Variation of constituent loads and concentrations with the flow in Gin river, Sri Lanka

This study was aimed at establishing a detailed understanding on the prevailing constituent loads and concentrations in the Gin river flow at Baddegama, and to reveal how they are related to the river flow. Concentrations and constituent loads in the Gin river at Baddegama (6°11’23” N, 80°11’53” E) during 2001 - 2009 were modelled in the study using load-discharge rating curve for estimating constituent loads in rivers. Constituents considered in the study included chloride, total alkalinity, total residue, total hardness, calcium and total iron. For each constituent, the samples tested generally at monthly frequency during 2001 - 2009 at Baddegama were used in conjunction with the observed daily stream flow data to develop and calibrate a multiple regression model.

The regression models developed for all constituent loads showed higher coefficients of determination values reflecting a strong relationship between the estimated rating curve and measured constituent loads. The estimated constituent loads had substantial temporal variation and generally peaked in May and October, coinciding with high flows. Load estimates of chloride, total alkalinity, total hardness, and calcium indicated statistically significant downward temporal trends. For the total residue, a statistically significant upward trend was indicated. Concentrations of chloride, total alkalinity, total residue, total hardness, and calcium were well below the highest desirable levels of specifications cited in the Sri Lanka Standards for potable water. However the concentration of total iron, which ranged between 0.8 mg/L and 4.8 mg/L significantly exceeded the highest desirable limit for potable water and the maximum permissible limit for inland waters of Sri Lanka.