The comparative study of flood modelling with the unsteady and the steady flow on Ngotok river

Abstract The Flood modeling in a river is usually modeled with the one-dimensional flow. The Flood is one form of unsteady flow that can be simulated with the HEC-RAS program. The unsteady flow modeling results often occur error due to unstable program analysis. The stability of the model is influenced by the river channel, the slope of the river bed and the cross-sectional of the river. In flood forecasting required by maximum discharge data and maximum flood elevation, then the steady flow model is often used as an alternative to the calculation of flood forecasting. This study aims to compare the advantages and disadvantages of flood modeling with a steady flow and unsteady flow. The location of study in Ngotok River, Mojokerto Regency, Indonesia. Hydrological modeling uses HEC-HMS and hydraulic modeling uses HEC-RAS. The resulting modeling shows that the water elevation profile of the steady flow model has a higher than the unsteady flow model. The time required for the simulation of the unsteady flow model is longer than the steady flow model. The average water level elevation produced by the unsteady flow model is +27.17 m while the steady flow model is +29.62 m.