Estimation of longshore sediment transport and shoreline evolution along kuakata beach by numerical modelling

Abstract

This study work has been conducted for erosion and deposition analysis of Kuakata beach, estimation of longshore sediment transport and coastline evolution as well. Satellite images of coastline during the period of 1978 to 2020 have been collected and analyzed using ArcGIS software. 24 km long Kuakata beach is subdivided into three parts like Lebur Char (13 km), Gangamatir Char (4 km) and Kawar Char (7 km) stretching from west to east. From Satellite image analysis, it is evident that Lebur Char (west part) is vulnerable to erosion, middle part of the Kuakata beach i.e., Gangamatir Char is more or less stable, and Kawar Char (east part) is accreting day by day. It is seen that 13 km long coastline has been eroded having an area of 4.8 km2 and 7 km coastline has been accreted having an area of 3.7 km2 has been accreted in last 42 years. During this period the average erosion rate and accretion rate are 9 m/yr and 12.2 m/yr respectively and for last it was 10 years 11.7 m/yr and 21.2 m/yr respectively. Dedicated hydrodynamic model using MIKE 21 FM (with/without wave action) is developed, calibrated and validated for studying nearshore hydrodynamic analysis. Model simulation for different critical hydrological and hydrodynamic condition reveals that there develops longshore current along the beach and eastward current magnitude dominates over westward current magnitude. Dedicated wave model has been developed using MIKE 21 SW and the simulated wave climate has been used in LITDRIFT model and LITLINE model. From wave rose analysis, it is found that waves hit the Kuakata beach angularly and eastward wave is most prominent, which generates longshore current from west to east. Simulated hydrodynamics of coupled wave-tide model are used in LITDRIFT model to estimate the rate of longshore sediment transport. It is found that overall net sediment transport occurs eastward of amount 5.94x105 m3/yr and 1.46x105 m3 is eroded for Lebur Char area and 2.36x105 m3 deposited in Kawar Char area per year, estimated by LITDRIFT model of LITPACK module under MIKE. Coastlines have been simulated by LITLINE model, which is calibrated and validated with the real filed data of coastline extracted from the satellite images of the year 2018 and 2016. LITLINE model has been simulated over the year 2010 to 2018 for erosion prone area of Kuakata. It is observed that coastline is moving towards land with time. Future caostline position is also simulated up to the year 2024. It is predicted that western part (Lebur Char area) of Kukata beach will further erode at a rate of 9.6 m/yr up to the year 2024.