River Flux Boundary Considerations in a Coupled Hydrologic-Hydrodynamic Modeling System

Coupled hydrologic-hydrodynamic modeling of coastal inundation requires the exchange of river flow information between the hydrologic and hydrodynamic models. The hydrodynamic model ADCIRC has been used extensively to model hurricane storm surge-induced inundation, and has recently been dynamically coupled to the SWAN wave model. In previous applications, river inflows applied to ADCIRC were usually constant values representative of average flow rates during landfalling storm systems, whereas coupling to a hydrologic model allows for the use of time-varying discharge hydrographs throughout the event. This study examines several methods to apply discharge along a boundary that has a time-varying lateral extent. Results show confining non-zero normal flux values on the boundary to the main river nodes does not adversely impact mass conservation or distribution of flow across the river cross-sections, except immediately adjacent to the boundary. Adjacent to the boundary, higher flow rates are found through the main channel, at the expense of flow across the flood plains.