As waves get closer to a beach they decrease in height.
Explanation:
As a wave crest approaches the shoreline, it is usual that one end of the line is closer to the shoreline than the other. The implication of this is that the energy in a wave is also spread over quite a larger area,this in turn reduces the height of the waves. In other words, refraction often makes waves smaller.
Waves are caused by wind. Wave height in the open ocean is determined by three factors. The greater the wind speed the larger the waves. The greater the duration of the wind (or storm) the larger the waves. The greater the fetch (area over which the wind is blowing - size of storm) the larger the waves.