Enhancing the Next Generation Water Resources Modeling Framework (NextGen) to Calculate Total Water Level in Coastal and Lake Environments

NOAA’s Office of Water Prediction (OWP) is developing the Next Generation Water Resources Modeling Framework (NextGen) with the goal of coupling coastal hydrodynamic, inland hydraulic, and hydrological models using the Basic Model Interface (BMI). The primary objective of developing NextGen is to increase flexibility in model selection and facilitate the deployment, testing, and scientific evaluation of different models through the use of data and model coupling standards.

Earlier versions of the NextGen Framework focused on modeling hydrological processes and it is now being enhanced to calculate total water level (TWL) in coastal and lake areas subject to compound flooding. Compound flooding arises from the interaction of significant freshwater and saltwater events, such as large discharge in streams, storm surge and high tide. Incorporation of compound flooding in the NextGen Framework is achieved through the coupling of coastal hydrodynamic models and inland hydraulic models in a more complete manner than implemented in version 3.0 of the National Water Model (NWM v3.0).

We identified the D-Flow Flexible Mesh (D-Flow FM) and the Semi-implicit Cross-scale Hydroscience Integrated System Model (SCHISM) coastal hydrodynamics models as candidates for calculating TWL in NextGen. Adding these coastal models to the system required developing BMI interfaces for both of them.

We coupled the SCHISM and D-Flow FM models to inland hydraulic models and applied them to calculate total water levels in Lake Champlain, Alaska and the Great Lakes model domains under selected extreme events. Great efforts were made to ensure that both models use similar bathymetry, roughness, horizontal mesh discretization and forcings.

Model results in terms of total water level are presented, discussed and compared against measurements. Overall, this study shows that both SCHISM and D-Flow FM exhibit skill in simulating TWL and that there was no significant difference in reproducing the measured water levels. Relative strengths and weaknesses of the SCHISM and D-Flow FM coastal models will also be discussed during the oral session, with emphasis on forecasting applications that are so important to NOAA NWS.