Future wave-climate driven longshore sediment transport along the Indian coast

Abstract

Longshore sediment transport is an important nearshore process that governs coastal erosion/accretion and in turn defines the orientation of coastlines. In this study, we assess the changes in longshore transport rates along the Indian coast due to the potential changes in wave parameters under the RCP4.5 climate scenario. The projected wave climate for two time slices, ‘near-term/present’ (2011–2040) and ‘mid-term/future’ (2041–2070) were used to investigate changes in the corresponding sediment transport rates. An empirical model accounting for major wave parameters, longshore current, resulting sediment transport and shoreline evolution was used. It was found that most of the Indian coast exhibited the same drift direction in both time slices, although changes in transport magnitude were present. To give a broad-brush characterisation of the coastline, the shoreline elements were classified as erosive, accretive or stable based on the comparative longshore transport rates of neighbouring elements. Similar characterisations, carried out for both time slices, showed that about 35% of the total coastline would remain unaffected due to the changing wave climate in the future (i.e. there is little to no change); about 20% is expected to ‘worsen’ (i.e. expected to undergo higher magnitudes of erosion wrt present rate) and 45% to ‘improve’ (i.e. expected to accrete/reach stability). It was also observed that the net annual transport rates pertaining to the future period are not expected to change significantly with respect to the current scenario. This indicates that the change in longshore transport rates arising from future changes in wave climate as represented by the RCP4.5 climate change scenario will have a broadly neutral effect.