Coastal Engineering Journal

Waves measured at a few locations along the west coast of India were analyzed to study modification and attenuation of wave energy in the nearshore regions. It has been found that the reduction in wave height is relatively lower (less than 10%) between two nearshore depths off Goa (25 m and 15 m) and Ratnagiri (35 m and 15 m), central west coast of India and is higher (22%) off Dwarka (30 m and 15 m), northwest coast of India. It is observed that the diurnal variation in waves decreases from north to south along the coast, as the intensity of sea breeze decreases from north to south. Swell attenuation due to opposing winds (from NE) is observed along the Ratnagiri coast during NE monsoon. The growth of wind seas (from NE) towards offshore and their modification by opposing swells (from SW/SSW) significantly contributed to the reduction in wave heights at shallow water depths off Dwarka. The role of opposing winds in the attenuation of swells along the west coast of India during NE monsoon season is significant. Numerical simulations were carried out to study the wave transformation between the depths 100, 50, 20, 10 and 5 m off Mumbai, Goa and Kochi. Diurnal variation is evident during the pre-monsoon season, and the magnitude of variation decreases from north to south.

The analysis of the water wave breaking phenomenon has been on-going for almost 150 years, and many research papers have been published approximating both the local geographic and geometric characteristics of breaking waves. This review of original empirical work, the relationships theorized by each author, and their regions of applicability are detailed to give a historical perspective of wave breaking research but also to illustrate advances in recent years. Subsequently published validity investigations by other authors show the variability and limitations of each approximation and illustrate that the level of understanding in wave breaking parameters has progressed considerably. The understanding of the defining variables in wave breaking progresses annually, however predicting the location, depth and shape of the wave at breaking is still not universally defined. This is in part due to the inherent variability in nature of breaking waves; however, it is compounded by a lack of a collective measurement and definition system for wave breaking parameters.

A similarity parameter is derived to describe surf zone dissipation using the classical energy dissipation model for surf zone bores. This parameter can also be interpreted as a relative beach slope parameter, β_γ, and, for shallow water sinusoidal waves, is the ratio of the local beach slope and the local wave steepness (H/L). β_γ = 1 defines the boundary between two different energy dissipation regimes. Conditions with β_γ<1 represent over-dissipative conditions, where the classical bore dissipation model provides more dissipation than that required for depth-limited waves (constant H/h) to be maintained. Conditions with β_γ>1 represent under-dissipative conditions, where the bore model provides insufficient dissipation for depth-limited conditions to occur. Conditions with β_γ = 1 at the breakpoint lead to locally saturated but not depth-limited surf. Hence, the new similarity parameter distinguishes between saturated and unsaturated surf conditions. Based on this bore dissipation model, an analytical model for the wave height transformation of monochromatic waves on planar beaches is derived. The cross-shore variation in wave height obtained from this model show different functional forms; concave upward for over-dissipative conditions and convex upward for under-dissipative conditions. Further, the analytical model shows that depth-limited conditions within the inner surf zone are not possible with this bore dissipation model and the model assumptions. Additional work is required to determine if this parameter is a useful predictor of other surf zone characteristics.

Highlights: We derive a similarity parameter to describe surf zone dissipation. The similarity parameter defines the boundary of two dissipation regimes. The parameter distinguishes between saturated and unsaturated surf conditions. The classical bore dissipation model cannot predict depth-limited wave heights on a plane beach.