‘Strategic placement of effluent discharge points can leverage natural filtering capabilities’
Abdul Wahab Khan
Panaji : A new mathematical model offers a glimmer of hope in managing pollution in the Mandovi river estuary. A study has demonstrated how strategic placement of effluent discharge points can leverage the estuary’s natural filtering capabilities.
The model considers both the movement of contaminants downstream through freshwater discharge and upstream through tidal exchange processes.
The analysis of the Mandovi estuary has revealed dramatic seasonal transformations that affect its filtering capacity. During the monsoon, the estuary undergoes significant changes in salinity and flow patterns.
The study has noted that “the vertical variation in salinity undergoes marked changes from season to season,” with differences ranging from negligible during pre-monsoon to about 20 parts per thousand during monsoon periods.
The research, published in the International Research Journal on Advanced Engineering and Management, was conducted by Dr Mangirish Varadkar, Associate Professor of Mathematics at Indira Priyadarshini Government Degree College for Women in Hyderabad.
“An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it and with a free connection to the open sea,” explains Dr Varadkar in the May 2024 publication.
“These freshwater estuaries also provide many of the ecosystem services and functions that brackish estuaries do, such as serving as natural filters for runoff,” he says.
The model’s innovation lies in its comprehensive approach to understanding tidal influences, seasonal variations, and the physics of water movement.
By incorporating factors such as the “equation of continuity and the equation of motion,” the research has established a framework for predicting how contaminants behave under various discharge scenarios.
The Mandovi estuary, which experiences dramatic seasonal changes during monsoon periods, serves as an ideal testing ground for the model. During the dry season, the estuary is vertically mixed with tidal influences dominating up to 45 km upstream. However, during the monsoon, the estuary undergoes significant transformation.
“During the wet spell of monsoon, the runoff in the estuary increases rapidly. As a result, the estuary dilutes about 75 per cent of its salt approximately in two months,” the research has noted, citing earlier studies by Shetye and Murthy.
The study’s numerical model examines two scenarios: pollutants discharged far upstream at the estuary’s head and pollutants introduced closer to the mouth. Results clearly showed reduced peak concentrations when discharge locations were optimised.
Through mathematical modelling, the research has determined that “the most feasible discharge location during high tide is the midpoint of the estuary i.e. 35 km upstream when the penetration is 65 km.”
This strategic positioning maximises the estuary’s natural filtering capacity before pollutants can reach more sensitive coastal waters.
The modelling approach examines multiple scenarios, finding that “the peak concentration reduces everywhere along the distance if the location of input source is moved towards the mouth.” This insight provides practical guidance for wastewater management in the region.
The research gas addressed a growing environmental concern, as “the most serious problem facing the estuary is its pollution.”
With increased industrial and domestic waste entering coastal systems, scientific approaches to pollution management have become essential for preserving these ecosystems.