- Hydrodynamic modeling of flood detention reservoirs is an effective tool to evaluate reservoir performance, to plan modifications, and to design new reservoirs. The one-dimensional (1D) Saint Venant equations (SVE) are suitable to simulate the standing waves and other degenerations that occur in the reservoirs. The accuracy of these simulations depends on the Courant numbers used in the simulations. Consequently, the use of an appropriate time step for a specific grid size is crucial for the accuracy of the solution. A series of numerical experiments were performed and compared to observed data to develop time step criteria for solving the 1D SVE using the Abbott-Ionescu scheme. The time step was normalized by the wave celerity to make it problem dependent. The new time step criteria were evaluated on a different reservoir and proved to be adequate for selecting a time step for reservoir modeling. The criteria could readily be integrated in existing models to be used in an adaptive time stepping scheme. 2007 ASCE.