HYMO flood routing

Abstract The Variable Travel Time (VTT) flood routing method was developed to account for the variation in travel time with stage and water-surface slope. The VTT method is suited for HYMO, a problem-oriented computer language for building hydrologic models because it requires little computer storage, routes both channel and floodplain flows, performs reliably under widely varied conditions, and gives consistent results over a wide range of routing intervals and reach lengths. Although the solution is iterative, the VTT method requires little computer time and is free of convergence problems often encountered in more complex routing methods. By accounting for the variation in water-surface slope, the VTT method yields results that are comparable to the accurate results obtained with an implicit solution of the unsteady flow equations of continuity and motion. Yet, the VTT method has the general applicability of storage methods. The use of the VTT method makes HYMO a useful and versatile model for water resources planning, water quality modeling, and hydrologic research.