It could be concluded from Fig. 3 that most of wave spectrum have higher first peak at station 3. This might be because of the low water depth at this station. However, for station 1, second peak of wave spectrum dominates. It is also obvious that peak frequency of spectrum that has higher first peak usually occurred in 0.07–0.09 Hz range of frequency. Here, the relation between significant wave height and peak frequency is explicitly presented in Fig. 3,although it could be extracted from two aforementioned diagrams, due to its importance.