Modelling of Hydrodynamics and Salinity Characteristics in Chilika Lagoon

Abstract

Hydrodynamic circulation is a primary factor for most of the physical and ecological processes in lagoon environments. Chilika – Asia’s largest brackish water lagoon is experiencing signficant transformations such as siltation, the growth of invasive macrophytes, northward migration of mouth and choking of the outer channel. These transformations are responsible for the reduced salinity, reduced water depth and weak lagoon-sea interaction, which in turn has led to decline in water spread area, increase in vegetated area and decrease in fish productivity. Chilika Development Authority (CDA) has taken up various initiatives to maintain the lagoon environment including improvement of Chilika mouth. Modelling is a useful tool to understand the influx of tides, wind stress and impact of freshwater influx into the lagoon and to analyse the hydrodynamic processes based on ‘what if’ scenario. A two-dimensional hydrodynamic model has been setup to investigate the changes in the hydrodynamics and salinity regime of the lagoon during the pre (1999) and post (2009) hydrological intervention period as well as the present scenario (2015). The study suggests that post-intervention period has significantly improved the lagoon-sea fluxes, seawater ingress and flushing of flood waters. With the advance of freshwater discharge during monsoon and post-monsoon, the mean salinity levels increased from 2.87 to 4.87 psu during 1999–2009 period, and subsequently reduced to the 3.4 psu in 2015.With all forcing factors, the annual increase in the mean salinity distribution during 2009 is 36% which has reduced to 18% in 2015. The increases in salinity underpin enhancement in several wetland ecosystem services and livelihood benefits to communities living in and around the lagoon. Reduction in salinity in later periods points to the need to maintain the inlets and dredged channels for sustainable management of the lagoon ecosystem.