Journal of Applied Sciences1812-56541812-5662Asian Network for Scientific Information10.3923/jas.2009.3575.3580HormwichianR.KangrangA.LamomA.HormwichianR.KangrangA.LamomA.122009919Rule curves are guidelines for long term reservoir operation. An efficient optimization technique is required to find the optimal rule curves that can mitigate water shortage in long-term operation. A Conditional Genetic Algorithms (CGAs) connected with simulation model was proposed to search the optimal rule curves of reservoir. The proposed model was applied to determine the optimal rule curves of the Lampao Reservoir (in the Northeast Region of Thailand). The results showed that the pattern of the obtained rule curves similar to both existing rule curve and the rule curves of traditional Genetic Algorithms (GAs). The CGAs model provided optimal solution faster than the traditional GAs model. Then all obtained rule curves were used to simulate the Lampao reservoir system with the 500 samples of synthetic inflow. Furthermore, these results of the obtained rule curves were compared to the obtained rule curves of simulation model and the traditional GAs. The results indicated that the situations of water shortage and excess release water of using the rule curves of CGAs are smaller than the situations of using the existing rule curves.]]>Dooge, J.C.I.,2002Jain, S.K., M.K. Goel and P.K. Agarwal,1998Bellman, R.E.,1957Yakowitz, S.,1982Esogbue, O.A.,1989Chaleeraktrakoon, C. and A. Kangrang,2007Chang, F.J., J.S. Lai and L.S. Kao, 2003Chen, L.,2003Chang, F.J., L. Chen and L.C. Chang,2005Kangrang, A. and C. Chleeraktrakoon,2008Kangrang, A. and C. Chaleeraktrakoon,2007US Army Corps of Engineers,1974Chaleeraktrakoon, C.,1999