Along the tropical coast, there is cyclic variation in wind, wave currents, water and sediment influx, and the coasts experience a monsoonal storm surge that reaches nearly 2–3 times higher than the rest of the year, and foreshores undergo a complex evolution during an annual cycle. Hence, knowledge of foreshore evolution is critical in shoreline management. In this paper, study results on meso-scale foreshore evolution in a low-energy headland bay beach, situated in the Central West Coast of India near Manki, are discussed based on their seasonal and decadal changes in sandy shoreline configuration, wave refraction, sediment movement and depositional process. Decadal changes in the shoreline configuration indicated headland-side erosion and bay growth whereas the southern end grown seawards between the period 1979 and 2001–2002, while the beaches adjacent to the creek present in the area showed accretion and farther south of the creek showed minor erosion, and the trend continued through 2015. Wave refraction patterns for the waves approaching from northwest (NW), west and southwest (SW) for the wave periods 6, 8, 10 and 12 s indicated (a) wave convergence at the central part of the Manki beach; for the waves approaching from NW for wave periods 6 s; (b) wave divergence for the waves approaching from west with wave periods 6, 8, 10 and 12 s and (c) wave convergence at the bay side for the SW as well as NW approach of waves for wave period 10 s. Seasonal beach modification, in general, indicated post-monsoonal to pre-monsoonal (September to April) accretion and May to September erosion. Foreshore is gentle and dissipative (${\le}$6°). Sediments in all the seasons are bimodal (at 2${\phi}$and 2.752${\phi}$) in nature, and show dominantly saltation to suspension mode of transport. A parabolic shoreline prediction model indicated negative sediment budget in the central and northern parts of the beach (near the headland) and positive sediment budget at the southern end of the beach. Integration of the foreshore profile, sediment movement pattern, results of parabolic shoreline prediction model and decadal changes in shoreline configuration indicated that sediment budget is a critical issue in headland-bounded beaches, and utmost care is needed in the management of such shore line.

$\bf{Highlights}$

$\bullet$ This paper uses seasonal variations in the foreshore morphology, beach volume, sediment characteristics and wave refraction pattern to understand the sediment movement within the beach.

$\bullet$ Based on Hsu et al.’s (2004) model shoreline position is predicted.

$\bullet$ For a finite sediment input beach, shoreline management strategy is suggested.

Identifying coastal stretches that are likely to erode under high wave conditions is essential to the coastal management community in addressing beach erosion-related issues. The manuscript presents a case study to predict erosion of a selected beach located on the eastern Indian coast during the 2018 southwest (SW) monsoon season. The pre-monsoon beach topography surveyed using DGPS is used as the initial topographic condition in the morphological model. The model simulates subsequent beach erosion during the SW monsoon season, which is forced by forecast waves. Beach erosion advisories that classify the beach as eroding, accreting and no change are disseminated with a lead period of 10 days. During the SW monsoon period, we have monitored the beach using the dumpy level, and the beach topography during the postmonsoon is generated using DGPS surveyed profiles and are used for model validation. The beach area under erosion observed from the model result is homologous with the in-situ observations. The model shows cross-shore sediment transport to dominate during the SW monsoon, particularly in the central and northern sectors of RK beach. The model estimated shoreline position agrees with the DGPS observations, where the central sector has undergone maximum erosion. The comparison shows the model’s ability to simulate beach morphodynamics like landward shifting of the berm crest under a high wave setup and oscillating water levels due to tides. The study highlights the importance of numerical modelling systems that decipher the beach response to the high monsoon waves.

$\bf{Highlights}$

$\bullet$ Beach erosion forecast system for RK Beach, India.

$\bullet$ Forecast system is developed using a combination of WAVEWATCHIII and Xbeach.

$\bullet$ Beach erosion advisories during monsoon period.