ONE- AND TWO-DIMENSIONAL COUPLING MODELING APPROACHES FOR FLOOD SIMULATIONS

The application of numerical models to calculate the inundation extent and exerted forces of flood events is critical in developing mitigation plans. One-dimensional (1D) models of open-channel flow are efficient for simulating in-channel hydrodynamics over long reaches and periods but cannot accurately predict overbank flows that require two-dimensional (2D) models. For rapid analysis of many different scenarios or to evaluate model uncertainty, a combination of 1D (in the channel) and 2D (on over-banks) open-channel flow computer models is preferred. This thesis presents the derivation and discussion of the behavior of the coupling terms for horizontal and vertical coupling of the governing equations of 1D and 2D flow. The coupling introduces transfer terms for mass and momentum. For both coupling methods and relatively high overbank flow depth, the advective momentum transfer exceeded the diffusive momentum transfer. The advective momentum transfer was one order of magnitude higher for the horizontal coupling approach than for the vertical coupling approach. This research compares vertical and horizontal coupling strategies of widely used 1D and 2D models to simulate flooding events. The study assesses the capability of both approaches to accurately model flooding events for an experiment of overbank flow in a meandering channel. The results showed that the horizontal coupling method yields inaccurate flow fields if the horizontal transfer of mass and momentum between floodplain flow and channel flow is inadequately accounted. The vertical coupling approach implicitly accounts for the lateral transfer between floodplain flow and channel flow and accounts for the vertical transfer of mass and momentum between overbank and in-bank flow. Finally, this work compares flooding results in Iquitos City, Peru, of a coupled 1D-2D HEC-RAS model against more traditional 2D HEC-RAS model. Although both models show similar flooding extension, the coupling 1D-2D model uses fewer elements in its discretization. Both models were able to predict flooding near critical infrastructure for the specified flow conditions. The incorporation of the climate change in the simulation shows higher flooding results in both models. The results show that flooding does not extend to the southwest areas of Iquitos city, making that zone safer for development