Abstract
Abstract. LISFLOOD-FP 8.0 includes second-order discontinuous Galerkin (DG2) and first-order finite-volume (FV1) solvers of the two-dimensional shallow-water equations for modelling a wide range of flows, including rapidly propagating, supercritical flows, shock waves or flows over very smooth surfaces. The solvers are parallelised on multi-core CPU and Nvidia GPU architectures and run existing LISFLOOD-FP modelling scenarios without modification. These new, fully two-dimensional solvers are available alongside the existing local inertia solver (called ACC), which is optimised for multi-core CPUs and integrates with the LISFLOOD-FP sub-grid channel model. The predictive capabilities and computational scalability of the new DG2 and FV1 solvers are studied for two Environment Agency benchmark tests and a real-world fluvial flood simulation driven by rainfall across a 2500 km2 catchment. DG2's second-order-accurate, piecewise-planar representation of topography and flow variables enables predictions on coarse grids that are competitive with FV1 and ACC predictions on 2–4 times finer grids, particularly where river channels are wider than half the grid spacing. Despite the simplified formulation of the local inertia solver, ACC is shown to be spatially second-order-accurate and yields predictions that are close to DG2. The DG2-CPU and FV1-CPU solvers achieve near-optimal scalability up to 16 CPU cores and achieve greater efficiency on grids with fewer than 0.1 million elements. The DG2-GPU and FV1-GPU solvers are most efficient on grids with more than 1 million elements, where the GPU solvers are 2.5–4 times faster than the corresponding 16-core CPU solvers. LISFLOOD-FP 8.0 therefore marks a new step towards operational DG2 flood inundation modelling at the catchment scale. LISFLOOD-FP 8.0 is freely available under the GPL v3 license, with additional documentation and case studies at https://www.seamlesswave.com/LISFLOOD8.0 (last access: 2 June 2021).
Highlights
LISFLOOD-FP is a freely available raster-based hydrodynamic model that has been applied in numerous studies from small-scale (Sampson et al, 2012) and reach-scale (Liu et al, 2019; Shustikova et al, 2019; O’Loughlin et al, 2020) to continental and global flood forecasting applications (Wing et al, 2020; Sampson et al, 2015)
While this friction scheme has been successfully adopted in finite-volume and discontinuous Galerkin settings for modelling dam break flows and urban flood events (Wang et al, 2011; Kesserwani and Wang, 2014), it can exhibit spuriously large velocities and correspondingly small time steps for large-scale, rainfall-induced overland flows, involving widespread, very thin water layers flowing down hill slopes and over steep riverbanks, as demonstrated by Xia et al (2017)
This paper presented new second-order discontinuous Galerkin (LISFLOOD-DG2) and first-order finite-volume (LISFLOOD-FV1) solvers that are parallelised for multicore CPU and Nvidia GPU architectures
Summary
LISFLOOD-FP is a freely available raster-based hydrodynamic model that has been applied in numerous studies from small-scale (Sampson et al, 2012) and reach-scale (Liu et al, 2019; Shustikova et al, 2019; O’Loughlin et al, 2020) to continental and global flood forecasting applications (Wing et al, 2020; Sampson et al, 2015). J. Shaw et al.: LISFLOOD-FP 8.0: the new discontinuous Galerkin shallow-water solver varying, subcritical flow over sufficiently rough surfaces with Manning’s coefficient of at least 0.03 sm−1/3 (Neal et al, 2012b; de Almeida and Bates, 2013). The final case reproduces fluvial flooding over the 2500 km Eden catchment in north-west England, caused by Storm Desmond in December 2015 (Xia et al, 2019) This is the first assessment of a DG2 hydrodynamic model in simulating a real-world storm event at catchment scale, with overland flow driven entirely by spatially and temporally varying rainfall data.
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