INFLUENCE OF DAILY REGULATION RESERVOIR ON THE DOWNSTREAM WATERWAY

摘要

Daily regulation is popularly adopted to meet variation of power load in dam operation, which will lead to water level fluctuation within a day, usually called daily-regulation wave. In dry seasons, the wave associated with the notable extra water surface slope will bring apparent influence on the navigation channel. In traditional researches in navigational engineering, hydrograph of flow and sediment discharge is always simplified as a columnar section to reduce the load of calculation. A mathematical model of steady flow is usually adopted to analyze concerned flow indicators in the waterway. However, in the case of daily reservoir operation, the power load varies largely in a short time period; as a result daily-regulation waves will clearly alter the water slope and velocity to a certain extent. Such changes are difficult to be simulated and predicted with routine methods mentioned above, and should not be neglected. In view of this, a new approach to simulate the influence of daily-regulation waves with an unsteady flow model is proposed in this paper. The use of the approach for the Three Gorges Project is discussed. Unsteady flow triggered by the Three Gorges project power station daily regulation and its influence on downstream water level are analyzed. The results indicate that during the course of load increment,the water surface slope is steeper than the numerical result of a steady flow model; moreover, during the course of load reduction, the water surface slope is smoother than the result of the steady flow model. Thus, the variation of the downstream water surface slope caused by the unsteady flow is obvious, where special attention should be paid to avoid dangerous water surface slope that endangers normal navigation in the downstream waterway. At the same time, small discharge should be avoided to meet the required depth of navigable channel during the load reduction course.