Water Management in a reservoir, among others, calls for a fairly accurate assessment of the capacity of the reservoir to store water at various levels. Tungabhadra Reservoir with a drainage area of 28,180 sq.km was designed for storing 133 TMCft. of water and was impounded for the first time in the year 1953. The full reservoir level (FRL) was fixed at RL 1633 ft. Capacity of the Reservoir at various levels was worked out based on the regular contour survey conducted in the river basin upstream of the Dam prior to the impounding of water in the reservoir. The survey was conducted with a contour interval of 10 ft and the capacity of the reservoir computed for every one-foot interval. According to this the Gross capacity of Tungabhadra Reservoir was taken to be 133.0 TMCft., (3766.1 M.cum) at an FRL of 1633 ft. (497.738M).
The River Tungabhadra derives its name from two streams viz., the Tunga, about 147 km (91.6 miles) long and the Bhadra, about 178 Km (110.9 miles) long which rise in the Western Ghats. The river after the influence of the two streams near Shimoga, runs for about 531 Km (330 miles) till it joins the river Krishna at Sangamaleshwaram in Andhra Pradesh. It runs for 382 Km (237 miles) in Karnataka, forms the boundary between Karnataka and Andhra Pradesh for 58 Km (36 miles) and further runs for the next 91 Km (57 miles) in Andhra Pradesh. The total catchment area of the river is 69,552 Sq Km (26,856 Sq miles) up to its confluence with Krishna and it is 28,177 Sq Km (10,880 Sq miles) up to Tungabhadra Dam. It is influenced chiefly by the South-West monsoon. It is a perennial river but the summer flows dwindle to as low as 2.83 to 1.42 cumec (100 to 50 cusec).