Isonami - Isonami

Breaking waves near the coast. When wind waves or swells reach shallow coastal waters, the waves begin to deform under the influence of the seabed. As the water becomes shallower, the wavelength becomes slightly longer and the wave height becomes lower at first, but as the water penetrates into shallower waters, the wavelength becomes shorter and the wave height increases, forming steeper waveforms, and eventually the waves become breaking waves and lose their energy. Surf waves can be very destructive, so it is important to estimate and predict surf waves when designing coastal structures and for disaster prevention. The conditions under which breaking waves occur have not yet been clearly defined, but charts for estimating breaking depth and breaking wave height have been presented based on experiments and observations.

[Kunio Sakurai]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

海岸近くのくだけ波。風浪やうねりが水深の浅い沿岸海域に伝わってくると、海底の影響を受けて波が変形を始める。水深が浅くなるにつれて、最初は波長がすこし長く、波高も低くなるが、さらに浅い海域に侵入してくると、波長は短く、波高は高くなって険しい波形となり、やがてはくだけ波となって波のエネルギーを失う。磯波は大きな破壊力をもつことがあり、海岸構造物の設計、防災にあたっては、磯波の推算、予測を行うことが重要である。くだけ波が生じる条件はまだ明確にされていないが、砕波水深や砕波波高を推定する図表が、実験や観測に基づいて提示されている。

［桜井邦雄］

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