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Time–Area method is one of the most widely applied techniques of watershed routing, and can be potentially used as a distributed model. In this paper, a fundamental flaw in the arrangement of subareas in the original time-area histogram is identified for one-dimensional flow. This is conducted on the basis of comparing time-area hydrograph with that of the kinematic wave theorem. Accordingly, a revised time-area algorithm is developed as a substitute for the original time-area. It is proved that in the revised approach, subareas must be reversely arranged. It is also shown that the revised time-area hydrograph is in perfect agreement with the hydrograph derived by the kinematics wave theory.