Author(s): Marcos Sanz-Ramos; Alejandro Lopez-Nunez; Luis Cea; Ernest Blade

Linked Author(s): Marcos Sanz Ramos

Keywords: Numerical modelling; Shallow water equations; Pressurized flow; Two-Component Pressure Approach (TPA); Preissmann Slot Method (PSM)

Abstract: Two-dimensional (2D) hydraulic models solve the Shallow Water Equations (SWE) for the simulation of free surface flows in rivers and estuaries. The necessity of considering in the calculations specific hydraulic structures, such as channels, gates, weirs, etc., besides bridges and culverts for representing more realistic flood scenarios, imply the implementation in the 2D-SWE of empirical equations that represent the flow through these structures. These empirical equations are usually implemented as internal conditions over a 1D line, modifying the equations with which the flow is calculated in the edges of the mesh elements located at both sides of the line. This approach can be good enough for representing the hydraulic behaviour in general, i.e. generating for example an increase of the water elevation upstream of the hydraulic structure, bridge or culvert when its hydraulic capacity is overtopped. However, this 1D condition over a line, which only affects the element edges, is not a good approximation for simulating the hydrodynamics of pressurized flows, as it is the case of culverts, very wide bridges and lids over channelized rivers. Aiming to provide new modelling strategies for simulating pressurized flows using the 2D-SWE, the Two-Component Pressure Approach method (TPA) and the Preissmann Slot Method (PSM) have been implemented into the 2D numerical model Iber (www.iberaula.com). The TPA method overcomes the problem of the artificial free surface flow regeneration by considering the total pressure as the sum of two components, a hydrostatic pressure and a dynamic pressure. On the other hand, the PSM is a one-equation model that consists of adding a hypothetical, indefinitely extended slot to the crown of the conduit. Both numerical strategies were compared through two real cases study . One of them is the coverage of a channelled river characterized by several abrupt curvature changes and a contraction/expansion of their wide. The limited hydraulic capacity of the channelling, besides the cross-waves generated by the changes on the channel curvature and width, produces pressurized flow conditions. The other case study consists of a bridge located in a river reach that obstructs most of the floodplain. The discharge capacity of the bridge is conditioned by the bridge abutment and a relatively small culvert located under this abutment. The location and geometry of the bridge, plus its limited hydraulic capacity during extreme flow scenarios, generate a partial pressurized flow at its upstream part. The TPA and PSM methods are presented as good numerical approaches for simulating pressurized flow for 2D-SWE-based models. In general, both methods fine-tune the hydraulic behaviour, and are able to represent the most critical regions when a pressurized flow is generated in hydraulic structures, lids, bridges and culverts.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022447

Year: 2022