Spatial Characterization of Flood Magnitudes over the Drainage Network of the Delaware River Basin

A framework to characterize the distribution of flood magnitudes over large river networks is developed using the Delaware River basin in the northeastern United States as a principal study region. Flood magnitudes are characterized by the flood index, which is defined as the ratio of the flood peak for a flood event to the historical 10-yr flood magnitude. Event flood peaks are computed continuously over the drainage network using a distributed hydrologic model, CUENCAS, with high-resolution radar rainfall fields as the principal forcing. The historical 10-yr flood is calculated based on scaling relationships between the 10-yr flood and drainage area. Summary statistics for characterizing the probability distribution and spatial correlation of flood magnitudes over the drainage network are developed based on the flood index. This framework is applied to four flood events in the Delaware River basin that reflect the principal flood-generating mechanisms in the eastern United States: landfalling tropical cyclones (Hurricane Ivan in September 2004 and Hurricane Irene in August 2011), late winter/early spring extratropical systems (April 2005), and warm season convective systems (June 2006). The framework can be utilized to characterize the spatial distribution of floods, most notably for floods caused by landfalling tropical cyclones, which play an important role in controlling the upper tail of flood peak magnitudes over much of the eastern United States.