Wednesday, 17 January 2007: 10:45 AM
Extreme Floods in Urban Watersheds (INVITED)
214A (Henry B. Gonzalez Convention Center)
The flood response of urban watersheds is examined through experimental and numerical modeling studies in Baltimore, Maryland and Princeton, New Jersey. Analyses focus on: 1) the role of urban infrastructure, rainfall variability and soil hydraulic properties of urban soils in controlling runoff processes in urban watersheds and 2) the role of the urban environment in altering the distribution of extreme flash flood producing rainfall. The Dead Run (14.3 sq. km.) and Moores Run (9.1 sq. km.) watersheds in Baltimore and Harry's Brook (6.7 sq. km.) watershed in Princeton are the study watersheds used for examining response properties of urban drainage basins. The Dead Run watershed has a nested network of 6 stream gages at basin scales ranging from 1.2 sq. km. to 14.3 sq. km. Analyses in Harry's Brook are based on a network of 4 stream gages. Hydrologic model analyses based on the EPA SWMM model are used to synthesize properties of the urban water balance and the control of urban infrastructure on the timing of flood response. The climatology of flash floods in urban regions of the eastern US is closely linked to the climatology of warm season thunderstorm systems. An important consequence of urbanization is to increase the sensitivity of urban watersheds to the distribution of short-duration rainfall rates. Climatological analyses of extreme rainfall rates from warm season thunderstorm systems in the Baltimore metropolitan region and central New Jersey are based on volume scan WSR-88D reflectivity observations and cloud-to-ground (CG) lightning observations from the National Lightning Detection Network (NLDN). Analyses address the alteration of thunderstorm rainfall that are tied to frictional effects associated with urban canopy, urban heat island effects and the effects of urban aerosols on storm microphysics and dynamics.