Development and application of dissolved oxygen ( DO ) and biological oxygen demand ( BOD ) model for P anshet and U jjani R eservoirs, M aharashtra, I ndia

Abstract

A model of dissolved oxygen (DO) and biological oxygen demand (BOD) was developed to assess the water quality of Panshet and Ujjani Reservoir in Maharashtra, India, to ascertain if their water was suitable for various beneficial and designated uses. The model was calibrated with observed data from these two reservoirs. Seasonal water quality variations were studied during 2010–2011 The pH of Panshet Reservoir water is almost neutral, whereas Ujjani Reservoir is marginally alkaline. A rapid decrease in DO with depth during the summer appeared to be a common phenomenon for both reservoirs. Although the mean phosphate concentrations of both reservoirs were comparable, biological growth was much higher in Ujjani Reservoir, being attributed to a higher dissolved salt concentration in Ujjani Reservoir. The nitrate (NO3−) concentrations in both reservoirs remained within a range close to the global average for unpolluted freshwater. Sewage contamination appears to be a major problem for Ujjani Reservoir, especially as it relates to domestic water uses. A two-layer, two-dimensional mathematical model also was developed to assess reservoir water quality. An explicit, second-order-accuracy finite-volume technique was used to solve two-dimensional shallow water equations. The governing equations were solved with a Mac Cormack predictor–corrector scheme. The Reynolds turbulence terms were modelled with a sub-grid-scale (SGS) model, using a large eddy simulation (LES) approach. An empirical relationship developed by Street and Phelps describing liquid–air phase demand and natural re-aeration was used to determine water quality parameters. The model was validated with numerical results from the literature. The field investigations were satisfactorily applied for the simulation of hydrodynamics and the prediction of DO and BOD in Panshet and Ujjani Reservoir.