A new model is developed for a cascade of four hydropower reservoirs operation. The aim is to improve the total power generation from the system. Daily data of reservoir level, release and power generated which varies from 4-20 years are used for analysis. Long-term data of reservoir level and inflow are used to determine the critical period. The critical period is classified into four seasons; these are filling, depleting, upper and lower level operating season. Mathematical models are used to rank the refill and the deplete order of the reservoirs. A new rule models are presented using the results of refill and depletion ranks. Power generation using the developed model is compared to the long-term historical generated; and it is found that the new rule model boost the daily power production by 5.3 and the plant factor by 2. © (2012) Trans Tech Publications, Switzerland.