• P G REMYA

      Articles written in Journal of Earth System Science

    • Evaluation of the impact of high-resolution winds on the coastal waves

      P SIRISHA P G REMYA ANURADHA MODI RABI RANJAN TRIPATHY T M BALAKRISHNAN NAIR B VENKATESWARA RAO

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      This study discusses the impact of high-resolution winds on the coastal waves and analyses the effectiveness of the high-resolution winds in recreating the fine-scale features along the coastal regions during the pre-monsoon season (March–May). The influence of the diurnal variation of winds on waves is studied for the Tamil Nadu coastal region using wind fields from weather research and forecast (WRF) (3 km) and European Centre for Medium-Range Weather Forecasts (ECMWF) (27.5 km). The improvement in the coastal forecast is then quantified with wave rider buoy observations. The high-resolution wind fields simulated fine-scale features like land–sea breeze events and showed good agreement with observation results. The error in the wave height and period is reduced by 8% and 46%, respectively, with the use of high-resolution forcing winds WRF over ECMWF, although the overestimation of wave energy on high frequencies due to overestimated WRF winds remains as a challenge in forecasting. The analysis also shows the importance of accurate wave forecast during a short-duration sudden wind ($\sim$12 m/s) occurrence in southern Tamil Nadu near Rameswaram during the pre-monsoon period. Low pressure forms over Tamil Nadu due to the land surface heating, resulting in a sudden increase of winds. High winds and steep waves which cause damage to the property of the coastal community near Rameswaram also were well simulated in the high-resolution forecast system with WRF winds.

    • The role of anomalous oceanic features on enhancing flooding duration in Kuttanad region, Kerala (India)

      ANURADHA MODI T M BALAKRISHNAN NAIR P G REMYA HARIKUMAR R SRINIVAS K SRINIVAS G

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      The present study describes the active role of met-ocean parameters on the heavy flooding that occurred during July 2018 in the Kuttanad region, Kerala. The model-derived data as well as observations showed a high anomaly of wave height in July 2018 off Kerala was not correlated with local wind anomaly and indicated possible connection of wave anomalies to swell waves. The high period and high amplitude swell waves suggest a wave setup formation near shore for flooding intensification in the Kuttanad region. The wave observation at an open ocean location (AD09) also confirms the presence of high swell waves during the same period. Anomalous elevated non-tidal sea level was evident in the tide gauge data. The narrow opening at Thottappally, is not able to discharge the outflow of the heavy flood water and it is further complicated by the wave setup at the entrance caused by long period swell waves.

    • A numerical modelling approach for beach erosion forecast during the southwest monsoon season

      R RATHEESH P G REMYA RITESH AGRAWAL CH VENKITESWARLU B GIREESH P AMARENDRA T M BALAKRISHNAN NAIR A S RAJAWAT

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      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.

    • Wave modulations in the Indian coastal area due to wave–tide interactions

      P SIRISHA P G REMYA K SRINIVAS T M BALAKRISHNAN NAIR

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      The present study highlights the wave–tide interactions in a tide-dominant coast Versova, along the west coast of India. Versova is a macro tidal area and is home to fisheries. Model simulations are carried out to investigate wave–tide interactions with and without incorporating water level (WL) variations in the model setup. The simulation results are compared with the observed data at Versova. Model comparison with wave observation shows that the simulated significant wave height (Hs) reproduced the observed wave heights with an accuracy of scatter index = 8% and correlation = 0.94 with the inclusion of WL variations. The incorporation of WL variations created the energy modulations in the low-frequency part of the wave spectra, raising the periodical modulations in wave height. This low-frequency wave energy modulation is absent in the without WL simulations, resulting in underestimation of energy density which causes underestimation of Hs by ${\sim}$1 m. Hence this study strongly suggests that water level variations must be incorporated into the wave model to accurately represent wave modulations which are significant during monsoon and extreme events in the tide-dominant coastal areas.

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