In this study the results of optimal water supply analysis by operating constraints of reservoirs during drought period are as follows. During drought period, water supply reliability is possible about 97~61% by CASE 1~CASE 5. Water supply reliability is possible about 97.3% in case of the Andong dam and 87.7% in case of the Imha dam by CASE 3. Also, under the constraints of CASE 4, water supply reliability is possible about 87.5% in case of the Andong dam and 73.3% in case of the Imha dam. The reason what low of available water supply ratio is decreased inflow of Imha dam. When compare standard deviation of average storage with standard deviation of storage, stable storage can be secured during successive drought period. And it also can minimize shortage of water during drought. therefore, it is impossible that reservoir supply sufficient water but change of operating condition is better than pervious on that followed by full reservoir level.
It is need that the study for optimal water supply during drought period has to be continued.

• 이순탁(영남대학교 토목도시환경공학부) | Soon-Tak Lee
• 박기범(영남대학교 토목도시환경공학부) | Ki-Bum Park Corresponding Author