Directional spreading of waves in the nearshore zone

You are here: Homepage > Search

Directional spreading of waves in the nearshore zone

Sundar, V. / Sannasiraj, S.A. / Kaldenhoff, H.

A study has been carried out to analyse the effect of a groin field on the behaviour of waves in the nearshore zone. The measurements of wave elevation and two horizontal velocities inside a groin field in the coastal zone of the island of Norderney, Germany, were analysed for their directional characteristics using the maximum entropy method. The directional wave spectrum becomes broader as the waves approach from deeper waters into the groin field. The magnitude of the spectral peak reduces as the waves enter the shallower region of the groin field. Due to the presence of long period swash oscillations near the shore, the spectral peak shifts towards lower frequencies in the shallower locations within the groin field. The frequency spectra of wave elevation and the two horizontal velocity components has a single peak outside the groin, whereas, inside the groin field they are multipeaked. The estimation of the directional spread at a particular location is unaffected by the elevation of the velocity measurement, provided the measured wave spectra are not broad banded. The overall mean wave direction for waves approaching a location outside the groin field at an angle tends to become normal to the shore as they propagate towards shallower waters. However, at locations inside the groin field, the angle of wave approach from the shore normal increases due to cross-reflections. Waves which are long-crested outside the groin field transform into a short-crested sea as they propagate into the groin field.