feasibility study with the primary aims to provide:
- calibrated and validated numerical models of the wave transformation processes at Lyall Bay;
- high-quality oceanographic field data for the Lyall Bay area;
- a general picture of circulation due to waves, wind and currents in the bay;
- recommendations about the most suitable site, which will provide the best possible surfing climate,while having no significant effects on the existing surfing break at the eastern end of Lyall Bay, adjacent to the airport, and minimal impact on the beach;
- cost estimate of consent application (including detailed reef design);
- cost estimate for construction.
STUDY FINDINGS
Lyall Bay stands out as the best location for an artificial reef because it has:
- the best wave climate;
- is the largest bay;
- flat and sandy bathymetry;
- good access/parking;
- good potential for land-based development.
The
lack of a suitably configured seabed is the over-riding factor that gives
Lyall Bay its reputation as a mediocre surf break. This particularly due
to the low seabed gradient and infrequent shore-normal sand bars, which
results in waves that mostly close-out and have low breaking intensity.
However, Lyall Bay is open to an energetic wave climate from the south
with wave height exceeding 2.5 m for 14 % of the time. The average wave
height and period is likely to be 1.2 m and 8.8 s, respectively.
Waves of heights and periods suitable for surfing (heights >0.75 m
and periods >6 s) occur around 60% of the time. A large wave height
gradient is present at Lyall Bay, with largest wave heights at the centre
of the bay, reducing towards each side.
