- Dona Paula, Goa, India.
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| Abstract Submission No. | ABS-2022-09-0415 |
| Title of Abstract | Decadal fluctuations in longshore sediment transport rates along the eastern Arabian Sea driven by Pacific climate variability. |
| Authors | Jesbin George*, Dr. Sanil Kumar V |
| Organisation | CSIR - National Institute of Oceanography |
| Address | Senior Project Associate, Ocean Engineering Division, CSIR - NIO Panaji, Goa, India Pincode: 403004 Mobile: 8806383804 E-mail: jesbingk@gmail.com |
| Country | India |
| Presentation | Oral |
| Abstract | Changes in large scale climate variability have a direct impact on the variations in wave heights and wave directions, which alters the morphodynamics of coasts due to deviations in longshore sediment transport (LST) supply. The present study examines decadal fluctuations in LST rates for six decades (1958-2016) along Ganpatipule coast, eastern Arabian Sea. ERA- 40 and ERA-Interim reanalysis wave parameters at deep water (~50 m water depth) is used as an input to a wave transformation model (Delft3D) and the nearshore wave parameters were estimated considering shallow water wave propagation, wave set-up, and breaking. The model simulations were carried out in stationary mode with a directional resolution of 10˿ and 24 frequency ranges (0.05- 1 Hz). The model performance was compared and validated using a measured wave data at 14 m water depth during the year 2011. The skill of the model is determined based on the amount of deviation, which is measured by root-mean-square-error (RMSE) and bias, between the model results and observational data and correlation coefficient (R). The measured and model results of SWH, period and direction shows a bias of -0.2 m, 0.44 s and -8, RMSE of 0.33 m, 0.8 s, and 28 and R values of 0.94, 0.81 and 0.5 respectively. The transformed breaking wave characteristics were extracted from the breaker zone, and LST is estimated using CERC (1984) equation, Q =0.023⿿(g/K_i ) H_b^2.5 sin(2θ) , Where, Q is the LST in volume per unit time, g is the acceleration due to gravity (9.81 m/s2), Hb is the breaking wave height (m), and θ is the angle between breaking wave crest and local shoreline (deg). Along the breaker zone, only small changes in Hb is observed during non-monsoon period, whereas during monsoon, variation is observed to be large indicating the growing importance of increasing breaker heights in the study region, particularly during the monsoon. The breaker angle in the study region tends to have a southward shift in the wave direction. The LST rates estimated in the present study are in good agreement with the previously reported LST rates along the eastern Arabian Sea. Considerable seasonal, annual and decadal variations are observed in the LST rates. The LST rates during monsoon, as expected, are high as compared to other seasons. The annual gross LST rates along the region vary from 3.2 ⿿ 9.1 ÿ 105 m3 yr-1 with an average value of 5.1 ÿ 105 m3 yr-1 whereas the annual net rate varies from 3.0 ⿿ 8.7 ÿ 105 m3 yr-1 with an average value of 4.9 ÿ 105 m3 yr-1 indicating a northward transport along the study region. LST rates along the study region have a weak negative correlation with the Oceanic Nino Index (ONI) and El Niño (La Nina) years are generally associated with low (high) LST rates as compared with other years. The signatures of Pacific Decadal Oscillation (PDO) variability on LST rates on both annual and decadal scales were examined with special attention given to understanding the variability in LST rates during both the warm and cold phases of PDO. A strong negative correlation between LST rates PDO is observed during the study period. The decadal variations observed in LST rates for the six decades were 48, 24, 21, 17, 15 and 19 % respectively |