CHEMICAL AND GEOTECHNICAL PROBLEMS ASSOCIATED WITH THE TBILISI WATER STORAGE RESERVOIR, GEORGIA

The Tbilisi reservoir (Georgia) represents an important water supply for the city of Tbilisi, but has suffered considerable problems over the past 50 years. Initially the problems related to leakage of stored water via the schistose bedrock. It contains soluble gypsum and is highly sensitive to particulate removal by the process of suffusion. To some extent the leakage problems were ameliorated by the construction of vertical grout curtains but they have never been fully resolved. In recent times, an additional problem has appeared related to the inflow of saline groundwater from the bedrock host during times when reservoir levels are low. This groundwater locally contains as much as 16,000 mg/l total dissolved solids due primarily to gypsum dissolution. This release of groundwater to the reservoir has impaired reservoir water quality, increasing total dissolved solids from about 250 mg/l in 1988 to almost 500 mg/l in 2002. This has important implications for the long-term viability of the reservoir as a supply of potable water for the city.