Creating Surf
69 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.
very good :)
HOT. LOL
Oh yea ;)
Thanks so much! This was a GREAT help! :)
Thanks so much! This was a GREAT help! :)
Give me waves or give me death!
nice
thanks this helped me a lot
simple but very good and thanks for the help :)
thats amazing help its easy to understand
thanks it helps alot but needs more information on what a wave is and what causes a wave
need more info about what a wave is and how it is formed
Check the Gimmie more links on the right hand sidebar above. There's several other articles that should help.
Thanx alot but add more information
This givees me alot of information about breaking waves
awsome needs more info on what a wave is
i need info about waves about how waves breack and i have all the info i need :)
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.
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
more info but good
thanks
you are a lad! thanks so much!
Thanks man, helped a lot with my physics homework "Why do waves break?"
This is so dope
thanks
thank you so much.
question; speed of an average 6' wave approximately?
Used it for part of my Science Fair Project. Very helpful
to fun to ocean waves
so much moisture
This was great to help on waves unit in Science.
It didn't help at all................
good help thanks so much
cool!
thats some good info there fellas
Best advice ever !!! LOL
Amazing
That's very cool!!
dope
woooooooooooooooooooooooooooooooooooooooooooooooooooooooo
thanks a lot
coooool
gig
thanks a lot very!
Give me waves or give me death! NAH
say what
what
Give me waves or give me death!
I doubt that that wave period decreases ... if for example, 350 waves approach the coast in an hour then 350 wave land on the beach an hour. ie wave period is 3600seconds / 350 waves, wave period 10.35 seconds in both localities. I think you should be saying the wave length decreases. This is because they do indeed slow down.
it seems that the 1.3 times the height of the wave rule is generally accepted but what about the hight of the wave changing as shoaling starts? and what is the hight of a wave anyway? the problem being that the wave shape is no longer sinusoidal? Any comment.
By the way great page -- made me think -ta
thank you, i have
a much clearer understanding
thanks it helped me a great lot
yeah what a vital source of information that was...
good informaton
Totally tubular dude!
dude gnarly brahada
Great homework help, which is very clear and easy to understand
Thanks
Thanks
thanks heaps
thank u !
Nicely explained. Thanks!! Could you cite your source please?
really cool!
surfers dream ? barrel wave
OH YEah ;)
was not helpful
need more information
this was really good
thatnks to who ever made this
i think thta kids should read this if they are curious to learn about waves in fact i am a 9 year old boy who read this artical you can find me waikele elamentry school in 4 th grade
Gimme WAVES or DEATH! Whooyaaa!!