11/30/22 Report - Wave Refraction and Beach Dynamics. Bigger Surf Coming.

 

Wriitten by the TrasureGuide for the esclusive use of the Treasure Beaches Report.

I received an email not too long ago from somebody asking about wave refraction and specifically if it could have been the reason for erosion at one particular spot. I promised to post some about wave refraction but kept putting it off because it can get pretty complex, /It isn't easy to boil it down to a single post or even make a single post clear.

Waves interact with the bottom surface. Shallow depths cause waves to slow, while deeper areas allow waves to speed on. Irregualar depths cause the waves to slow in some areas, which results in the waves changing direction. As you can see in the photo above, the waves look like they are wrapping around the areas where it appears that the shoreline is projecting. It is not the shape of the shoreline that is causing the change in direction, though, it is the water interacting with the surface under the wave. People tend to talk about what they see, which is the visible shoreline and water surface, but what is under the water is also important but seldom talked about when it comes to discussions of erosion.

If you look at the illustration at the top of this post, and look at the three waves at tthe bottom, they are in a line and would be transporting sand on the beach front down and to the right along the shoreline.

Looking at this second illustration, notice that the wave energy focuses in front of the point, the waves thee would pile up and break. That would tend awahy the sand and deposit the sand in shallow areas. So why don't the points get worn away and the recessions get filled? The shoreline should straighten out over the years and centuries, but there are reasons that some points and recessions remain. One reason is underwater structures, such as reefs, and another reason is there are areas where sand has been depleted and so the process is interrupted. One example of that is Bathtub beach, which should naturally fill according to the above illustration, but as we know, it erodes and erodes and erodes. The reason is to the north of Bathtub beach is rocks and houses that disrupt whatever flow of sand would otherwise be expected. The sand transport process is interrupted.

One of the biggest complications comes from the matter of scale. If you look at the Treasure Coast, some beaches will erode while others do not. If the Treasure Coast beaches are eroded, that does not mean that all of them are.  There will be spots that are and others that are not.  Or if they are not generally eroded, there can still be a few spots that are.  You can talk about individual beaches, such as Seagrape Trail, but that is a relatively large area too, and some areas will erode while other build.  Remember, the area you are looking at is a relatively small area, and dips and hot spots will be very small in relation to the entire beach.

One thing I've said before, is when sand is building one place, it is coming from another. That is no big secret. It is obvious, but it is also telling. Work backwards to find where the sand is leaving.

Another thing that is often not taken into account is the backflow.  When water comes onto the beach, it doesn't just stay there.  It returns, and if it is flowing fast enough, the backflow will take the sand out, and it can work against the primary swell.  And there can be waves coming from two directions at the same time: a primary and secondary swell.  You can often see them.  You can often see little wind driven waves.

The shoreline is not a straight line, and the waves will refract.   So even when the waves are generally hitting from the northeast, there will be variations in the angles all along the beach.   

I can carry this on for a long time because there are a lot of complications.  I haven't even mentioned tides and some other things.

Here is a link for more on wave refraction.  What is wave refraction? (surfertoday.com)

I'll have to pick up with that some other time.  Do, however, remember wave refraction as one thing to consider when trhying to figure out what is going on.

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Concerning Terry's finds that I posted yesterday, Warren D. sent the following email.

I remember back in the 70's the Australian LPGA lady golfer, Jan Stephenson came to Brevard to visit fellow LPGA player and Satellite Beach resident, Laura Baugh. They were the first golf "glamour girls" who made more in endorsement money than in winnings. The rumors of their partying were legendary.

Jan later designed and developed the Walkabout Golf Course in North Brevard.

Maybe these coins were stashed in a beach house that later collapsed?

I would send Jan a letter, it could be a good story.

Beaches will obliterate manmade structures and leave no sign of them. Many years about I saw a concrete foundation uncovered north of John Brooks. Haven't seen it agaiin in probably thrity or forty years. And Nicole I mentioned some other things that were recently uncovered by Nicole, such as the old fence line and concrete bases.

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Source: MagicSeaWeed.com.

So Thursday we're supposed to see a decent increase in the surf.  

Happy hunting,

Treasureguide@comcsst.net