Analysing the trend of beach–dune erosion in Digha coastal tract in response to nearshore wave processes and coastal protection structures

Abstract

Digha is one of the largest sea resorts in eastern India, facing a long history of erosion and has been engineered extensively since 1970s. It extends for 5.45 km along the Medinipur coast, which can be divided into three sectors viz. New Digha, Old Digha and Gangadharpur based on the beach character. The current study aims to identify the erosion–accretion trend of the coast and link it with the phases of construction of the coastal engineering structures in this zone, understanding the nearshore wave climate, and finally quantify the influence of these structures on the spatio-temporal variability of beach dynamics. Keeping these objectives in mind, DSAS was used to generate data on erosion–accretion regimes of the study area. A number of beach-profiles have been systematically surveyed during 2011–2019. The results show that between 1973 and 1998, the coastline at Old and New Digha retreated by about 200 m and 180 m, respectively, and were later constrained by the sea wall, while Gangadharpur suffered severe erosion (about 350 m) due to the impact of the refracted waves at the abrupt termination of the sea wall after Old Digha. Due to the low chance of energy dissipation , the beach at Old and New Digha has lowered drastically (average 3.50 m and 1.5 m respectively) and has largely moved away from the equilibrium condition. At Gangadharpur, the effect of the groyne in raising the beach elevation is jeopardised by a newly constructed wall in this sector, which has interrupted the process of beach–dune sediment exchange in this area.