Recent Advances in Channel Routing for River Networks for the Next Generation National Water Model

The core modeling component of the current operational National Water Model (NWM) is the Water Research and Forecasting Hydrological model (WRF-Hydro), supported by the National Center for Atmospheric Research (NCAR). WRF-Hydro computes water movement across land surfaces, subsurface areas, stream channels, reservoirs, and lakes. With the planned implementation of the National Water Model (NWM) using the Next Generation Water Resources Modeling Framework (NextGen), a Tree-Based Channel Routing (T-Route) model will replace the routing functions of WRF-Hydro including streamflow and reservoir outflow data assimilation. T-Route is a dendritic channel routing framework that simulates processes such as 1-D channel routing within the entire network as well as reservoir routing. Utilizing parallel computing on independent sub-channel networks, it is applicable at various scales, from small catchments to continental domains, to simulate observed and forecasted streamflow, lake and reservoir outflow, and/or water depth. Recent enhancements to T-Route include the ability to ingest output data from multiple coastal-estuary models, integrating water depth into user-defined locations for downstream boundary conditions required by hydraulic routing methods. Additionally, T-Route now supports the ingestion of both synthetic and natural channel cross-section data for its channel routing modules. The diffusive wave kernel of T-Route particularly benefits from using natural cross-section data, such as the CONUS-wide available Digital Elevation Model (DEM) based data, by enhancing routing accuracy. This capability facilitates the seamless integration of advanced channel routing methods that require accurate representation of channel cross-sections. Furthermore, T-Route implements hybrid channel routing, enabling the exchange of fluxes among different channel routing models during runtime. This includes facilitating exchanges of fluxes between channels and reservoirs, potentially allowing T-Route to enable any size and location of channel sub-networks to selectively choose advanced channel routing methods for accurate streamflow information during specific storm events. Additionally, T-Route is fully compatible with the NextGen hydrofabric, making it agnostic to the hydrofabrics of any version of the NWM. Mainly by combining smaller stream segments into larger ones, the NextGen hydrofabric has demonstrated signifcantly enhanced computational efficiency and accuracy for channel routing compared to previous versions of the NWM hydrofabric. A detailed discussion of these enhancements, including test domains, forcing data, and results, will be presented.