Environmental aspects and their effects on blackish water lagoon management and ecosystem sustainability: A case study of Chilika Lagoon, India

The geomorphology, hydrodynamics, and ecological balance of blackish water lagoons are significantly shaped by environmental factors like wave action, tidal currents, longshore drift, and relative sea level rise. These factors also have a direct impact on the management and long-term sustainability of these lagoons. This study looks at shoreline dynamics and related environmental effects in the Chilika Lagoon in India as a representative case. Natural episodic events like waves, tides, currents, and global sea level rise are all responsible for the Chilika Lagoon's dynamic coastal environment's constant reshaping. This study specifically examines shoreline lateral displacement, recognising that volumetric sediment changes are not captured by this method. Because of the high-energy interactions between wave action, tidal currents, and longshore drift along the coastal front, lateral movement of the shoreline can result in either accretion or erosion. This study evaluates the shoreline configuration changes of Chilika Lagoon and surrounding coastal areas over a 42-year period using the Digital Shoreline Analysis System (DSAS) of the U.S. Geological Survey. The analysis shows that, with some notable exceptions in certain depositional zones like Palibandha, the western flank of the new mouth inlet, the section from the old mouth to Harchandi Temple, and the stretch from Pentukota to Konark beach, the majority of the region shows net erosional trends. Shoreline retreat can reach 40.29 meters in the northeastern lagoon sector, which is closest to the present new mouth and shows the highest rates of erosion. A secondary line of barrier bars is now visible due to the frontal barrier spit breaching, which is the cause of this erosion. At the Rushikulya River's mouth, a comparable erosional pattern is visible. However, with a maximum advancement of 11.69 meters, the western side of the new mouth inlet exhibits notable accretion. The dynamic behaviors of the lagoonal inlets affects these morphological changes, with longshore drift and wave energy concentration becoming more dominant due to the Rushikulya River's reduced sediment supply. The foreshores of the Chilika Sand Spits and the Puri township coast exhibit moderate shoreline changes. These are mostly caused by high water levels during the monsoon season and wave breakers created by seasonal winds. Coastal retreat and sediment loss have been made worse by the lack of notable post-event recovery after the effects of cyclones Phailin and Hudhud. Gornitz et al. (1994) developed the Coastal Vulnerability Index (CVI) method to measure coastal vulnerability. This method incorporates a number of factors, such as shoreline change rate, mean tidal range, mean wave height, slope, relative sea level rise, and coastal geomorphology. Relative sea level rise stands out as the most important factor influencing vulnerability among these. A relative sea level rise of roughly 0.77 mm/year is indicated by data from the Paradip station (NOAA-PSMSL, 2015). The study area's CVI values, which are based on these parameters, show notable spatial variability in coastal risk throughout the Chilika region, ranging from 2.64 (very low vulnerability) to 21.45 (high vulnerability).