Optimal High Frequency Cut-off in SWAN Wave Model

This study investigates the importance of selecting an appropriate cut-off frequency in the SWAN model when it is applied to areas with limited fetches. In SWAN, the cut-off frequency is a constant value set by user in the model, and its appropriate selection plays an important role in the accuracy and optimization of the wave model; very high value increases the computational cost and might lead to increase of approximations in the nonlinear wave-wave interaction term. On the other hand, very low value affects the wave growth dynamics due to inaccurate nonlinear wave interactions. In this study SWAN was applied to the northern part of the Gulf of Mexico as a semi-enclosed basin and to the Lake Ijssell as a closed basin. The results showed that as wind fetch decreases, a higher value for the cut-off frequency is required to determine the prognostic region of the wave spectrum in the model. Based on the outputs, in coastal areas such as the northern Gulf of Mexico, 0.6 Hz is proposed for the cut-off frequency, while in small areas such as Lake Ijssel,0.9 Hz is a good choice.