Central Water and Power Research Station, Water Quality Analysis and Modeling Division, India
Online published on 12 January, 2015.
Freshwater is fundamental for all life because water is finite in quantity. Natural and artificial reservoirs contain more than 90% of liquid freshwater on our planet's surface. The lakes provide the greatest range of ecosystem services to humanity. These are generally interlinked with other lake, river, groundwater or coastal water systems. The hydrologic linkages between lotic (flowing) and lentic (pooled) water systems influence the availability and nature of all water systems.
‘Access to safe and sufficient water and sanitation are the basic needs and are essential to health, well being and empowerment of people’ this fact was stressed in The Hague conference at the break of new millennium. In India, reservoirs are the most easily accessible freshwater source and are also prone to pollution. It is observed that water pollution is initially noticed near outfall; spreads over the whole reservoir and further to down-stream areas. Thus, preserving the water quality in reservoir would ensure the good quality in the river stretches down-stream of dam.
The ever increasing capabilities of computers to simulate the spatial and temporal evolution of systems have lead to identification of hydrodynamic and water quality simulation model as an essential tool in management and planning for sustainable use of the reservoirs.
Application of the above aspects in 2D simulation of a large reservoir in Gujarat state is presented. The studies highlight a number of combinations of runs to decide the location in each of three different zones namely (1) Lacustrine Zone (2) Transitional Zone and (3) Riverine Zone of the reservoir and concentration of a pollutant load in terms of BOD to be let out in reservoir that would lead to minimum damage to ambient water quality. Threshold value of a pollutant load of BOD 200 mg/l is derived for use, satisfying Class A and B criteria of CPCB. Higher concentrations would lead to deterioration of water quality under Class D as well as for fisheries and wildlife propagation.
It was found that spatial variation of pollution load has a significant effect on the resultant BOD and DO concentrations in the reservoir. It was observed that keeping pollution source in Riverine Zone and Transitional Zone yielded almost same results, where as keeping the source in Lacustrine Zone improved the resultant quality of water with respect to DO. Hence this zone for outfall is preferred for survival of fish. Present study would be helpful in designing the strategy of pollution control.
