Spatial Characterization of Flood Magnitudes from Hurricane Irene (2011) over Delaware River Basin

Flooding from landfalling tropical cyclones can affect drainage networks over a large range of basin scales. We develop a method to characterize the spatial distribution of flood magnitudes continuously over a drainage network, with focus on flooding from landfalling tropical cyclones. We use hydrologic modeling to translate precipitation fields into a continuous representation of flood peaks over the drainage network. The CUENCAS model (Cunha 2012) is chosen because of its ability to predict flooding over various scales with minimal calibration. Taking advantage of scaling properties of flood magnitudes, a dimensionless flood index (Smith 1989, Villarini and Smith 2010) is obtained for a better representation of flood magnitudes for which the effects of basin scales are reduced. Case study analyses from Hurricane Irene are carried for the Delaware River using Stage IV radar rainfall fields. Reservoir regulation is implemented in CUENCAS since the Delaware River, like many large rivers, is strongly regulated. With limited info of dam operation and initial water level, reservoirs are represented as filters that directly reduce streamflow downstream, as a trade-off between efficiency and accuracy. Results show a correlation coefficient greater than 0.9 for all the available flood peak observations. Uncertainties are mostly from errors in rainfall fields for small watersheds, and reservoir regulation for large ones. The hydrological modeling can also be driven by simulated rainfall from historical or synthetic storms: this study fits into our long-term goal of developing a methodology to quantify the risk of inland flooding associated with landfalling tropical cyclone.