Comparison of scenarios with and without bridges and analysis of backwater effect in 1-D and 2-D river flood modeling

In this paper the impact induced by bridges on the river flow is studied applying 1-D and 2-D unsteady flow models. Both the models are based on the Shallow Water Equations written in conservative form and solved with first order upwind schemes. In particular, the effect of bridges on the flow behavior simulated by the models is discussed from a practical point of view, with reference to the longitudinal and cross-section water surface profiles. Two cases characterized by bridges perpendicular to the principle flow direction are presented. The bridges are located in almost rectilinear river reaches whose cross-sections are confined by vertical artificial walls. Therefore, these cases represent typical situations for which 1-D approaches should be recommended. However, analysis of such results highlights two-dimensional features of the river flow that might influence the flood hazard assessment.