Field observation of wave reflection from plunging cliff coasts of Chabahar

In this study, a linear formulation is found to estimate the wave reflection coefficient (K-r) from plunging cliff coasts of Chabahar city according to field data measurements. The field measurement included directional wave data via three bursts for each hour and in total 1345 bursts during summer Southern-West monsoon using an ADCP gague. The significant wave heights reached 2.5 m and the corresponding peak periods were greater than 11 s. It was observed that the wave reflection coefficients are fully tidally modulated. The maximum values of K-r reached 0.7 in a flood period of spring tide, while the minimum values were greater than 0.3 and corresponded to ebb periods in spring tide. The corresponding dimensionless parameters of wave height to depth, wave steepness and Ursell number to the highest values of K-r were obtained as 0.17, 0.014, and 22, respectively. The variation ranges of reflection coefficient pertaining to the effect of four main tidal constituents as M2, S2, K1, and O1 were achieved as similar to 9.6, 4.1, 7.1, and 3.6%, respectively. Finally, a linear formulation as a function of the tidal level was resulted to estimate the most accurate values of K-r in the studied area. The averaged inaccuracy of resulted formulation was approximately 6.5%. The frequency reflection coefficients K-r(f) was also investigated in this study. The results indicated the values close to 1 for long infragravity waves, because of occurrence of no significant dissipation. However, the similar values for short waves (fr > 0.25 Hz) were greater than 1 due to wind wave breaking as a result of the cliff toe collision. The temporal histogram of K-r(f) revealed the tidally controlled variations of this parameter.