11-Lake water quality & budget of Durgamcheruvu Lake near Hitec city Hyderabad

Abstract

Durgamcheruvu watershed covering Durgamcheruvu and an area of about 14.85 sq. km. Durgamcheruvu, a head waters lake covers an area of about 50 ha (about 120 acres) and situated at about 550 m (amsl) to the north of old Hyderabad - Mumbai road near Gachibowli village. Urbanization in general and transformation of Madhapur into prestigious Hi-tech city has started showing their adverse effects on lake water quality. Lake water samples have been collected at 7 locations since October 2002 and analyzed for DO, COD, BOD, TP, TN concentrations. DO at a depth of 5 m in lake water seems to be less than the value at lake surface and the average DO in lake water is 4.9 mg/I. The lake water has shown BOD concentration ranging from 8 — 78 mg/I, whereas average BOD in the inlet channel is 40 mg/I and average BOD of lake water is < 25 mg/I with highest BOD concentrations reported during summer months. Trophic State Index has been computed using bimonthly measurements of Total Nitrogen and Total phosphorous concentrations of lake water and found that the lake has reached hyper- eutrophic condition. The computed groundwater balance in the watershed indicates that to some extent evaporation losses may be compensated by groundwater effluence of about 465 m3/day (0.46 MLD) to the lake, which is an insignificant one. Considering the lake water spread of about 50 ha and an average evaporation rate of about 4.5 mm/day, the lake would lose about 2.25 MLD through evaporation losses alone from the lake. For maintaining Full Tank Level (FTL) of the lake, there should be a balance between total inflows and outflows in the lake. The lake then would require inflow about 3.5 MLD considering enhanced seepage losses of 1.0 MLD for maintaining FTL in the lake. Conservatively the envisaged plan of establishing a Tertiary Sewage Treatment Plant (STP) of 5 MLD at Durgamcheruvu by HUDA seems to be initially satisfy the lake water budget