Aim of the present research is to find the best optimal daily management and operation policy of Dokan dam reservoir using Discrete Differential Dynamic Programming(DDDP) at minimum levels of inflow discharge during the period of 30 years for maximizing the hydropower generation (1965-1995). The results of this study were compared with previous results for an optimal monthly management and operation policy for the same reservoir and the same year. .
It has been found that the total annual hydroelectric generation power for the case under investigation is 1073 MW, ie, an increase of 93 MW from the monthly operation of 980 MW.
Also,it has been found that the number of trials to reach the optimal management ranged between 70and 90 trials in the daily operation, while the optimal management was observed in the case of monthly operation at were trialsfrom35to70. All results obtained for the daily optimal operation policy were good without neglecting any restrictions demanded taken in to consideration.

Key words: water resources, optimal management, hydroelectric power