Towards robust methods to couple lumped rainfall–runoff models and hydraulic models: A sensitivity analysis on the Illinois River

Accurate prediction of a flood inundation area constitutes an essential part of a flood forecasting system. When a river reach receives significant lateral inflows, flood inundation modelling requires the joint application of a hydrological model to calculate lateral inflows and a hydraulic model to calculate water levels along the river reach. In this study, we compared different strategies to couple the GR4J lumped rainfall–runoff model and the linearised diffusive wave propagation model. These strategies introduced variations in the nature of the connections between the two models using combinations of point and uniformly distributed lateral inflows. The coupled model was then applied to the Illinois River case study for which 10 years of hourly data were made available within the Distributed Model Intercomparison Project, now in phase 2. The simulations were assessed at the downstream end of the reach and at two interior points considered to be ungauged during the calibration process.