The quantity of water available is the most basic figure for any dam project. However, the amount of water actually available for the SSP continues to be debated hotly. Table 2 illustrates the existing controversy over this most basic figure : the amount of water actually available for use.

There is about 17 % less water in the river than planned for. The amount of water actually available for use at the dam site at 75 % dependability is only 22.69 MAF (Million Acre Feet) and not 27.22 MAF as assumed by the dam builders.

How did the project authorities fail to accurately measure this most basic quantity ? The Narmada Water Disputes Tribunal Award (NWDTA), on the basis of which the SSP was designed, used the amount of water available at the SSP dam site for 3 out of 4 years (called the 75 % dependabile yield) to apportion water between the states. When the award was made, actual flow data were available for only 22 years (1948-1969). The government estimated flow in the river using rainfall data from 1891-1947, a procedure known as hindcasting. The resulting combination of hindcasted and actual flow data led to an estimate of 27.22 MAF as the 75 % dependable yield (henceforth referred to as the yield).