Validation of ADCIRC Tide and Storm Surge Prediction Models with Embedded Open Channel Networks

In this presentation, validation of tide and storm surge prediction models with embedded intricate open channel networks is discussed. We have developed an enhancement to the ADCIRC hydrodynamic model so that open channel networks can be embedded in an unstructured mesh in a seamless and computationally efficient manner [1-3]. The enhancement consists of two techniques. One allows the topographic and bathymetric elevations in a computational mesh to have jumps and facilitates an efficient approximation of channel beds and banks. The other removes the constraint in time step selection due to the channel width. The combination of the two techniques enables modeling of channels with widths approaching zero without reducing a time step in an explicit time integration method. The focus of the work presented here is to validate the new approach in comparisons with observations. Intricate channel networks are embedded in our ADCIRC operational tide and storm surge prediction model that has high resolution along the coast of North Carolina. The widths of the embedded channels are as small as 5 m. Our approach to obtain the necessary data for the modeling such as channel center lines, widths and depths are also presented. The storms, such as Florence 2018 and Ian 202, that influenced water levels along the coasts of North Carolina are chosen to be simulated so that the new model is validated by the water level observations of tides and storm surges during the events. In some of the Florence simulations, river discharges are imposed as boundary conditions to consider the fluvial component of compound flooding. The discharge data are extracted from the USGS station observations and the National Water Model simulation outputs. The series of validations demonstrates practical applicability of the ADCIRC model with the open channel flow enhancement to produce high fidelity predictions considering finer scale interactions between channel flows and floodplain inundation.

[1] S. Bunya, R. Luettich and B. O. Blanton, “Enhancement of the ADCIRC Storm Surge Forecasting Model to Accommodate Smaller Rivers and Channels on Oceanic-Scale Grids”, The 102nd American Meteorological Society Annual Meeting, The 20th Symposium on the Coastal Environment, January 25, 2022.

[2] S. Bunya, R. Luettich, J. D. Ratcliff and B. O. Blanton, “Substantial Reduction of Computational Cost to Represent Open Channels in ADCIRC Tide and Storm Surge Prediction Model”, The 103nd American Meteorological Society Annual Meeting, J15A Impacts in the Coastal Environment Due to Climate Change, January 12, 2023.

[3] S. Bunya, R. A. Luettich, and B. O. Blanton, “Techniques to Embed Channels in Finite Element Shallow Water Equation Models”, Advances in Engineering Software, 185, 2023, 103516. https://doi.org/10.1016/j.advengsoft.2023.103516.