Ocean Science 101: How our surf is made (Part 4: Breaking Waves)

Breaking Waves

This is where all the hard work of tracking a storm, watching a swell form, and then tracking it halfway across the world pays off. Breaking waves are the end result of all of this storm and swell activity...they are the meat and potatoes of surfing. In fact most surfers, in particular experienced surfers, know a lot about breaking waves, and know it on an almost instinctual level.

The size, shape, and power of a wave determine what and how we ride. You see it everywhere, from longboarding slow soft waves at Tourmaline or San-O, or driving down fast hollow sections at 56th Street on your fish, or big arcing cutbacks on your thruster as you speed through long sections at C-street. The characteristics of the breaking wave will set the rules on what type of board, gear, or surfing style is going to work the best.

Shoaling (waves hitting the beach)

Shoaling is the actual process of a swell moving from deeper water, turning into a wave, and eventually breaking along a surf spot.

Part of this process is actually driven by some of those characteristics of swell period. You may recall back is part #3 where I said that the energy in a swell actually extends downward in sort of a swell “column”…well shoaling starts to occur as the swell energy starts to reach the sea floor.
As the water depth decreases the energy of the swell is forced upward, which make the swell on the surface start to increase in height. As the energy moves into shallower water the swell starts to take the shape of a wave. It is important to note that the energy that is being squished into the sea floor is starting to reduce in speed thanks to friction. Eventually the water depth reaches a critical point where the wave can no longer support the top portion of water, which is moving faster than the base of the wave, and everything destabilizes. This is the point were the wave breaks and the crest of the wave spills forward in front of the base releasing a good portion of the waves energy.

Wave Shape

Wave shape is determined by a few different things. Water depth, swell-period, swell-height, and the shape & orientation of the beach can all play very important roles in wave shape.

Waves generally break in a water depth that is about half of the wave height. So an 8-foot wave would potentially break in about 4-feet of water. The actual math for determining water depth for a breaking wave is actually a lot more complex but the 1.75:1 or 2:1 ratio is a good general rule of thumb.

How the breaking portion of the wave is shaped is almost exclusively determined by water depth. Almost all waves that can throw decent barrels have the same characteristic…they all have a sea-floor that goes from very deep to very shallow in a short distance. In opposite of that is true as well…most longboard waves have a very long-gradual sea-floor shape where the wave slowly loses power before it finally spills over.

Now beyond water depth, the energy in a swell (both period and wave height) makes a difference in wave shape as well. The more energy in a swell the quicker it starts feeling the sea-floor and the more energy it has to spare creating the wave as the swell starts to shoal. A large long-period swell can throw some solid dumping waves on even the most gradual of sea-floor slopes. The converse is true as well a small short-period swell can make it almost all the way to dry sand before it has to break…and in some cases it may not break at all…just surge on to the beach in a sort of last gasp sputter.

Lastly beach shape and orientation are also important factors and can basically make or break a wave. In the case of both of these it is almost the imperfections that can cause a well shaped wave to form. Maybe it is a deep hole that has formed in the sandbar, or a jetty that piles up sand on one side but not the other, or a chunk of reef that is missing, or even a simple headland that has slowly eroded into place over the millennium…all of these “imperfections” in the sea floor allow a wave to break unevenly. The uneven breaking means that there is still an open rideable section ahead of the breaking section, and in cases where the sea floor is nice and steep the wave can be moving fast enough to create a hollow section. (if you are lucky, or if you live in Indo, which is sort of like being lucky all the time).

Constructive and Destructive interference (aka combo swells)

Some wave shape is determined by the types of swell directions that a beach is exposed to. When you have a beach with an open swell window you can get what is called constructive and deconstructive interference. This occurs when you have 2 swells coming in from different directions that hit the beach at the same time.

The overlapping nature of the swells, and the peak-to-trough-to-peak pattern, means that in some areas the swells will double up energy creating a taller breaking wave, and in other areas the swells will cancel each other out and there will be no waves at all.

This is the process that sets up those crossed-up, peaky days. These swells are actually more fun on a wider beach with a fairly consistent water depth…basically beaches that would normally close out on single swells like most beach breaks. Other breaks that have a more varied water depth can still be fun but generally don’t work as well as they could on a single pure swell.

Wave Refraction

Refraction occurs when a wave starts to feel the ocean floor. What happens is that the energy in the wave or swell starts to feel the sea-floor and begins to slow down thanks to friction. As the wave slows down it starts to change direction, generally pulling the waves energy toward shallower water.

Refraction can occur in all kinds of different water depths…long-period swells can feel the bottom at about 1000-feet, so you can start to see influences of refraction quite a ways offshore. Short-period swells don’t feel the bottom until much shallower water depths and can experience refraction in as little as 15-20’ of water.

Probably the most dramatic, and for surfers one of the most fun, examples of refraction is what occurs at point breaks.

At a point break you generally have a small headland that extends out into the deeper water along a coastline. Now most points are not sheer cliffs, they have a sea-floor that slopes away from the headland…usually this shallower area drops off pretty fast, particularly as you move along to the inside sections of the point…if you are very lucky there will be a deep bay protected by the point.

What happens is that the swell will hit along the top of the point and start to break as it hits the shallow water there. As the wave moves past the top of the point the energy that is still feeling the shallow water will continue to pull back towards the beach effectively extending the breaking portion of the wave…if the point is shaped properly, and the swell period is just right, it will wrap a ton of energy around the point and set up a very long ride. Next time you see Rincon on a big swell watch how the wave wraps in.

Wave Reflection

The last process that affects a breaking wave is called Reflection. This occurs when the swell energy hits a solid object, like a jetty or a cliff, and bounces off. Usually the wave will lose a lot of energy in the “bounce” but if the rest of the beach is shaped in the right way you can actually get the bounce energy to reflect back and add energy into a portion of the swell that did not hit the object.

Probably the best example of this is the Wedge in Newport Beach…hell the name alone should explain the process. Basically you get a big S swell that marches down the end of the North Newport Harbor Jetty. The swell instead of spreading out as it moves into the beach starts to pile up water and energy along the jetty. Eventually the swell moves out of the very deep water into extremely shallow water (or sometimes dry sand) and the energy piled up along the jetty bounces across the breaking wave, creating a large wedge shaped peak that throws some of the most retarded looking waves in SoCal. Other spots that are good, but lesser publicized, examples of reflection, are Surfside in HB and South Mission Jetty down in San Diego.


What this all means

I really believe that the more that you can learn about the ocean the better of a surfer and waterman that you become.

I don’t think you need to be an oceanographer, a meteorologist, or a surf-forecaster to have fun and score a few good waves (though it helps to be a surf forecaster)… but I think it is important to have at least a minimal understanding of the processes that go into creating surf.

Once you start to get some of the basic concepts down you will start to see how everything is connected, and eventually (at least in my experience) you will start to make better choices when it comes to surfing. You will find yourself getting more, quality surf, with smaller crowds, and better conditions…and really as a surfer can you ask for anything more.

Part 1: Overview – Types of Waves
Part 2: Wave Creation and Swell Generation
Part 3: Characteristics of swells

Ocean Science 101: How our surf is made (Part 3: Characteristics of swells)

Swell

The swell stage of a wind wave life-cycle occurs both in the generation phase and the swell phase (duh Adam), which is why the surf gets big when a storm or heavy winds move right over your beach. Usually though the swell phase occurs when the energy of a storm moves away from the area it was created.

As the swell energy moves away from the storm center it becomes more organized and structured. The energy generally moves along the path that was established by the strongest areas of fetch, but because storms are circular in nature swell move out in all directions and is very similar to dropping a rock into a pond…a better description though would be a rock thrown into a pond, where the biggest waves move out along the direction the rock was traveling when it hit the water (stupid rock analogy).

We measure swell energy in a rather unique way…it is actually a time based measurement called swell-period. This refers to the interval between the passage of two successive swell crests past a fixed location in the ocean and is measured in seconds. Swells with periods of 16-seconds or more are generally referred to as “long-period swells”. Swells in the 12- to 15-second range are considered “medium-period swells”. Swells that are 11-seconds and below are called “short-period swells”



Generally the longer the swell-period the more energy it has and the faster it moves. So as swell first starts to leave the storm area all of the swell energy will be piled up and moving more or less together but as it starts to travel across the longer distances the swell energy starts to separate. The long-period swells move faster than the shorter ones so eventually they out-distance them.

The longer the distance between the storm and the beach the more separated out the swell periods will get. For example a swell generated several thousand miles away in the South Pacific will arrive with very distinct differences in swell period. The swell will hit the buoys with the long-period energy first and will follow the progression down through the shorter periods.

A closer storm, like the ones that form just off the coast of California, will blast us with the full spectrum of swell periods almost at the same time…you may get a little jump in long-period energy first but then the peak of the energy will come through in a large lump…it may jump from a 18-second swell straight to a 12-second swell and peak with a bunch of energy in-between.

More Random and complicated stuff about swells

Swells are complex beasts and they live in a weird state of physics, which makes them even more complicated.

To even start the discussion you need to know (and hopefully understand) a thing known as the Coriolis Effect.

Wikipedia describes (because I am getting a headache) the Coriolis Effect as “an apparent deflection of moving objects from a straight path when they are viewed from a rotating frame of reference.

Freely moving objects on the surface of the Earth experience a Coriolis force, and appear to veer to the right in the northern hemisphere, and to the left in the southern. Movements of air in the atmosphere and water in the ocean are notable examples of this behavior: rather than flowing directly from areas of high pressure to low pressure, as they would on a non-rotating planet, winds and currents tend to flow to the right (left) of this direction north (south) of the equator. This effect is responsible for the rotation of large cyclones”



On the surface this seems straight forward enough but with swell it takes on a slightly different twist. Coriolis only affects objects with mass. A swell is almost entirely energy, which has no mass, so it is NOT affected by Coriolis. (I really hate physics sometimes).

The tricky part is that air and water molecules have mass, so you have to take Coriolis into account when you are dealing with currents and storms, (basically all the things that help to create a swell), but the second a swell leaves a storm area as energy in the water it is no longer affected by Coriolis.

I am sure a lot of you are swearing at me right now for even bringing this up but it actually plays a very important role in tracking swells. Because the swell is not affected by Coriolis it travels in a straight line. You can basically draw a line from the storm’s fetch straight to your surf break…if no land gets in the way then you will see waves from that swell.

Important Safety Tip: Oh yeah that straight line, from storm to break, has to be on a globe…not a flat map…when you draw it on a flat map you have to take into account the curvature of the earth, which means that the straight line has to curve along what is called a “great circle line” or is sometimes referred to as a “Rum Line” in ship navigation.

Swell decay

From time to time you will hear a term called swell-decay…this is another one of those tricky concepts. Remember a couple of paragraphs ago when I said swells are energy and have no mass? Well it is not entirely true…if a swell was pure energy it wouldn’t have any friction and all swell periods would move at the same speed and be able to travel across the entirety of the ocean. In reality there is a little bit of mass in a swell, or at least friction.

This occurs as the swell moves through the water…the energy actually extends downward as well as along the surface. The longer the swell period the deeper the energy goes. In this “column” of swell (for lack of a better word) there is some circular motion of water molecules. It is this slight motion of actual mass that allows some of the swell energy to bleed off as friction. In short period swells there is a lot of this circular motion (mostly because the swell’s waves are so close together). It is this energy reduction that is usually referred to as swell-decay.

What happens is that swells will lose energy as they travel longer distances…the longer they go the more they lose. Short-period swells lose the most energy the fastest…so a swell with a period under 10-seconds can only go a couple hundred miles before it has lost so much energy that it can’t create waves any longer.

A long-period swell decays much slower and will only lose a small amount of energy over long distances. It is possible for a 18-20 second swell to travel thousands of miles and only lose 2/3rds of its energy before it hits the beach. So if a swell started off with 10’ of long-period energy it would still have almost 3’ of energy when it arrived at the beach.

This is one of the reasons why Southern California never gets short-period energy from the South Pacific…all of it decays away before it reaches us.

Part 1: Overview – Types of Waves
Part 2: Wave Creation and Swell Generation
Part 4: Breaking waves

Ocean Science 101: How our surf is made (Part 2: Wave Creation and Swell Generation)

For surfing wind waves are the end-all be-all of the sport. Without wind waves there would be no surfing at all…so everything else like conditions, tides, beach shape, it is all just window dressing.

Generally wind waves have 3 different phases in their life-cycle; Generation, Swell, and breaking waves.

The first is generation, which occurs underneath a consistent area of winds going the same direction, called a Fetch.



Fetch can occur in a variety of situations and can be found in anything from a frontal storm, hurricane, trade winds, or even just consistent winds around an area of high-pressure. Fetch is measured in 5 ways.

1. Intensity – the strength of the winds in the fetch area

2. Length – how long is the fetch? This can affect the swell strength…think of the fetch-length as a rifle barrel…the longer a swell can stay in the “barrel” the more energy that the winds will be able to add to it.

3. Width – How wide is the fetch? The wider an area of fetch the broader the swell direction will be…this is particularly important for SoCal where a spot can get totally skunked by a swell that is just a few degrees outside of its swell window.

4. Duration – How long have the winds been blowing on a particular area of ocean? The more time they spend the bigger a swell can become.

5. Movement – Storms and Fetch are not stationary…they are in constant movement. Direction of movement is very important. The more that a swell moves “toward” a spot the more energy that it will impart to the swell. If the fetch is moving obliquely or away from a location that hampers the swell strength. Speed of movement is also a factor…if the fetch area moves to fast or to slow it allows the swell to move out of the area and away from its energy source.

Once an area of fetch has been established, (hopefully aimed at and moving toward your surf spot), and the winds are blowing over the surface of the water they start to impart energy into the ocean as the air molecules run up against the water molecules (I just really wanted to write molecules in this post somewhere). The friction between the air and the water is the process that moves energy from the atmosphere into the ocean.

At first, if the sea is calm, you will start to see small ripples forming as the friction from the air gains purchase. These are called capillary waves.


Capillary waves act like grip-tap on a skateboard…once they have formed they add a more exposed surface area to the wind allowing it to gain more purchase and add more energy to the waves (I bet you can see where this is going).

If the wind is strong enough these capillary waves continue to grow along with the space between the crests of the waves. Once the larger waves are formed this is sometimes called a sea-state (or at least sea-state refers to the conditions of the seas within the target area).


As the winds become more intense, or the duration of the wind becomes longer. These waves grow.



And grow…



Eventually if the winds are super intense you get huge waves at the storm core. (The boat in this picture is bummed).



Now an area of fetch doesn’t have to be world-ending intense to create a swell. You can have a swell with almost any amount of wind, but the more wind, the bigger the seas, and the larger the fetch. The larger the fetch means that more energy will make it into the swell, which in turn means that the swell will have a better chance of making it across a longer distance (eventually hitting your break).


Part 1: Overview – Types of Waves
Part 3: Characteristics of swells
Part 4: Breaking waves

Ocean Science 101: How our surf is made

OK this will probably review for a lot of you, but I thought I would go back and cover some of the basics in surf forecasting. I have been posting forecasts, reports, maps, and other random nonsense for a while now and I started to realize that a lot of the stuff that I have been throwing at you assumes that you have an idea of how our surf is generated. It isn’t really that hard to find on the interweb, (I mean, come on, that is what Wikipedia was invented for people), but I decided to throw it up here too so that you didn’t have to hunt around for it.

Why it matters

I am sure that there are some of you out there that don’t really care about where the waves come from and are fine with just knowing if the surf is going to be good tomorrow. That is totally cool…I hope that I keep my forecasts simple enough that you can keep scoring…or at least save some gas money now and then.

Personally I think that you become a better surfer, and a better waterman, if you get in tune with the ocean, the weather, and the processes that create the conditions that we, as surfers, are looking for. You don’t need to be a forecaster or anything but I do think that knowing the general principles behind how waves are made will keep you a step ahead of other surfers, which is nice, particularly when that step could mean the difference between scoring empty surf and slogging it out with the rest of the crowd that is a day late and a dollar short.

Types of Waves

There are actually 3 types of waves that occur in the ocean.

1. Tsunamis
2. Tidal Waves
3. Wind Waves


Tsunami



Tsunamis, if you were living under a rock or something, are waves that are usually generated by earthquakes. They actually used to be called “Tidal waves” because of the way they behaved as they hit an area. The true definition is that a Tsunami is actually caused by anything that quickly displaces a large amount of water. That could be anything from a volcanic eruption, a collapse of an undersea cliff or shelf, an asteroid/meteor hitting the ocean, or even something man made like a nuclear weapon. It just so happens that all of those other things are rare and earthquakes are fairly common. Also Tsunamis don’t have to occur in the ocean…they can occur in any large body of water.

Tsunamis are not actually surfable…in fact the characteristics of tsunamis are very similar to a low-to-high tide swing, albeit much larger and much more violent. In general the tsunami “wave” is moving much too fast and the swell period is measured in hundreds of miles, both of which do not allow the wave to take a “rideable shape”.




Tidal Waves (aka the tides)





Tidal Waves are the high and low tide that your beach experiences each day. These waves are caused by the gravity of the sun, the moon, along with the spin of the Earth in relation to those celestial bodies. The basics behind it is that there are 2 bulges of water in the ocean, one of which points to the sun, the other to the moon. As the Earth spins these bulges eventually get ran into land…as these causes them to reflect back and bounce all around the various ocean basins.


What is really crazy is that there are almost 200 different factors that have to be accounted for when you predict a high and low tide for a location. What is even crazier is that almost all of those factors are fairly stable so once you take them into account all you have to do is change the date on the forecast and the numbers fall into place. It is possible, though I am not sure why you would want to, to get a tidal forecast for a particular location 10, 20, or 200 years in advance…I guess it is probably something that oceanographers do when they are really bored.

These waves are also not-surfable but since the tide plays an important roll in surfing you definitely want to keep track of how it is behaving.



Wind Waves




Wind Waves are another properly named type of wave (I love some of the terminology in Oceanography, much of it is amazing straightforward). Winds waves are generated by wind blowing over the ocean. The more intense the wind, the longer the duration, and the bigger the area that the wind is blowing over, the bigger the wind waves will be.


These are the waves that we actually surf…from an energy/swell period perspective they are actually the weakest type of waves with the shortest swell periods…not that it matters much…a 20’ wave at Jaws can kill you just as fast as a tsunami.


Continued in these posts
Part 2: Wave Creation and Swell Generation
Part 3: Characteristics of swells
Part 4: Breaking waves