A Comparison of 1D Vs. 2D Hydraulic Models for a Coupled Model System in the Tar River and Pamlico Sound

The Coastal and Inland Flooding Observation and Warning (CI-FLOW) project is a multi-organizational, inter-disciplinary research and development effort focused on improving NOAA's monitoring and prediction of total water level within tidally influenced watersheds. The CI-FLOW system couples precipitation estimates, a hydrologic model ensemble, a storm surge model, and a wave model to obtain not only flood inundation extents, but also other information, such as significant wave heights. This system is utilized in the Tar-Pamlico and Neuse basins in North Carolina.

Currently, the CI-FLOW system uses the ADvanced CIRCulation (ADCIRC) storm surge model to simulate river flow in the Tar and the Neuse rivers as well as tidal, surge, and wave interactions. While this approach produces adequate results, simulating relatively small (10-30 m) rivers using a 2D storm surge model is computationally expensive. As a result, the geographic extent of the system is limited and it can only be run in a single, deterministic fashion. It may be possible to reduce the computational cost of the system while preserving accuracy by using a simpler, 1D model as middleware to forecast the storm response of each river.

This research investigates the benefits, drawbacks, and characteristics of using the Hydrologic Engineering Centers River Analysis System (HEC-RAS) as middleware between the hydrologic model and ADCIRC. High water marks and gauge data are used to quantify the differences between the HEC-RAS and ADCIRC solutions for the response of the Tar-Pamlico river basin to five test events. In addition, three variants of the ADCIRC grid are used to determine the sensitivity of the HEC-RAS solution to the ADCIRC resolution. The computational savings information for each model configuration is combined with the accuracy of each HEC-RAS solution to determine a rudimentary cost-benefit analysis for the use of HEC-RAS in place of finely resolved ADCIRC.

This study will improve the body of knowledge about each model's relative performance in riverine and estuarine areas. These results will inform and assist researchers and forecasters in selecting and developing similarly paired models for coastal river systems. As a result, more meaningful and accurate predictions can save lives and property in coastal, storm-sensitive riverine areas.