How Deep is the Water That Waves Break In?

Everyone knows that waves break when they hit shallow water.  But how shallow?  There's a simple rule of thumb.  Waves break in water 1.3 times their height. 

A 10 foot wave, for example, breaks in 13 feet of water depth.  That's 10 x 1.3 = 13.  

How is this useful?  Wherever you see breaking waves, you can estimate their height, and therefore the depth of the water.  This works on the bar, on the beach or if you see waves breaking on a reef. 

From a mariner's perspective a wave approaching breaking is steep, hazardous and scary, long before it actually breaks.  The aforementioned 10 foot wave would be dangerous even in 25 feet of water.

Just remember 1.3

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