Pipelines are widely used for the irrigation channels in Japan. The maintenance of the pipeline system is considerd to be easy because the daily water management is simple and the trash does not go into the pipeline. On the other hand, it is difficult to operate the pipeline system: the operator must perform laborious tasks in setting the amount of discharge, since the operation of one valve affects the discharge at the other valves. In this paper, the problems associated with water management will be outlined and the operation support system for the diversion valve by which the operator can determine the optimum value of valve opening will be introduced. The support system which was applied to the irrigation pipeline system in the N-district for the diversion valve operation was found to be useful for systematic valve operation.