HOW MUCH WATER IS AVAILABLE ?
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.
75 % Dependable Yield of the Narmada
2 : Calculated from CWC 1992
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).