Sunday, November 23, 2008

What is happening to the beach?

The beach along Venus Bay has been eroding significantly this year, with many high scarps left around beaches 1, 2 & 3, So what is going on? Superficially it looks like it might be evidence of sea level rise, perhaps strong evidence of global warning. However if that were the case the beach should be higher and narrower, whereas the beach is wider than normal for this time of year and lower.

The erosion has been occurring at specific location associated with specific high tide events. The king tides (higher spring tides) and some storm tides (mainly due to strong onshore winds & swells rather than storms) have been responsible for specific stretches of erosion rather that a continuous event along the beach. At the same time the beach profile has deepened exposing shell beds in many locations and is clearly lower at most locations,

I suspect that many of these changes started last spring with the king tides, when a few erosion scarps occurred in only a couple of places along the beach, At the same time the normal change of the profile from its winter shape to summer shape did not occur along much of the beach at all last summer. The winter berm, (the beach’s winter shape) has a distinct parabolic shape with a steeper gradient at the back of the beach. The same winter profile appears to be continuing this year. The summer berm, (the beach’s summer shape) has a flat upper dry section at the back of the beach and long flat foreshore with extensive development of sandbars. This flatter profile in the tidal zone now seems to be occurring at many places but under an obvious winter berm at the top of the beach.

I have been trying to work out the source of all the sand that builds the venus bay spit and direction of sand drift for a few years now. I have also noticed that last year the dominant sand drift direction has been fluctuating locally from a general northern drift over previous years. My current thoughts are that the beach is not washing away, the sand is just being moved up and down the coast but that the beach profile has been rotated down a little, I suspect that the shape of the coast is trying to adjust to a subtle change in the equilibrium of the forces that shape it, currents, swells, tides, storms and climate generally.

This blog is a place for everyone to recorded their observations.

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