TY - BOOK

T1 - A Sub-model Approach for fast large-scale high resolution two-dimensional urban flood modelling

AU - Zhao, Guohan

PY - 2020

Y1 - 2020

N2 - Flood threats towards urban areas are escalating due to climate change, which increases the frequency of extreme rainfall events, and due to the growth of sealed surfaces caused by urbanisation. One-dimensional (1D) hydrodynamic and two-dimensional (2D) hydrodynamic urban flood models are used worldwide to better understand how the flood risk can be reduced at an acceptable level. 2D models are preferred over 1D models due to higher simulation accuracy, but this benefit comes at a computational expense that hinders the use of 2D models for real-time, high-resolution and large-scale modelling. To optimise the computational efficiency of 2D models, this PhD study developed a sub-model approach to rapidly identifying the relevant areas that may cause flooding of the targeted object (e.g. infrastructures in a city or in a specific district, or a single building), excluding the irrelevant areas (i.e. 2D model grids), and thus resulting in a significantly reduced number of computational cells and hence a much faster computation. The tailor-made sub-models for fast simulations are obtained through the following programming steps: i) computationally important sinks are identified from basin-wide detected sinks by referring a Volume Ratio Sink Screening, while accumulated effects of volume losses from eliminated sinks are still controlled; ii) the drainage basin area is discretized into a collection of sub-impact zones based on the spatial distribution of important sinks, and a 1D surface network is delineated accordingly; iii) the link-based fast-inundation algorithm is programmed for fast computation of the basin-wide flow conditions using 1D static routing; iv) according to the target objects, relevant sub-impact zones are identified by tracing 1D flow conditions; v) the critical computational cells for a 2D hydrodynamic model can be extracted based on these identified sub-impact zones, suggesting the reduced domain as well as the optimized boundary condition for model configuration. The suggested method was validated by five model experiments, using MIKE FLOOD as a reference for full 2D hydrodynamic models. The results revealed that the sub-model approach yields comparably accurate results (flood extents, depths and flow velocities) while offering a significantly improved computational efficiency with robust performance, compared to the modelling for the full basin. The sub-model approach identifies a promising solution to the realization of real-time applications of high-resolution 2D urban flood models at a large scale. Future research for implementation in real-time forecasting system including real-time weather radar monitoring, parallel computing, adaptive-grids, enhanced 1D network representations is recommended for future research.

AB - Flood threats towards urban areas are escalating due to climate change, which increases the frequency of extreme rainfall events, and due to the growth of sealed surfaces caused by urbanisation. One-dimensional (1D) hydrodynamic and two-dimensional (2D) hydrodynamic urban flood models are used worldwide to better understand how the flood risk can be reduced at an acceptable level. 2D models are preferred over 1D models due to higher simulation accuracy, but this benefit comes at a computational expense that hinders the use of 2D models for real-time, high-resolution and large-scale modelling. To optimise the computational efficiency of 2D models, this PhD study developed a sub-model approach to rapidly identifying the relevant areas that may cause flooding of the targeted object (e.g. infrastructures in a city or in a specific district, or a single building), excluding the irrelevant areas (i.e. 2D model grids), and thus resulting in a significantly reduced number of computational cells and hence a much faster computation. The tailor-made sub-models for fast simulations are obtained through the following programming steps: i) computationally important sinks are identified from basin-wide detected sinks by referring a Volume Ratio Sink Screening, while accumulated effects of volume losses from eliminated sinks are still controlled; ii) the drainage basin area is discretized into a collection of sub-impact zones based on the spatial distribution of important sinks, and a 1D surface network is delineated accordingly; iii) the link-based fast-inundation algorithm is programmed for fast computation of the basin-wide flow conditions using 1D static routing; iv) according to the target objects, relevant sub-impact zones are identified by tracing 1D flow conditions; v) the critical computational cells for a 2D hydrodynamic model can be extracted based on these identified sub-impact zones, suggesting the reduced domain as well as the optimized boundary condition for model configuration. The suggested method was validated by five model experiments, using MIKE FLOOD as a reference for full 2D hydrodynamic models. The results revealed that the sub-model approach yields comparably accurate results (flood extents, depths and flow velocities) while offering a significantly improved computational efficiency with robust performance, compared to the modelling for the full basin. The sub-model approach identifies a promising solution to the realization of real-time applications of high-resolution 2D urban flood models at a large scale. Future research for implementation in real-time forecasting system including real-time weather radar monitoring, parallel computing, adaptive-grids, enhanced 1D network representations is recommended for future research.

M3 - Ph.D. thesis

BT - A Sub-model Approach for fast large-scale high resolution two-dimensional urban flood modelling

PB - Department of Geosciences and Natural Resource Management, Faculty of Science, University of Copenhagen

ER -