Salinity intrusion and seasonal water quality variations in the tidal canals of Cochin

Abstract

The study was carried out during the water year 2003-2004 on the 111aJor tidal canals of Greater Cochin. It had a multi-pronged approach with the following succinct objectives. (i) To identify salinity intrusion profile of each canal over a hydrologic year. (ii) To spell out the seasonal and possibly cyclic water quality variation of the surface waters of the canals and to find out the Water Quality Index of the fresh water segments of the canals where salinity does not cross economically meaningful levels. (iii) To identify the hierarchical utility of the water bodies and to identify management options to upgrade their quality and economic potentials. (iv). To carry out salinity and nutrient budget modeling on Chithrappuzha so as to have a better understanding of the fate of non-conservative components in the water body. Water samples were collected from sixteen selected tidal canals on a monthly basis with the sampling points fixed to be around 500 m apart. The parameters monitored were pH, temperature, alkalinity, conductivity, DO, COD, BaD, chloride, total hardness, calcium hardness, dissolved phosphate, nitrate, total iron, sulphate, turbidity, Total Coliform, and SUVA at 254 nm. A standard operating procedure (SOP) was prepared for the study. The tidal canals of Greater Cochin were found to be creeks extending to the interior, canals inter connecting parts of the estuary or canals with seasonally broken segments. Based on utility the canals could be classified as: 1. Canals heavily polluted and very saline 2. Canals polluted by urban waste but having fresh water for some part of the year 3. Canals having fresh water for most part of the year and not much polluted and 4. Fresh water bodies heavily polluted. During the rainy months carbon fixation by plankton is nonexistent, and during the dry months Chithrappuzha becomes a sink of phosphate. The study indicated abiotic subroutes for dissolved phosphate and revealed the potential pitfalls in LOICZ modeling exercise on sewage laden tidal canals. It was also found that all canals except for the canals of West Cochin and Chittoorpuzha have fresh water for some part of the year. The water quality index in the durable fresh water stretches was found to be of below average category.