In the tropical monsoon area, the existence of a reservoir ensuring water supply for the dry season by storing excess water during the wet season is indispensable for the practice of rice double cropping. Water management in an irrigation system with a reservoir should be functioning effectively from the water source to the terminal lots. The irrigation system ought to be operated so as to distribute timely the required irrigation water to the fields. Water saving attempt at the terminal level should contribute to the reduction of the dependence on reservoir water. Management of the conveyance and distribution system has a significant meaning in connecting the supply and demand organically. The time lag of water running in the system which is an important factor determining the loss of irrigation water in the system itself ought to be kept in mind all the time for the dam operation. In this paper, several aspects which ought to be considered for improving the management of irrigation systems with a
reservoir are discussed based on the studies which were carried out in the Muda Irrigation Scheme of Malaysia and the dry zone area of Sri Lanka.