Computation Method for Regulating Unsteady Flow in Open Channels

Unsteady flow problems in open channels can be classified as simulation‐ and operation‐type problems, according to the objectives of the study. The simulation problem is for predicting the discharge and water level in the channel during the future time series under given conditions. The operation problem, on the other hand, is for defining inflow at the upstream end of the channel or the operation schedule of controlling structures in order to get the desired outflow at the downstream end of the channel. In this paper, a finite difference computation method is derived for solving operation‐type problems in open channels. The method is explicit and numerically stable. It was applied to solve the St. Venant equations, discretized by the Preissmann scheme. The computation results were compared with the results obtained using the double‐sweep method, and there was good agreement between the two methods. The complete momentum equation was used in both methods. This computation method is called a backward‐operation method since it is for solving operation‐type problems, and the computation is performed backward both in space and time.