At spring high tides, Fish Hoek beach is flooded all the way up to the barrier at the top of the beach. I’ve seen the subway flooded with waist deep water at times. One Sunday evening in September on a sunset stroll, Tony and I discovered that watching the waves roll in to the top of the beach when the tide is approaching its maximum is very soothing (if you like the sound of noisy water), and provides a nice object lesson about some aspects of wave behaviour.
When wave trains collide, they interfere with each other. This is mostly in evidence (from our point of view) when reading a swell forecast on MagicSeaweed. The direction of the swell that arrives at False Bay can be determined by multiple storms far out in the Southern Ocean. Waves generated by winds blowing in different directions collide – they interfere with each other – and travel to make landfall far away. The direction and height of the resulting swell arriving on the beach is derived from all the distant winds that combined to form it.
At Fish Hoek beach none of this is happening, except for swells making landfall. What does happen is that incoming waves curve in the shallower water against Jager Walk along the side of the beach. They then strike the wall in front of the subway and are deflected down the beach, perpendicular to the rest of the waves that haven’t curved because they’re still in deeper water. Where these sets of waves combine, we get to see interference at work. Here’s a video of the process. It’s like having one’s own personal wave tank to look at.
[youtube=”http://www.youtube.com/watch?v=oQSTgzBWzVE&w=540″]
Here’s some more footage, with very expert commentary by me and Tony:
[youtube=”http://www.youtube.com/watch?v=SzpRwiLYUDA&w=540″]
