A coarse-grid approach to representing building blockage effects in 2D urban flood modelling

Copyright © 2012 Elsevier. NOTICE: this is the author’s version of a work that was accepted for publication in Journal of Hydrology. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Hydrology, Vol. 426-427, pp. 1-16 (March 2012), DOI: 10.1016/j.jhydrol.2012.01.007The latest information and communications technology has enabled flood modelling in urban areas using high quality terrain data to simulate the detailed flow dynamics in local areas. However, the computational cost rises exponentially as the resolution goes finer. The advance of computing hardware is still a limiting factor for large-scale area or risk/uncertainty analysis modelling with fine resolution that describes the details of building features. Grid coarsening is the straightforward way to reduce the computing efforts for 2D flood modelling. The traditional approach to grid coarsening usually takes the average elevation of a fine grid as the new terrain model for the coarse grid. This approach often results in loss of information that introduces errors to modelling. In this study, the building features in coarse grids were abstracted using the building coverage ratio (BCR) and the conveyance reduction factor (CRF) parameters in a 2D model to simulate flooding in urban areas. The outcome of 2D case studies showed the proposed model can minimise the errors due to terrain averaging and provide a much better accuracy of modelling results at a marginally increased computing cost

Topography discretization techniques for Godunov-type shallow water numerical models: a comparative study

This paper compares various topography discretization approaches for Godunov-type shallow water numerical models. Many different approaches have emerged popular with Godunov-type water wave models. To date, literature lacks an investigative study distinguishing their pros and the cons, and assessing their reliability relating to issues of practical interest. To address this gap, this work reviews and assesses five standard topography discretization methods that consist of the Upwind, the surface gradient method (SGM), the mathematically balanced set of the SWE (Etta-SWE), the hydrostatic reconstruction technique (Hydr-Rec) and the RKDG2 model. The study further considers mix-mode approaches that incorporate wetting and drying together with the topography discretization. Steady and transient hydraulic tests are employed to measure the performance of the approaches relating to the issues of mesh size, topography’s differentiability, accuracy-order of the numerical scheme, and impact of wetting and drying

Two models solutions for the Douro Estuary: flood risk assessment and breakwater effects

Estuarine floods are one of the most harmful and complex extreme events occurring in coastal environments. To predict the associated effects, characterize areas of risk and promote population safety, numerical modelling is essential. This work performs a comparison and a combination of two 2-dimensional depth averaged estuarine models (based on openTELEMAC-MASCARET and Delft3D hydrodynamic software packages), to develop a two-model ensemble approach that will improve forecast robustness when compared to a one-model approach. The ensemble was applied to one of the main Portuguese estuaries, the Douro river estuary, to predict the expected water levels associated with extreme river discharges in the present-day configuration with the new breakwaters. This is a region that is periodically under heavy flooding, which entails economic losses and damage to protected landscape areas and hydraulic structures. Both models accurately simulated water levels and currents for tidal- and flood-dominated validation simulations, with correlation values close to 1, "RMSE" below 15%, small "Bias" and "Skill" coefficient close to 1. The two-model ensemble results revealed that the present-day estuarine mouth configuration will produce harsher effects for the riverine populations in case identical historical river floods take place. This is mainly due to the increase in the area and volume of the estuary?s sand spit related to the construction of the new breakwaters.This research was supported by the Research Line ECOSERVICES, integrated in the Structured Program of R&D&I INNOVMAR: Innovation and Sustainability in the Management and Exploitation of Marine Resources (NORTE-01-0145-FEDER-000035), funded by the Northern Regional Operational Programme (NORTE2020) through the European Regional Development Fund (ERDF), and by the Brazilian National Council for Scientific and Technological Development (CNPq) through a scholarship granted to the 2nd author (Process 200016 / 2014-8).info:eu-repo/semantics/publishedVersio