Natural opening of a new inlet in Chilika Lagoon: A cause and impact analysis

Abstract

Natural opening of inlet(s) is very common along the shorefront of Chilika Lagoon. Inlet openings in most of the cases have been triggered due to the narrow spit width and cyclonic storm/ depression (CS/D). Wave height and energy get further enhanced when the CS/D occurs concurrently with a full moon/ new moon with a lag/lead of 2–3 days. This has happened many times in the past. Recently, a new inlet was opened on 13th July 2022 due to deep depression (DD) over the northwestern Bay of Bengal from 09th to 12th July 2022. A cyclonic circulation prevailed over the northwest and adjoining west-central Bay of Bengal off the south Odisha-north Andhra Pradesh coast in lower and mid-tropospheric levels tilting southwestwards with height. Wave heights during the pre and post-inlet opening period spanning over one month suggest the peak wave condition coinciding with the period of the inlet opening. Geomorphological conditions of the spit before and after the inlet opening were monitored. Results indicate fast expansion of inlet width due to erosion of the spit on both sides of the inlet and the tidal incursion into the lagoon predominantly during the full-moon day/new moon day. After the opening of a narrow inlet of width 246 m on 13 July 2022, it was doubled within a month. Shoreline analysis using Sentinel 2A imagery for pre- and post-inlet opening was carried out and validated with observations. Oceanographic conditions near the new inlet were simulated and monitored by deploying a Seaguard RCM current meter with a pressure and temperature sensor. This study assessed the reasons for the inlet opening and monitored the geomorphological changes after the inlet opening. More importantly, the impact of the new inlet on lagoon ecosystem was assessed, which has severe implications for the management of the lagoon ecosystem.