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KNYSNA NEWS - According to SA National Parks (Sanparks) marine ecologist Kyle Smith, high tide came just after 16:00 on
28 October, and the water level was estimated to have reached 2.16m. This, along with a swell of 5m over a period of 13 seconds "would have pushed the water level up higher than normal", Smith pointed out.
Sanparks Knysna manager Megan Taplin also indicated that by Monday the area had received 53mm of rain in the preceding two weeks, which would have also contributed to the high water levels.
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"Spring tides occur twice every lunar month when the moon and the sun are aligned, and are not related to season," explained Smith. "However, each year over the equinoxes (March and September) the alignment of the sun and equator accentuates the tides and we experience lower-than-normal low tides and higher-than-normal high tides.
"In South Africa we experience two high tides and two low tides each day. These tides are called semidiurnal, the time between each high or low tide being 12 hours and 25 minutes."
The SA Weather Service and the Garden Route District Municipality had also issued a warning on 28 October that high seas with wave heights of 6-7m were expected between Cape Point and Plettenberg Bay during the evening into Tuesday morning.
"Generally heavy seas or damaging waves are a result of strong winds blowing over a large area called a 'fetch' combined with low-pressure systems," said Sanparks spokesperson Nandi Mgwadlamba. "Long-period swells are often very dangerous to tankers as they may literally snap them in half.
"Dangerous waves or surges may also be caused by storm surges and tsunamis, resulting in widespread coastal damage and loss of life," she said.
"In oceanography, a sea state is the general condition of the free surface on a large body of water – with respect to wind waves and swell – at a certain location and moment. A sea state is characterised by statistics, including the wave height, period, and power spectrum. The sea state varies with time, as the wind conditions or swell conditions change."
Read a related article: Precautions for ships in storm surges and high seas
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