Influence of a fishing harbour on coastal geomorphology of the southwest coast of India and predictions of its future trends

Abstract

In the present study, we estimated the shoreline change along Ponnani Fishing Harbour (PFH), the coastal part of Malappuram, India, using the Digital Shoreline Analysis System (DSAS) version 5.0. We also assessed the land use and land cover (LULC) changes in the gateway of Ponnani Fishing Harbour (PFH) and its surrounds using Geographical Information System (GIS) and Remote Sensing (RS) techniques. LULC estimated that vegetation cover was more in 2004 than in 2020, supported by the values shown by VSB (Vegetation with Scattered Built-up) and BSV (Built-up with Scattered Vegetation) show a significant areal change in the study area. On the comparison of erosion and accretion in the two zones of the study area, erosional activities are dominant in Ponnani, which is in the southern part. Based on the Linear Regression Rate (LRR) values, the maximum erosion rate was -7.41 m/year at Ponnani. The southern sector is also undergoing a maximum accretion rate of 8.11 m/year in the Ponnani Harbour region. The End Point Rate (EPR) estimated similar trends of the highest erosion -43.24 m/year and highest accretion, 37.34 m/year rates in the southern sector. The Net Shoreline Movement (NSM) values demonstrate that the shoreline retreated by -285.9 m, and the shoreline accreted by 132.32 m at the Ponnani Harbour area over the last three decades. The Kalman filter model predicted that the shoreline at Ponnani and Puthuponnani beaches might experience further erosion of approximately a 100-metre shift by 2030. An increase in the erosion rate could erode another 140 m from the shoreline by 2040. The Ponnani and Puthuponnani beach extents must be considered high erosion risk zones in the perspective of the estimated results. This assessment indicates that the southern stretch of the area under the study of the PFH coastline is eroding. The significant changes in land use and land cover that have been seen over the past few years following the construction of PFH are expected to be the main cause of the severe loss of the coast in the southern part. The main reason for erosion in PFH would be construction operations that put pressure on the coastline side. The limited supply of sand used to replenish the coast naturally causes shoreline change due to the large drop in sediment load from the river, which is evident by the shrinking of the braided island size. The methods employed in this study and the results might help manage the PFH coast sustainably. The outcomes of this assessment suggest that similar studies should be conducted in other regions of India's western coastline to understand the shoreline evolution and develop a better coastal management strategy.