5-Lake water budget of Mir-Alam-Tank, Hyderabad City

Abstract

Lake water budget study in Mir-Alam Tank has covered hydrological, geohydrological, geophysical and water quality analyses, lake water quality, trophic status, groundwater flow and mass transport modeling studies in the Mir Alam Tank Watershed. The granitic watershed covers about 18.5 sq. km. The Mir-Alam- Lake is formed on a third order stream. Surface water flow direction is from South to North. Bathymetric survey had been carried out during May 2003 indicated that between the islands 1 and 2 (range lines 10 to 17) in the lake, a submerged weir i.e. masonry retaining wall of about 0.6 m below the present water level on both sides of the island was noticed, which indicate that there may be an old anicut prior to formation of Mir-Alam tank. The water level noticed during May 2003 is +515.375 m with water spread area of 1.3806 M .sq.m. The volume of water estimated from capacity curve at the water level (RL 516.53 m) is 6.09576 MCM. Mir-Alam tank has a volume has been computed as 7.42516 MCM at the FTL + 517.4 m. Maximum depth of 9.6 m has been noticed in the tank ( +506.775 m (amsl)) during May 2003. If one assumes a total outflow of 25 MLD from the Mir Alam Tank, the residence time of lake-water would be 300 days(< year). The lake has lost about 700 ML capacity during last two decades due to encroachments. Flow measurements on inlet channels have shown an average total inflow of 8 MLD with maximum total inflow observed being 13 MLD. Lake water samples have been collected at 14 locations in the Mir Alam Tank and analyzed for major cations and anionic concentrations, trace element concentrations to assess their presence if any, in lake water. Pesticide residue analyses of lake water have been carried out during January 2004 for assessing persistence of organo-chlorine pesticide residues. Persistence of Endosulfan and metabolites of DDT suggest that a substantial agricultural runoff seems to be entering the lake. Trophic status index has been computed from Total nitrogen and total phosphorous concentrations indicate the hyper eutrophic condition. Katedan IDA established two decades back is catering to the industrial needs of textiles, metallic industries and battery manufacturing in the Mir Alam Watershed. The IDA is situated in the, recharge area of watershed and whatever effluent outflows from IDA may travel down the flow path and likely to contaminate groundwater in the watershed. Thus trace element analyses of groundwater samples indicated that except one or two places the concentration of Arsenic, Nickel was found slightly in elevated concentrations. The lake water budget has been computed through groundwater modeling of the watershed. Considering growing urbanization during near future, an STP of 10 MLD has been suggested for tertiary treatment of influent streams entering the lake.