Dredging impact on water quality in Bomuruella Reservoir in Nuwara Eliya, Sri Lanka

The main objective of this study was to assess the difference of water quality of Bomuruwella reservoir before and after the dredging operations of the reservoir, which was carried out between June and September 2014. Water sampling was conducted from February to December 2014 on monthly basis at randomly selected 10 sampling locations. Dissolved oxygen (DO), pH, turbidity, electrical conductivity (EC), total dissolved solids (TDS), and salinity were determined in situ, and collected water samples were analyzed in accordance with the standard methods. All statistical analyses were performed using MINITAB 14 statistical software. Mean values of EC, DO, Turbidity, TSS, ammoniacal-nitrogen, nitrate-nitrogen, total hardness and Ca hardness, total discharge of nutrients increased while ortho-phosphate, nitrite-nitrogen, alkalinity, and chloride decreased after dredging operation. There were significant differences (p<0.05) between all the mean water quality parameters measured except for EC, BOD, and nitrite-nitrogen following the dredging. Also, the mean total discharge ammoniacal-nitrogen, nitrate-nitrogen, nitrite-nitrogen and orthophosphate before and after dredging period from sluice gate were 4,031.1 m³/day; 7,986.6 m³/day, 2,747.4 m³/day; 208.9 m³/day and 388,469.4 m³/day, 309,479.8 m³/day; 29,324.49 m³/day, 2,157.67 m³/day, respectively. In conclusion, dredging operation had impact on the water quality parameters in the reservoir, except chloride, alkalinity, ortho-phosphate, DO and nitrite, where they improved after dredging.