Improving bridge scour calculations using detailed 2D ...



Can Two-Dimensional Models be fast enough for Operational River Flood Forecast?

Reinaldo Garcia1, Pedro Restrepo2 Mike DeWeese2 Mark Ziemer2,Justin Palmer2, Jonathon Thornburg2, Pilar Garcia-Navarro3, Asier Lacasta3

1 Hydronia, LLC.Florida, USA

E-mail:rey@

Phone: (954) 251-7130

2 NOAA NWS NCRFC.

Chanhassen, MN, USA.

3Computational Hydraulics Group

University of Zaragoza. Spain.

One-dimensional (1D) models have traditionally been used for river flood prediction in large river reaches, mainly because they run fast due to the simplified flow equations used. However, in complex floodplains or where the flow is unconfined, 1D models may not provide an adequate solution due to the limitations of uniform water velocity and constant water surface elevation on each cross section. This warrants the use of more accurate two-dimensional (2D) models. However, the numerical solution of the 2D dynamic equations and the requirement of flexible meshes to resolve complex terrain characteristics, had made until recently 2D models considerably much more demanding in computer times than 1D models. Recent advances in massive parallelization techniques for 2D hydraulic models are able to reduce computer times by orders of magnitude making 2D applications competitive and practical for operational flood prediction in large river reaches. Moreover, high performance code development can take advantage of general purpose and inexpensive Graphical Processing Units (GPU), allowing to run 2D simulations more than 100 times faster than old generation 2D codes, in some cases.

This work describes the application of the RiverFlow2D GPU model to a 200-mile reach of the Red River in North Dakota and Minnesota and is a collaborative effort between NOAA and Hydronia to assess the accuracy and performance the RiverFlow2D model at the North Central River Forecast Center as a 2D operational model for river flood forecasting. Test runs so far indicate that routing a 40-day hydrograph using a one-million cell mesh can run in little more than than 2 hours on a NVIDIA GTX 780 2,304 GPU-core hardware. Ongoing efforts include tests on a more powerful NVIDIA TESLA K20 hardware, extension of the project to a 400-mile reach and refining the mesh to include all man-made features on the flood plain, such as levees, road embankments, bridges culverts, structures, etc. Results so far are promising and suggest that 2D GPU models such as RiverFlow2D will be able to achieve the performance required by NOAA operation models,

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