Integrated Coastal-River-Urban Total Water Level Forecast System for
Tidal Rivers: Calibration, Validation, and Operational Evaluation
Abstract
Existing real-time coastal flooding guidance systems in the US tend to
underestimate total water level (TWL) predictions in upstream tidal
areas of the Chesapeake Bay rivers, impacting flood forecasts for highly
vulnerable areas, such as the National Capital Region. These
under-predictions are mostly due to missing physical processes, lack of
integration between hydrological and hydrodynamic models, and an
oversimplification of the model setups used to predict TWL. In this
study, an integrated TWL forecast system was introduced, where a
high-resolution two-dimensional coastal storm surge model (ADCIRC) was
implemented to simulate the combined influence of various flood drivers
(storm tide, river flows, urban runoff, and local wind forcing) in the
Potomac River. In this framework, the downstream boundaries of storm
tide predictions are provided by existing coastal guidance systems,
whereas, streamflow forecasts at upstream rivers and local urban runoff
are provided by the National Weather Service and the National Water
Model. Additionally, high-resolution wind fields from the North American
Mesoscale and the National Blend of Models are added to account for
local wind effects on TWL. This model setup was successfully validated
with a range of historical events and it also demonstrated improved
forecast performance against the existing large-scale coastal guidance
systems in a reforecast evaluation during 2020. Unlike other studies, we
provided a comprehensive evaluation on the influence of individual flood
drivers on TWL modeling and clearly demonstrated that the absence of one
or more flood drivers in the model framework can underestimate simulated
TWL in the National Capital Region.