Authors: David Baude, Kehinde Ojansaya, Rebecca Diehl, Kristen Underwood, Ijaz Ul Haq, Beverley Wemple – University of Vermont; Juli Scamardo – Utah State University; Scott Lawson – Dewberry
Title: Classification of Optimal Channel Routing Method for Improved Streamflow Prediction
Presentation Type: Poster
Abstract: Floodplains can significantly attenuate floodwaters and minimize downstream impacts on infrastructure, riprarian habitat, and water quality. Yet, they are poorly represented in broad-scale flood routing models (i.e. National Water Model). The National Water Model currently utilizes the Muskingum-Cunge (MC) routing method, which does not adequately capture flood dynamics in some settings, such as those with floodplains. More complex representations of flood routing dynamics (e.g., diffusive of dynamic wave) are computationally expensive and thus, there is a need to identify the settings that require additional hydraulic process representation to accurately predict streamflow. We propose a scalable approach for the identification of appropriate model choice that relies on the classification of hydraulically-relevant river types, which have been previously shown to have distinct influences on flood routing. We assess if the simplified MC routing scheme currently used in the National Water Model is appropriate for six floodplain types, identified for the Lake Champlain Basin of Vermont, and for reaches determined to have minimal attenuation. We rely on a dimensionless diffusion coefficient calculated from the output of 1D HEC-RAS model scenarios for the seven reach types, for a range of different flood magnitudes (Q2-Q100) to discern appropriate wave type approximations for each type of setting. Our results suggest that the hydraulic classification approach can be used to distinguish the appropriate routing method. Where MC is sufficient the difference in attenuation estimated by the MC approach and by the dynamic wave is relatively small (average of 5%) compared to reaches for which a more complex routing approach is needed (average of 63%). For the 2,335 reaches classified as one of seven hydraulic settings in the Lake Champlain Basin, MC may be appropriate for 67% of them. For the remaining 33%, oversimplification of routing processes, may result in significant flood routing errors. The proposed approach highlights how classification based on hydraulic and geomorphic processes may be used to provide broad-scale model guidance in a relatively efficient way.