Creating Surf
25 commentsAs a swell approaches the coastline and comes into contact with the sea floor the waves will start to slow down. Some of the waves' energy is lost through contact with the sea floor. The shallower the water becomes the slower they move. As they slow down they have to squash together. (i.e. they shorten their wave period.) This process is called shoaling and results in increasing wave height. The steeper the sea floor gradient the more pronounced the wave height will increase. The increase in wave height begins to occur at depths of around one half of the wavelength.
Wave height increase in shallowing water
Breaking Waves
As the wave moves into increasingly shallow water, the bottom of the wave decreases speed. There comes a point where the top of the wave overtakes it and starts to spill forward — the wave starts to break. We're surfing! In general a wave will start to break when it reaches a water depth of 1.3 times the wave height.
The type of wave that is produced is dependent on different factors.
- Type of swell
- Wind direction
- Slope of sea bed
- Sea floor features
Type of Swell
Groundswell is best for creating good waves. The longer wavelength waves will move quickly and get into shallow water before starting to break. The breaking waves will be steeper and faster.
Wind swell will tend to break in deeper water and will not pack such a punch. The waves tend to be much more crumbly.
Wind Direction
Offshore wind is most desirable for creating good waves. The wind blows against the top part of the wave and helps delay the top part from overtaking the bottom part. This results in the waves breaking later than they normally would in calm conditions.
When you watch waves or see them in surfing magazines with huge plumes of spray blowing back over the top of the wave, you're looking at offshore surf.
An onshore wind will have the opposite effect. The onshore wind pushes the top of the wave forward causing the wave to break before the normal breaking depth is reached. Waves tend to be lumpier and fail to reach their optimum peak.
Slope of Sea Floor
If you've read everything we have written up to this point, you know that it's the action of the sea bed slowing the bottom part of the wave that causes the wave to break. A gently sloping approach causes the bottom of the wave to drag and will result in the top of the wave prematurely overtaking the bottom resulting in the wave breaking in deeper water. These crumbling waves won't be steep and will lack punch. If you're learning how to surf, then these waves are ideally what you are after.
Examples of this type of slope can be seen at average beach breaks all over the place. (We've all surfed them.)
Wave breaking on sloping sea floor
The contrast to the gently sloping sea floor is a steep slope or a reef. The swell approaches the beach / reef at a greater speed. From the diagram below it can be seen that the wave "jacks up" due to the rapid change in depth creating a higher wave. The breaking depth is reached much later that on the gently sloped bottom. The top of the wave quickly overtakes the bottom and pitches forward. (Often taking the inexperienced surfer with it.) The waves created by the rapid change in depth are much steeper and hollower, and — thus the tube is born!
Rapid depth change creates steep pitching waves
Reef breaks such as Pipeline in Hawaii are examples of this type of break.
Sea Floor Features
Sea floor features are especially important when surfing beach breaks. Surfing a flat beach can be a boring experience. The waves constantly close out, and you can't get a decent ride. The sea floor needs to have different depths at different points of the wave so waves will peel along their length. Big storms and the action of waves moving sand create sand bars which alter the depth of the beach at certain points. Deeper water will run alongside the shallower sand bar giving the depth difference that a peeling wave needs.
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Comments
 | Guest on May 3, 2011 | very good :) |
| Guest on May 18, 2011 | HOT. LOL |
| Guest on May 27, 2011 | Oh yea ;) |
| Guest on Jun 15, 2011 | Thanks so much! This was a GREAT help! :) |
| Guest on Jun 15, 2011 | Thanks so much! This was a GREAT help! :) |
| Guest on Sep 24, 2011 | Give me waves or give me death! |
| Guest on Oct 19, 2011 | nice |
| surfer on Jan 23, 2012 | thanks this helped me a lot |
| Guest on Feb 14, 2012 | simple but very good and thanks for the help :) |
| Guest on Feb 16, 2012 | thats amazing help its easy to understand |
| Guest on Mar 1, 2012 | thanks it helps alot but needs more information on what a wave is and what causes a wave |
| Guest on Mar 13, 2012 | need more info about what a wave is and how it is formed |
 | surf patrol on Mar 13, 2012 | Check the Gimmie more links on the right hand sidebar above. There's several other articles that should help. |
| Cyndy on Mar 29, 2012 | Thanx alot but add more information |
| Guest on May 10, 2012 | This givees me alot of information about breaking waves |
| Guest on May 11, 2012 | awsome needs more info on what a wave is |
| Guest on Jun 8, 2012 | i need info about waves about how waves breack and i have all the info i need :) |
| Guest on Jun 26, 2012 | This is great, but a small correction. As a wave approaches shallow water and begins to shoal, wave length (not period) decreases. Wave period is always conserved. |
| Guest on Oct 23, 2012 | give me waves or give we death dude ride to live, live to ride ! waves are my life ride like a white whale dude ! 4 eva <3 |
| Guest on Nov 1, 2012 | more info but good |
| Guest on Nov 14, 2012 | thanks |
| The Spam on Dec 13, 2012 | you are a lad! thanks so much! |
| Jesus Christ on Dec 19, 2012 | Thanks man, helped a lot with my physics homework "Why do waves break?" |
| Lazarus on Feb 11, 2013 | This is so dope |
| balls on Mar 26, 2013 | thanks |